Non-CO₂ GHG Emissions

Abstract

There is still a substantial gap between the Intended Nationally Determined Contributions (INDCs) submitted by countries to the UNFCCC secretariat and the lower levels of emissions needed to hold warming below 2 ℃ and 1.5 ℃. If the temperature rise is to be limited to 2 ℃, total emissions in 2030 must be reduced by another 15 billion tons of CO₂e on top of the existing INDCs; and to enable 1.5 ℃, 32 billion tons of CO₂e must be cut.

6.1 Scope and Status of Non-CO₂ GHG Emissions

There is still a substantial gap between the Intended Nationally Determined Contributions (INDCs) submitted by countries to the UNFCCC secretariat and the lower levels of emissions needed to hold warming below 2 ℃ and 1.5 ℃. If the temperature rise is to be limited to 2 ℃, total emissions in 2030 must be reduced by another 15 billion tons of CO₂e on top of the existing INDCs; and to enable 1.5 ℃, 32 billion tons of CO₂e must be cut. This means that from 2020 to 2030, an annual emission reduction of 2.7% is required to achieve the 2 ℃ goal, and emissions must be cut by 7.6% on average annually to cap warming below 1.5 ℃ [1]. CO₂ emissions which accounts for the largest share of greenhouse gases, are a major cause of global climate change. However, a great many studies also highlight the unneglectable impact of non-CO₂ GHG emissions. The Fifth Assessment Report of the United Nations Intergovernmental Panel on Climate Change shows that non-CO₂ emissions have consistently hovered around 25% of the global GHG emissions. A host of international agencies, including the U.S. Environmental Protection Agency (EPA), anticipate that non-CO₂ emissions will continue to rise in the future, and without effective control, could offset efforts in carbon reduction. Studies have demonstrated that the reduction of non-CO₂ GHG emissions, as a vital alternative emissions reduction plan, features the edge of being low-cost, highly flexible and responsive, and synergistic, hence its extensive application in developed countries. To narrow the emissions gap, the reduction of non-CO₂ GHG emissions has gained more prominence and interest in the global response to climate change.

To effectively mitigating GHG emissions in tackling global climate change, Articles 4.1 and 12 of the UNFCCC stipulate that national communications—the most critical component of which is national inventories of anthropogenic emissions and removals by sinks of all GHGs—are an obligation of Parties to the Climate Change Convention. The 16th and 17th sessions of the Conference of the Parties to the UNFCCC held in 2010 and 2011 adopted decisions 1/CP.16 [2] and 2/CP.17, which mandated that beginning in 2014, non-Annex I Parties shall submit a biennial update report covering national GHG inventories, mitigation actions, finance, technology and capacity-building needs and support received that is consistent with the Party’s level of international support, and that the report should be subject to international consultation and analysis.

The non-CO₂ GHGs covered in this report are primarily methane, nitrous oxide, and F-gases. The main emission sources and sectors involved are presented in Table 6.1 (CO₂ emissions generated from industrial production processes are analyzed in Chapter 3).

Table 6.1 The scope of non-CO₂ GHG emissions defined by this report

This chapter summarizes non-CO₂ data from official emissions inventories such as the Initial National Communication on Climate Change of the People’s Republic of China [3] (hereinafter referred to as the Initial Communication), the Second National Communication on Climate Change of the People’s Republic of China [4] (hereinafter referred to as the Second Communication), the PRC’s First Biennial Update Report on Climate Change [5] (hereinafter referred to as the Biennial Update Report), and the Second Biennial Update Report on Climate Change. The specific results are shown in Fig. 6.1.

Fig. 6.1

Non-CO₂ GHG emissions in China

In 1994, China’s total non-CO₂ GHG emissions stood at 980 million tCO₂e. That number rose to roughly 1.49 billion tCO₂e in 2005, and more than 2.06 billion tCO₂e in 2014. In 2014, non-CO₂ GHGs comprised 16% of China’s total emissions, as shown in Fig. 6.2. Methane emissions, which stemmed mainly from energy and agriculture activities, made up 56% of total non-CO₂ emissions and were approximately three times the level in 1994.

Fig. 6.2

Breakdown of GHG emissions by gas in 2014

Total GHG emissions from waste treatment amounted to 195 million tCO₂e, of which 100 million tCO₂e arose from the treatment of solid waste (landfill, incineration, and biological treatment), accounting for 52.4% of total emissions, and 91 million tCO₂e resulted from wastewater treatment, or 47.6% of the total. HFCs were first introduced into the market by developed countries in the late 1980s and were mostly used as raw materials to produce refrigerants, foaming agents, fire extinguishing agents, aerosols, and chemical products in a wide array of industrial sectors. SF6 emissions principally involve four sectors: power transmission and distribution equipment (electric equipment for short), magnesium smelting, semiconductor production, and SF₆ production. Currently, China has, by and large, ceased the use of SF₆ [6, 7] in the production of semiconductors and magnesium, and electric equipment is now the primary source of SF₆ emissions. Studies have shown that the increase in global SF₆ emissions mainly stems from Non-Annex I countries, and in particular China [8]. The global warming potential (GWP) of perfluorocarbons (PFCs) is 6,500–9,200 times that of CO₂, and its main emission sources are the production of electrolytic aluminum, which contributes over 95% of the emissions, and semiconductors [9]. Therefore, the emission of non-CO₂ GHGs from industrial processes constitutes an essential part of China’s overall strategy on climate change.

6.2 Scenarios and Results of Non-CO₂ GHG Emissions

Four scenarios are outlined in this chapter to examine non-CO₂ emissions and reduction potential. 2015 is chosen as the base year, and 2050 the target year. The policy scenario is used as the basis for comparison, and a reinforced policy scenario is built on of that to intensify the reduction in non-CO₂ GHGs under the current policy. The 2 ℃ scenario is also built to accommodate the trend of non-CO₂ GHGs under foreseeable emission reduction policies and technological potential. Last but not least, the 1.5 ℃ scenario is created to examine various emission reduction policies and the potential of applying all possible emission reduction technologies available.

