Comprehensive Overview on the Present State and Evolution of Global Warming, Climate Change, Greenhouse Gasses and Renewable Energy

Abstract

The impact of the climate and environmental problems experienced in the world with the Industrial Revolution has prominently begun to be felt today, and the consequences of climate change on the environment and public health have now become visible. The increase in greenhouse gas emissions resulting from human activities, which is the main cause of global climate change, caused the global surface temperature to be 1.1 °C higher between 2011 and 2020 compared to 1850–1900. In parallel with this global problem, the transition to clean energy has increased significantly with Russia's invasion of Ukraine, more aggressive energy and climate policies, technological developments, and increasing concerns about energy security. In this study, global climate change indicators, including land and sea surface air temperatures, sea level rise, sea ice extent, ocean heat content, surface humidity, and total column water vapor, are reviewed and updated in parallel with a comprehensive analysis of the progress in renewable energy. The results showed that if no measures are taken to reduce human-induced greenhouse gas emissions, the global average temperature will increase further in the coming years and the negative effects of other climate parameters will be felt even more. It has been emphasized that limiting human-induced global warming requires renewable and sustainable energy sources and net zero CO₂ emissions and that the simultaneous adoption of emission reduction and adaptation strategies will be the most effective economic and technical solution to the global warming problem.

1 Introduction

The gases released due to industrial and agricultural activities retain more energy in the world, causing temperatures to rise and the natural greenhouse gas effect to be felt more [1]. This situation relates to the concepts of climate change and global warming [2]. Human activities, particularly the excessive use of fossil fuels as energy sources, contribute significantly to global warming as a critical outcome. This phenomenon results from the heightened concentration of greenhouse gases (GHGs), including carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and water vapor, in the atmosphere. This elevated GHG concentration leads to an increase in the global mean surface temperature [3]. Global warming describes the current increase in the global temperature due to the GHG effect released into the atmosphere by humans, and it contributes to climate change. Climate change encompasses the diverse effects of global warming on the Earth’s climate system. These encompass elevated sea levels, glacier melt, shifts in precipitation patterns, and alterations in the frequency of extreme weather events (such as flash floods and heat waves), varying seasons, and crop yield fluctuations [4]. These changing patterns in climate data, higher temperatures and increased frequency of extreme weather events also pose significant threats to agriculture, which can disrupt food production and reduce crop yields [5].

The first agenda on climate change under global environmental protection was introduced by the United Nations in 1988, following the establishment of the Intergovernmental Panel on Climate Change (IPCC) in collaboration with the United Nations Environment Programme [6]. A detailed presentation of the current status and anticipated impacts of climate change and global warming worldwide can be found in the Fifth Assessment Report of the IPCC, and scientific studies on the subject continue in detail. The most important consequences of climate change influences may be a decrease in freshwater resources, difficulties in growing food products, and an increase in deaths due to floods, storms, and heat waves [7]. According to Bartow-Gillies et al. [8], since 1880, the yearly average global surface temperature has been on the rise with an average rate of increase ranging from 0.08 to 0.09 °C per decade. This rate has more than doubled, indicating a faster pace of temperature rise in recent decades since 1981. In 2022, the global surface temperature, ranging between 0.25 and 0.30 °C above the 1991–2010 average, secured its position as the fifth or sixth highest annual global temperature since records were initiated in the mid-to-late 1800s. During 2022, the global ocean heat content, assessed in both the surface layers up to 700 m deep and the depth range of 700 to 2,000 m, continued its upward trajectory, reaching unprecedented levels. The annual average global mean sea level also set a new record high, measuring 101.2 mm above the level recorded in 1993, the year when satellite altimetry techniques were introduced. This underscores an annual increasing pattern of 3.4 ± 0.4 mm over the past 29 years. The year of 2022 marked the 11th consecutive year of global mean sea level increase compared with the preceding year [8]. Addressing climate change constitutes one of the significant challenges confronting humanity in the current century.

Scientists have reported that forthcoming climate change and its associated effects will vary across different regions worldwide. Anticipated warming is projected to be more pronounced over land than over the oceans, reaching its peak in the Arctic and leading to the ongoing retreat of glaciers, permafrost, and sea ice [9]. Garcia-Soto et al. [10] assert that the rapid global warming observed in recent decades has far-reaching implications for weather, climate, ecosystems, human society, and the economy. The surplus heat within the climate system is evident in various oceanic changes, such as elevated interior temperatures, rising sea levels, ice sheets, and permafrost melting, modifications to the hydrological cycle shift in atmospheric and oceanic circulation, and intensification of tropical cyclones with augmented rainfall. Elevated ocean heat content and sea surface temperatures contribute to the heightened intensity, size, and duration of tropical cyclones, amplifying their potential for devastating flooding. Research, as outlined in Alifu et al. [11], indicates that extreme weather events, such as intense precipitation and flooding, can result in profound consequences for both human society and the environment. Heavy precipitation events, which are a primary factor in the occurrence of flooding, have witnessed a notable rise in recent times. This increase is particularly evident in numerous regions of the Northern Hemisphere based on climate change induced by human activities, specifically the escalation of GHGs. According to Meyssignac et al. [12], the Earth’s radiation into space falls short of offsetting the solar radiation it receives, resulting in a slightly positive energy imbalance in the upper atmosphere (0.4–1 Wm⁻²). This disparity, termed Earth’s Energy Imbalance (EEI), is predominantly based on human-induced greenhouse gas emissions and is a key factor in ongoing global warming. According to Cheng et al. [13], because of rising concentrations of greenhouse gases in the atmosphere, there is an imbalance between the energy emitted by the Earth system and the incoming solar radiation, leading to EEI within the climate system. More than 90% of EEI is stored in the oceans, contributing to an increase in ocean heat content. Ocean warming results in heightened vertical stratification, thermal expansion, and a subsequent rise in sea levels. These operations provide an interesting tool for measuring climate change. Accurate monitoring of EEI is crucial for evaluating the present state of climate change and predicting its future trajectory [12].

Increasing population, internationalization and industrialization have contributed to the spread and increase of hazardous substances in the environment, especially CO₂, in recent years [14]. In conjunction with global warming, the escalating concentrations of CO₂ in the atmosphere directly impact the ocean’s chemistry through CO₂ absorption by surface waters. According to Garcia-Soto et al. [10], approximately a quarter of the total CO₂ emissions since the pre-industrial era have been absorbed by oceans. The heightened CO₂ levels in the water lead to a reduction in pH, a phenomenon termed ocean acidification. This acidification poses challenges for certain marine organisms such as corals, oysters, and pteropods, hindering their ability to create calcium carbonate shells and skeletons. Studies have demonstrated that ocean acidification can adversely affect the fitness of various species, including coccolithophores, crabs, sea urchins, and the early life stages of fish. Research endeavors have significantly advanced our understanding of how ocean acidification, both independently and in conjunction with other stressors such as eutrophication, warming, and hypoxia, may affect marine species, ecosystems, and biogeochemical cycles.

From the analysis of detailed literature studies, it has been shown that there are many studies on global warming, climate change, greenhouse gases and renewable energy, which represent an essential component of the Earth’s natural mechanisms. Apart from the primary scientific, socio-economic, and technical literature, there exist thorough scientific evaluations of the developing body of knowledge [7], along with focused reviews. For example, Garcia-Soto et al. [10] conducted a review and revision of global trends in both the physical and chemical aspects of the ocean, using seven crucial indicators related to ocean climate change. These indicators include the temperature of the sea surface, sea level, heat content and pH value of the ocean, dissolved oxygen concentration, Arctic sea ice extent, volume, and thickness, as well as the magnitude of the Atlantic meridional overturning circulation. Meyssignac et al. [12] reviewed the four state-of-the-art methods to estimate global ocean heat content changes and evaluated their relevance to derive Earth’s energy imbalance estimates on different time scales. Morice et al. [15] introduced an updated version of the Met Office Hadley Centre/Climatic Research Unit global surface temperature dataset, known as HadCRUT5. This dataset illustrates monthly mean near-surface temperature anomalies for the 1961–1990 period, presented on a regular 5° latitude by 5° longitude grid spanning the years 1850 to 2018. Simmons et al. [16] revised and expanded various prior assessments of the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis surface air temperature products which include comparisons with one or more other reanalyses, conventional climatological datasets, and direct observations. Hansen et al. [17] updated the Goddard Institute for Space Studies (GISS) examination of worldwide surface temperature alteration, compared alternative analyses, and addressed questions regarding the perception and reality of global warming. Twardosz et al. [18] identified the extent of annual and seasonal temperature variations in Europe and its nearby regions using data collected from 210 weather stations spanning the period from 1951 to 2020. Cheng et al. [13] provided global and regional analyses of recent ocean heat content changes through 2021 using two types of international data obtained from the Institute of Atmospheric Physics (IAP) at the Chinese Academy of Sciences (CAS) and the National Centers for Environmental Information (NCEI) of the National Oceanic and Atmospheric Administration (NOAA).

