Publications

Global carbon emissions in 2023 | Nature Reviews Earth & Environment, April 4, 2024

Zhu Liu, Zhu Deng, Steven J. Davis & Philippe Ciais

Global CO₂ emissions for 2023 increased by only 0.1% relative to 2022 (following increases of 5.4% and 1.9% in 2021 and 2022, respectively), reaching 35.8 Gt CO₂. These 2023 emissions consumed 10–66.7% of the remaining carbon budget to limit warming to 1.5°C, suggesting permissible emissions could be depleted within 0.5–6 years (67% likelihood).

Assessment of methane emissions from oil, gas and coal sectors across inventories and atmospheric inversions | Communications Earth & Environment volume, January 9, 2024

Kushal Tibrewal, Philippe Ciais, Marielle Saunois, Adrien Martinez, Xin Lin, Joel Thanwerdas, Zhu Deng, Frederic Chevallier, Clément Giron, Clément Albergel, Katsumasa Tanaka, Prabir Patra, Aki Tsuruta, Bo Zheng, Dmitry Belikov, Yosuke Niwa, Rajesh Janardanan, Shamil Maksyutov, Arjo Segers, Zitely A. Tzompa-Sosa, Philppe Bousquet & Jean Sciare

Changes in terrestrial carbon storage under environmental and land-use changes remain a critical source of Emissions from fossil fuel exploitation are a leading contributor to global anthropogenic methane emissions, but are highly uncertain. The lack of reliable estimates hinders monitoring of the progress on pledges towards methane reductions. Here we analyze methane emissions from exploitation of coal, oil and gas for major producing nations across a suite of bottom-up inventories and global inversions. Larger disagreement in emissions exists for the oil/gas sector across the inventories compared to coal, arising mostly from disparate data sources for emission factors. Moreover, emissions reported to the United Nations Framework Convention on Climate Change are lower than other bottom-up and inversion estimates, with many countries lacking reporting in the past decades. Finally, comparison with previous global inversions, revealed a strong influence of the prior inventory on the inferred sub-sectoral emissions magnitude. This study highlights the need to improve consensus on the methodological inputs among the bottom-up inventories in order to obtain more consistent inverse modelling results at the sub-sectoral level.

Global increase in biomass carbon stock dominated by growth of northern young forests over past decade | Nature Geoscience, October 2, 2023

Hui Yang, Philippe Ciais, Frédéric Frappart, Xiaojun Li, Martin Brandt, Rasmus Fensholt, Lei Fan, Sassan Saatchi, Simon Besnard, Zhu Deng, Simon Bowring & Jean-Pierre Wigneron

Changes in terrestrial carbon storage under environmental and land-use changes remain a critical source of uncertainty in regional and global carbon budgets. We generated global maps of annual live vegetation biomass using L-band microwave vegetation optical depth. Globally, biomass carbon stocks increased from 2010 to 2019 at a rate of 0.50 ± 0.20 PgC yr⁻¹ with a year-to-year variability, closely mirroring the observations of the global atmospheric CO₂ growth rate. The main contributors to the global carbon sink are boreal and temperate forests, while wet tropical forests are small carbon sources, from deforestation and agriculture-related disturbances. We found that the tropical deforested and degraded old-growth forests (>140 yr) are nearly carbon neutral whereas temperate and boreal young (< 50 yr) and middle-aged (50–140 yr) forests are the largest sinks. By contrast, dynamic global vegetation models show that all old-growth forests are large sinks and largely ignore the impacts of deforestation and degradation on tropical biomass. Our findings highlight the importance of forest demography when predicting dynamics of future carbon sink under changing climate.

Monitoring global carbon emissions in 2022 | Nature Reviews Earth & Environment, March 13, 2023

Zhu Liu, Zhu Deng, Philippe Ciais & Steven J. Davis

Global CO2 emissions for 2022 increased by 1.5% relative to 2021 (+7.9% and +2.0% relative to 2020 and 2019, respectively), reaching 36.1 GtCO2. These 2022 emissions consumed 13%–36% of the remaining carbon budget to limit warming to 1.5 °C, suggesting permissible emissions could be depleted within 2–7 years (67% likelihood).