The differences between the various scenarios lie, on the one hand, in the changes in activity levels, and on the other hand, in the degree of diffusion of emission reduction technologies. Changes in the activity levels of industries are, in large measure, aligned with changes in the level of economic development. Take methane emissions from coal mining as an example. With the continuous advancement of China’s policy on curbing coal-fired power, coal production has seen a steady decline, which has in turn played a critical role in reining in methane emissions from mining. Emission reduction pathways for various industries mainly include the complete reduction of demand, replacement of demand, end-of-pipe recycling, disposal and decomposition measures. The latter scenario always represents more aggressive emission reduction targets and higher levels of technology adoption than the previous one. With the progression of scenarios, each is assigned a more intensified position in such aspects as the level of technology diffusion and demand reduction than the one before.

6.2.1 Non-CO₂ GHG Emissions Under the Policy Scenario

Under the policy scenario, non-CO₂ GHG emissions climb from 2.17 billion tCO₂e in 2015 to 3.17 billion tCO₂e in 2050, up 46.2% with an average annual growth of roughly 1.1% (Fig. 6.3 and Table 6.2). The growth of emissions primarily arises from HFC refrigerants and the agricultural sector during the 2015–2050 period. Non-CO₂ GHG emissions from the waste sector largely remain stable, and energy-related methane emissions no longer increase due to the peaking of coal consumption.

Fig. 6.3

Non-CO₂ GHG emissions under the policy scenario

Table 6.2 Non-CO₂ emissions under various scenarios (excluding LULUCF) (GtCO₂e)

6.2.1.1 Methane

Under the policy scenario, CH₄ emissions amount to roughly 1.22 billion tCO₂e in 2015 and grow by 14.2% to 1.39 billion tCO₂e in 2030, up nearly 0.9% year-on-year. However, between 2030 and 2050, CH₄ emissions are slated to drop by an average of 0.7% annually, to 1.2 billion tCO₂e in 2050.

In terms of the distribution of emissions by sector, coal mining is the largest source of methane emissions. CH₄ emissions from coal mines are projected to slide slowly from 540 million tCO₂e in 2015 to 530 million tCO₂e in 2020 before falling steadily to 310 million tCO₂e in 2050. Between 2015 and 2030, the share of methane emitted during coal mining ranges between 38.8 and 44.2%, and that number drops incrementally to 25.5% by 2050. Enteric fermentation in animals and rice cultivation in the agricultural sector are also major sources of CH₄ emissions. Methane emissions from these sources are estimated to rise from nearly 470 million tCO₂e in 2015 to 580 million tCO₂e in 2030, and to 630 million tCO₂e in 2050. Their share in total CH₄ emissions, by and large, stabilizes at 38.5–42.4% from 2015 to 2030, and climbs to 52.8% by the middle of this century, a growth of nearly 10 percentage points from the base year. Landfilling waste also contributes to CH₄ emissions. Emissions from this category are slated to maintain a growth trajectory from 80 million tCO₂e in 2015—6.8% of total methane emissions—to 104 million and 80 million tCO₂e in 2030 and 2050, respectively, with the share rising to 7.5% in 2030.

On the makeup of emission increase, the growth in CH₄ emissions amounts to roughly 167 million tCO₂e between 2015 and 2030. The most significant drivers of growth are enteric fermentation, oil and gas leaks, and the landfilling of solid waste, which resulted in 120, 30, and 20 million tCO₂e, respectively. The increase in CH₄ emissions is reduced by 180 million tCO₂e between 2030 and 2050, during which the primary source of growth is intestinal fermentation—40 million tCO₂e. The decline in coal consumption leads to a continuous reduction in methane emissions during the mining process after 2030. Approximately 180 million tCO₂e is projected to be cut at the end of the model’s time-frame compared to 2030.

6.2.1.2 Nitrous Oxide

Under the policy scenario, N₂O emissions stands at roughly 490 million tCO₂e in 2015 and are projected to register a 44% growth and increase at an annual average of 2.3% to reach 700 million tCO₂e in 2030. The growth of N₂O emissions slows dramatically between 2030 and 2050 when they maintain at a level of less than 700 million tCO₂e.

On the sources of emissions, the fertilization of agricultural soils using nitrogen fertilizers and manure is the largest source of nitrous oxide emissions. Under the policy scenario, N₂O emissions from nitrogen fertilizers are slated to grow steadily from 360 million tCO₂e in 2015 to peak at 450 million tCO₂e in 2020, and then witness gradual growth in the ensuing plateau period. This projection largely aligns with China’s commitment to peak the use of nitrogen fertilizers in 2020 as proposed in its NDC. The proportion of N₂O emissions from using nitrogen fertilizers and manure is set to decline gradually from 74.0% in 2015 to 66.9% of total N₂O emissions. The sources of N₂O emissions are diverse. Apart from the primary sources—agricultural soils, the production of nitric acid and adipic acid in industrial processes, waste-water treatment, and animal manure management in the agricultural sector all contribute to N₂O emissions, with adipic acid representing the largest share. Under the policy scenario, N₂O emissions from adipic acid production peak at 210 million tCO₂e in 2025, with the share growing from 14.1% in 2015 to 27.7% in 2030 before trending slightly downward to 24.2%.

From 2015 to 2030, N₂O emissions grow by roughly 220 million tCO₂e, of which the biggest drivers are adipic acid, nitrogen fertilizers, manure management and the use of manure as a fertilizer, contributing 130 and 80 million tCO₂e, respectively. Between 2030 and 2050, the increase in N₂O emissions is significantly reduced to 20 million tCO₂e. The major sources of growth during this stage are manure management, energy activities, and the use of manure as a fertilizer. As emissions from other sources are slated to decrease, all growth stems from the above-mentioned sources.

6.2.1.3 F-Gases

Under the policy scenario, F-gas emissions soar by 93.8% from roughly 450 million tCO₂e in 2015 to 870 million tCO₂e in 2030, averaging 4.5% growth annually. Between 2030 and 2050, the growth sees a notable drop to around 1.9%. Emissions in 2050 are up 181% relative to the base year, reaching 1.27 billion tCO₂e.