Wu et al. [19] recalculated the global average surface temperature based on observations using ensemble empirical mode decomposition (EEMD), which represents a significant enhancement of the initial EMD method. Al-Ghussain [3] reviewed the driving forces of global warming, highlighted the major contributors to this phenomenon, and presented some mitigation techniques. In the study conducted by He et al. [20], the objective was to assess flood risks resulting from global warming through a uniform set of models and to ensure the comparability of results at the country level by incorporating climate scenarios, initial and future periods, and hazard metrics. For this purpose, the authors selected six countries that are considered sensitive to climate change: Egypt, Ethiopia, Ghana, China, India, and Brazil. De Freitas et al. [21] conducted a reevaluation of long-term trends in surface air temperature in New Zealand from 1909 to 1975. Shen et al. [22] examined temperature variations in major countries between 1981 and 2019. They analyzed the spatial–temporal features of global temperature changes by reanalyzing data from seven generally recognized datasets, encompassing the tendency in climate change and spatial interpolation of land air temperature data. In the study conducted by Eayrs et al. [23], the reasons for the rapid decline in Antarctic sea ice recently were investigated and the effects of these results on future changes were emphasized. Cheng et al. [24] reconstructed past worldwide monthly patterns of atmospheric CO₂ concentrations, documented from 1850 to 2013 by the Carbon Dioxide Information Analysis Center. The researchers produced spatial distributions of nonuniform CO₂ levels from 2015 to 2150. This was done within the context of shared socio-economic pathways and representative concentration pathways scenarios, considering spatial, seasonal, and interannual changes in the existing CO₂ fractions. Bedair et al. [25] explored the effects of climate change on human health, the agricultural sector, and food security in Africa, drawing comparisons with other continents. It assessed future change predictions and underscored the importance of African leaders in both mitigating and adapting to these impacts. The analysis of these effects was conducted using artificial intelligence, remote sensing, and advanced algorithms. Almazroui et al. [26] scrutinized information from 27 global climate models participating in the sixth phase of the Coupled Model Intercomparison Project (CMIP6). The study focused on assessing the anticipated alterations in temperature and precipitation across the African continent for the upcoming periods, namely 2030–2059 (near term) and 2070–2099 (long-term).

Szulejko et al. [27] performed the global warming projections until 2100 based on the CO₂ climate sensitivity factor and CO₂ greenhouse gas modeling. Using a single set of risk models and a consistent set of socio-economic and climate change scenarios, Warren et al. [28] synthesized the harmonized assessment of anticipated future climate change hazards in six nations offered by the Topical Collection. Rummukainen [29] highlighted and reviewed climate change indicators such as air temperature, precipitation, wind, and sea level using existing scientific information relevant to the energy sector. According to this study, both gradual and sudden shifts in climate influence the potential of renewable energy resources. Various renewable energy sources display direct connections to climate patterns, such as wind and hydropower, whereas others, such as biomass, are indirectly affected. Climate change also changes the operational conditions of energy infrastructure, which is influenced by the effects of changing heat waves, droughts, and potential storms. This, in turn, affects the demand for energy for heating and cooling and the accessibility of new conventional energy sources. Extreme weather events and climate changes can affect diverse energy generation applications and transmitting systems, occasionally leading to episodic peaks in energy consumption, particularly during heat waves. Market dynamics could result in indirect impacts of climate change on the energy sector.

The demand for global energy has been on the rise due to advancements in technology and population growth; while, the use of fossil fuels has seen a significant decline over the past decades. Regarding the risk of running out of fossil fuels, the focus has shifted to substitutes like renewable energy sources [30]. Projections suggest a 21% rise in overall energy requests by 2030. Escalating concerns about climate change are compelling governments worldwide to explore alternative energy sources to curb greenhouse gas emissions and mitigate adverse ecological impacts. The energy sector is the source of nearly three-quarters of greenhouse gas emissions today and holds the key to preventing the worst effects of climate change, perhaps the greatest challenge facing humanity. The wave of investment and spending to support the economic recovery in energy around the world needs to be aligned with reducing global CO₂ emissions to net zero by 2050. Without changes to existing policies, the International Energy Agency [31] warns that global energy-related CO₂ emissions could surge by approximately 50% by 2030 compared with current levels. Since the 1997 launch of the Kyoto Protocol and the most recent United Nations Climate Change Conference of the Parties (COP26), numerous industrial sectors have made efforts to reduce greenhouse gas emissions, particularly the energy sector, given the growing demand for the generation of renewable and clean energies.

2 Novelty and Objective of the Study

From the abovementioned studies, global warming and climate change are closely tied to the Earth’s natural processes, particularly the global carbon cycle, which plays a crucial role. This carbon cycle plays a pivotal role in controlling the Earth’s climate and atmospheric composition [32]. It is vital to use renewable energy resources effectively, and effective energy management policies to avoid the effects of global warming. To gain a deeper understanding of these phenomena, it is crucial to analyze and assess the pattern of greenhouse gas emissions and their interaction with climate change and global warming. It has become a necessity to conduct comprehensive research on global warming, climate change, greenhouse gases, and renewable energy to solve energy production and environmental problems around the world. However, the number of studies in the literature where all these global parameters are evaluated together and correlated with each other is limited. In the current study, the influences of global warming, climate change, and greenhouse gases, which are important atmospheric indicators in recent years, on the development of renewable energy, the current situation, and historical trends are presented. A conclusive visual representation of the indicators of climate change, such as land and sea surface air temperatures, sea level rise, sea ice extent, ocean heat content, surface humidity, and total column water vapor, is presented. The novelty of the study is summarized below:

• Presenting in detail the current status of global warming, climate change, and greenhouse gases, which are important atmospheric indicators of recent years, their historical trends, and their effects on the development of renewable energy.

• Providing a definitive visual representation of climate change indicators such as land and sea surface air temperatures, sea level rise, sea ice extent, ocean heat content, surface moisture, and total column water vapor.

• Reviewing strategies to provide the most effective economic and technical solutions to the problem of global warming, reducing global CO2 emissions, and simultaneously adopting adaptation strategies.

• Reviewing the drivers of global warming, highlighting the main factors contributing to this phenomenon, and revealing some mitigation techniques.

• Analyzing the global impacts of extreme weather events both numerically and visually.

3 Global Warming

Global warming is the increment in temperature of the Earth’s surface due to the effect of greenhouse gases released into the atmosphere by humans. As is known, an increase in the greenhouse gas effect induces the upper part of the atmosphere, that is, the stratosphere, to cool down and the lower troposphere to warm up. The most important reason for global warming, which has increased significantly in the last century, is the significant increase in the emissions of GHG in the atmosphere due to human actions along with industrialization [3, 4]. According to scientists, some of global warming can be attributed to natural events. Throughout earth’s existence, volcanic eruptions, fluctuations in solar radiation, tectonic shifts, and even small changes in our orbit have had observable effects on the planet's heating and cooling patterns. It is stated that the main drivers of global warming worldwide are human activities such as burning fossil fuels, public transportation, electricity generation, industry and manufacturing, agriculture, farming livestock, oil and gas development, buildings, deforestation, and our lifestyle choices. According to NASA [33], global temperature increases caused by man-made greenhouse gases will continue and their effects will be felt deeply. Severe weather damage will also increase and intensify. Effects such as loss of sea ice, melting of glaciers and ice sheets, sea level rise, and more intense heat waves are already being experienced. Potential future impacts of global warming include more frequent wildfires, longer drought periods in some regions, and increases in wind intensity and precipitation from tropical cyclones.

