1. Introduction
Climate change is one of the most severe challenges facing the world today. Since its establishment in 1988, the Intergovernmental Panel on Climate Change (IPCC) has conducted multiple rounds of assessments, systematically summarizing and forecasting the progress of scientific research on climate change
[1]. These assessments not only reveal the mechanisms and impacts of changes in the climate system but also provide a scientific basis for policymaking. In recent years, with the increase in global greenhouse gas emissions and the frequent occurrence of extreme weather events, the risks of climate change have become increasingly prominent, and its impacts on society and the economy have intensified
[2]. To address this challenge, countries have committed to achieving carbon neutrality, with the aim of holding the increase in the global average temperature to well below 2 °C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5 °C above pre-industrial levels, as stipulated by the Paris Agreement
[3].
As the world’s largest developing country in East Asia, China has committed to achieving a carbon peak by 2030 and striving for carbon neutrality by 2060. These goals are crucial for China’s sustainable development and have significant implications for global climate change, including the future trends of extreme events, climate tipping points, the climate crisis, and the notion that the world has moved from a warming to a boiling era. How to reduce greenhouse gas emissions while balancing national development and security is a key issue that China must address in the context of global climate change.
This study aims to assess China’s response strategies to the challenges of global climate change, explore China’s pathways to achieve a carbon peak and carbon neutrality while aiming for the Paris Agreement’s goal of limiting global warming to no more than 2 °C, and assess and discuss the potential impacts of these pathways on future climate change issues. It also discusses the issue of methane reduction in international climate change cooperation and its impact on China, emphasizing the balance between equity and efficiency in global climate governance.
2. How to achieve a carbon peak/carbon neutrality path that aligns with China’s actual conditions
2.1. The 2 and 1.5 °C targets in the Paris Agreement
In international climate change research, numerous papers have been published on controlling the decadal rise of the global mean surface temperature (GMST) to 2 or 1.5 °C by 2100 (relative to the average temperature level of 1850–1900). The core content of these papers is on introducing the development of a path for anthropogenic carbon dioxide (CO
2) emission reductions under the goal of carbon neutrality. An important aspect of the Paris Agreement is that, if the countries that have signed the agreement achieve net-zero CO
2 emissions by 2075, there is a high likelihood of keeping the world’s temperature rise to within about 2 °C by 2100. China has signed the Paris Agreement and is committed to striving for carbon neutrality by 2060, 15 years ahead of the international target. The Paris Agreement also proposes that countries strive for a target of 1.5 °C, which would require achieving net-zero CO
2 emissions around 2055
[3]. To correspond to the 1.5 °C target, China’s anthropogenic CO
2 emissions should peak around 2021 and significantly decline around 2055. This scenario is highly idealized and unrealistic for China to achieve (
Fig. 1).
The data in
Fig. 1 were obtained by comparing the projected anthropogenic carbon emissions data over China from the China Meteorological Administration (CMA)’s China Carbon Monitoring Verification and Supporting (CCMVS v1.0) system with the data obtained based on the IPCC Sixth Assessment Report (AR6) Shared Socioeconomic Pathways (SSPs) and Scenarios. The CCMVS system is a four-nested grid operational anthropogenic CO
2 emissions and sink monitoring, verification, and support system developed by the Monitoring and Assessment Center for Greenhouse Gases and Carbon Neutrality of the CMA, aligned with the 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories.
† It assimilates the world’s largest amount of atmospheric CO
2 concentration data, as observed by China’s national greenhouse gas observation network and internationally shared with other parts of the world. The CCMVS system is designed to accurately monitor and verify carbon emissions from various sources in a timely manner, using a combination of satellite data, ground-based measurements, and modeling tools, in order to support policy decisions and carbon-mitigation efforts by providing reliable data on carbon sinks and sources across different regions
[4],
[5],
[6].