On the distribution of emissions by sector, HCFC-22 production and air conditioning are the biggest contributors to F-gas emissions. Emissions from HCFC-22 production are projected to grow steadily from 110 million tCO₂e to the peak at 160 million tCO₂e in 2025 before entering a plateau. In the meantime, emissions from indoor, automobile and commercial air conditioning witness exponential rise at an average of 4.5% annually from 220 million tCO₂e in 2015 to 430 million tCO₂e in 2030, double the level relative to the base year. Between 2030 and 2050, the growth slows to around 2.3%. Total emissions hit 690 million tCO₂e, up 213% from the base year. Resulting from the substantial increase in emissions from air conditioning, the share of F-gas emissions from HCFC-22 production in the total F-gas emissions is projected to plunge from 38.8% in 2015 to 23.9% and 16.9% in 2030 and 2050, respectively. The share of F-gas emissions from air conditioning jumps from 50.9% in the base year to 66.4% in 2030 and 76.4% in 2050.

F-gas emissions are expected to climb by 420 million tCO₂e from 2015 to 2030, the biggest drivers of which are air conditioning and HCFC-22 production, which contribute 290 and 40 million tCO₂e, respectively. Together they account for 89.2% of the total increase, of which the contribution of air conditioning stands at 77.8%. From 2030 to 2050, the increase in F-gas emissions falls to 390 million tCO₂e. At this stage, emissions attributed to air conditioning, the chief source of increase rise by 260 million tCO₂e, comprising over 95% of the total increase. Air conditioning and indoor cooling are the largest growth drivers, accounting for approximately 77.5% of the total increase.

6.2.1.4 Carbon Sink

Forest carbon sinks and grassland carbon sinks/emissions are vital parts of the global carbon cycle in terrestrial ecosystems. The cycle mainly consists of photosynthesis, respiration, the burning and decaying of biomass, and the decomposition of soil and other organic matter. Forests store large amounts of carbon. Forest biomass is most closely linked to the stage of the life cycle, and the accumulation rate of carbon is the largest in middle-aged forests while mature and over-mature forests—whose biomass largely ceases to grow—are in equilibrium with a net carbon balance. This report presents three scenarios for evaluating changes in forest carbon sinks. The policy and reinforced scenarios are similar and thus merged into one. Under the three scenarios, China’s forest stock keeps continuous growth through to 2050, and the changes in carbon uptake and storage by forests are precisely in sync with that of forest stock. However, carbon sink capacity reflects the rate of change in forest carbon storage during a given time interval (one year or multiple years) and the ability to cleanse carbon accumulations in different periods.

Under the policy/reinforced policy scenarios, the primary consideration is to appropriately implement measures such as creating new forest areas, increasing the share of young and middle-aged forests, and harvesting mature forests, so that by 2030, the forest stock jumps by more than 20% compared with 2015, while the carbon sequestration capacity increases by less than 1% to reach 412 million tCO₂, and Chinese forests’ capacity to absorb and store carbon grows gradually to 424 million tCO₂ in 2050, almost double the amount in 2015. Under the 2 ℃ scenario, more sophisticated and intensified measures are adopted, including afforestation, and the judicious selection of plant species, growth rate and age for afforestation. The carbon sequestration capacity is projected to hit 654 million tCO₂ in 2030 before a slight decrease to 502 million tCO₂ by 2050. Under the 1.5 ℃ scenario, the capacity exceeds 900 million tCO₂ in 2030, and in 2050, the forest stock surges by 90% over the 2015 level, and the carbon sequestration capacity increases by 1.7 times to reach 576 million tCO₂.

Carbon emissions and sequestration in grasslands are part and parcel of the ecosystem carbon cycle. The majority of carbon sequestered in grasslands is stored in vegetation and soil organic matter. There are numerous types of grasslands in China with great discrepancies in carbon storage capacities. Climate and vegetation zonality exert a profound impact on the carbon storage capacity of grasslands. Changes in the carbon storage volume and area of grasslands are closely associated with grassland management policies and measures after 2020. Wetlands, forests, and grasslands are collectively known as the three major terrestrial ecosystems. Wetlands sequester carbon primarily through soils and plant biomass, with the former accounting for over 90% of total carbon storage in wetlands. An analysis of the scenario in this paper shows that the capacity of China’s grasslands and wetlands to sequester carbon from the atmosphere remains at roughly 200 million tCO₂ in 2050.

It can be established from the scenario analysis in conjunction with related research that the capacity of China’s forests, grasslands, and wetlands to store carbon stands at 700–800 million tCO₂ in 2050.

6.2.2 The Emission Reduction Potential of Non-CO₂ GHGs

Under the reinforced policy scenario, non-CO₂ GHG emissions are estimated to peak around 2030 before entering a plateau and experiencing a gradual decline. The peak is at roughly 2.78 billion tCO₂e with an average annual growth of around 1.7% during this period. From 2030 to 2050, emissions slowly drop to 2.37 billion tCO₂e, down 0.8% year-on-year. Emissions are reduced by roughly 25% compared with the policy scenario. Detailed data are shown in Table 6.3 and Fig. 6.4. The emissions of non-CO₂ GHGs are expected to peak simultaneously with CO₂ emissions in 2030 under this scenario. Due consideration should be given to establishing non-CO₂ peaking targets in China’s future NDC ambitions, which will underline the importance of non-CO₂ GHGs to the country’s overall climate strategy. Currently, nearly one-third of the emission reductions in developed countries is achieved through the abatement of non-CO₂ GHGs, which indeed warrants wider attention.

Table 6.3 Non-CO₂ GHG emissions in 2030 and 2050 under the reinforced policy scenario (MtCO₂e)

Fig. 6.4

Forest carbon sink scenarios

Under the 2 ℃ scenario, non-CO₂ GHG emissions are estimated to peak in 2025 at approximately 2.51 billion tCO₂e, with an average annual growth of 1.5% during this period, falling to 1.76 billion tCO₂e in 2050, down 1.4% annually. Compared with the reinforced policy scenario, non-CO₂ emissions are slashed under the 2 ℃ scenario to 1.76 billion tCO₂e by 2050, roughly 44% lower than the policy scenario. Under the 1.5 ℃ scenario, non-CO₂ emissions peak in 2020 at 2.38 billion tCO₂e before dropping to 1.2 billion tCO₂e in 2050, around 60% lower than the policy scenario and half of its peak. The details are presented in Table 6.4 and Fig. 6.5, which show that even when all emission reduction technologies are adopted, the most radical efforts toward cutting non-CO₂ GHG emissions would fail to deliver near-zero emission by 2050. Moreover, the costs of technologies for near-zero emissions are exceedingly high. It is estimated that there would be a gap of at least 1.2 billion tCO₂e. Therefore, early opportunities must be seized upon when it comes to the emission reduction of non-CO₂ GHGs, and the aggressive implementation of negative emission technologies holds the key in the latter phases.