Temperature is emphasized as an important indicator of climate change. A systematic increase in the air temperature on Earth is the most characteristic feature of contemporary climate change [18]. The mean temperature of a zone and its variation throughout the year significantly impact people’s lives, the types of crops that can be grown, and the planning of structures and various community facilities [34]. Significant and sudden fluctuations from one year to the next can affect food generation and the proliferation of pests and diseases. Extreme cold and heat can negatively impact food safety and people’s health, as well as infrastructure elements such as roads and railways, along with energy demand [35]. The temperature of ocean water also plays a crucial role in supporting marine life. The formation and progression of hurricanes typically occurring in warmer waters are influenced by ocean temperatures. Temperature patterns like El Niño in the ocean alter the weather in various regions across the globe [36].

Oxygen serves as a life-supporting element for most oceanic organisms, delineating habitat boundary limits for marine life. Oxygen can only be obtained in the uppermost water layers through processes such as photosynthesis or the exchange of gases between air and sea. As water mass moves away from the surface, the levels of oxygen decrease because of consumption. The increase in global warming results in a decline in the solubility of oxygen at the surface, reducing the original quantity of subducted and convected oxygen. Warming of the upper ocean has repercussions on biological activity, oceanic stratification and overturning, and various other systems, all of which could reduce oceanic oxygen levels [10].

Figure 1a shows the annual global mean temperature difference between 1850 and 2023 relative to the reference average temperature between 1850 and 1900. In this graph, the value 0 considered the pre-industrial temperature level, refers to the average temperature between 1850 and 1900. As can be seen from the figure, the different global average temperature data are highly correlated with each other. There is good agreement on the overall evolution and year-to-year variability of annual global mean temperature anomaly data measured by various scientific institutions, including HadCRUT, NOAAGlobalTemp, GISTEMP, and Berkeley Earth, as well as two reanalyzes, ERA5 and JRA-55. The results show an increasing trend in the global average annual surface temperature anomaly values between 1850 and 2023 caused by global warming because of anthropogenic greenhouse gas emissions. According to these multiple independently produced datasets, the global mean surface temperature during 2011–2020 shows a warming of 1.09 °C compared with that during 1850–1900. Since the 1970s, a faster trend has been observed than in any other 50-year period in at least the last 2000 years. Within this long-term upward trend, there are short-term variations due to natural internal variability. While the global average annual surface temperature anomaly values with the HadCRUT dataset were detected as 0.23 °C, 0.67 °C, and 1.31 °C in the years 1975, 2020, and 2023, they were recorded as 0.26 °C, 0.67 °C and 1.3 °C for the GISTEMP dataset and 0.2 °C, 0.68 °C and 1.22 °C for the JRA-55 dataset. It can be interpreted that although there are small changes in the mean temperature differences of individual years between 1850 and 2023 from the reference average temperature between 1850 and 1900 depending on the method used, the temperature difference increases from year to year. Especially after 2010, aggressive increases in temperature differences have been observed, and this situation threatens our future.

Fig. 1

Source: Data from Morice et al. [15]; Zhang et al. [37]; GISTEMP Team [38]; Hersbach et al. [39; Lenssen et al. 40]; Kobayashi [41]; Rohde et al. [42]; Kennedy et al. [43]; Kennedy et al. [44]; Kennedy et al. [45]; Huang et al. [46]; Huang et al. [47]; Osborn et al. [48]; Jones et al. [49]; Menne et al. [50]; Met Office Hadley Centre [51] and Climate Reanalyzer [52]

a Annual global mean temperature anomaly for years between 1850 and 2023 relative to the reference average temperature between years of 1850–1900, b Annual global mean sea surface temperature difference between 1850 and 2023 relative to the reference average temperature between years of 1981–2010, c Annual global mean land surface temperature difference between 1850 and 2023 relative to the reference average temperature between years of 1981–2010, d Annual mean temperature anomaly relative to years 1961–1990 for the northern and southern hemispheres and the world (HadCRUT5 data set).

Sea surface temperature represents a substantial physical property of oceans throughout the world. Sea surface temperature increases as oceans absorb more heat. Changes occur in ocean circulation patterns that carry hot and cold water around the world. Marine ecosystems can change in various ways because of these changes in sea surface temperature. Figure 1b shows the annual global mean sea surface temperature difference relative to the reference average sea surface temperature between 1981 and 2010. The value 0 refers to the average sea surface temperature between 1981 and 2010. The results show good agreement on the long-term warming of surface oceans and year-to-year variability, as indicated by the three different datasets, HadSST4, HadSST3, and ERSSTv5. Ocean temperatures have increased significantly around the world in recent years. Sea surface temperatures have remained consistently elevated over the last thirty years, surpassing any previous levels recorded since the beginning of confident measurements in 1880. Rises in sea surface temperature have predominantly emerged during two notable periods: from 1910 to 1940 and approximately from 1970 to the present. It appears that the sea surface temperature experienced a decline from 1880 to 1910. Sea surface temperature increases of 0.17 °C, 0.18 °C, and 0.38 °C were observed in 2003, 2013, and 2022 for the HadSST4 dataset. In the same years, these values were recorded as 0.19 °C, 0.17 °C, and 0.29 °C for the HadSST3 dataset and as 0.14 °C, 0.15 °C, and 0.3 °C for the ERSSTv5 dataset.

Figure 1c shows the annual global mean land surface temperature difference between 1850 and 2023 relative to the reference average land surface temperature between 1981 and 2010. In this graph, the value 0 refers to the average land surface temperature between 1981 and 2010. Across four different datasets, there is very good agreement on long-term warming, the overall evolution of global temperature, and year-to-year variability. The global average land surface temperature increase has been rising sharply since the 1970s. According to the GHCN dataset, the global average land surface temperature in 2023 increased by around 0.82 °C relative to the reference average temperature between 1981 and 2010. According to the CRUTEM5 dataset, the annual global mean land surface temperature increased by 0.2 °C, 0.26 °C, and 0.51 °C in 2001, 2011, and 2021, respectively. In the same years, the CRUTEM4 dataset documented temperature increments as 0.21 °C, 0.25 °C, and 0.6 °C with respect to the reference average temperature. These values were reported as 0.19 °C, 0.31 °C, and 0.65 °C with the Berkeley Earth Land dataset in 2001, 2011, and 2021. Since 1979, the global average land surface temperature has risen approximately twice as fast as the average temperature increase in the oceans. Ocean temperatures rise more slowly than those on land because the oceans have a higher heat capacity and lose more heat through evaporation. Thermal stagnation in the oceans and slow responses to other indirect effects cause it to take centuries to adapt to past changes.

Figure 1d shows the annual mean temperature anomaly between 1850 and 2023 relative to the average temperature between 1961 and 1990 for the northern and southern hemispheres and the world. The results show that the temperature increase in the Northern Hemisphere is greater than in the Southern Hemisphere. The most important reason for this is that, with the Industrial Revolution in the eighteenth century, the temperature difference between the world’s hemispheres began to increase with the melting of sea ice and snow in the northern hemisphere. Greenhouse gas emissions occur more in the northern hemisphere than in the southern hemisphere, and greenhouse gases persist long enough to spread in both hemispheres, affecting the temperature difference between the hemispheres. According to the HadCRUT5 data set results, as seen in Fig. 1d, the average temperature anomaly values for both the global and the northern and southern hemispheres have a very high increasing trend, especially since 1970. In the northern hemisphere region, while the temperature difference between the mean temperature in 1980 and the reference average temperature between 1961 and 1990 was detected as 0.14 °C, these values increased to 0.49 °C and 1.28 °C in 2000 and 2020, respectively. These temperature difference values were recorded as 0.25 °C, 0.18 °C, and 0.57 °C in the same years for the southern hemisphere region.