2.2. China can follow the carbon neutrality pathway to fulfill the Paris Agreement’s 2 °C target
Based on the carbon emission coefficients published by the National Development and Reform Commission and the Ministry of Ecology and Environment of the People’s Republic of China, combined with calculations from Tsinghua University (THU) and information provided by multiple units, China’s total emissions from energy activities and industrial processes in 2021 were approximately 11.6 billion tonnes of CO
2. However, using atmospheric CO
2 concentration observation data-assimilation inversion methods
[4], the CMA estimated that this total was about 11.9 billion tonnes in 2021
[6]. After unifying the criteria, China’s total carbon emissions from energy-related and industrial processes in 2021 were found to range between 11.3 billion and 12.0 billion tonnes, with 11.9 billion tonnes being a reasonable base figure. The uncertainty range for China’s total greenhouse gas emissions in 2014 was –5.2% to 5.3%, so an uncertainty range of –5.0% to 5.0% can be applied to the CO
2 emission figures.
THU and the Chinese Academy of Meteorological Sciences (CAMS) collaborated to publish a study that constructs a carbon neutrality pathway aligned with the emission reductions needed to meet the Paris Agreement’s 2 °C target
[7]. Based on the baseline carbon neutrality scenario, the assumptions for China’s future economic growth rate are shown in
Table 1 [7]. Since China has not yet fully transitioned from carbon intensity control to total carbon control, this study still proposes an emission–reduction pace measured in terms of carbon intensity and estimates the future key points of China’s anthropogenic CO
2 emissions based on gross domestic product (GDP) forecasts. The emission–reduction efforts in the baseline scenario are based on China’s proposal to achieve peak carbon emissions before 2030 and carbon neutrality before 2060, as well as keeping the temperature rise within 2 °C.
According to the IPCC assessment results, in order to achieve the 2 °C warming control target with a probability of over 66%, global carbon neutrality should be achieved around 2075, assuming no emission–reduction burden-sharing mechanisms and that reductions occur at the most cost-effective locations and times. Expressed in terms of carbon intensity reduction rates, the global carbon intensity needs to decrease by 4.0%–9.0% annually from 2020 to 2030, by 6.0%–9.0% from 2030 to 2040, by 7.0%–9.0% from 2040 to 2050, and by 11.0%–19.0% from 2050 to 2060. Meanwhile, China’s 14th Five-Year Plan has set a target of an 18% reduction in carbon intensity, which translates to an annual reduction rate of about 4%. Therefore, this study sets a stepped carbon intensity reduction rate, assuming a reduction rate of 3.9%–4.4% from 2020 to 2030, 6.0%–8.0% from 2030 to 2040, 12.0%–14.0% from 2040 to 2050, and 14.0%–16.0% from 2050 to 2060.
Considering the significant uncertainty in China’s medium- to long-term GDP and carbon intensity reduction rates, Zhang et al.
[7] add four settings—namely, high and low economic growth and high and low carbon intensity reduction rates—based on the baseline scenario, as detailed in
Table 1. From these settings, the possible pathways and uncertainty range for China to achieve carbon neutrality can be derived
[7].
Due to the strong rebound of China’s economy in 2023 after the end of the coronavirus disease 2019 (COVID-19) pandemic, the carbon intensity only decreased by about 0.3% that year, with a cumulative decrease of about 4.7% in the first three years of the 14th Five-Year Plan. This differs from the original assumption of an annual decrease of 3.9% and a cumulative decrease of 18% over five years. Considering this situation, this paper adjusts the carbon intensity reduction rate during the 14th Five-Year Plan period to a cumulative 11.3% (vs the original pathway with 18%). The reduction rate during the 15th Five-Year Plan period remains unchanged, with a cumulative decrease of 20%. After making these adjustments, the revised emission pathway from 2023 to 2030 does not differ significantly from the original pathway and will not substantially affect the design of the emission reduction pathway after 2030. In this way, China’s updated carbon neutrality pathway is obtained to achieve the 2 °C target (
Fig. 2). According to the research results, China can propose the following nationally determined contribution target: By 2035, energy-related CO
2 emissions will decrease by about 10% compared with 2030—roughly equivalent to the research-proposed target of a nearly 12% decrease by 2035 compared with 2030. The post-2035 reduction trajectory can then follow the pathway designed in the research.
