Introduction

In November 2022, the U.S. Environmental Protection Agency (US EPA) proposed regulations that would reduce methane (CH4) emissions from oil and gas supply chains in the U.S. by 87%, compared to 2005 levels (EPA, 2022). If emission reductions of this magnitude were deployed globally, they would result in reductions that could abate 80 Tg of CH4 per year (IEA, 2022). Technologies capable of reducing these emissions already exist. In many cases, they are economically attractive because they reduce loss and leakage of salable product.

Efforts to reduce CH4 emissions from the oil and gas sector are already underway. The Global Methane Pledge and commitments at COP26 targeted 30% CH4 emission reductions by 2030 (DOS, 2021). More recently, COP27 highlighted the importance of reducing CH4 emission from oil and gas value chains for achieving net zero by 2050. In the US, the Inflation Reduction Act (IRA) 2022 incorporated fees for entities along the oil and gas supply chain that report CH4 emissions above specified thresholds, starting in 2024 (H.R.5376, 2022). These efforts are part of a broader trend that emphasizes emission reductions of short-lived climate forcers like CH4 (Solomon et al. 2010; Dreyfus et al. 2022; Singh et al. 2022). Reducing CH4 emissions could bring benefits in the near-term when compared to reducing emissions of longer-lived climate forcers like CO2 (Abernethy et al. 2021; Cain et al. 2022; Ming et al. 2022; Abernethy and Jackson 2022). Besides rapid deployment, CH4 reductions in the energy sector have the additional advantage of high short-term reductions in radiative forcing.

In this paper, we compare the climate change mitigation benefits of cutting large amounts of CH4 emissions from the global energy sector on short time scales with reducing an equivalent amount (on a global warming potential basis) of CO2 using carbon capture and storage (CCS), a technology that would require significant infrastructure development. While both of these approaches can be pursued simultaneously, our analysis illustrates the short-term benefits of exploiting available, economically viable, and scalable CH4 emission reduction technologies.

Methane and carbon dioxide reduction scenarios

Oil and gas CH4 emissions are currently reported as approximately 80 Tg per year, although they may be 25 to 40% greater than this estimate (Hmiel et al. 2020). Our analysis, therefore, assumes a business-as-usual emissions level of 100 Tg of CH4 per year. We then evaluated the changes in radiative forcing and consequent global-average surface temperature change from reducing these emissions by 30%, which is in line with current global targets. A second scenario assumes 80% emission reductions to highlight the advantages of pushing past current targets for achieving reductions similar to those proposed by the US EPA (EPA, 2022). To evaluate emission reduction scenarios that decrease an equivalent amount of CO2, we converted CH4 to CO2 emissions using a fossil CH4 GWP20 (global warming potential at year 20) of 82.5 as reported in the Sixth Assessment Report (IPCC, 2022). Table 1 describes the proposed scenarios.

Table 1 Scenarios for emissions reductions of CH4 and equivalent amount of CO2 from business-as-usual† levels
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Using CCS to reduce CO2 emissions requires manufacturing of large-scale equipment, and construction of foundations, pipelines and auxiliary systems. Such activities generate additional GHG emissions that might vary depending on particular characteristics and these systems have a range of emission estimates reported in the literature. Manufacturing and construction emissions for CCS are reported to be between 0.07 and 0.33 Tg of CO2 emitted per unit of throughput in Tg of CO2 sequestered per year (Koornneef et al. 2008; Cuellar-Franca and Azapagic, 2015). We adopted the average of this range to develop the scenarios in Table 1, which include infrastructure emissions and construction times (Townsend and Gillespie 2020). These scenarios take account of the changes over time in emissions associated with manufacturing the steel and materials required to build CCS facilities.

CH4 emission reduction technology options are less infrastructure-intensive than CCS. Nonetheless, we assessed whether we would need to include GHG emissions from infrastructure build out to deploy them. These options include replacing pneumatic pumps with electrical pumps, replacing pneumatic devices with mechanical controllers, and replacing high-bleed or high-emitting pneumatic devices with intermittent or low-bleed devices (Methane Guiding Principles 2022). We used the Economic Input–Output Life Cycle Assessment (EIO-LCA) model (Green Design Institute, 2022) and reported construction costs (Methane Guiding Principles 2022) to evaluate construction emissions associated with these transitions. Construction emissions are approximately 0.01% (installing electric pumps) to 0.5% (accelerated installation of low-bleed devices) of one year’s worth of emissions reductions. In our analysis, these emissions are treated as negligible. Furthermore, CH4 mitigation technologies applicable to the oil and gas sector are off-the-shelf with minimal lead time for construction. We, therefore, assumed installation could begin immediately.