Table 6.4 Non-CO₂ GHG emissions in 2030 and 2050 under the 2 ℃ scenario (MtCO₂e)

Fig. 6.5

Non-CO₂ emission reduction in different scenarios

In 2015, non-CO₂ GHG emissions amounted to roughly 2.17 billion tCO₂e, of which methane, nitrous oxide, and F-gases took up 56.3%, 22.8%, and 20.9%, respectively. Under the policy scenario, emissions of various GHGs increase in 2050, albeit at different rates. F-gas emissions spike to account for 40.1% of total emissions while the share of methane emissions is down to 37.9% and that of nitrous oxide emissions remains broadly unchanged. The details are presented in Fig. 6.6. Under the reinforced policy scenario and the 2 ℃ scenario, methane still represents the highest share in 2050 at about 50.3% and 45.5%, respectively. The sharp rise of F-gas emissions pushes up their shares under the two scenarios to 26.8% and 28.7%, both higher than the levels in 2015. Under the 1.5 ℃ scenario, the share of methane emissions is 5 percentage points higher than that of F-gases, standing at 40.5% of the total, which means methane remains the largest source of non-CO₂ GHG emissions. The proportion of nitrous oxide emissions sees moderate growth to 25%. However, the gap in the share of emissions among the three is be narrowed.

Fig. 6.6

Volume and share of non-CO₂ GHG emissions in different scenarios

Based on comparisons of the various scenarios, it is anticipated that as socio-economic development and energy transition accelerate, CO₂ emissions will take a nosedive, and the share of non-CO₂ GHG emissions will grow year by year. In 2015, non-CO₂ gases comprised roughly 18% of all GHG emissions (national net GHG emissions being 11.2 billion tCO₂e). In 2050, the share of non-CO₂ GHG emissions in the reinforced policy scenario is projected to rise to 37%, and it further grows to 58% under the 2 ℃ and 95% under the 1.5 ℃. Therefore, prompt efforts to curtail non-CO₂ emissions are vital to fast-track China’s low-carbon transition and development.

6.2.2.1 Methane

CH₄ emissions are set to drop by a certain extent under the reinforced policy scenario compared with the policy scenario. CH₄ emissions peak in 2030 at 1.37 billion tCO₂e under the reinforced policy scenario; under the 2 ℃ scenario, its peaking occurs earlier in 2020 at a reduced level of 1.22 billion tCO₂e; and under the 1.5 ℃ scenario, the peak is moved up further to the time around 2015 at 1.22 billion tCO₂e; in 2030 under the reinforced, 2 ℃ and 1.5 ℃ scenarios, CH₄ emissions amount to 1.38 billion, 1.18 billion, and 790 million tCO₂e, respectively, down 0.7%, 14.2%, and 43.0% from the levels in policy scenario.

In terms of the distribution of emissions reduction by sector, under the 2 ℃ scenario, total CH₄ emission reduction is 200 million tCO₂e in 2030. The sectors contributing the most to the reduction are coal mining, solid waste treatment, rice cultivation, enteric fermentation, and animal manure management, with 140, 20, 20, and 20 million tCO₂e cut, respectively.

Under the 2 ℃ scenario, the reduction of CH₄ emissions grows to 400 million tCO₂e in 2050, which is primarily attributed to coal mining, animal intestinal fermentation, rice cultivation, and solid waste management, which witness a cut of 190, 170, and 10 million tCO₂e respectively. More ambitious efforts on non-CO₂ reduction are seen in the 1.5 ℃ scenario, with emission reduction reaching 590 million tCO₂e in 2030 and 680 million tCO₂e in 2050. A comparison of the scenarios reveals that part of the increase in emissions reduction in 2030 comes from the coal mining process, while the growth in 2050 is chiefly due to efforts coal mining, animal intestinal fermentation, and solid waste treatment.

6.2.2.2 Nitrous Oxide

N₂O emissions under reinforced policy, 2 ℃ and 1.5 ℃ scenarios witness a downward trajectory relative to the policy scenario, with the overall decrease exceeding that of CH₄ emissions. Under the reinforced policy scenario, N₂O emissions trend slowly downward after peaking in 2020, and maintain at 560–650 million tCO₂e from 2030 to 2050. At 2 ℃ scenario, the peak of N₂O emissions arrives in 2020 at 650 million tCO₂e. At 1.5 ℃ scenario, the peak remains in 2020 at a slightly reduced level of 580 million tCO₂e. Under these three scenarios, N₂O emissions in 2030 amount to 630, 570 and 420 million tCO₂e, which are 11.9%, 18.9% and 40.6% lower than the policy scenario.

In terms of the distribution of emission reduction by sector, under the 2 ℃ scenario, N₂O emissions are cut by 240 million tCO₂e in 2030, and the sectors with the highest contribution are nitrogen fertilizer application, animal manure management and manure as a fertilizer, which help reduce 77, 23 and 20 million tCO₂e respectively. In 2050, N₂O emissions are down by 150 million tCO₂e, mostly from energy activities such as nitrogen fertilizer application and biomass combustion and mobile sources, which contribute 80 and 64 million tCO₂e respectively. The 1.5 ℃ scenario sees stronger efforts in N₂O emission reduction, which rises to 280 and 380 million tCO₂e in 2030 and 2050 respectively. The incremental part was mainly achieved through the emission reduction measures during the production of adipic acid and nitrogen fertilizer application.