Based on the results of this study, to achieve the Paris Agreement’s goal of limiting global temperature rise to 2 °C, China can achieve carbon neutrality by 2060 without relying on the adoption of negative-emission technologies such as direct air carbon capture and storage (DACCS) and biomass carbon capture and storage (BECCS) at an early stage and on a large scale under the climate change “overshoot” scenario (
Fig. 2). To be specific, China’s anthropogenic CO
2 emissions will peak between 2028 and 2029, with peak emissions of around 12.8 billion tonnes. Emissions will then continuously decline as China focuses on prioritizing renewable energy development along its pathway to transform its energy system, achieving carbon neutrality around 2060 by offsetting emissions with 2.1 billion tonnes of carbon sinks from terrestrial ecosystems.
Based on the global emission scenarios driven by China’s 2 °C target pathway, we used three emulators to predict the future warming of the global surface mean temperature relative to 1850–1900 and found that the rise in global surface temperature (GST) in 2100 is about 2 °C with a margin of error. We also found that the increase in GST after the 2050s is smaller than previously predicted by the SSP2-4.5 scenario. This finding tells us that the 2 °C target of the Paris Agreement can be achieved through China’s carbon-neutral path that integrates development and security and may have implications for projections of tipping points and extreme events (further details will be elaborated in a separate study). The three emulators are the model for the assessment of greenhouse-gas induced climate change (MAGICC)
[8], the finite amplitude impulse response model (FaIR)
[9],
[10], and the CICERO simple climate model (CICERO-SCM)
[11].
2.3. Natural ecosystem carbon sinks will play a positive role in helping China achieve carbon neutrality and offset remaining emissions, but emission reduction remains the key to achieving carbon neutrality
The IPCC defines carbon neutrality as a balance between anthropogenic CO
2 emissions and anthropogenic CO
2 removals
[1]. In reality, natural ecosystems acting as carbon sinks also help neutralize a portion of anthropogenic CO
2 emissions
[12],
[13]. Since Earth system models first require the input of future anthropogenic CO
2 emissions as a driver to obtain the corresponding carbon sinks of natural ecosystems, the IPCC’s definition of carbon neutrality—while indicating that anthropogenic CO
2 emissions are neutralized through anthropogenic efforts—also proposes carbon neutrality based on natural-based solutions
[14], pointing out that carbon sinks in natural ecosystems can ultimately be used to offset anthropogenic CO
2 reductions
[14]. The estimated range of carbon sinks in China’s terrestrial ecosystems is approximately 1 billion
[15],
[16] to 4.1 billion tonnes
[17] (
Fig. 3). The CAMS estimates that the average annual carbon sink of China’s terrestrial ecosystems from 2018 to 2021 was 2.09 billion tonnes of CO
2 [6], and this level is expected to be maintained or slightly increased in the process of achieving carbon neutrality by 2060. This estimate is mainly based on the understanding that the carbon sinks of terrestrial and marine ecosystems will not significantly increase and may even decrease with future climate warming
[18]. The IPCC AR6 projects that the effectiveness of ocean carbon sinks will decline under future climate change. Ocean and land carbon sinks currently absorb over half of human-induced CO
2 emissions; however, as global temperatures rise, the capacity of these sinks to sequester CO
2 will weaken. The report’s scenarios highlight that, especially under high-emission trajectories, the ability of oceans to act as carbon sinks diminishes significantly. If global efforts can reduce emissions drastically, some of this decline in ocean carbon sink capacity can be mitigated
[19]. The carbon sink level of around 2 billion tonnes accounted for only about 18% of China’s approximately 11.9 billion tonnes of anthropogenic CO
2 emissions in 2021
[6]. Given China’s requirements for “red lines for arable land” (protecting arable land from development) and “ecological red lines” (protecting large areas of China’s ecology and resources from development) in land use, as well as the fact that water resources
[20] are a limiting factor in China, the role of natural ecosystem carbon sinks in achieving carbon neutrality in China is useful but is not the main battlefield.