National CO₂ budgets (2015–2020) inferred from atmospheric CO₂ observations in support of the Global Stocktake | Earth System Science Data, March 7, 2023

Brendan Byrne, David F. Baker, Sourish Basu, Michael Bertolacci, Kevin W. Bowman, Dustin Carroll, Abhishek Chatterjee, Frédéric Chevallier, Philippe Ciais, Noel Cressie, David Crisp, Sean Crowell, Feng Deng, Zhu Deng, Nicholas M. Deutscher, Manvendra K. Dubey, Sha Feng, Omaira E. García, David W. T. Griffith, Benedikt Herkommer, Lei Hu, Andrew R. Jacobson, Rajesh Janardanan, Sujong Jeong, Matthew S. Johnson, Dylan B. A. Jones, Rigel Kivi, Junjie Liu, Zhiqiang Liu, Shamil Maksyutov, John B. Miller, Scot M. Miller, Isamu Morino, Justus Notholt, Tomohiro Oda, Christopher W. O’Dell, Young-Suk Oh, Hirofumi Ohyama, Prabir K. Patra, Hélène Peiro, Christof Petri, Sajeev Philip, David F. Pollard, Benjamin Poulter, Marine Remaud, Andrew Schuh, Mahesh K. Sha, Kei Shiomi, Kimberly Strong, Colm Sweeney, Yao Té, Hanqin Tian, Voltaire A. Velazco, Mihalis Vrekoussis, Thorsten Warneke, John R. Worden, Debra Wunch, Yuanzhi Yao, Jeongmin Yun, Andrew Zammit-Mangion & Ning Zeng

Accurate accounting of emissions and removals of CO₂ is critical for the planning and verification of emission reduction targets in support of the Paris Agreement. Here, we present a pilot dataset of country-specific net carbon exchange (NCE; fossil plus terrestrial ecosystem fluxes) and terrestrial carbon stock changes aimed at informing countries’ carbon budgets. These estimates are based on “top-down” NCE outputs from the v10 Orbiting Carbon Observatory (OCO-2) modeling intercomparison project (MIP), wherein an ensemble of inverse modeling groups conducted standardized experiments assimilating OCO-2 column-averaged dry-air mole fraction () retrievals (ACOS v10), in situ CO₂ measurements or combinations of these data. The v10 OCO-2 MIP NCE estimates are combined with “bottom-up” estimates of fossil fuel emissions and lateral carbon fluxes to estimate changes in terrestrial carbon stocks, which are impacted by anthropogenic and natural drivers. These flux and stock change estimates are reported annually (2015–2020) as both a global 1^∘ × 1^∘ gridded dataset and a country-level dataset and are available for download from the Committee on Earth Observation Satellites’ (CEOS) website: https://doi.org/10.48588/npf6-sw92 (Byrne et al., 2022). Across the v10 OCO-2 MIP experiments, we obtain increases in the ensemble median terrestrial carbon stocks of 3.29–4.58 Pg CO₂ yr⁻¹ (0.90–1.25 Pg C yr⁻¹). This is a result of broad increases in terrestrial carbon stocks across the northern extratropics, while the tropics generally have stock losses but with considerable regional variability and differences between v10 OCO-2 MIP experiments. We discuss the state of the science for tracking emissions and removals using top-down methods, including current limitations and future developments towards top-down monitoring and verification systems.

A Carbon Monitoring Strategy through Near-real-time Data and Space Technology | The Innovation, November 3, 2022

Zhu Liu, Zhu Deng, Xiaoting Huang

In this Perspective, we proposed an innovative strategy that coupled the near-real-time emission data with the satellite observation to make a reliable and precise global carbon monitoring system.

Global patterns of daily CO₂ emissions rebound from the COVID-19 pandemic in the first year of COVID-19 | Nature Geoscience, June 30, 2022

Zhu Liu^#,*, Zhu Deng^#, Biqing Zhu, Philippe Ciais, Steven J. Davis, Jianguang Tan, Robbie M. Andrew, Olivier Boucher, Simon Ben Arous, Josep G. Canadell, Xinyu Dou, Pierre Friedlingstein, Pierre Gentine, Rui Guo, Chaopeng Hong, Robert B. Jackson, Daniel M. Kammen, Piyu Ke, Corinne Le Quéré, Crippa Monica, Greet Janssens-Maenhout, Glen P. Peters, Katsumasa Tanaka, Yilong Wang, Bo Zheng, Haiwang Zhong, Taochun Sun & Hans Joachim Schellnhuber

