Land Carbon Storage Research Articles

Dynamic simulation of land use change and assessment of carbon storage based on climate change scenarios at the city level: A case study of Bortala, China

Exploring future changes in land use and carbon storage (CS) under different climate scenarios is important for optimizing regional ecosystem service functions and formulating sustainable socioeconomic development policies. We proposed a framework that integrates the system dynamics (SD) model, patch-generating land use simulation (PLUS) model, and Integrated Valuation of Ecosystem Service and Tradeoffs (InVEST) model to dynamically simulate changes in land use/cover change (LUCC) and CS at the city level based on SSP-RCP scenarios provided by the CMIP6. The simulations were applied to Bortala Mongol Autonomous Prefecture in Xinjiang. Changes in LUCC were similar under the SSP126 and SSP245 scenarios, but woodland expansion was more rapid under the SSP126 scenario. Changes in LUCC under the SSP585 scenario were different from those under the other two scenarios, and this was mainly caused by the continuous reduction in woodland area and the rapid expansion of construction land and cultivated land. By 2050, the simulation results revealed that CS was highest under the SSP126 scenario (193.20 Tg), followed by the SSP245 scenario (192.75 Tg) and SSP585 scenario (185.17 Tg). Overall, the results of this study suggest that increases in CS could be achieved by controlling economic growth and population growth, promoting an energy transition, and expanding woodland in the study area.

Assessing the Potential Impact of Land Use on Carbon Storage Driven by Economic Growth: A Case Study in Yangtze River Delta Urban Agglomeration

Economic development and land-use change can strongly affect terrestrial ecosystems’ carbon balance. This paper quantifies the changes in land use of Yangtze River Delta urban agglomeration (YRD) in 2020 and 2035 under three economic growth scenarios, exploring the concurrent impact on carbon storage. The results showed that the land carbon storage of YRD had decreased by 1453.80 Tg in 2000–2020, and will continue to decrease by 982.38 Tg, 1417.62 Tg, and 1636.21 Tg under the scenarios of a slow, medium, and rapid economic growth from 2020 to 2035, respectively. The large-scale occupation of cultivated land and woodland for construction land caused by economic development and population growth was an important reason. The occupation of cultivated land by construction land in Nanjing, Shanghai, and its surrounding areas had further intensified, while the reduction in carbon storage caused by the reduction in woodland had become more prominent in Hangzhou, Shaoxing, Jinhua, and the surrounding areas.

Impact of rehabilitation and status area change on land cover and carbon storage in Paliyan Wildlife Reserve, Gunung Kidul, Indonesia

Abstract. Puspanti A, Kusumandari A, Faida LRW, Sudaryatno. 2021. Impact of rehabilitation and status area change on land cover and carbon storage in Paliyan Wildlife Reserve, Gunung Kidul, Indonesia. Biodiversitas 22: 3964-3971. This study analyzed the land cover change and carbon storage after the rehabilitation of Paliyan forest. This study mainly focused on the forest status during 1999-2019, especially after establishing a wildlife reserve forest and after rehabilitation activity. We used a combination of canopy density model, carbon conversion, and changes of management-related data to analyze land cover classes in two decades of 1999-2009 and 2009-2019 representing the change in status of the area, rehabilitation, and management dynamics through the time. The result shows that at baseline (1999), the status was still production plantation forest dominated by non-forest/open land with the most carbon storage in plantation forest of 5463.04 tons of carbon. In the first decade, important events occurred such as continuing illegal logging until 2001; change of area status to wildlife reserve forest; and initiation of rehabilitation in 2003. There was an increase in non-forest areas during the first decade, and carbon storage decreased mostly in plantation forests with only 867.71 tons of carbon remaining. In the second decade, rehabilitation has shown a positive impact in increasing forested areas, and altered non-forest to the forested area dominated by open forest/mixed agriculture area, followed by plantation forest, and secondary forest. In this decade, the legality of the area status and rehabilitation activity underwent to be more advance. The carbon storage also shows the positive result with the most increase of storage in plantation forest of 4072.932 tons carbon, or almost 4.7 times higher than that in 2009. Total carbon storage in 2019 was 13257.50 tons, or almost three times higher than that in 2009. The rehabilitation required a longer period to achieve a more dense forest condition as in 2019 the area was still dominated by open forest or agriculture. The smallholder farmers and high dependency of the surrounding community manage the land to feed their livestock, impede the rehabilitation and restoration process, and de-escalate the transition from non-forest to forest resulted in the more vegetated area. This result is important for stakeholders for designing appropriate forest-related policies and supporting further rehabilitation strategies.