2.4. It is unnecessary for negative-emission technologies to be adopted on a large scale at an early stage on China’s path to carbon neutrality
The global economies’ and energy systems’ reliance on fossil fuels since the industrial revolution era has led to the accumulation of huge amounts of greenhouse gases in the atmosphere. Even if emission–reduction measures are taken immediately, the presence of these gases will continue to cause the Earth’s temperature to rise. This “inertia” may make it difficult to achieve climate goals in the short term. Therefore, the concept of climate overshoot has been proposed internationally, referring to the need to exceed the temperature target at some stage in the future in order to achieve long-term climate goals, such as limiting the global average warming to 1.5 °C above pre-industrial levels and then reducing the temperature below the target level through artificial negative-emission measures
[21]. The Climate Overshoot Commission’s 2023 report
[22] emphasizes that the gases already released will continue to cause global temperatures to rise, even if global greenhouse gas emissions stop immediately. The report recommends taking multiple measures, including accelerating emission reductions, developing carbon-removal technologies, researching solar radiation management technologies, and strengthening climate adaptation measures and climate finance support, especially for low-income countries
[22]. According to the World Wildlife Fund (WWF)
†, most climate models predict that global temperatures will temporarily exceed the 1.5 °C target and then fall back. The Fund emphasizes that climate overshoot may lead to prolonged high temperatures, causing severe impacts on ecosystems, biodiversity, and human society. The world must take swift and decisive action to limit carbon emissions and implement sustainable goals.
To bring temperatures back below target levels, large-scale deployment of carbon-removal and carbon capture, utilization, and storage (CCUS) technologies is required, posing significant challenges to technological development and economic affordability
[23]. For example, the technology and large scientific installations required for direct air capture (DAC) from the atmosphere currently have capture costs ranging from several hundred to over a thousand dollars per tonne of CO
2, depending on specific technologies and operational conditions, with relatively small application scales
[23]. Although some companies and research institutions have already initiated DAC pilot and demonstration projects globally, DAC is still primarily in the stage of verifying technical feasibility and economic viability
[24],
[25]. China’s largest full-industry-chain demonstration project for CCUS—the Qilu Petrochemical–Shengli Oilfield Million-Tonne Carbon CCUS Project—can reduce CO
2 emissions by 1 million tonnes annually. If China were to rely entirely on CCUS technologies to achieve carbon neutrality, thousands of similar-scale projects would be needed, imposing enormous economic pressure. Therefore, although CCUS technologies will likely play a role in the future carbon neutrality process, there should be no illusion of first emitting and then eliminating climate overshoot. Instead, the large-scale application of renewable energy in China’s power system should be continuously accelerated, the application of green electricity in the full life cycle of key and advantageous industrial chain products in China should be significantly increased, and China’s industrial structure should be actively adjusted to continuously reduce the development of high fossil fuel consumption and high-emission industries.
Certainly, the IPCC AR6 highlights the potential role of carbon capture and storage (CCS) and other negative-emission technologies as key strategies for achieving carbon neutrality, especially in the later stages
[26]. The literature on the United Nations (UN) Framework Convention on Climate Change (UNFCCC) website
‡‡ https://unfccc.int/documents/629380.
also discusses the technical potential of CCS and the current technical, economic, and sociocultural barriers it presents.
3. Climate warming level and possible consequences after China’s carbon peak and along its path to carbon neutrality
3.1. As China reaches its carbon peak and enters the process of carbon neutrality, will the risk of exceeding the climate change “tipping point” remain as expected?
The factors influencing global climate warming include both natural and anthropogenic factors. Since the 1950s, the controlling factor for climate warming has been the continuously increasing anthropogenic CO
2 emissions
[27]. In 2023, approximately 37.4 billion tonnes of anthropogenic CO
2 were emitted into the atmosphere globally
[28], leading to an annual increase of about 2–3 parts per million (ppm) in the background atmospheric CO
2 concentration, as observed by China’s greenhouse gas observation network and global atmospheric observation networks
[6],
[29]. China’s anthropogenic CO
2 emissions account for approximately 11.9 billion tonnes of the global emissions, significantly impacting global climate change.