Day-to-day changes in CO₂ emissions from human activities, in particular fossil-fuel combustion and cement production, reflect a complex balance of influences from seasonality, working days, weather and, most recently, the COVID-19 pandemic. Here, we provide a daily CO₂ emissions dataset for the whole year of 2020, calculated from inventory and near-real-time activity data. We find a global reduction of 6.3% (2,232 MtCO₂) in CO₂emissions compared with 2019. The drop in daily emissions during the first part of the year resulted from reduced global economic activity due to the pandemic lockdowns, including a large decrease in emissions from the transportation sector. However, daily CO₂ emissions gradually recovered towards 2019 levels from late April with the partial reopening of economic activity. Subsequent waves of lockdowns in late 2020 continued to cause smaller CO₂ reductions, primarily in western countries. The extraordinary fall in emissions during 2020 is similar in magnitude to the sustained annual emissions reductions necessary to limit global warming at 1.5 °C. This underscores the magnitude and speed at which the energy transition needs to advance.

Comparing national greenhouse gas budgets reported in UNFCCC inventories against atmospheric inversions | Earth System Science Data, April 11, 2022

Zhu Deng^#, Philippe Ciais^#,*, Zitely A Tzompa-Sosa, Marielle Saunois, Chunjing Qiu, Chang Tan, Taochun Sun, Piyu Ke, Yanan Cui, Katsumasa Tanaka, Xin Lin, Rona L Thompson, Hanqin Tian, Yuanzhi Yao, Yuanyuan Huang, Ronny Lauerwald, Atul K Jain, Xiaoming Xu, Ana Bastos, Stephen Sitch, Paul I Palmer, Thomas Lauvaux, Alexandre d’Aspremont, Clément Giron, Antoine Benoit, Benjamin Poulter, Jinfeng Chang, Ana Maria Roxana Petrescu, Steven J Davis, Zhu Liu^*, Giacomo Grassi, Clément Albergel, Francesco N Tubiello, Lucia Perugini, Wouter Peters, Frédéric Chevallier

In support of the global stocktake of the Paris Agreement on climate change, this study presents a comprehensive framework to process the results of an ensemble of atmospheric inversions in order to make their net ecosystem exchange (NEE) carbon dioxide (CO₂) flux suitable for evaluating national greenhouse gas inventories (NGHGIs) submitted by countries to the United Nations Framework Convention on Climate Change (UNFCCC). From inversions we also deduced anthropogenic methane (CH₄) emissions regrouped into fossil and agriculture and waste emissions, as well as anthropogenic nitrous oxide (N₂O) emissions. To compare inversion results with national reports, we compiled a new global harmonized database of emissions and removals from periodical UNFCCC inventories by Annex I countries, and from sporadic and less detailed emissions reports by non-Annex I countries, given by national communications and biennial update reports. No gap filling was applied. The method to reconcile inversions with inventories is applied to selected large countries covering ∼90 % of the global land carbon uptake for CO₂ and top emitters of CH₄and N₂O. Our method uses results from an ensemble of global inversions produced by the Global Carbon Project for the three greenhouse gases, with ancillary data. We examine the role of CO₂ fluxes caused by lateral transfer processes from rivers and from trade in crop and wood products and the role of carbon uptake in unmanaged lands, both not accounted for by NGHGIs. Here we show that, despite a large spread across the inversions, the median of available inversion models points to a larger terrestrial carbon sink than inventories over temperate countries or groups of countries of the Northern Hemisphere like Russia, Canada and the European Union. For CH₄, we find good consistency between the inversions assimilating only data from the global in situ network and those using satellite CH₄ retrievals and a tendency for inversions to diagnose higher CH₄ emission estimates than reported by NGHGIs. In particular, oil- and gas-extracting countries in central Asia and the Persian Gulf region tend to systematically report lower emissions compared to those estimated by inversions. For N₂O, inversions tend to produce higher anthropogenic emissions than inventories for tropical countries, even when attempting to consider only managed land emissions. In the inventories of many non-Annex I countries, this can be tentatively attributed to a lack of reporting indirect N₂O emissions from atmospheric deposition and from leaching to rivers, to the existence of natural sources intertwined with managed lands, or to an underestimation of N₂O emission factors for direct agricultural soil emissions. Inversions provide insights into seasonal and interannual greenhouse gas fluxes anomalies, e.g., during extreme events such as drought or abnormal fire episodes, whereas inventory methods are established to estimate trends and multi-annual changes. As a much denser sampling of atmospheric CO₂and CH₄ concentrations by different satellites coordinated into a global constellation is expected in the coming years, the methodology proposed here to compare inversion results with inventory reports (e.g., NGHGIs) could be applied regularly for monitoring the effectiveness of mitigation policy and progress by countries to meet the objective of their pledges. The dataset constructed by this study is publicly available at https://doi.org/10.5281/zenodo.5089799 (Deng et al., 2021).