6.2.2.3 F-Gases

The emissions of F-gases start to decline slowly after 2035 under the reinforced policy scenario, while the growth of F-gases in the 2 ℃ scenario and the 1.5 ℃ scenario largely slows down after 2030 after peaking at 730 million tCO₂e, which is 16.3% lower relative to policy scenario. In 2050, F-gas emissions are 510 million and 440 million tCO₂e, down 60.3% and 65.5% compared to policy scenario.

The 2 ℃ scenario is characterized by a F-gas reduction of 140 million tCO₂e compared with the policy scenario, the biggest contributors being household air conditioners, HCFC-22 production and automobile air conditioners, with an emission reduction of 80, 30 and 30 million tCO₂e. By 2050, emission reduction rises to 760 million tCO₂e, mostly from refrigerant substitution in household and automobile air conditioners, which reduce 470 million and 290 million tCO₂e respectively. The 1.5 ℃ scenario features rising emission reduction to 150 and 830 million tCO₂e in 2030 and 2050. It is found that the increase of F-gas emission reduction in 2030 is largely contributed by the production process of HCFC-22 (120 million tCO₂e), while the contribution in 2050 mainly comes from the production process of HCFC-22 (20%), household air conditioners (19%) and automobile air conditioners (19%), etc.

6.2.2.4 Carbon Sink Analysis of Land Use and Land Use Changes

Land use is responsible for 25% of global greenhouse gas emissions, with agricultural production directly responsible for 10–14%; and the other 12–17% are caused by vegetation changes, including forest degradation [10]. The greenhouse gas inventory report of China’s land use, land use changes and forestry in 2014 covers greenhouse gas emissions and carbon sequestration from six types of land use, including woodland, agricultural land, grassland, wetland, construction land and others. The enormous potential of land use in cutting greenhouse gas emissions has long been neglected. The sustainable management of land use and regulation of land carbon cycle not only facilitate carbon emission reduction per unit of land area, but also carbon storage of soil.

Stopping deforestation and massive tree planting represent one of the most effective approaches, as healthy forests support local economic development by ensuring water security, improving soil health, and helping regulate the climate. Under the reinforced policy scenario, China’s forestry carbon sink in 2030 can reduce 412 million tons of CO₂, which not only mitigates climate risks, but also enhances adaptation to climate change. And the 2 ℃ scenario sees even higher contribution of forest—a reduction of 654 million tons of CO₂—a potential that should be reckoned with.

Compared with forest ecosystem, grassland carbon sink/carbon absorption is more susceptible to natural factors. Temperature, precipitation and evaporation are the main climatic factors affecting the carbon cycle of grassland ecosystem. Yet human measures for grassland preservation and restoration are also crucial for enhancing its potential of carbon sequestration. For the existing grasslands in China, the carbon sequestration potential of the three measures of enclosure, grass planting and conversion of cultivated land to grassland reaches 39.06Tg·a⁻¹ [11], equivalent to the carbon sequestration capacity of 140 million tCO₂.

Forestry, grassland and wetland are major components of China’s emission reduction efforts, and the international community is also turning greater attention to the role of forestry and grassland in global emission reduction. Forestry and grassland are unique in coping with climate change, as they can be either “carbon sources” or “carbon sinks”, depending on the actions and measures of humanity.

6.3 Important Technologies and Measures to Reduce Non-CO₂ GHG Emissions

6.3.1 Key Technologies for Non-CO₂ Emission Reduction

6.3.1.1 Industrial Process

Greenhouse gas emissions from industrial production are mostly attributed to the process of physical and (or) chemical changes, which confines available emission reduction pathways to raw material substitution or the choice of solvent and reducing agent, with only a few technological options to choose from, hence the need to leverage other technologies from downstream production process to maximize energy conservation and emissions reduction in the industry.

N₂O emission reduction technology in industrial production process can be grouped into source control technology, process control technology and end treatment technology according to the stage of its action or workshop section.

• Cyclohexane production is the mainstream technology in China for producing adipic acid, whose capacity in this regard comprises over 95% of the total output of adipic acid in the country, and the N₂O source control mainly takes place through substituting other raw materials or methods for the cyclohexane adipic acid capacity. First applied by Japan-based Asahi Kasei Corporation, the cyclohexanol method enables N₂O emission reduction thanks to the dramatically reduced consumption of hydrogen and nitric acid compared to the cyclohexane method despite similar raw materials. Not only that, literature reveals other N₂O-free pathway for adipic acid production [12], which features 30% hydrogen peroxide under the effect of sodium tungstate and catalyst for a direct oxidation of cyclohexene into adipic acid, with a 90% yield. Yet this technology—yet to be industrialized—is not attractive unless hydrogen peroxide is cheap enough and the policy framework puts a tight leash on N₂O emissions. Devoid of nitric acid oxidation, butadiene [13] and ozone plus ultraviolet irradiation [14] are also free from N₂O emissions, and are currently under laboratory research.

• No process control technology is available in adipic acid industry to reduce N₂O emissions. But the end control technology of catalytic decomposition is available, whose mechanism is similar to the end control of nitric acid industry. Still, it’s not a viable option given its apparent drawback in high catalyst cost and short lifespan. What is more commonly used in China is thermal decomposition [15] for terminal treatment, a method that directly sends N₂O tail gas into the incinerator and decomposes it into N₂, O₂ and NO at high temperature without catalyst, and recycles part of the nitric acid and waste heat. But its flaw lies in the consumption of fuel, whose combustion produces additional carbon dioxide emissions. Other literature outlines the direct purification of N₂O in chemical production process before being recycled to produce phenol and medical nitrous oxide anaesthetic, etc. These methods are closely associated with the demand-side pricing factor of downstream products and have not been commercialized yet.

As the substitute for the Ozone Depleting Substances (ODS) of CFCs and HCFCs, HFCs have witnessed notable growth in its global consumption and emissions along the journey to phase out ODS and are mostly used as refrigerants, foaming agents, fire extinguishing agents, aerosols and raw materials for chemical products, involving a range of industrial sectors.

• 1. In the refrigeration and air conditioning industry, fluorine-containing gases, as refrigerants, exchange energy with the outside through changes in their thermal state for the purpose of refrigeration.