Figure 2 shows the annual global mean temperature and its anomalies in 1940 and 2022. The data in these maps reflect the warmth or coldness of each region according to the base period 1979–2000. The results show that the annual worldwide mean surface temperature has been increasing at a mean rate ranging from 0.08 to 0.09 °C per decade since 1880 and has more than doubled since 1981. As reported by ECMWF European Reanalysis v5 [53], the annual average global temperature has risen by a minimum of 1.1 °C since 1880. Most of the warming has occurred since 1975, with an average rate of approximately 0.15 to 0.20 °C per decade. The year 2022 ranked as one of the six hottest years since records began in the mid-to-late 1800s. As can be seen on the maps, global warming does not increase at the same rate everywhere on Earth at all times. While temperatures may rise by 5 °C in one zone, they may drop by 2 °C in the other zone. For example, extremely cold winters in one location might be balanced by highly warm winters in another region of the Earth. Land experiences more significant warming than oceans because of the slower absorption and release of heat by water, known as thermal inertia. Warming can exhibit substantial variation within particular land masses and ocean basins.

Fig. 2

Source: ECMWF ERA5 (0.5 × 0.5 deg) data [53], Maps from Climate Reanalyzer [52]

Annual global mean temperature and its anomaly in 1940 and 2022 according to the base period of 1979–2000.

The IPCC [54] generated projections of future variations in global surface temperature relative to 1850–1900 by combining multimodel projections with observational constraints. The assessment involved evaluating equilibrium climate sensitivity and transient climate response. This projection presents future predictions of global surface temperature changes up to 2100 under various greenhouse gas emission scenarios, including very low (SSP1-1.9), low (SSP1-2.6), medium (SSP2-4.5), high (SSP3-7.0), and very high (SSP5-8.5) scenarios. Within five illustrative scenarios derived from the Shared Socioeconomic Pathways (SSPs) encompassing a spectrum of potential developments in anthropogenic drivers of climate change, scenarios with high and very high greenhouse gas emissions (SSP3-7.0 and SSP5-8.5) predict a roughly twofold increase in CO₂ emissions by 2100 and 2050compared to present levels. In the medium greenhouse gas emissions scenario (SSP2-4.5), CO₂ emissions are projected to remain at current levels until the mid-century. In scenarios characterized by very low and low GHG emissions (SSP1-1.9 and SSP1-2.6), it is anticipated that CO₂ emissions will reach net zero around 2050 and 2070. Subsequently, these scenarios project varying degrees of net zero CO₂ emissions. As a result, the best estimates of the global surface temperature for these different scenarios up to 2100 were calculated as 1.4 °C for SSP1–1.9, 1.8 °C for SSP1-2.6, 2.7 °C for SSP2-4.5, 3.6 °C for SSP3-7.0, and 4.4 °C for SSP-8.5.

4 Global Climate Change

4.1 Sea Level Rise

Sea level is scientifically important because it reflects changes in the temperature of the oceans and the mass of water they contain. The addition of water to the oceans by melting glaciers and the thermal expansion of warming oceans are the most important causes of the increase in global mean sea levels. The results show that the sea level rise rate has increased since the early 1990s, when satellite altimeter records began. Observations in 1971 show with high confidence that thermal expansion and glaciers explain 75% of the observed increase. According to the IPCC [54], the acceleration of sea level rise is attributed to a combination of heightened ice loss from the Greenland and Antarctic ice sheets. The sea level did not rise at the same rate everywhere. Some regions experienced a faster rise or fall in sea level; whereas, others experienced a slower rise or fall. The increase in sea levels presents a significant danger to low-lying islands, coastlines, and communities globally, resulting in flooding, coastal erosion, and the pollution of freshwater reservoirs and crops [10].

Increases in the global average sea level can be attributed to four primary mechanisms: variations in water mass, temperature, salinity, and ocean circulation [55]. The addition of water to the ocean can result from heightened rainfall or river runoff, with glacier melting contributing to this influx. Conversely, the creation of artificial reservoirs can decrease runoff, leading to a reduced flow of water into the ocean. Elevated evaporation levels also contribute to a decrease in the water mass. As water warms, it expands, causing an increase in sea levels. This phenomenon not only results in seasonal variations but also year-to-year fluctuations associated with climate events such as El Niño. Long-term temperature changes further impact sea levels. The density of water is influenced by its salinity, with saltier water exhibiting lower levels. Salinity variations may occur because of freshwater input (increased runoff, precipitation, or ice melting), leading to decreased salinity, or through increased evaporation or glaciation, which increases salinity. Changes in sea level can be linked to alterations in ocean circulation. Figure 3 displays the regional gridded trend in sea level from 1993 to the current date. Despite the general rise in the global mean sea level over this period, the distribution of sea levels across the globe exhibits considerable heterogeneity. In specific regions, the rise in sea level can significantly exceed the global average of 3.6 mm per year.

Fig. 3

Source: Maps from the Climate Data Store (CDS) [56]

Regional gridded trend in sea level from 1993 to the current date (in mm/year).

Figure 4 demonstrates the monthly global mean sea level difference between 1993 and 2023 relative to the reference global mean sea level between 1993 and 2010. It can be seen from the figure that the results obtained from several satellite-based datasets such as CSIRO, AVISO, CMEMS, University of Colorado, and NASA are consistent in their year-to-year changes and long-term increases. The rise in global mean sea level is accelerating from a trend of 2.6 ± 0.7 mm/year during 1993–2008 to a trend of 4.2 ± 0.4 mm/year during 2007–2022, representing an increase of 61%. This corresponds to an acceleration of 1.1 ± 0.6 mm/year per decade during the past 30 years. The outcomes show that the global mean sea level has increased by 3.3 ± 0.3 mm per year since 1993. This represents a total increase of 9.7 cm in the last 30 years. Approximately 30% of this increase is due to ocean thermal expansion, and 60% is due to the melting of land ice from glaciers and the Antarctic and Greenland ice sheets. The remaining 10% is attributed to alterations in land water storage, including factors such as soil moisture, surface water, and groundwater.

Fig. 4

Source: Data from Watson et al. [57], Legeais et al. [58], Pujol et al. [59], Ablain et al. [60], Escudier et al. [61], Nerem et al. [62], Beckley et al. [63], Beckley et al. [64], Beckley et al. [65], Met Office Hadley Centre [51], and Climate Reanalyzer [52]

Monthly global mean sea level difference between 1993 and 2023 relative to the reference average sea level between 1993 and 2010.

According to the global average sea level change relative to 1900 obtained by the IPCC [54], it seems inevitable that the sea level will continue to rise due to ongoing ice sheet melting and deep ocean warming. Sea levels are predicted to remain high for thousands of years. Nevertheless, significant, swift, and consistent decreases in GHG emissions are anticipated to restrict the additional acceleration of sea level rise and the predicted long-term increase in sea levels. When compared to the years 1995–2014, the possible global average sea level increase within the scope of the SSP1-1.9 greenhouse gas emission scenario is predicted to be from 0.15 to 0.23 m by 2050 and from 0.28 to 0.55 m by 2100. Under the SSP5-8.5 greenhouse gas emission scenario, the anticipated increase in global average sea levels is forecasted to be 0.20–0.29 m by 2050 and 0.63–1.01 m by 2100. In the coming 2000 years, the forecasted global mean sea level increase will be around 2–3 m if warming is constrained to 1.5 °C and 2–6 m if the warming is restricted to 2 °C.

4.2 Sea Ice Extent

Sea ice, a crucial element in polar ecosystems, performs a critical function within the climate system by governing heat and momentum exchange between the atmosphere and the ocean [23]. Measurement of sea ice in the Arctic and Antarctic involves assessing its "extent," defined as the overall area of the ocean where at least 15% of the surrounding surface is covered by ice [66]. This extent varies throughout the year, as sea ice experiences growth and melting in accordance with shifting seasons. In contrast to the substantial decrease observed in Arctic sea ice over the satellite record, the entirety of Antarctic sea ice exhibits a subtle yet generally positive linear trend [23]. Being lightweight, sea ice effectively reflects the majority of incoming sunlight. In contrast, open water appears darker and absorbs light, resulting in increased surface energy absorption when sea ice undergoes melting.