Emissions rebound from the COVID-19 pandemic | Nature Climate Change, March 31, 2022

Steven J. Davis, Zhu Liu, Zhu Deng, Biqing Zhu, Piyu Ke, Taochun Sun, Rui Guo, Chaopeng Hong, Bo Zheng, Yilong Wang, Olivier Boucher, Pierre Gentine, Philippe Ciais

Global CO₂ emissions in 2021 were only 1% less than the record levels of 2019, driven by increases in power- and industry-related emissions from China and India and a return of the carbon intensity of electricity to pre-pandemic levels. Is this resumed growth in fossil energy, or a final fleeting surge before a long decline?

Monitoring global carbon emissions in 2021 | Nature Reviews Earth & Environment, March 21, 2022

Zhu Liu, Zhu Deng, Steven J. Davis, Clement Giron, Philippe Ciais

Following record-level declines in 2020, near-real-time data indicate that global CO₂ emissions rebounded by 4.8% in 2021, reaching 34.9 GtCO₂. These 2021 emissions consumed 8.7% of the remaining carbon budget for limiting anthropogenic warming to 1.5 °C, which if current trajectories continue, might be used up in 9.5 years at 67% likelihood.

Global fossil carbon emissions rebound near pre-COVID-19 levels | Environmental Research Letter, March 7, 2022

R B Jackson1, P Friedlingstein, C Le Quéré, S Abernethy1 R M Andrew, J G Canadell, P Ciais, S J Davis, Zhu Deng, Zhu Liu, J I Korsbakken and G P Peters

Fossil CO₂ emissions in 2021 grew an estimated 4.2% (3.5%–4.8%) to 36.2 billion metric tons compared with 2020, pushing global emissions back close to 2019 levels (36.7 Gt CO₂).

Challenges and opportunities for carbon neutrality in China | Nature Reviews Earth & Environment, December 21, 2021

Zhu Liu, Zhu Deng, Gang He, Hailin Wang, Xian Zhang, Jiang Lin, Ye Qi, Xi Liang

China is currently the world’s largest emitter of carbon dioxide (CO₂). China therefore has a key role in global climate change mitigation. Policies and commitments are required to enable decarbonization. In this Perspective, we summarize the key features of China’s CO₂emissions, its reduction processes and successes in meeting climate targets. China’s CO₂emissions reductions have been substantial: by 2020, carbon intensity decreased by 48.4% compared to 2005 levels, achieving objectives outlined in the Nationally Appropriate Mitigation Actions and Nationally Determined Contributions. These reductions rely on the achievements of sectoral and sub-national targets outlined by China’s Five-Year Plans. However, China still faces the challenges of reaching its peak total CO₂ emissions before 2030 and achieving carbon neutrality before 2060. Key steps towards China’s carbon neutrality include increasing its non-fossil energy share, deploying negative-emission technologies at large scale, promoting regional low-carbon development and establishing a nationwide ‘green market’. To achieve these steps, top-down socio-economic development plans must coincide with bottom-up economic incentives and technology development.

