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Climate extremes such as droughts and heatwaves have a large impact on terrestrial carbon uptake by reducing gross primary production (GPP). While the evidence for increasing frequency and intensity of climate extremes over the last decades is growing, potential systematic adverse shifts in GPP have not been assessed. Using observationally-constrained and process-based model data, we estimate that particularly northern midlatitude ecosystems experienced a +10.6% increase in negative GPP extremes in the period 2000–2016 compared to 1982–1998. We attribute this increase predominantly to a greater impact of warm droughts, in particular over northern temperate grasslands (+95.0% corresponding mean increase) and croplands (+84.0%), in and after the peak growing season. These results highlight the growing vulnerability of ecosystem productivity to warm droughts, implying increased adverse impacts of these climate extremes on terrestrial carbon sinks as well as a rising pressure on global food security.The authors show increased negative extremes in gross primary productivity in northern midlatitude ecosystems, particularly over grasslands and croplands, attributed to impacts of warm droughts. This highlights the vulnerability of terrestrial carbon sinks and food security to increasing extreme events.

Land ecosystems absorb on average 30 per cent of anthropogenic carbon dioxide (CO 2 ) emissions, thereby slowing the increase of CO 2 concentration in the atmosphere 1 . Year-to-year variations in the atmospheric CO 2 growth rate are mostly due to fluctuating carbon uptake by land ecosystems 1 . The sensitivity of these fluctuations to changes in tropical temperature has been well documented 2 – 6 , but identifying the role of global water availability has proved to be elusive. So far, the only usable proxies for water availability have been time-lagged precipitation anomalies and drought indices 3 – 5 , owing to a lack of direct observations. Here, we use recent observations of terrestrial water storage changes derived from satellite gravimetry 7 to investigate terrestrial water effects on carbon cycle variability at global to regional scales. We show that the CO 2 growth rate is strongly sensitive to observed changes in terrestrial water storage, drier years being associated with faster atmospheric CO 2 growth. We demonstrate that this global relationship is independent of known temperature effects and is underestimated in current carbon cycle models. Our results indicate that interannual fluctuations in terrestrial water storage strongly affect the terrestrial carbon sink and highlight the importance of the interactions between the water and carbon cycles. The growth rate of global atmospheric CO 2 concentration is faster in drier years, independently of temperature; this relationship is underestimated in current carbon cycle models.

Carbon budget accounting relies heavily on Food and Agriculture Organization land-use data reported by governments. Here we develop a new land-use and cover-change database for China, finding that differing historical survey methods biased China’s reported data causing large errors in Food and Agriculture Organization databases. Land ecosystem model simulations driven with the new data reveal a strong carbon sink of 8.9 ± 0.8 Pg carbon from 1980 to 2019 in China, which was not captured in Food and Agriculture Organization data-based estimations due to biased land-use and cover-change signals. The land-use and cover-change in China, characterized by a rapid forest expansion from 1980 to 2019, contributed to nearly 44% of the national terrestrial carbon sink. In contrast, climate changes (22.3%), increasing nitrogen deposition (12.9%), and rising carbon dioxide (8.1%) are less important contributors. This indicates that previous studies have greatly underestimated the impact of land-use and cover-change on the terrestrial carbon balance of China. This study underlines the importance of reliable land-use and cover-change databases in global carbon budget accounting. The impact of land-use and cover-change (LUCC) on ecosystem carbon stock in China is poorly known due to large biases in existing databases. Here the authors develop a new LUCC database with corrected false signals and reveal that forest expansion is the dominant driver of China’s recent carbon sink.

Forest carbon sequestration capacity in China remains uncertain due to underrepresented tree demographic dynamics and overlooked of harvest impacts. In this study, we employ a process-based biogeochemical model to make projections by using national forest inventories, covering approximately 415,000 permanent plots, revealing an expansion in biomass carbon stock by 13.6 ± 1.5 Pg C from 2020 to 2100, with additional sink through augmentation of wood product pool (0.6-2.0 Pg C) and spatiotemporal optimization of forest management (2.3 ± 0.03 Pg C). We find that statistical model might cause large bias in long-term projection due to underrepresentation or neglect of wood harvest and forest demographic changes. Remarkably, disregarding the repercussions of harvesting on forest age can result in a premature shift in the timing of the carbon sink peak by 1–3 decades. Our findings emphasize the pressing necessity for the swift implementation of optimal forest management strategies for carbon sequestration enhancement. The authors show China’s forests can sequester 172.3 million tons of carbon per year in biomass by 2100, with an additional 28.1 million tons from improved management practices, but neglecting wood harvest impacts will distort long-term future projections.