According to Garcia-Soto et al. [10], sea ice at the poles is essential for preserving global heat equilibrium. Solar shortwave radiation is concentrated at the equator, and the Earth’s atmospheric and oceanic circulations transport this heat toward the comparatively colder poles. The elevated albedo of sea ice and the cryosphere enhances the ability of the global system to reflect entering solar radiation and emit longwave heat, thereby regulating the overall heat balance of the planet. The reduction of ice in the cryosphere diminishes the planetary albedo, enabling more heat transfer from the ocean to the atmosphere through finer sea ice and larger expanses of open water, ultimately weakening the Earth’s capacity to sustain a worldwide heat equilibrium. Sea ice further plays a crucial role in the freshwater and salt dynamics of the oceans worldwide. During sea ice growth, salt is expelled, and the drifting ice, carried by winds and ocean currents, transports fresh water to regions where it can melt in summer. Sea ice significantly influences wildlife with many species relying on it for habitat, subsistence, and cultural practices [10].

Figure 5 illustrates the monthly differences in Arctic and Antarctic sea ice extent for years between 1979 and 2023 relative to the average sea ice extent between 1981 and 2010. The behavior of Arctic and Antarctic sea ice varies and is influenced by distinct configurations of the surrounding ocean and land near each pole. As evident from Fig. 5a, the monthly Arctic sea ice extent is depicted as a deviation from the 1981–2010 average, using two datasets (OSI-SAF and NSIDC). Both datasets consistently depict a month-to-month and long-term reduction in the Arctic sea ice level. The Arctic, enclosed by land, experiences sea ice coverage in its high latitudes throughout the year, reaching its highest level in March and its lowest in September. Notably, despite September 2012 holding the record for the lowest monthly Arctic sea ice extent, October 2020 exhibits a lower ice extent anomaly, positioning it lower on the graph. Since the late 1970s, when regular satellite monitoring began, Arctic sea ice extent projections indicate that this decline is anticipated to persist in the future.

Fig. 5

Source: Data from EUMETSAT OSI SAF Sea Ice Index v2.1 [67], Lavergne et al. [68], National Snow and Ice Data Center [69], Fetterer et al. [70], and Met Office Hadley Centre [51]

Differences in monthly arctic and Antarctic sea ice extents relative to the average sea ice extent between 1981 and 2010

The monthly deviation of the Antarctic sea ice extent from the 1981–2010 average is depicted in Fig. 5b, using two datasets: OSI-SAF and NSIDC. These datasets consistently show agreement regarding both month-to-month variations and long-term trends in Antarctic sea ice levels. Surrounding the Antarctic continent, a land mass encircled by the ocean, sea ice forms a fringe. The minimum extent occurs in February or March when sea ice retreats almost to the coast; whereas, the maximum extent is observed in September or October. Historically, there was a slight long-term increase in Antarctic ice extent until 2015. In late 2016, there was a sudden drop in Antarctic sea ice extent, and it has remained relatively low since then. The results show that short-term weather events predominantly influence year-to-year fluctuations around the long-term trend. Scientists have pointed out that the influence of anthropogenic greenhouse gas forcing could play a role in warming the tropical Indian Ocean. This, in turn, may lead to notable reductions in Antarctic sea ice, as evidenced by the record declines observed in 2016. Eayrs et al. [23] argues that the recent abrupt reduction in Antarctic sea ice is predominantly attributable to coincidental yet naturally occurring variability. This decline is primarily linked to a shift in phase rather than amplitude, which is characterized by an earlier (August instead of the end of September) and more rapid seasonal retreat than typical patterns.

The atmosphere and ocean have a significant impact on sea ice, and minor temperature fluctuations can result in substantial alterations to the annual cycle of sea ice melting and growth. With the rise in global temperatures, polar amplification is leading to a faster increase in Arctic temperatures compared to the rest of the planet, resulting in annual decreases in both maximum and minimum sea ice extent. Figure 6 illustrates the variation in Arctic Sea ice extent for March and September from 1979 to 2023. The findings indicate that the Arctic sea ice typically attains its maximum level around March and its minimum level in September. The average Arctic sea ice extent in September 1979 was 7.1 million km², whereas in September 2023, the Arctic sea ice extent decreased to 4.37 million km². The average Arctic sea ice extents for March 1979 and 2023 were calculated as 16.3 million km² and 14.4 million km², respectively.

Fig. 6

Source: Maps from the National Snow and Ice Data Center [69]

Change in sea ice extent of the Arctic Sea between 1979 and 2023,

Figure 7 shows the change in the extent of sea ice in the Antarctic Sea between 1979 and 2023 for February and September. The results show that Antarctic sea ice typically attains its highest level in September and lowest in February. The average Antarctic sea ice extent in September 1979 was 18.2 million km², whereas in September 2023, the Antarctic sea ice extent decreased to 16.8 million km². The average Antarctic sea ice extents for February 1979 and 2023 were calculated as 3.1 million km² and 1.9 million km², respectively.

Fig. 7

Source: Map from the National Snow and Ice Data Center [69]

Change in sea ice extent of the Antarctic Sea between 1979 and 2023,

4.3 Ocean Heat Content

The Earth’s climate system has an energy imbalance due to natural energy flows being disrupted by human activity’s emission of heat-trapping greenhouse gases. Over 90% of the surplus heat accumulates in the Earth’s oceans, resulting in an increase in the ocean heat content. Ocean heat content, a key indicator of global warming, refers to the energy absorbed and retained by the oceans. According to Cheng et al. [71], it is a direct measure of the accumulation of energy in the oceans. The world’s oceans have a huge volume; therefore, even small temperature changes can correspond to large changes in energy. Variations in ocean temperature have implications for the dissolution of oxygen and carbon dioxide in seawater, consequently influencing the atmospheric concentrations of these gases generally, warmer water tends to dissolve less gas, holding other factors constant. Unlike surface temperatures, which can exhibit significant year-to-year variations due to phenomena like El Niño and La Niña, ocean heat content demonstrates a more gradual increase. In this regard, to assess the ocean heat content, it is crucial to measure the ocean temperatures at various locations and depths.

Figure 8a illustrates the annual global ocean heat content down to a depth of 700 m, expressed as a deviation from the 1981–2010 average. The results show a consensus among the datasets regarding the overall warming trend in the ocean, and the long-term tendency obtained from different data analyses demonstrates that the upper 700 m of the oceans have experienced warming since 1950. Figure 8b displays alterations in the heat content of the upper 2,000 m of the Earth’s oceans from 1955 to 2020. The ocean heat content is contrasted with the baseline of the 1971–2000 average, established at zero for reference. These findings suggest that over time, the heat absorbed by surface waters extends to greater depths. While greenhouse gas fractions have increased at a relatively consistent pace over recent decades, the rate of variation in ocean heat content can fluctuate from one year to another. Fluctuations from one year to the next are impacted by occurrences such as volcanic eruptions and regular ocean– atmosphere patterns such as El Niño.

Fig. 8

Source: Data from Good et al. [72], Gouretski and Cheng [73], Cheng et al. [74], Levitus et al. [75], Levitus et al. [76], Cowley et al. [77], Gouretski and Reseghetti [78], Cheng et al. [79], Ishii et al. [80], IAP [81], NOAA [82], MRI/JMA [83]

Annual global ocean heat content difference for years between 1940 and 2022 for different depths, a relative to the years of 1981–2010, b relative to 1971–2000, and c relative to 1955.

Oceans play a crucial role in influencing the global climate due to their extensive coverage, encompassing approximately 70% of the Earth’s surface, and their substantial heat capacity [7]. As per the findings of the Intergovernmental Panel on Climate Change Sixth Assessment Report [54], approximately 56% of the net energy accumulation in the climate system between 1971 and 2022 remains stored in the upper ocean (0–700 m), while approximately 35% is retained below 700 m. Warming of the ocean leads to an increase in sea levels through thermal expansion and has consequences for marine ecosystems. Figure 8c presents a time series depiction of the globally integrated ocean heat content at various depth intervals relative to 1955. The findings indicate a high level of certainty that the global integrals of ocean heat content in the 0 to 2000 m range increased between 1955 and 2022, exhibiting a long-term trend with interannual variations at a rate of 6.09 ± 0.42 × 10²² J per decade. The globally averaged ocean temperature in the 0 to 2000 m range experienced an increase of 0.021 ± 0.001 °C per decade in conjunction with the rise in ocean heat content. Since the mid-1990s, there has been a noticeable warming of the oceans. Scientists attribute these long-term trends to global warming, which results from elevated concentrations of anthropogenic greenhouse gases such as CO₂, along with natural variability.