As global and Chinese anthropogenic CO
2 emissions peak, the observed growth rate of atmospheric CO
2 concentration will slow down. This is because North America, which has the largest cumulative anthropogenic CO
2 emissions globally, peaked in 2007
†† https://www.epa.gov/climate-indicators/climate-change-indicators-us-green-house-gas-emissions.
, and Europe, the second-largest cumulative emitter, peaked in 2008
‡‡ https://www.eea.europa.eu/en/analysis/indicators/total-greenhouse-gas-emis-sion-trends.
. Accompanied by East Asia, the third-largest cumulative emission region, where China’s CO
2 emissions are expected to peak around 2028
[7], this implies that global anthropogenic carbon emissions may not exceed the levels of 2030. As global anthropogenic carbon emissions peak and the world enters the carbon-neutrality phase, the annual reduction in anthropogenic carbon emissions will slow the growth rate of atmospheric CO
2 concentration. However, since there will still be anthropogenic CO
2 emissions below the peak level each year, there will still be CO
2 outside the natural cycle in the atmosphere, which will continue to affect the Earth’s energy balance, preventing the climate warming process from stopping immediately and causing it to continue for some time. Until global annual anthropogenic CO
2 emissions achieve neutrality through a combination of anthropogenic emission reductions and natural carbon sinks before 2100, the GST will still be higher than the early industrial revolution period due to the residual CO
2 and other greenhouse gases in the atmosphere since the industrial revolution. However, by 2100, the temperature rise will be controlled to within 2 °C compared with the average temperature of 1850–1900 and will show a cooling trend.
The IPCC defines a climate change tipping point as “a critical threshold at which global or regional climate changes from one stable state to another stable state,” referring to elements of the Earth system that—once pushed beyond a certain point—can trigger irreversible changes
[27]. In a seminal study on tipping points in the Earth’s climate system, Lenton et al.
[30] identified and discussed various climate tipping points that human activities could trigger, such as the melting of the Siberian permafrost and the disappearance of the Amazon rainforest. Steffen et al.
[31] discussed the potential trajectories of the Earth system in the Anthropocene, particularly noting that, if certain tipping points are exceeded, the Earth system could enter a “hothouse Earth” state. Rockström et al.
[32] introduced the concept of “planetary boundaries,” defining environmental limits within which humanity can safely operate, and emphasized that crossing these limits could trigger irreversible environmental changes and tipping point phenomena. Changes at these tipping points could lead to dramatic and unpredictable shifts in the global climate system. Ritchie et al.
[33] pointed out that even small external pushes (e.g., increased anthropogenic greenhouse gas emissions) could lead to significant and irreversible changes in components of the Earth system (referred to as “tipping elements”). As the concentration of greenhouse gases in the atmosphere continues to rise due to fossil fuel combustion, human activities may trigger these tipping points, and the impacts of these changes will be difficult to adapt. Previous studies have shown that critical tipping points (e.g., ice sheet melting) had lower global warming thresholds under pre-industrial global climate conditions
[34]. However, this assumption may be flawed, especially for slow-occurring tipping elements (e.g., the collapse of the Atlantic meridional overturning circulation)
[34]. Recent research has found that, if the time spent exceeding the threshold is short and lower than the effective timescale of the tipping points, the threshold may be temporarily exceeded without triggering a change in the system state
[35].
China’s peak in anthropogenic CO
2 emissions around 2028 and its entry into the carbon neutrality process will help slow down the global greenhouse gas emission rate, thereby playing a key role in controlling the global temperature rise to the 2 °C target. The likelihood of the world reaching a tipping point will not be greater than current expectations
[36]. China’s actions may inspire other countries—especially developing countries—to take more proactive climate actions. Such global cooperation would increase the possibility of avoiding or delaying the reaching of tipping points. Future research should focus on how to develop Earth system models that more accurately describe the multi-scale characteristics of the complex Earth system, how to accurately quantify the level of climate warming, and what the contributions of China’s carbon peak and carbon neutrality to different tipping points will be, based on more realistic scenarios.