  • For small car air conditioning, the refrigerant alternatives mainly include HFO-1234yf, CO₂, HFC-152a and Mexichem AC6. A slightly flammable refrigerant, HFO-1234yf has got the nod for United States SNAP, Europe REACH and China new material registration, and has been widely commercialized, with more than 60 million vehicles using the refrigerants globally in 2018, including some Chinese brands with car exports to Europe and the United States. CO₂, a natural working medium, has been used successfully as a refrigerant. For small and light systems such as automotive and mobile air conditioning, CO₂ systems represent a promising option. HFC-152A enjoys the potential of fuel-saving, low refrigerant price, higher system efficiency and available deceleration for refrigeration, but lacks a full-fledged SAE (Society of Automotive Engineers) standard.

  • The refrigerant alternatives for indoor air conditioners mainly include HFC-32 and R290, the former being a slightly flammable refrigerant whose cooling performance is comparable to HFC-410A with less refrigerant charge under the same refrigerating capacity. The technology has been adopted in the markets of Japan, Europe and the United States. R290, with fairly close physical parameters to HCFC-22, is a very close direct substitute, plus its GWP is less than 20 and is 15% more efficient than conventional systems. However, its flammability raised concern from the United States, which outlawed hydrocarbons as an alternative to HFCs. Several Chinese companies have established production lines for R290 air conditioners. With enhanced safety, heightened safety awareness and the enactment and improvement of regulations, R290 is poised to gain more penetration in air conditioning.

  • As products vary greatly in the refrigeration for industrial and commercial air conditioners, a wider portfolio of alternatives is available. Apart from the CO₂ and HCs mentioned above, natural working medium ammonia, with zero ODP and GWP, represents an environmentally friendly refrigerant with outstanding thermal and physical properties, large cooling capacity per unit volume, small viscosity, low price and high operating efficiency. Ammonia refrigerant is still being used in many large industrial systems, including mid-and-large freezers in China. Nevertheless, its toxicity and flammability have always been a cause for concern.

• 2. Cyclopentane demonstrates the most practical value out of HCs foaming agents. Compared with other HCs foaming agents, it features the lowest thermal conductivity, which explains its best thermal insulation performance. A relatively mature technology, hydrocarbon is already widely used in PU foam industry. Water is arguably a universal foaming agent for PU foam; it’s environmentally friendly, safe and requires no changes of foaming equipment compared to other alternatives; besides, it’s the most economically viable option considering the cost of equipment and plant renovation and changes in product production. HCFO-1233zd and HFO-1336mzz, with their non-flammability, low GWP value, high energy efficiency and superior insulation performance, represent extremely promising new generation foaming agents, which have obtained certification of US SNAP and the EU REACH. Honeywell and Arkema have registered the patent for HCFO-1233zd foaming agent, while Dupont owns the patent for HFO-1336mzz, but the massive worldwide penetration is yet to begin.

• 3. There are three main approaches for cutting HFC-23 emissions:

  • Incineration of HFC-23. A mainstream solution to the treatment of HFC-23 in businesses at home and abroad, the method includes thermal oxygen decomposition and plasma digestion, etc. As China is involved in CDM projects implementation, HCFC-22 producers mostly opt for incineration and decomposition to dispose HFC-23, and the technologies are mature.

  • Reducing HFC-23 by-product rate. By improving the production process of HFC-22, developed countries have managed to keep the by-product rate of HFC-23 at 1.5 ~ 3%, and below 2% on average. At present, due to process, equipment or management obstacles, the by-product rate of HFC-23 hovers at a high level of 3% in most domestic enterprises.

  • HFC-23 recycling, that is, converting HFC-23 into fluoride compound with economic value through chemical reaction, and achieving the effective utilization of fluorine resources.

6.3.1.2 Agricultural Production

The sources of agricultural GHG emissions mainly include animal intestinal fermentation, animal manure management, rice cultivation and agricultural land, which account for 24%, 16%, 19% and 40% of GHG emissions respectively.

• 1. The emission reduction technologies in rice fields can be divided into five categories: variety selection, water management, fertilizer management, tillage management and new technologies [16,17,18], as shown in Table 6.5.

  Table 6.5 Methane emission reduction technology system in rice field

The study shows that if nitrogen fertilizer application in the rice field is reduced from 225–450 kg N ha⁻¹ to 90–200 kg N ha⁻¹, N₂O emissions from rice field would be down by 42%. A 10–70% drop in nitrogen fertilizer would make for an 8–57% reduction in N₂O emissions without significant impact on CH₄ emissions from rice fields and SOC fixation [19]. Water-saving irrigation technologies, such as shallow wet irrigation, controlled irrigation, intermittent irrigation and film-covered dry farming, have been made widely available. Such water-saving irrigation technologies not only saves large quantities of water for rice, but also lowers greenhouse gas emissions. Other studies suggest that controlled irrigation can effectively reduce the global warming potential, and the total amount of CH₄ discharged from paddy fields under controlled irrigation would be down by more than 80% [20]. Under intermittent irrigation, CH₄ emissions of the paddy field was 5.4% of that under continuous flooding. Despite a 6.5-fold increase in N₂O emissions, the comprehensive greenhouse effect under intermittent irrigation is reduced by 90% [21].

• 2. The emission reduction technology system of nitrous oxide in upland can be grouped into four categories: variety selection, fertilizer management, tillage technology and new preparations (see Table 6.6).

  Table 6.6 Technology system for reducing nitrous oxide emissions from upland fields

Nitrogen fertilizer reduction is the most direct approach for reducing dryland. Studies show that if nitrogen fertilizer is reduced by 10–30%, N₂O emissions from wheat, corn and vegetable crops would be down by 11–22%, 17–30% and 27–45%, respectively [19]. Analysis indicates that for different types of farmland, including wheat, corn, and vegetable field, adding nitrification inhibitors serves to bring down N₂O emission coefficient by around 40%. SRFs and CRFs, which enable nitrogen to be slowly released for the sustained crop absorption and growth, is the best alternative to traditional organic fertilizer and the preferred choice for enhancing utilization of fertilizer and reducing its environmental impact.