While there has been a significant increase in the global average ocean heat content, the ocean warming rate has not been uniform across all regions. Figure 9 presents the estimated trend (10⁵ J/m³) in the observed annual upper 2000 m ocean heat content anomaly relative to the 1850–1900 average for the years 1955 and 2022. The Fig. 8 also shows the sea surface temperature anomaly maps for the same years. As seen in the figure, the ocean heat content change and the sea surface temperature change show a similar trend. It is recognized that the most pronounced warming in the upper 2000 m occurred in the Southern Ocean, North Atlantic, and South Atlantic. According to the WMO [7], the Southern Ocean represents the largest repository of heat, contributing to approximately 36% of the global increase in ocean heat content in the upper 2000 m since 1958. Substantial warming is linked to the uptake of anthropogenic heat by the cold upwelling waters, which are subsequently transported to the northern edge of the Antarctic circumpolar current through background overturning circulation.

Fig. 9

Source: Maps from NOAA [84] and Levitus et al. [75]

Estimated trend (10⁵ J/m.³) in the observed annual upper 2000 m ocean heat content anomaly relative to the 1850–1900 average for the years 1955 and 2022 and sea surface temperature anomaly maps for the same years.

4.4 Surface Humidity

In recent years, humidity has become a crucial climate indicator affected by global warming. Humidity, a vital component of the global water cycle, expresses the essential water vapor that supports life on Earth. It facilitates the movement of water from oceans and land surfaces into the worldwide atmosphere, leading to precipitation. Elevated levels of water vapor are closely associated with more intense precipitation events [51]. The increased water vapor also plays a key role in global warming by trapping outgoing long wave radiation. As the atmosphere warms, more energy is available to evaporate surface water and store it as vapor in the air. The rise in specific humidity is directly linked to increasing air and ocean temperatures, particularly during strong El Niño years [36].

Figure 10 shows the annual average specific humidity anomalies from the 1991–2020 average for the Northern and Southern Hemisphere, Tropics, and Global. As can be seen from the figure, specific humidity has generally increased in the northern hemisphere, tropical regions, and throughout the world since 1970; while, it has remained stable in the southern hemisphere. According to the HadISDH dataset, 2022 had slightly higher water vapor content than 2021, except in the tropics. Specific humidity anomaly values in the northern hemisphere, southern hemisphere, tropical regions, and the world increased by 0.12, 0.06, 0.11, and 0.11 g/kg, respectively, from the 1991–2020 average.

Fig. 10

Source: Data from Freeman et al. [85], Smith et al. [86], Willett et al. [87,88,89,90,91]

Annual average specific humidity anomalies from the 1991–2020 average, a Northern Hemisphere, b Southern Hemisphere, c Tropics, and d Global. 2-σ uncertainty is shown for the HadISDH dataset.

Figure 11 shows the annual average relative humidity anomalies from the 1991–2020 average for the Northern and Southern Hemisphere, Tropics, and Global. The results show that the relative humidity values for all regions are more humid than 2021 in terms of saturation. While relative humidity anomaly values remained lower than the 1991–2020 average for the northern hemisphere and the global, they remained higher than the average for the southern hemisphere and the tropics. It is clear from the figure that relative humidity has generally decreased slightly in the northern and southern hemispheres and throughout the world since 1970; while, it has remained almost stable in the tropical regions. In 2022, the relative humidity values over the Northern and Southern Hemisphere, Tropics, and Global were − 1.03, 0.43, 0.32, and − 0.37%rh above the 1991–2020 average, respectively.

Fig. 11

Source: Data from Freeman et al. [85], Smith et al. [86], Willett et al. [87,88,89,90,91]

Annual average relative humidity anomalies from the 1991–2020 average, a Northern Hemisphere, b Southern Hemisphere, c Tropics, and d Global. 2-σ uncertainty is shown for the HadISDH dataset.

Figure 12 shows the specific and relative humidity HadISDH 1.4.1.2022f decadal trends between 1973 and 2022 by the Met Office Hadley Centre [51]. Since the early 1970s, specific humidity has increased at a rate of 0.09 g/kg per decade over land, 0.08 g/kg per decade over the ocean, and 0.08 g/kg per decade when considering land and ocean combined. Despite the overall increase in water vapor since the 1970s, the air over land has become less saturated, with a notable decline in relative humidity since around 2000 at a rate of 0.16%rh per decade. Over the ocean, relative humidity data carries larger uncertainty, showing a slight decrease in -0.09%rh per decade. The noteworthy surge in specific humidity is likely attributable to the increase in greenhouse gas emissions. A seemingly paradoxical trend is the decrease in relative humidity over land despite higher water vapor levels. This phenomenon is primarily driven by the concurrent increase in temperature. While water vapor has increased over land and oceans (the primary water vapor source for land), it has not kept pace with rising land temperatures. The saturation level over the land has decreased, causing a decline in relative humidity. The rate of water vapor increase is slightly higher over land than over oceans; whereas, the temperature rise is significantly greater over land than over the ocean, contributing to reduced relative humidity over land [51].

Fig. 12

Source: Maps from Willett et al. [89, 90]

Specific and relative humidity HadISDH 1.4.1.2022f decadal trends between 1973 and 2022 by Met Office Hadley Centre [51].

4.5 Total Column Water Vapor

As the most prevalent gas in the atmosphere, water vapor is thought to play a significant role in providing feedback about the climate and, consequently, global warming. Two-thirds of global warming can be attributed to water vapor, and the amount of water vapor that enters the atmosphere determines how much more warming occurs there. Because water vapor has a limited lifecycle, the atmosphere now maintains a steady balance between temperature and water vapor content. When temperatures rise, the equilibrium will be destroyed, leading to an increase in global warming, where water vapor can double the warming brought on by carbon dioxide [3].

The indirect effects of water vapor on global warming can also be seen; as temperatures rise, so does the amount of water vapor in the atmosphere, increasing the likelihood that clouds will form. Brighter clouds reflect solar radiation back into space, which aids in cooling the globe. Clouds are a major factor in warming or cooling the world. On the other hand, clouds can both absorb and release energy in the infrared spectrum. This is because low clouds emit nearly the same amount of infrared radiation because of their similar temperature to that of the Earth’s surface. Because high cold clouds take energy from the lower atmosphere, they also emit less energy because of their low temperature. This implies that high clouds hinder the earth’s capacity to cool, which raises the planet’s temperature [3].

Water vapor is the Earth’s primary greenhouse gas, trapping more heat than CO₂, and is a critical component of Earth’s climate systems. The movement of water vapor is also crucial in determining the amount of precipitation in a region. The total column water vapor, on the other hand, is a measure of the integrated water vapor content present in a vertical column of the atmosphere. It is essential for energy transfer because it affects patterns of precipitation and evaporation, which in turn affects the frequency of floods and droughts. Because a warmer atmosphere can contain more moisture, differences in surface and atmospheric temperatures are strongly related to changes in the amount of water vapor on Earth. As seen in Fig. 13, data from Climate Reanalyzer [52] and different satellites have shown a progressive increase in atmospheric water vapor over the Northern and Southern Hemisphere, Tropics, and Global since the 1980s. Despite the presence of La Niña conditions in the tropical Pacific Ocean, which usually results in reduced water vapor due to lower tropospheric temperatures, the global averages of total column water vapor over land and oceans in 2022 were near or slightly above the climatological averages for the period 1991–2020.

Fig. 13

Source: Data from Climate Reanalyzer [52]

Annual average Total column water vapor anomalies from the 1991–2020 average, a Northern Hemisphere, b Southern Hemisphere, c Tropics, and d Global.

