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Climate change is shifting the phenological cycles of plants.sup.1, thereby altering the functioning of ecosystems, which in turn induces feedbacks to the climate system.sup.2. In northern (north of 30° N) ecosystems, warmer springs lead generally to an earlier onset of the growing season.sup.3,4 and increased ecosystem productivity early in the season.sup.5. In situ.sup.6 and regional.sup.7-9 studies also provide evidence for lagged effects of spring warmth on plant productivity during the subsequent summer and autumn. However, our current understanding of these lagged effects, including their direction (beneficial or adverse) and geographic distribution, is still very limited. Here we analyse satellite, field-based and modelled data for the period 1982-2011 and show that there are widespread and contrasting lagged productivity responses to spring warmth across northern ecosystems. On the basis of the observational data, we find that roughly 15 per cent of the total study area of about 41 million square kilometres exhibits adverse lagged effects and that roughly 5 per cent of the total study area exhibits beneficial lagged effects. By contrast, current-generation terrestrial carbon-cycle models predict much lower areal fractions of adverse lagged effects (ranging from 1 to 14 per cent) and much higher areal fractions of beneficial lagged effects (ranging from 9 to 54 per cent). We find that elevation and seasonal precipitation patterns largely dictate the geographic pattern and direction of the lagged effects. Inadequate consideration in current models of the effects of the seasonal build-up of water stress on seasonal vegetation growth may therefore be able to explain the differences that we found between our observation-constrained estimates and the model-constrained estimates of lagged effects associated with spring warming. Overall, our results suggest that for many northern ecosystems the benefits of warmer springs on growing-season ecosystem productivity are effectively compensated for by the accumulation of seasonal water deficits, despite the fact that northern ecosystems are thought to be largely temperature- and radiation-limited.sup.10.Widespread but contrasting delayed responses of ecosystem productivity to spring warmth across northern ecosystems is inferred from satellite data, with higher areal fractions of adverse effects than beneficial effects., Author(s): Wolfgang Buermann [sup.1] [sup.2] , Matthias Forkel [sup.3] , Michael O'Sullivan [sup.1] , Stephen Sitch [sup.4] , Pierre Friedlingstein [sup.5] , Vanessa Haverd [sup.6] , Atul K. Jain [sup.7] [...]

The terrestrial biosphere can release or absorb the greenhouse gases, carbon dioxide (C[O.sub.2]), methane (C[H.sub.4]) and nitrous oxide ([N.sub.2]O), and therefore has an important role in regulating atmospheric composition and [...]

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 Nina 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., Each year, on average, land and ocean carbon sinks absorb the equivalent of about half of the global fossil fuel emissions, thereby providing a critical service that slows the rise [...]

Land ecosystems absorb on average 30 per cent of anthropogenic carbon dioxide (CO.sub.2) emissions, thereby slowing the increase of CO.sub.2 concentration in the atmosphere.sup.1. Year-to-year variations in the atmospheric CO.sub.2 growth rate are mostly due to fluctuating carbon uptake by land ecosystems.sup.1. The sensitivity of these fluctuations to changes in tropical temperature has been well documented.sup.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.sup.3-5, owing to a lack of direct observations. Here, we use recent observations of terrestrial water storage changes derived from satellite gravimetry.sup.7 to investigate terrestrial water effects on carbon cycle variability at global to regional scales. We show that the CO.sub.2 growth rate is strongly sensitive to observed changes in terrestrial water storage, drier years being associated with faster atmospheric CO.sub.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.sub.2 concentration is faster in drier years, independently of temperature; this relationship is underestimated in current carbon cycle models., Author(s): Vincent Humphrey [sup.1] , Jakob Zscheischler [sup.1] , Philippe Ciais [sup.2] , Lukas Gudmundsson [sup.1] , Stephen Sitch [sup.3] , Sonia I. Seneviratne [sup.1] Author Affiliations:(1) Institute for Atmospheric [...]

Plant photosynthesis tends to increase with irradiance. However, recent theoretical and observational studies have demonstrated that photosynthesis is also more efficient under diffuse light conditions (1-5). Changes in cloud cover or atmospheric aerosol loadings, arising from either volcanic or anthropogenic emissions, alter both the total photosynthetically active radiation reaching the surface and the fraction of this radiation that is diffuse, with uncertain overall effects on global plant productivity and the land carbon sink. Here we estimate the impact of variations in diffuse fraction on the land carbon sink using a global model modified to account for the effects of variations in both direct and diffuse radiation on canopy photosynthesis. We estimate that variations in diffuse fraction, associated largely with the 'global dimming' period (6-8), enhanced the land carbon sink by approximately one-quarter between 1960 and 1999. However, under a climate mitigation scenario for the twenty-first century in which sulphate aerosols decline before atmospheric C[O.sup.2] is stabilized, this 'diffuse-radiation' fertilization effect declines rapidly to near zero by the end of the twenty-first century., The solar radiation reaching the Earth's surface is the primary driver of plant photosynthesis. Leaf photosynthesis increases nonlinearly with incident photosynthetically active radiation (PAR), saturating at light levels that are [...]

Global terrestrial ecosystems absorbed carbon at a rate of 1-4 Pg [yr.sup.-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 (1-3). With increasing scientific and political interest in regional aspects of the global carbon rycle, there is a strong impetus to better understand the carbon balance of China (1-3). This is not only because China is the world's most populous country and the largest emitter of fossil-fuel C[O.sub.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 C[O.sub.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., In parallel with the recent economic boom in China, there has been a steep rise in energy demand, sustained by the use of fossil fuels. Fossil-fuel C[O.sub.2] emissions have thus [...]

Land ecosystems absorb on average 30 per cent of anthropogenic carbon dioxide (CO2) emissions, thereby slowing the increase of CO2 concentration in the atmosphere1. Year-to-year variations in the atmospheric CO2 growth rate are mostly due to fluctuating carbon uptake by land ecosystems1. The sensitivity of these fluctuations to changes in tropical temperature has been well documented2-6, 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 indices3-5, owing to a lack of direct observations. Here, we use recent observations of terrestrial water storage changes derived from satellite gravimetry7 to investigate terrestrial water effects on carbon cycle variability at global to regional scales. We show that the CO2 growth rate is strongly sensitive to observed changes in terrestrial water storage, drier years being associated with faster atmospheric CO2 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 CO2 concentration is faster in drier years, independently of temperature; this relationship is underestimated in current carbon cycle models. [ABSTRACT FROM AUTHOR]

Large interannual variations in the measured growth rate of atmospheric carbon dioxide (CO2) originate primarily from fluctuations in carbon uptake by land ecosystems. It remains uncertain, however, to what extent temperature and water availability control the carbon balance of land ecosystems across spatial and temporal scales. Here we use empirical models based on eddy covariance data and process-based models 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 balance. Our study indicates that spatial climate covariation drives the global carbon cycle response. [ABSTRACT FROM AUTHOR]