• 3. The GHG gases in livestock and poultry breeding mainly stem from CH₄ in livestock and poultry intestines and CH₄ and N₂O produced in the process of excrement management. At present, GHG emission reduction technologies in livestock and poultry industry include four categories [16, 17, 22, 23], namely grain ration management, improved breeding, feces collection and storage, and feces treatment (as shown in Table 6.7).

  Table 6.7 GHG emission reduction technology system for livestock and poultry industry

Studies find that feed conversion can reduce CH₄ emissions by 4–6%, and improving the management of feed or energy intake can facilitate a 11% reduction in CH₄ emissions (equivalent to reducing 142.7 kg CO₂e of CH₄ emissions per head of beef cattle per year). Revising the feed mix of ruminants, especially adding lipid additives, can slash CH₄ by about 15% (equivalent to reducing 142.7 kg CO₂e of CH₄ emissions per head of beef cattle per year) [19].

• 4. The past 30 years have witnessed an overall increase in China’s surface soil organic carbon (SOC) pool, which have served as a carbon sink (see Table 6.8). The annual carbon sequestration of soil at a depth of 20 cm in farmland ranged from 9.6 to 25.5 Tg, and the depth of 30 cm from 11 to 36.5 Tg. Carbon sequestration rate per unit of cultivated land is 74–184 kg C/ha per year at 20 cm depth and 85–281 kg C/ha per year at 30 cm depth [24].

  Table 6.8 Technology system of carbon sequestration in farmland soil and grassland

Adjusting grazing density proves to be a major contributor to avoiding soil SOC loss and promoting grazing for soil carbon sequestration. High grazing intensity significantly reduces soil SOC content. Studies find that by lowering grazing density from high to medium or low level, the soil SOC content would increase by 0.77 tons of CO₂ ha⁻¹ yr⁻¹. Rest-rotation grazing could enable a 1.48% improvement in the soil SOC, or 1.06 tons of CO₂ ha⁻¹ yr⁻¹. Remediation of degraded soil could increase the soil carbon sequestration by 4.22 tons of CO₂ ha⁻¹ yr⁻¹.

Figure 6.7 illustrates the aggregate non-CO₂ gas emission reduction in selected sectors in 2030 and 2050 under the 1.5 ℃ scenario. It’s found that the six sectors of coal mining, HCFC-22 production, household air conditioning, animal intestinal fermentation, nitrogen fertilizer application and automobile air conditioning contributed to the largest reduction of total non-CO₂ gases, standing at 410, 200, 90, 60, 60 and 30 million tCO₂e respectively in 2030, which adds up to 82.6% of total reduction. In 2050, the figure is 520, 170, 300, 220, 110 and 160 million tCO₂e respectively, with a minor drop of the cumulative contribution to 78.3%.

Fig. 6.7

Key areas for China’s non-CO₂ GHG emission reduction (MtCO₂e)

6.3.1.3 Summary

Given the characteristics of non-CO₂ emission reduction technologies occurring in different stages during implementation, this report groups them into six technology categories, namely complete reduction of demand, replacement of original demand, improvement of production mode and utilization efficiency, end-of-pipe recovery, disposal and decomposition.

In 2030, non-CO₂ gas emissions in the 2 ℃ scenario are 490 million tons less than the policy scenario, which is primarily attributed to complete reduction in demand, replacement of original demand, and end-of-pipe recycling, disposal and decomposition—steps that account for 37.6%, 17.6%, 21.5% and 10.9% of total emission reduction. The emission reduction of non-CO₂ gases in the 1.5 ℃ scenario grows by 540 million tons relative to the 2 ℃ scenario, which derives from increased end-of-pipe recycling, disposal and decomposition, strengthened efforts in demand reduction and substitution in the early stage—measures that contribute 28.5%, 23.0%, 27.6% and 13.3% of emission reduction respectively.

In 2050, the composition of technology category for non-CO₂ gas emission reduction in the 2 ℃ scenario is similar to that in 2030, with complete reduction of demand, replacement of original demand, end-of-pipe recycling, disposal and decomposition contributing 55.2%, 19.9%, 11.6%, and 6.5% to emission reduction. In contrast to 2030, the incremental non-CO₂ emission reduction under 1.5 ℃ scenario is primarily due to early demand reduction and substitution, with much less contribution from end-of-pipe disposal and decomposition. Additional emission reduction from the above three measures is estimated at 150, 210, and 160 million tCO₂e, or 47.1%, 26.6% and 14.8%, respectively.

Research and practice suggest that in the near and medium term, the spread and use of end-of-pipe recycling and disposal measures, such as the recovery of coalbed methane and the catalytic decomposition and treatment of industrial exhaust gases, should be prioritized for the reduction of non-CO₂ gas emissions. In the long run, more contribution is expected from the steady progress of upfront demand reduction or substitution, such as the encouragement of a healthier diet structure and substitution of new refrigerant with low GWP.

6.3.2 Key Measures for Non-CO₂ Emission Reduction

This report classifies non-CO₂ gas emission reduction technologies into three stages—early stage, intermediate stage and behind stage, based on the phases and modes of emission reduction behaviors (as shown in Table 6.9).

Table 6.9 Grouping of non-CO₂ emission reduction measures

The early stage—prior to the release of non-CO₂ gases—includes two groups of emission reduction measures, namely complete reduction of demand and replacement of original demand. The so-called demand reduction represents the curb and reduction of activity levels of the emission sources, including transforming the energy system to cut coal consumption and subsequently dampen activities in coal mining; encouraging a shift to healthier diet to reduce the consumption of red meat, which indirectly leads to the decrease of the stock of livestock breeds; and diverting solid waste from landfill to incineration to cut back on the amount of landfill at the source, thus achieving a decline in emissions before landfill gas is generated. For the replacement of original demand or activity level, typical examples can be found in automobile air conditioning, where HFC-134A with a higher GWP value is replaced by HFO-1234yf with a lower GWP value as a refrigerant, and the use of R290 as a working medium replaces R410a in indoor air conditioning.