Tropical secondary forests sequester carbon up to 20 times faster than old-growth forests. This rate does not capture spatial regrowth patterns due to environmental and disturbance drivers. Here we quantify the influence of such drivers on the rate and spatial patterns of regrowth in the Brazilian Amazon using satellite data. Carbon sequestration rates of young secondary forests (<20 years) in the west are ~60% higher (3.0 ± 1.0 Mg C ha −1  yr −1 ) compared to those in the east (1.3 ± 0.3 Mg C ha −1  yr −1 ). Disturbances reduce regrowth rates by 8–55%. The 2017 secondary forest carbon stock, of 294 Tg C, could be 8% higher by avoiding fires and repeated deforestation. Maintaining the 2017 secondary forest area has the potential to accumulate ~19.0 Tg C yr −1 until 2030, contributing ~5.5% to Brazil’s 2030 net emissions reduction target. Implementing legal mechanisms to protect and expand secondary forests whilst supporting old-growth conservation is, therefore, key to realising their potential as a nature-based climate solution. This study uses regional and global remote sensing data to assess the regrowth of secondary forests in the Brazilian Amazon biome. The authors find differences of regrowth rates due to climate, forest fires and deforestation actions and further quantify their carbon capture potential.

China's carbon balance The publication of a comprehensive assessment of China's terrestrial carbon budget fills a major gap in the geographical spread of carbon balance data, and helps to further reduce uncertainties in the Northern Hemisphere carbon balance. Three different indicators were used to monitor China's carbon balance and its driving mechanisms during the 1980s and 1990s: biomass and soil carbon inventories extrapolated from satellite greenness measurements, ecosystem models and atmospheric inversions. The three methods produce similar estimates for the net carbon sink at 0.19 to 0.26 petagrams per year. Global terrestrial ecosystems, in comparison, have absorbed carbon at a rate of 1 to 4 Pg carbon per year during the 1980s and 1990s, which offsets 10–60% of fossil fuel emissions. Northeast China is a net source of CO 2 to the atmosphere as a result over-harvesting and degradation of forests. In contrast, southern China accounts for over 65% of the carbon sink, attributable to regional climate change, tree planting and shrub recovery. This paper analyses the terrestrial carbon balance of China during the 1980s and 1990s using biomass and soil carbon inventories extrapolated by satellite greenness measurements, ecosystem models and atmospheric inversions. These three methods produce similar estimates of a net sink of 0.19–0.26 billion tonnes of carbon per year, indicating that China absorbed 28–37 per cent of its fossil carbon emissions over these two decades, mainly attributable to regional climate change, large-scale plantation programmes and shrub recovery. Global terrestrial ecosystems absorbed carbon at a rate of 1–4 Pg yr -1 during the 1980s and 1990s, offsetting 10–60 per cent of the fossil-fuel emissions 1 , 2 . The regional patterns and causes of terrestrial carbon sources and sinks, however, remain uncertain 1 , 2 , 3 . With increasing scientific and political interest in regional aspects of the global carbon cycle, there is a strong impetus to better understand the carbon balance of China 1 , 2 , 3 . This is not only because China is the world’s most populous country and the largest emitter of fossil-fuel CO 2 into the atmosphere 4 , but also because it has experienced regionally distinct land-use histories and climate trends 1 , which together control the carbon budget of its ecosystems. Here we analyse the current terrestrial carbon balance of China and its driving mechanisms during the 1980s and 1990s using three different methods: biomass and soil carbon inventories extrapolated by satellite greenness measurements, ecosystem models and atmospheric inversions. The three methods produce similar estimates of a net carbon sink in the range of 0.19–0.26 Pg carbon (PgC) per year, which is smaller than that in the conterminous United States 5 but comparable to that in geographic Europe 6 . We find that northeast China is a net source of CO 2 to the atmosphere owing to overharvesting and degradation of forests. By contrast, southern China accounts for more than 65 per cent of the carbon sink, which can be attributed to regional climate change, large-scale plantation programmes active since the 1980s and shrub recovery. Shrub recovery is identified as the most uncertain factor contributing to the carbon sink. Our data and model results together indicate that China’s terrestrial ecosystems absorbed 28–37 per cent of its cumulated fossil carbon emissions during the 1980s and 1990s.

The year 2022 saw record breaking temperatures in Europe during both summer and fall. Similar to the recent 2018 drought, close to 30% (3.0 million km 2 ) of the European continent was under severe summer drought. In 2022, the drought was located in central and southeastern Europe, contrasting the Northern-centered 2018 drought. We show, using multiple sets of observations, a reduction of net biospheric carbon uptake in summer (56-62 TgC) over the drought area. Specific sites in France even showed a widespread summertime carbon release by forests, additional to wildfires. Partial compensation (32%) for the decreased carbon uptake due to drought was offered by a warm autumn with prolonged biospheric carbon uptake. The severity of this second drought event in 5 years suggests drought-induced reduced carbon uptake to no longer be exceptional, and important to factor into Europe’s developing plans for net-zero greenhouse gas emissions that rely on carbon uptake by forests. Heat and moisture stress can reduce carbon uptake by forests. Here, the authors quantify this effect for the extreme 2022 European summer drought. The widespread reduction of photosynthesis exceeded the large local carbon release by intense fires.