Competing effects of nitrogen deposition and ozone exposure on northern hemispheric terrestrial carbon uptake and storage, 1850–2099

Abstract. Tropospheric ozone (O3) and nitrogen deposition affect vegetation growth and, thereby, the ability of the land biosphere to take up and store carbon. However, the magnitude of these effects on the contemporary and future terrestrial carbon balance is insufficiently understood. Here, we apply an extended version of the O–CN terrestrial biosphere model that simulates the atmosphere to canopy transport of O3, its surface and stomatal uptake, the O3-induced leaf injury, and the coupled terrestrial carbon and nitrogen cycles. We use this model to simulate past and future impacts of air pollution against a background of concurrent changes in climate and carbon dioxide concentrations (CO2) for two contrasting representative concentration pathway (RCP) scenarios (RCP2.6 and RCP8.5). The simulations show that O3-related damage considerably reduced northern hemispheric gross primary production (GPP) and long-term carbon storage between 1850 and the 2010s. The simulated O3 effect on GPP in the Northern Hemisphere peaked towards the end of the 20th century, with reductions of 4 %, causing a reduction in the northern hemispheric carbon sink of 0.4 Pg C yr−1. During the 21st century, O3-induced reductions in GPP and carbon storage are projected to decline, through a combination of direct air pollution control methods that reduce near-surface O3 and the indirect effects of rising atmospheric CO2, which reduces stomatal uptake of O3 concurrent with increases of leaf-level water use efficiency. However, in hot spot regions such as East Asia, the model simulations suggest a sustained decrease in GPP by more than 8 % throughout the 21st century. O3 exposure reduces projected carbon storage at the end of the 21st century by up to 15 % in parts of Europe, the US, and East Asia. Our simulations suggest that the stimulating effect of nitrogen deposition on regional GPP and carbon storage is lower in magnitude compared to the detrimental effect of O3 during most of the simulation period for both RCPs. In the second half of the 21st century, the detrimental effect of O3 on GPP is outweighed by nitrogen deposition, but the effect of nitrogen deposition on land carbon storage remains lower than the effect of O3. Accounting for the stimulating effects of nitrogen deposition but omitting the detrimental effect of O3 may lead to an overestimation of projected carbon uptake and storage.

Modelled land use and land cover change emissions – a spatio-temporal comparison of different approaches

Abstract. Quantifying the net carbon flux from land use and land cover changes (fLULCC) is critical for understanding the global carbon cycle and, hence, to support climate change mitigation. However, large-scale fLULCC is not directly measurable and has to be inferred from models instead, such as semi-empirical bookkeeping models and process-based dynamic global vegetation models (DGVMs). By definition, fLULCC estimates are not directly comparable between these two different model types. As an important example, DGVM-based fLULCC in the annual global carbon budgets is estimated under transient environmental forcing and includes the so-called loss of additional sink capacity (LASC). The LASC results from the impact of environmental changes on land carbon storage potential of managed land compared to potential vegetation and accumulates over time, which is not captured in bookkeeping models. The fLULCC from transient DGVM simulations, thus, strongly depends on the timing of land use and land cover changes mainly because LASC accumulation is cut off at the end of the simulated period. To estimate the LASC, the fLULCC from pre-industrial DGVM simulations, which is independent of changing environmental conditions, can be used. Additionally, DGVMs using constant present-day environmental forcing enable an approximation of bookkeeping estimates. Here, we analyse these three DGVM-derived fLULCC estimations (under transient, pre-industrial, and present-day forcing) for 12 models within 18 regions and quantify their differences as well as climate- and CO2-induced components and compare them to bookkeeping estimates. Averaged across the models, we find a global fLULCC (under transient conditions) of 2.0±0.6 PgC yr−1 for 2009–2018, of which ∼40 % are attributable to the LASC (0.8±0.3 PgC yr−1). From 1850 onward, the fLULCC accumulated to 189±56 PgC with 40±15 PgC from the LASC. Around 1960, the accumulating nature of the LASC causes global transient fLULCC estimates to exceed estimates under present-day conditions, despite generally increased carbon stocks in the latter. Regional hotspots of high cumulative and annual LASC values are found in the USA, China, Brazil, equatorial Africa, and Southeast Asia, mainly due to deforestation for cropland. Distinct negative LASC estimates in Europe (early reforestation) and from 2000 onward in the Ukraine (recultivation of post-Soviet abandoned agricultural land), indicate that fLULCC estimates in these regions are lower in transient DGVM compared to bookkeeping approaches. Our study unravels the strong dependence of fLULCC estimates on the time a certain land use and land cover change event happened to occur and on the chosen time period for the forcing of environmental conditions in the underlying simulations. We argue for an approach that provides an accounting of the fLULCC that is more robust against these choices, for example by estimating a mean DGVM ensemble fLULCC and LASC for a defined reference period and homogeneous environmental changes (CO2 only).