Based on the 1991–2020 reference period, Fig. 14 shows the yearly worldwide mean total column water vapor and its anomaly for 1973 and 2022. A notable low vapor anomaly is observed in the center equatorial Pacific on the global map of total column water vapor anomalies for 2022. This is contrasted with a large high vapor anomaly to the south and west, which covers most of Australia and the eastern Indian Ocean south of the equator. High anomalies are observed in several areas of the extratropical Northern Hemisphere; these are most evident in the Tibetan Plateau, Northern India, and the North Pacific. The yearly mean for 2022 showed record-high or record-low vapor levels in several locations.

Fig. 14

Source: ECMWF ERA5 (0.5 × 0.5 deg) data [53], Maps from Climate Reanalyzer [52]

Annual global mean total column water vapor and its anomaly in 1973 and 2022 according to the base period of 1991–2020.

5 Greenhouse Gases

It is a known fact that life on Earth depends on the energy coming from the Sun. Approximately half of the solar radiation reaching the Earth's atmosphere is absorbed through the air and clouds to the surface and radiated as infrared heat. While some of this emitted infrared radiation passes through the atmosphere, approximately 90% is absorbed by greenhouse gases and re-emitted by the atmosphere in all directions. This effect causes the earth's surface and lower atmosphere to warm. Since the Industrial Revolution, human activity has led to an increase in the atmospheric concentration of greenhouse gases, which has resulted in the observed rise in global temperature [1]. Climate forcing (radiative forcing) is defined by the Intergovernmental Panel on Climate Change [54] as an externally imposed perturbation in the Earth’s radiative energy budget caused by variations in solar radiation, Earth’s albedo, or atmospheric gases and aerosol particles. Climate forcing induces alterations in climate patterns. Among these forces, the most substantial and least uncertain perturbation is associated with changes in the atmospheric concentrations of long-lived, uniformly distributed greenhouse gases, notably CO₂, CH₄, N₂O, and halogenated compounds (predominantly CFCs) [92]. CO₂, CH₄, N₂O, along with dichlorodifluoromethane (CFC-12) and trichlorofluoromethane (CFC-11), collectively contribute to approximately 96% of the radiative forcing attributed to long-lived greenhouse gases (LLGHGs) [7].

The dangerous trend of constant rise in surface and ocean temperatures worldwide, known as global warming, is caused by the buildup of CO₂ in the atmosphere, which traps the infrared radiation released from the Earth’s surface after sunlight is absorbed [2]. Approximately 64% of the radiative forcing resulting from long-lived greenhouse gases is attributed to CO₂, making it the primary anthropogenic greenhouse gas [7]. The majority of CO2 emissions come from burning coal, oil and natural gas. According to Al-Ghussain [3], doubling or halving the amount of CO₂ in the atmosphere could cause the world temperature to change by + 3.8 °C or − 3.6 °C. Figure 15a shows the global change in the concentration of CO₂ throughout history until 2022. As can be seen, the value of CO₂ in the air is increasing significantly globally and has reached levels that have not existed for millions of years. The CO₂ concentration was 278.3 ppm at pre-industrial times, indicating a balance between terrestrial, oceanic, and atmospheric fluxes. The average global CO₂ concentration by 2022 was 417.9 ± 0.2 ppm. The 2.2% annual growth rate from 2021 to 2022 was marginally less than the 2.5% increase from 2020 to 2021 and less than the 2.46% annual growth rate that has been the average over the past ten years [7]. Figure 16 shows the spatial distribution of historical CO₂ concentrations, with high CO₂ concentrations occurring in developed regions such as Europe, China, and the eastern part of the United States [24].

Fig. 15

Source: Data from Keeling et al. [93], Tans and Keeling [94], Masarie and Tans [95], WMO [96], Dlugokencky et al. [97], Lan et al. [98]

Changes in globally averaged CO₂, CH₄, and N₂O concentrations throughout history until 2022.

Fig. 16

Average global historical atmospheric CO2 concentrations (ppm) a during 1890–1989 and b during 2004–2013 [24]

CH₄ emissions are the second largest human cause of global warming. Approximately 19% of the radiative forcing caused by long-lived greenhouse gases is attributed to CH₄. When natural gas is extracted, produced, transported, refined, and distributed, anthropogenic CH₄ may be emitted into the atmosphere. Livestock, agriculture, human waste, and landfills contribute significantly to CH₄ emissions. CH₄ molecules are ten times more efficient than carbon dioxide molecules at absorbing and reradiating energy. Nonetheless, in their calculations, scientists typically concentrate on the overall amount of emissions rather than their intensity, given that CO₂ has a 200-fold higher concentration than CH₄ and a much longer half-life than atmospheric methane [3]. Figure 15b shows the global change in the concentration of CH₄ throughout history until 2022. In the past 150 years, methane emissions have more than doubled, and approximately 60% of these emissions are thought to be caused by human activity. The global average CH₄ concentration increased by 16 ppb from the previous year to a new high of 1923 ± 2 ppb in 2022. This growth surpasses the average yearly increase of 10.2 ppb over the previous ten years, even though it is just less than the 17 ppb increase seen between 2020 and 2021. Since 2007, atmospheric CH₄ has significantly increased, mostly from anthropogenic sources such as agricultural practices, to 264% of the pre-industrial level by 2022 [7].

In comparison to CO₂, N₂O has a warming capacity greater than 300-fold. Compared with CO₂, the concentration of N₂O is substantially lower [3]. N₂O is the third most important individual contributor to the radiative forcing caused by long-lived greenhouse gases accounting for approximately 6% of the total. Both natural and man-made sources, such as soils, oceans, burning biomass, fertilizer use, and industrial processes, are responsible for its emissions. Figure 15c shows the global change in the concentration of N₂O throughout history until 2022. The average global concentration of N₂O in 2022 was 335.8 ± 0.1 ppb, up 1.4 ppb from the year before and above 124% of the pre-industrial level. The yearly growth rate from 2021 to 2022 surpassed the growth rate from 2020 to 2021 and beat the average growth rate for the previous ten years [7].

6 Innovative Technologies and Approaches to Global Warming

The first step in mitigating global warming and lowering greenhouse gas emissions is to reinforce policies that will hasten the adoption of clean and efficient energy technologies. To steer consumer spending and business expenditures toward the most efficient technology, standards and guidelines are two essential components. The change in the electrical sector can be accelerated by solar and wind power through competitive tenders and targets. Appropriate price signals could be achieved via carbon pricing, phasing out fossil fuel subsidies, and other market changes. Certain fuels and technologies, such as unreduced coal-fired power plants, gas boilers, and cars with internal combustion engines, should be restricted or discouraged by policy. When it comes to organizing and advocating for significant infrastructure expenditures, such as intelligent transmission and distribution networks, governments ought to take the lead.

It is evident from creative technologies that significant advancements in clean energy innovation will be necessary to achieve net zero emissions by 2050. Both the rapid adoption of recently released technology and the rapid dispersion of available technologies will be necessary. Emission reductions from current research and development efforts are critical for heavy industry and long-distance transportation. Considering climate change, researchers stress the significance of switching to renewable energy sources and adopting sustainable practices. A move toward greener options is necessary because the fossil fuel sector still contributes significantly to greenhouse gas emissions. Although there are many obstacles associated with climate change, coordinated global action may be able to reduce warming and the harm that comes from greenhouse gas emissions. Collaboration and dedication on a worldwide scale are necessary to effectively tackle climate change. To cut emissions, for instance, initiatives to stop deforestation, encourage afforestation, and save natural carbon sinks are essential. Transportation-related emissions can be greatly reduced by using electrified vehicles and sustainable transportation. There may be ways to lower emissions through the creation and application of innovative technologies such as carbon capture and storage. The carbon footprint of food production can be decreased by adopting sustainable farming methods, cutting back on food waste, and altering one’s diet. Campaigns for education and awareness are crucial in creating a sense of personal and societal accountability in the fight against climate change. It needs to be backed by the massive infrastructure building that innovative technologies will require in the upcoming years. Table 1 summarizes the various mitigation technologies or approaches to reduce GHG emissions [3].