The unusually large land carbon sink reported in 2011 can mostly be attributed to semi-arid vegetation growth in the Southern Hemisphere following increased rainfall and long-term greening trends. Australia driving carbon uptake Land and ocean take up around half of the annual anthropogenic carbon emissions, and a thorough understanding of this process is important for predicting future greenhouse gas concentrations and thus climate change. This study investigates the largest uptake of land carbon since atmospheric CO 2 measurements began in 1958. Three independent methods of global carbon budget determination point to an exceptionally large land carbon sink in response to extraordinary La Niña rainfall in semi-arid regions in the Southern Hemisphere, with almost 60% of carbon uptake attributed to the Australian ecosystem and an increase in the sensitivity of continental net carbon uptake to precipitation. Tropical rainforests have been thought to dominate the terrestrial processes driving global carbon cycle interannual variability, but this work suggests that semi-arid biomes might become the dominant drivers in future. The land and ocean act as a sink for fossil-fuel emissions, thereby slowing the rise of atmospheric carbon dioxide concentrations 1 . Although the uptake of carbon by oceanic and terrestrial processes has kept pace with accelerating carbon dioxide emissions until now, atmospheric carbon dioxide concentrations exhibit a large variability on interannual timescales 2 , considered to be driven primarily by terrestrial ecosystem processes dominated by tropical rainforests 3 . We use a terrestrial biogeochemical model, atmospheric carbon dioxide inversion and global carbon budget accounting methods to investigate the evolution of the terrestrial carbon sink over the past 30 years, with a focus on the underlying mechanisms responsible for the exceptionally large land carbon sink reported in 2011 (ref. 2 ). Here we show that our three terrestrial carbon sink estimates are in good agreement and support the finding of a 2011 record land carbon sink. Surprisingly, we find that the global carbon sink anomaly was driven by growth of semi-arid vegetation in the Southern Hemisphere, with almost 60 per cent of carbon uptake attributed to Australian ecosystems, where prevalent La Niña conditions caused up to six consecutive seasons of increased precipitation. In addition, since 1981, a six per cent expansion of vegetation cover over Australia was associated with a fourfold increase in the sensitivity of continental net carbon uptake to precipitation. Our findings suggest that the higher turnover rates of carbon pools in semi-arid biomes are an increasingly important driver of global carbon cycle inter-annual variability and that tropical rainforests may become less relevant drivers in the future. More research is needed to identify to what extent the carbon stocks accumulated during wet years are vulnerable to rapid decomposition or loss through fire in subsequent years.

Large interannual variations in the measured growth rate of atmospheric carbon dioxide (CO2) originate primarily from fluctuations in carbon uptake by land ecosystems13. It remains uncertain, however, to what extent temperature and water availability control the carbon balance of land ecosystems across spatial and temporal scales314. Here we use empirical models based on eddy covariance data15 and process-based models16,17 to investigate the effect of changes in temperature and water availability on gross primary productivity (GPP), terrestrial ecosystem respiration (TER) and net ecosystem exchange (NEE) at local and global scales. We find that water availability is the dominant driver of the local interannual variability in GPP and TER. To a lesser extent this is true also for NEE at the local scale, but when integrated globally, temporal NEE variability is mostly driven by temperature fluctuations. We suggest that this apparent paradox can be explained by two compensatory water effects. Temporal water-driven GPP and TER variations compensate locally, dampening water-driven NEE variability. Spatial water availability anomalies also compensate, leaving a dominant temperature signal in the year-to-year fluctuations of the land carbon sink. These findings help to reconcile seemingly contradictory reports regarding the importance of temperature and water in controlling the interannual variability of the terrestrial carbon balance36,9,11,12,14. Our study indicates that spatial climate covariation drives the global carbon cycle response.

Global fluctuations in annual land carbon uptake (NEE IAV ) depend on water and temperature variability, yet debate remains about local and seasonal controls of the global dependences. Here, we quantify regional and seasonal contributions to the correlations of globally-averaged NEE IAV against terrestrial water storage (TWS) and temperature, and respective uncertainties, using three approaches: atmospheric inversions, process-based vegetation models, and data-driven models. The three approaches agree that the tropics contribute over 63% of the global correlations, but differ on the dominant driver of the global NEE IAV , because they disagree on seasonal temperature effects in the Northern Hemisphere (NH, >25°N). In the NH, inversions and process-based models show inter-seasonal compensation of temperature effects, inducing a global TWS dominance supported by observations. Data-driven models show weaker seasonal compensation, thereby estimating a global temperature dominance. We provide a roadmap to fully understand drivers of global NEE IAV and discuss their implications for future carbon–climate feedbacks. The dominant driver of variations in global land carbon sink remains unclear. Here the authors show that the seasonal compensation of temperature effects on land carbon sink in the Northern Hemisphere could induce a global water dominance.