Change detection (1985-2020): Projections on land-use land cover, carbon storage, sequestration, and valuation in Southwestern Gambia

This study assesses land-use/land cover (LULC) change in the southwestern region of The Gambia, using remotely sensed satellite imagery. Using a geographic information system (GIS) software, I cond...

Afforestation increases ecosystem productivity and carbon storage in China during the 2000s

China is experiencing fast afforestation and sensible climate change in recent decades. However, their impacts on regional carbon cycle remain unclear. Here, we explore the effects of climate and land cover change (LCC) on ecosystem productivity and carbon storage in China during 2001-2012 by forcing a dynamic vegetation model with satellite-based land cover and two different climate datasets. The model predicts a significant increase of 0.065 m2 m−2 decade−1 in annual mean leaf area index, higher than the observed trend of 0.038 m2 m−2 decade−1. Meanwhile, national annual total gross primary productivity increases by 0.041 ± 0.007 Pg C yr−2, which is contributed by CO2 fertilization (0.035 ± 0.001 Pg C yr−2), LCC (0.036 ± 0.001 Pg C yr−2), and climate change (-0.032 ± 0.01 Pg C yr−2). Consequently, the total land carbon storage in China increases by 0.99 Pg C yr−1, to which the LCC alone contributes 0.77 Pg C yr−1. The maximum enhancement of >1 g C m−2 yr−1 in land carbon stock is found over the central west, where a large fraction of shrublands is converted to forests. Our results suggest that afforestation in China provides a strong mitigation to the regional carbon emissions during the 2000s.

Land cover changes and carbon storage before and after community forestry program in Bleberan village, Gunungkidul, Indonesia, 1999–2018

This study investigated the land cover changes, carbon storage dynamics and their underlying socio-economic processes before and after a community forest permit in Bleberan village, Gunungkidul, Indonesia, during 1999–2018. We used a combination of the forest canopy density model, carbon conversion and socio-economic related data to analyze land cover classes in the periods of 1999–2003, 2003–2009, and 2009–2018, representing the phases of several years before community forestry permit, initial phase of community forestry establishment and several years after community forestry permit, respectively. Results showed that at baseline (1999), where illegal logging was started on the ground, the condition of the 40 ha investigated area was dominated by non-forest in the form of open land by 54% with an amounted carbon storage of 1352.62 ton. In the phase of before community forestry permit (1999–2003), when there was continuous illegal logging, the open land rise quickly achieved to 83%, with only 312.09 ton of carbon storage remaining. In the initial phase of community forestry establishment (2003–2009), when the government issued a legalization of community forest, the mixed dryland agriculture shifted to dominate the area by 55%, with the carbon storage being increased to 1840.94 ton. The last phase, several years after community forestry permit (2009–2018), which characterized by active engagement of the community in forest rehabilitation, the area was altered to fully stocked teak plantation forest by 82%, with a carbon storage enhancement of 3379.16 ton or two times higher than that at baseline. Such results are important for the forest community authority and related stakeholder for designing appropriate forest-related policies and supporting REDD + implementation.

National mitigation potential from natural climate solutions in the tropics.