3.2. With China’s carbon neutrality process, will extreme weather and climate events still occur as frequently and repeatedly as expected?
On a global scale, the frequency and intensity of extreme heat events have increased
[37], while those of extreme cold events have decreased. This trend is evident in most regions worldwide. Human-induced greenhouse gas emissions are the main drivers of changes in heat and cold extremes on a global scale
[38]. As China is expected to reach its peak anthropogenic CO
2 emissions around 2028 and rapidly advance its carbon neutrality process, this significant transition holds a crucial position in global climate action. China’s policy actions have potentially profound impacts on the global climate, particularly influencing the frequency and intensity of global extreme weather events. Theoretically, if greenhouse gas emissions are controlled, it would help reduce the continuous rise in global average temperatures, thereby mitigating the frequency and intensity of extreme weather and climate events. On the other hand, it is important to take into account the climate system’s complex lag effects and nonlinear characteristics. The accumulated greenhouse gases may continue to heat the Earth for some time, making it difficult to fully mitigate the risk of extreme events in the short term
[39]. Future research should focus on gaining a deeper understanding of the changes in climate system extremes and their driving mechanisms, as well as how to carry out quantitative climate change adaptation actions and what role engineering can play in reducing the impacts and risks of climate change.
4. Issues of loss and damage under climate warming
Distinguishing and quantifying the loss and damage caused by climate warming is an important research direction in the field of climate change studies
[40]. This topic is also challenging, because assessing and quantifying the loss and damage issues caused by climate change is a complex problem
[2]. Below are some common assessment methods:
(1) Disaster loss assessment: This approach involves comparing the intensity of climate disasters before and after climate change, with the incremental part being the loss caused by climate change. For example, for natural disasters such as hurricanes and floods, it is possible to compare changes in indicators such as frequency, intensity, and impact range.
(2) Scenario analysis: This method involves a scenario analysis based on cost curves and economic models to simulate the impacts and shocks of different levels of temperature rise on ecosystems, economic development, and various industries. It can predict potential future losses due to climate change and provide a scientific basis for policymaking.
(3)
Willingness-to-pay surveys: This approach quantifies climate change losses by surveying the public’s willingness to pay to avoid climate disasters. This method can reflect the public’s perception of and attitude toward climate change, as well as their values regarding environmental protection
[41].
Many other related fields of literature, such as environmental economics, ecology, and meteorology, also provide important theoretical and methodological support for assessing and quantifying the loss and damage caused by climate change
[42]. It should be noted that, due to the complexity and uncertainty of climate change, assessing and quantifying its loss and damage is still in an initial stage and requires continuous development and improvement.
5. Equity issues in China’s carbon neutrality process: The concepts of carbon neutrality and methane reduction
The IPCC’s definition of carbon neutrality does not include the neutralization of other greenhouse gases, such as methane
[1]. In contrast, the carbon neutrality mentioned in the Paris Agreement refers to the neutralization of greenhouse gases including methane
[3]. Agricultural activities are a significant source of methane
[43], including methane produced during the digestive processes of ruminant animals such as cattle and sheep, methane generated during the growth of rice in paddies, and methane produced from compost storage and organic waste treatment
[44]. China has a land area similar to that of the United States or all of Europe, but its population is four times that of the United States and more than twice that of Europe. The consumption of beef, lamb, and rice in China is several times that of Western countries, making methane inclusion in carbon neutrality a greater challenge for China. Other major sources of methane include fossil fuel extraction and utilization, as coal mining, natural gas extraction, and oil production are significant sources of methane
[43],
[44]. In oil and gas extraction, methane is produced during mine emissions, gas leaks, and combustion processes. Additionally, landfills and wastewater treatment plants are important sources of methane
[45].