Impact of Lockdowns and Winter Temperatures on Natural Gas Consumption in Europe | Earth’s Future, December 11, 2021

Philippe Ciais, François-Marie Bréon, Stijn Dellaert, Yilong Wang, Katsumasa Tanaka, Léna Gurriaran, Yann Françoise, Steven J. Davis, Chaopeng Hong, Josep Penuelas, Ivan Janssens, Michael Obersteiner, Zhu Deng, Zhu Liu

As the COVID-19 virus spread over the world, governments restricted mobility to slow transmission. Public health measures had different intensities across European countries but all had significant impact on people’s daily lives and economic activities, causing a drop of CO₂ emissions of about 10% for the whole year 2020. Here, we analyze changes in natural gas use in the industry and gas distribution to the built environment during the first half of year 2020 with daily gas flows data from pipeline and storage facilities in Europe. We find that reductions of industrial gas use reflect decreases in industrial production across most countries. Surprisingly, natural gas use in the built environment also decreased despite most people being confined at home and cold spells in March 2020. Those reductions that we attribute to the impacts of COVID-19 remain of comparable magnitude to previous variations induced by cold or warm climate anomalies in the cold season. We conclude that climate variations played a larger role than COVID-19 induced stay-home orders in natural gas consumption across Europe.

Near-real-time monitoring of global CO₂ emissions reveals the effects of the COVID-19 pandemic | Nature Communications, October 14, 2020

Zhu Liu^#,*, Philippe Ciais^#, Zhu Deng^#, Ruixue Lei, Steven J. Davis, Sha Feng, Bo Zheng, Duo Cui, Xinyu Dou, Biqing Zhu, Rui Guo, Piyu Ke, Taochun Sun, Chenxi Lu, Pan He, Yuan Wang, Xu Yue, Yilong Wang, Yadong Lei, Hao Zhou, Zhaonan Cai, Yuhui Wu, Runtao Guo, Tingxuan Han, Jinjun Xue, Olivier Boucher, Eulalie Boucher, Frédéric Chevallier, Katsumasa Tanaka, Yiming Wei, Haiwang Zhong, Chongqing Kang, Ning Zhang, Bin Chen, Fengming Xi, Miaomiao Liu, François-Marie Bréon, Yonglong Lu, Qiang Zhang, Dabo Guan, Peng Gong, Daniel M. Kammen, Kebin He & Hans Joachim Schellnhuber

The COVID-19 pandemic is impacting human activities, and in turn energy use and carbon dioxide (CO₂) emissions. Here we present daily estimates of country-level CO₂ emissions for different sectors based on near-real-time activity data. The key result is an abrupt 8.8% decrease in global CO₂ emissions (−1551 Mt CO₂) in the first half of 2020 compared to the same period in 2019. The magnitude of this decrease is larger than during previous economic downturns or World War II. The timing of emissions decreases corresponds to lockdown measures in each country. By July 1st, the pandemic’s effects on global emissions diminished as lockdown restrictions relaxed and some economic activities restarted, especially in China and several European countries, but substantial differences persist between countries, with continuing emission declines in the U.S. where coronavirus cases are still increasing substantially.

China’s non-fossil fuel CO₂ emissions from industrial processes | Applied Energy, August 8, 2019

Duo Cui, Zhu Deng, Zhu Liu

China is the largest contributor of global CO₂ emissions, to date more than quarter of the world total CO₂ is from China. Well known on the fossil fuel combustion and cement production as the major emission sources, however, “non-fossil fuel CO₂ emissions” are rarely reported by literature (except the emission from cement production). As China becomes the center for global manufacturing, it is critical to understand the magnitude and dynamics of China’s non-fossil fuel CO₂ emissions so effective mitigation policy can be addressed. Here we collected data for all kinds of industrial processes CO₂ emissions, and based on available data we calculated the CO₂ emissions from the production of lime, plate glass, ammonia, calcium carbide, soda ash, ethylene, ferroalloys, alumina, lead and zinc in 2003–2018. We found that China’s CO₂ emissions from these ten industrial processes reached 466 Mt CO₂ in 2016, which is equivalent to 5% of China’s total CO₂ emissions (9000 Mt CO₂) from fossil fuel combustion and cement production process. The 466 Mt CO₂ is approximate to total fossil fuel CO₂ emissions from Brazil, the world top 11 CO₂ emitter. The CO₂ emissions from these ten industrial production processes show a fast increase before 2014, and fluctuate in 2014–2018. Quantifying such emission is critical for understanding the global carbon budget and developing a suitable climate policy given the significant magnitude and recent dynamics of China’s non-fossil fuel CO₂ emissions.