The CH4 and CO2 mitigation scenarios in Table 1 were compared on the basis of relative global-average surface temperature increase avoided with respect to the business-as-usual scenario. The higher the value is, the better the mitigation effort. We used global surface temperature change models reported in the literature in our calculations (IPCC, 2022; Abernethy & Jackson 2022; Gasser et al 2017). The interested reader can find more information on the scenarios and modeling approach in the Supporting Information.

Rapidly scalable CH4 reduction technologies outperform longer term options to cut CO2 emissions

Figure 1 displays the effects of mitigation efforts over a 40-year time horizon. In interpreting this illustration, we focus on two primary results. First, the change in surface temperature increase avoided eventually levels off in the CH4 reduction scenarios. This phenomenon reflects the short life of CH4 in the atmosphere (half-life of 11.8 years) (IPCC, 2022). Given CH4’s short atmospheric lifetime, ultimately, the reduced CH4 in the atmosphere leads to a reduction equivalent to technology-based emission reductions and the temperature change plateaus. Second, although the avoided surface temperature rise in CO2 reduction scenarios is initially lower than in CH4 reduction scenarios, eventually it catches up. After a crossover point, CO2 emission reduction scenarios offer greater benefits. The dashed vertical lines in Fig. 1 mark this crossover point, which is on the order of decades.

Fig. 1
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Surface temperature change avoided relative to business-as-usual levels over a 40-year time horizon. Dashed vertical lines indicate the year at which ∆T avoided is equivalent for CH4 and CO2 reduction scenarios

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Figure 1a compares the strategies that achieve 30% reduction in business-as-usual annual levels (100 Tg CH4 or 8250 Tg CO2). CH4 reduction technologies are rapidly scalable and benefits associated with CH4 reductions are evident beginning in year three. In contrast, the waiting period and emissions associated with construction of CCS facilities delay benefits from CO2 emissions reductions until year eight. Accordingly, there is a five-year longer wait for any relief from climate change compared to its equivalent CH4 scenario. Avoided temperature increases in the CH4 scenario, however, begins to plateau after year 20. At this point, the temperature change avoided by CH4 mitigation is 28 mK while the CO2 mitigation scenario reaches only 20 mK. After about 31 years, the benefits of mitigating CO2 exceed those of mitigating CH4. At timescales beyond this point, the benefits of reducing CO2 will outweigh those of reducing CH4 by a large extent.

The trends in Fig. 1b, which reflect an aggressive 80% reduction in business-as-usual CH4 emissions, are similar to those in Fig. 1a. However, global surface temperature change is more quickly avoided. For example, the first 20 mK of avoided surface temperature rise for CH4 and CO2 occur between years 14 to 20 when the emission reduction target is 30%, and between years 8 to 15 when it is 80%. The gap in the time required to achieve this benefit (between CH4 and CO2) is six and seven years, respectively. Avoided surface temperature rise takes 17 years longer to plateau in the 80% reduction scenario as compared to the 30% reduction scenario. The greater amount of CH4 reduced (80% versus 30%) causes benefits to accrue for longer. The benefits of reducing CO2 emissions with CCS outstrip those of reducing CH4 in the oil and gas sector in year 35 at 80% reductions. At this point, the avoided surface temperature rise is 97 mK, 62 mK greater than when the reduction target is 30%.

Relief from climate change comes sooner with scalable technology

Our analysis emphasizes two main points. First, construction and associated emissions delay the benefits of climate change mitigation technologies. Prioritizing quickly-deployable options that require limited construction helps to bring relief sooner. Second, GHG mitigation options that require longer to scale up can take decades to overtake quickly scalable solutions. The results we present add urgency to pursuit of rapidly scalable technologies.

One of the primary drivers of our analysis is the long lead times required for emissions from CCS to materialize. CCS is not unique in this regard. For example, transitioning from internal combustion engines to electric vehicles in the light-duty fleet will take decades. This transtition entails manufacturing and installation of charging infrastructure along with building factories to produce enough lithium-ion batteries to meet demand.

While our analysis emphasizes the importance of reducing CH4 emissions in achieving short term climate goals, it is important to note that reducing CH4 and CO2 emissions does not require an either-or choice. CO2 reductions provide long term benefits while CH4 reductions provide near-term reductions in warming that will be important in mitigating the current impacts (Weiskopf et al. 2020; Sarkodie et al. 2022) of a changing climate.