Due to its large population and economic scale, China generates more methane than Western countries, making the inclusion of methane in carbon neutrality a potential risk issue for China in global climate change negotiations. At the 26th Conference of the Parties (COP26) following the Paris Agreement, the European Union (EU) and the United States proposed the Global Methane Pledge, emphasizing the threat this greenhouse gas poses to its temperature goals and insisting on a 30% reduction in its emissions by 2030. China did not sign this pledge. If methane were included in the carbon neutrality commitment, China’s carbon neutrality achievement might be delayed until 2075, which is inconsistent with China’s efforts to achieve carbon neutrality. China’s commitment to carbon neutrality aligns with its governance and development philosophy of “following the right path and achieving virtue,” placing it on a favorable moral high ground in global climate change negotiations. It also reflects China’s need to embark on a new green, low-carbon, and high-quality development path, distinct from the past 40 years of remarkable achievements. Carbon neutrality will have profound and long-term impacts on China’s energy structure, industrial structure, and socio–economic development, representing a major opportunity for China to face and even lead the fourth industrial revolution. It may also change how the world economy and society have operated since the industrial revolution era of 1750.
6. Summary
This paper addressed key issues such as China’s pathways to a carbon peak and neutrality, global warming trends after China has achieved carbon neutrality, and fairness considerations in the carbon neutrality process. It discussed the 2 and 1.5 °C targets in the Paris Agreement, pathways for China to achieve carbon neutrality aligned with the 2 °C target, climate overshoot, tipping points, extreme events, loss and damage, the concept of carbon neutrality, and international considerations on methane reduction. Based on the reflections on these important issues, the following research areas are suggested:
(1) More realistic carbon neutrality pathways and emission scenarios. The assessment of climate projections by Working Group I (WGI) of the IPCC has always been enabled by the World Climate Research Programme’s (WCRP) Climate Model Intercomparison Projects (CMIP). In the Scenario-Model Intercomparison Project (MIP) experiment, Earth system models run a set of illustrative scenarios that are designed to span a wide range of possible futures, based on a community effort to develop pathways that are plausible, facilitate integrated research, and answer targeted science and policy-relevant questions. The last Scenario-MIP exercise (CMIP6), which largely underpinned the AR6 assessment, was started ten years ago. Given current policy developments, emission levels and warming trends, both the very high warming scenario (RCP8.5/SSP5-8.5) and the very low stabilization scenario (SSP1-1.9) assessed in AR6 have since been criticized as unrealistic. Mitigation ambition and policies in major emitting countries and regions, as well as the expected impacts on economy and society, render a very high emissions scenario with high societal and economic development implausible. On the other hand, due to the high and still rising level of greenhouse gas emissions and the failure to peak in the early 2020s as needed in most scenarios achieving the 2015 Paris Agreement temperature targets, the lowest stabilization scenario would require emission cuts and CO2 removal at a rate and scope that is considered increasingly less feasible.
A round of new scenarios (CMIP7 and other scenarios), starting in 2025 instead of 2015, will probably be analyzed during the IPCC Seventh Assessment Report (AR7), with plausibility constraints and other considerations (e.g., emission-based, overshoot, and equity) are being designed and will provide fresh results. The emergence of new global emission scenarios accounting for the current trends in emissions by the world’s major carbon-emitting regions (e.g., peaking and moving toward carbon neutrality) will refine our knowledge of warming levels. The world needs research to lead to new insights into how to achieve the goals of the Paris Agreement.
(2) More accurate Earth system models: There is a need to develop Earth system models that can more accurately describe the multi-scale characteristics of the complex Earth system, achieve coupling between Earth system models and integrated assessment models of the economy and society, and precisely quantify global warming levels based on more realistic scenarios, with particular attention being paid to the carbon budget under the 2 or 1.5 °C targets and their high-precision climate change projections.
(3) Precise observational research: Precise research is needed to support the prediction, estimation, and rapid attribution of extreme weather and climate events, gain a deep understanding of extreme changes in the climate system and their driving mechanisms, and accurately and quickly quantify the relative contributions of anthropogenic activities and natural forcing.