Table 1 Various mitigation technologies or approaches to reduce GHG emissions

Owing to rising energy consumption, declining CO₂ levels, depletion of fossil fuel stocks, and climate change, numerous nations worldwide are still looking for sustainable and renewable alternatives to their current energy infrastructure. Following the Paris Agreement, they examine the possible financial advantages and difficulties of a low-carbon energy transition aimed at cutting greenhouse gas emissions by 60% to 80% by the year 2050. Since the energy industry is the major source of greenhouse gas emissions, the move to low-carbon energy is a global trend since these emissions have an impact on two of the most pressing global issues: climate change and global warming. A multitude of social, economic, environmental, technological, and institutional obstacles must be overcome by researchers and decision-makers in the socio-technical transition to low-carbon energy. This energy system, which necessitates quick and drastic socio-technical adjustments, is a solution to the dual concerns of climate change and sustainable growth. To precisely adhere to the deadlines specified in international agreements like the Paris Agreement, decision-makers and researchers must thoroughly examine the issues and how to resolve them [99].

7 Renewable Energy

The goal of the net zero GHG emissions by 2050 scenario is to illustrate the necessary steps, together with the timelines for each actor, across the major sectors to reach net zero CO₂ emissions connected to energy and industrial processes by that date. Achieving zero net global CO₂ emissions by 2050 aligns with keeping the average global temperature increase to 1.5 °C over the long run. Technologies based on renewable energy hold the key to cutting emissions from the world’s electricity supply. While hydropower has been a prominent source of low-emission energy for many years, the growth of wind and solar power is primarily responsible for the triplet of renewable energy generation by 2030 and the more than eightfold rise in net zero GHG emissions by 2050. Globally, the percentage of renewable energy generated in total electricity generation will rise from 29% in 2020 to over 60% in 2030 and almost 90% in 2050. The yearly capacity additions of solar and wind between 2020 and 2050 must be five times more than the average of the previous three years to accomplish this goal. In addition to additional low-carbon generation, energy storage, and strong electricity networks, undispatchable renewable energy sources are essential for preserving electricity security [31].

The COVID-19 pandemic and the Russian Federation’s invasion of Ukraine have severely affected the world’s supply systems for energy and technology. Gas, oil, and coal prices have increased significantly because of this disruption, and shortages of vital minerals, semiconductors, and other materials needed to produce sustainable energy technology have also occurred. The current global energy crisis threatens future economic opportunities and makes the adoption of clean energy technology risky. It also emphasizes the financial case for increasing investments in energy efficiency, renewable energy, and other clean energy technologies to hasten the shift away from fossil fuels. The recent increase in extreme weather occurrences across the globe is a clear indication of the urgent need to reduce greenhouse gas emissions [100].

The energy industry worldwide is on track for a significant transformation, moving from a predominantly fossil fuel-based sector to one where renewable energy sources and various clean energy technologies will play a dominant role over the next few decades. The emergence of a new global energy economy is increasingly evident, marked by the swift expansion of solar and wind energy, the rise of electric vehicles, and the adoption of technologies such as electrolyzers for hydrogen production. This transition is reshaping the sectors responsible for providing materials and products essential to the energy system, signaling the onset of a new industrial era: the era of manufacturing clean energy technologies [100].

Increasing the use of renewable energy sources is one way to combat the impending energy shortage and reliance on the depletion of non-renewable energy sources. In addition to being renewable, renewable energy is environmentally friendly since it doesn't release greenhouse gases, which is a key drawback of fossil fuels [101]. To secure a sustainable energy future, many economic, environmental, and social problems have compelled governments and policymakers to adopt renewable energy technology [102]. Socioeconomic factors such as economic growth, poverty, income, health, welfare, agricultural productivity, water resources, energy supply, energy demand, and energy security can significantly shape effectiveness and action toward climate change and the transition to renewable energy. Addressing these issues requires an integrated approach that takes into account economic, social, political and technological dimensions to achieve sustainable and equitable outcomes [103].

Figure 17 shows the percentages of global electricity output in electric power plants for 2011, 2012, 2021, and 2022. This figure shows that in 2022, as in previous years, the share of fossil fuels is observed to be higher than that of any other power generation technologies. Nonetheless, it is a positive and encouraging development that the use of fossil fuels has decreased from 68% in 2011 to 61% in 2022; while, the use of renewable energy sources has increased from 20.4% in 2011 to 29.9% in 2022. This circumstance demonstrates how, even as the world’s reliance on fossil fuels declines, it is shifting toward more efficient, ecologically benign, and cleaner renewable energy sources to meet its energy needs. The use of solar and wind power has increased significantly from 2% to 12.1% of total electricity from 2011 to 2022. Conversely, throughout the last decade, there has been no significant shift in the power share of other electricity producing methods. This places the use of wind and solar energy ahead of other current energy generation technologies. As a result, solar and wind energy technologies are now among the world’s fastest developing energy systems technologies, and the energy production industry has the fastest growing investment due to investor demand.

Fig. 17

Share of global electricity generation by energy source between 2011 and 2022

Figure 18 shows the cumulative installed capacity of renewable energy sources between 2017 and 2022 and the net zero scenarios for 2030, 2040, and 2050. According to the installed power capacity distribution of renewable energy technologies, the solar energy installed power capacity increased from 405 GW in 2017 to 1,185 GW in 2022, an increase of 193%. Solar energy installed power capacity is expected to increase to 4,956 GW, 10,980 GW, and 14,458 GW in 2030, 2040, and 2050, respectively. While the installed power capacity of wind energy was 540 GW in 2017, it reached 923 GW in 2022, with an increase of 71%. This capacity is expected to reach 3,101 GW, 6,525 GW, and 8,365 GW in 2030, 2040, and 2050. Therefore, solar and wind energy, along with hydro energy, will be among the most important renewable energy sources in the world in the coming years.

Fig. 18

Cumulative installed capacity of renewable energy sources between 2017 and 2022 and to achieve net zero scenarios for 2030, 2040, and 2050

8 Conclusion

The current study presents and discusses the influences and progress of global warming, climate change, and greenhouse gases, together with the current situation and development of renewable energy. For this purpose, a conclusive visual representation of the indicators of climate change, such as land and sea surface air temperatures, sea level rise, sea ice extent, ocean heat content, surface humidity, and total column water vapor, is presented. The results show an increasing trend in the global average annual surface temperature anomaly values between 1850 and 2023 caused by global warming because of anthropogenic greenhouse gas emissions. Until the mid-twentieth century, most atmospheric scientists assumed that climate changes were caused solely by natural factors and processes. After the 1960s, this approach also changed as global warming tended to increase further. In addition to natural causes, throughout human history, the idea that various human activities can also have effects on the climate system has become dominant. The global mean surface temperature during 2011–2020 increased to 1.1 °C compared with that during 1850–1900. Greenhouse gas emissions occur more in the northern hemisphere than in the southern hemisphere, and greenhouse gases persist long enough to spread in both hemispheres, affecting the temperature difference between the hemispheres. It is revealed that the temperature increment is higher in the northern hemisphere with the passing years because of the higher greenhouse gas emissions and melting of sea ice and snow.

According to the results obtained, as long as human beings continue their activities that harm the environment, especially fossil fuels, the average surface temperature of the world will continue to increase. Based on the CO₂ emission scenarios, it is projected that by the end of the twenty-first century, the average surface temperature will rise by 2–6 °C. As atmospheric temperatures rise, the capacity to hold water vapor increases, leading to decreased relative humidity and increased absolute humidity in regions with traditionally low humidity and temperatures, such as the poles. This added water vapor and heat can significantly elevate temperatures. With higher absolute humidity in the atmosphere, the potential for more intense precipitation events increases. These events will become shorter and less frequent, requiring more time for the atmosphere to replenish its moisture. Global warming will enhance the atmosphere's moisture retention and raise seawater surface temperatures, intensifying storms and increasing the probability of hurricanes through higher wind speeds. Very dry regions worldwide will expand further due to global warming. As the global average temperature rises, snow will melt sooner, and evaporation from vegetation and soil will accelerate. Rainfall patterns will shift from moderate and light rains to shorter, heavier downpours. The climate will make the transition toward a warmer state, resulting in more extreme weather events.