The intermediate stage refers to the process of non-CO₂ gas generation, and the emission reduction measures comprise improvement of production mode and utilization efficiency. Typical measures of the former include: promoting the combination of wet irrigation and intermittent irrigation in rice planting process, and of intermittent drainage and baked field during growing period; rationing the concentrated/coarse feed ratio for livestock raising; substituting automatic quenching anodic effect and non-effect aluminum electrolysis process for the original production line with obvious anodic effect in the aluminum smelting industry. The emission reduction measure through enhancing utilization efficiency mainly include the popularization of soil test formula fertilization in the application of nitrogen fertilizer to improve the efficiency of nitrogen fertilizer.

The behind stage, meaning post non-CO₂ release period, primarily features end-of-pipe recycling, disposal and decomposition for non-CO₂ emission reduction. To illustrate, CH₄ emissions from coal mining and solid waste landfill can be recycled to generate electricity; and emissions from HCFC-22, nitric acid and adipic acid production require heat treatment or catalytic processing to be eliminated.

6.3.3 Emission Reduction Cost of Non-CO₂ GHG Emissions

Research shows the marginal cost curve of non-CO₂ emission reduction features a flat pattern in the first half but a pretty steep trajectory in the latter half (as shown in Fig. 6.8), which indicates that despite the physical constraints of emission reduction technologies, non-CO₂ emissions can be further reduced through a proper level of carbon tax. However, the marginal cost of emission reduction sees a surge when certain emission reduction threshold is crossed. Modeling suggests the threshold ranges from 40 to 50% of emission reduction in 2030, and from 50 to 70% in 2050. Moreover, owning to technology limitation, zero emission of non-CO₂ gases is hard to come by—around 40% of such emissions remain stubborn under the 1.5 ℃ scenario.

Fig. 6.8

Cost curve of Non-CO₂ emission reduction (2030 and 2050)

With a carbon price of CNY 20/tCO₂e, N₂O, F-gas, CH₄ would be down by 31.2%, 12.9% and 14.5% respectively in 2030 and by 50%, 21.5% and 42.5% in 2050—equivalent to a reduction of 53 million tons and 130 million tCO₂e by 2030 and 2050. Under the reinforced policy scenario, the cost of emission reduction in 2030 stands at CNY 3.85 billion and CNY 16.05 billion in 2050; whereas the 2 ℃ scenario sees the cost soaring to CNY 10.58 billion in 2030 and CNY 30.62 billion in 2050. Furthermore, the maximum economically achievable emission reduction is limited by the physical constraints of technologies. Once carbon is priced above CNY 200/tCO₂e (around $30/tCO₂e), the level of emission reduction would not increase in proportion to price rises. Assuming the cost of technology remains constant, the cost for non-CO₂ emission reduction in the 1.5 ℃ scenario would multiply that in the 2 ℃ scenario by a minimum of 3–5 times. Future R&D and technological advances may result in a reduction in technology outlay. Yet due to the scarcity of data on the cost reduction of non-CO₂ emission reduction technologies, future cost reduction prompted by technological progress is not taken into account in this study.

The conclusion is that, first, such non-CO₂ gases as methane is an aggressive greenhouse gas, whose greenhouse effect is equivalent to 80 times of CO₂ in 20 years. So it’s essential to take non-CO₂ emission reduction seriously by creating a strategy that targets non-CO₂ gases under the umbrella of the national strategy for long-term low-carbon development. Second, the potential for cutting non-CO₂ gases can be fulfilled in the early period through low cost technologies and carbon pricing. But when certain threshold is reached, deeper emission reduction can only be enabled through behavior change to reduce the activities, which renders emission reduction more challenging. Third, the cost and difficulty of non-CO₂ emission reduction demonstrate non-linear rises after the threshold, prompting the use of negative emission technology for the remaining emissions in order to achieve net zero greenhouse gas emission by 2050.

6.3.4 Nature-Based Solutions

The notion of Nature-based Solutions (NbS) first appeared in the World Bank’s report entitled Biodiversity, Climate Change, and Adaptation: Nature-Based Solutions from the World Bank Portfolio World Bank (2008–09), which underscored the importance of biodiversity conservation for climate change mitigation and adaptation. “Nature-based Solutions” is a nature-inspired solution that supports and utilizes nature to address social challenges with effective and appropriate means, enhancing social resilience, and bringing economic, social, and environmental benefits.

“Nature-based solutions” fall into three categories based on different ways of using ecosystems:

• The direct use of ecosystems with no or minimum intervention, such as natural ventilation for air purification, rain flood management through urban green space;

• The repair of ecosystems such as soil management and restoration of soil ecosystem function;

• The imitation of nature to create ecosystems, such as new green roofs and green wall façade to adjust microclimate.

Nature-based climate solutions produce both economic benefits and efficiency perks, and showcase fully the importance of trees, soil and other natural elements in tackling climate change. The proposition of nature-based climate solutions provides a path toward the harmonious development of man and nature, and is expected to inspire more ambitious and effective actions and reasonable use of various resources by Contracting Parties on climate change issues.

Forestry carbon sink is a practical embodiment of “nature-based solutions” for managing climate change in the forestry and grassland sectors. It taps into the carbon storage service of forests through afforestation, strengthened forest management, reduced deforestation, preservation and restoration of forest vegetation, etc. Under the policy and reinforced policy scenarios, China’s forest stock is on track to reach 20.8 billion cubic meters in 2030 and 26.2 billion cubic meters in 2050, and the forestry carbon sink is stabilized at a level of 400 million tons per year. The 2 ℃ scenario would push up the stock to 22.7 billion and 30 billion cubic meters in 2030 and 2050 respectively with a carbon sink of 650 million tons in 2030 and 500 million tons in 2050.

Considering the analysis and conclusions of related research, plus around 200 million tons of carbon sink in grassland, wetland and forest products, it is generally estimated the total carbon sink of China would reach at 700 to 800 million tons by 2050. As non-CO₂ gas emission sources are relatively dispersed, and the cost for reducing them would experience a non-linear surge after reaching a certain reduction rate, hence enormous challenge in driving emissions down on this front. This necessitates the efforts to tap into carbon sink potential, which is one of the important avenues to near-zero emissions. It is advised to coordinate agroforestry and rural development strategies to unleash the full potential of blending technology-based and nature-based solutions, and make better use of the sinks from agroforestry and land use change in order to offset technically difficult emission reductions in other sectors.