(4) Grid layouts, loss and damage, and tipping points: More research is needed on renewable energy grid layout predictions, loss and damage, climate tipping points, and other aspects that are closer to actual conditions.
(5) Ecosystem–climate change feedback: Further research is required on the mutual feedback between quantitative structural and functional ecosystem changes and climate change.
(6) Risks and mitigation: Quantitative research must be conducted on the role of climate warming adaptation actions and projects in reducing impacts and in risk mitigation/prevention, and on the impact and comprehensive risks of major ecological projects under extreme climate conditions. It is also necessary to reveal the economic and societal impacts of extreme events and the mechanisms of disaster causation, and to assess their comprehensive risks and their environmental/ecological effects.
(7) Increasing efficiency and reducing costs: Theories and methods are needed for enhancing efficiency and reducing costs in greenhouse gas emission reduction, key unit technologies, ecosystem carbon sequestration technologies, and system integration technologies.
(8) Disruptive technologies: Research is needed on the driving mechanisms and development patterns of disruptive technologies for greenhouse gas emission reduction.
(9) Geoengineering: Research should be conducted on geoengineering for medium- and long-term climate response and resilient cities and efficient synergy technologies for infrastructure energy utilization. Research is also needed on future transportation, application, source-load interaction, and integration synergy technologies and systems for renewable energy.
It should be pointed out that there are many uncertainties in China’s future peak CO2 emissions and its path toward carbon neutrality, which are worthy of readers’ attention. The main sources of these uncertainties are as follows.
The first uncertainty involves the change in China’s energy consumption structure. With the economic development model, industrial structure adjustment, and the emergence of new technologies, the future energy consumption structure of the country may change in ways that are difficult to accurately predict. For example, the pattern of energy demand in emerging industries may be very different from that of traditional industries. If new industries with high energy consumption but great development potential emerge, energy consumption forecasting will be more complicated.
Second, there may be discrepancies in the estimate of how much renewable energy will be installed in China every year in the future. The development of renewable energy is affected by a variety of factors such as policies, technological breakthroughs, new achievements in resource exploration, and enthusiasm for market investment. Policy adjustments may change the construction speed of renewable energy projects, while technological breakthroughs may cause renewable energy that originally lacked the conditions for development to become a new installed growth point. On the other hand, technical bottlenecks may hinder the growth of installed capacity.
Third, the future estimations of China's annual energy growth are uncertain. This includes not only the impact of changes in the domestic economic situation regarding energy demand, such as a large increase in energy consumption caused by the economic growth rate exceeding expectations, but also the impact of fluctuations in the international energy market on China’s energy import and use strategies.
Fourth, the development of negative-emission technologies such as CCS is unknown. If these technologies can be applied on a large scale and at low cost in the future, they will greatly change the path and speed of carbon neutrality; however, there are still great uncertainties about their technological maturity and commercial application prospects.
Fifth, the synergy and implementation of emission–reduction actions differ in different regions. China has a vast territory, and the economic development level and emission reduction capacity of different regions are uneven. In the process of implementing a national peak in CO2 emissions and China’s carbon neutrality target, differences in local policy implementation and the synergistic effect of inter-regional emission reduction may be different from what is expected, affecting the overall anticipated time and path.
These uncertainties are like a fog hanging over China’s goals of achieving a peak in CO2 emissions and reaching carbon neutrality. We must clearly recognize their existence in order to prepare for various changes on the way forward and ensure the smooth achievement of China’s dual carbon goals.
Acknowledgments
This research was supported by the top-level design of the National Natural Science Foundation of China (NSFC) Major Project “Realization of optimal carbon neutral pathway and coupling of multi-scale interaction patterns of natural-social systems in China” (42341202) and the Basic Scientific Research Fund of the Chinese Academy of Meteorological Sciences (2021Z014).
Compliance with ethics guidelines
Xiaoye Zhang, Junting Zhong, Xiliang Zhang, Da Zhang, Changhong Miao, Deying Wang, and Lifeng Guo declare that they have no conflict of interst or financial conflicts to disclose.
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