Better land stewardship is needed to achieve the Paris Agreement's temperature goal, particularly in the tropics, where greenhouse gas emissions from the destruction of ecosystems are largest, and where the potential for additional land carbon storage is greatest. As countries enhance their nationally determined contributions (NDCs) to the Paris Agreement, confusion persists about the potential contribution of better land stewardship to meeting the Agreement's goal to hold global warming below 2°C. We assess cost-effective tropical country-level potential of natural climate solutions (NCS)—protection, improved management and restoration of ecosystems—to deliver climate mitigation linked with sustainable development goals (SDGs). We identify groups of countries with distinctive NCS portfolios, and we explore factors (governance, financial capacity) influencing the feasibility of unlocking national NCS potential. Cost-effective tropical NCS offers globally significant climate mitigation in the coming decades (6.56 Pg CO2e yr−1 at less than 100 US$ per Mg CO2e). In half of the tropical countries, cost-effective NCS could mitigate over half of national emissions. In more than a quarter of tropical countries, cost-effective NCS potential is greater than national emissions. We identify countries where, with international financing and political will, NCS can cost-effectively deliver the majority of enhanced NDCs while transforming national economies and contributing to SDGs.This article is part of the theme issue ‘Climate change and ecosystems: threats, opportunities and solutions’.

Spatiotemporal modeling of urban land cover changes and carbon storage ecosystem services: case study in Qaem Shahr County, Iran

Considering the level of carbon stored in green lands, vast forest ecosystems with large volumes of biomass can play an important role in carbon sequestration and reduction of man-made CO2 emissions. Accordingly, the present study aims to determine the amount of carbon stored in Qaem Shahr County, north of Iran, as part of the remaining Hyrcanian forests. To achieve the research objective, land cover (LC) classification is performed by object-oriented classification. Also, LC changes are modeled for 2027 using CA–Markov model. Then, the carbon storage sub-model of Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model is used to estimate carbon storage level and distribution in the area under study. The results show that the highest amount of stored carbon is in forest areas, which is estimated to be 18.228 megagram (Mg) in 2014. Also, results show that in case of continuation of the current trends, the amount of stored carbon will be reduced by 321,216.68 Mg by 2027. The main reason of this reduction is attributed to the decrease in plant biomass and soil affected by this ecosystem, which has been caused by increased built area in the region, destruction of forest, and range of LCs in recent years. Finally, the results show that urban development and the built lands, in general, have a considerable effect on reducing carbon storage in a nearby town with broad-leaved forests as expected. Therefore, proper planning and management of the development process is necessary in the region.

What was the source of the atmospheric CO<sub>2</sub> increase during the Holocene?

Abstract. The atmospheric CO2 concentration increased by about 20 ppm from 6000 BCE to the pre-industrial period (1850 CE). Several hypotheses have been proposed to explain mechanisms of this CO2 growth based on either ocean or land carbon sources. Here, we apply the Earth system model MPI-ESM-LR for two transient simulations of climate and carbon cycle dynamics during this period. In the first simulation, atmospheric CO2 is prescribed following ice-core CO2 data. In response to the growing atmospheric CO2 concentration, land carbon storage increases until 2000 BCE, stagnates afterwards, and decreases from 1 CE, while the ocean continuously takes CO2 out of the atmosphere after 4000 BCE. This leads to a missing source of 166 Pg of carbon in the ocean–land–atmosphere system by the end of the simulation. In the second experiment, we applied a CO2 nudging technique using surface alkalinity forcing to follow the reconstructed CO2 concentration while keeping the carbon cycle interactive. In that case the ocean is a source of CO2 from 6000 to 2000 BCE due to a decrease in the surface ocean alkalinity. In the prescribed CO2 simulation, surface alkalinity declines as well. However, it is not sufficient to turn the ocean into a CO2 source. The carbonate ion concentration in the deep Atlantic decreases in both the prescribed and the interactive CO2 simulations, while the magnitude of the decrease in the prescribed CO2 experiment is underestimated in comparison with available proxies. As the land serves as a carbon sink until 2000 BCE due to natural carbon cycle processes in both experiments, the missing source of carbon for land and atmosphere can only be attributed to the ocean. Within our model framework, an additional mechanism, such as surface alkalinity decrease, for example due to unaccounted for carbonate accumulation processes on shelves, is required for consistency with ice-core CO2 data. Consequently, our simulations support the hypothesis that the ocean was a source of CO2 until the late Holocene when anthropogenic CO2 sources started to affect atmospheric CO2.

Impacts of Urban Expansion on Terrestrial Carbon Storage in China.

Urban expansion is one of the main factors driving terrestrial carbon storage (TCS) changes. Accurate accounting of TCS and rigorous quantification of its changes caused by historical urban expansion may help us to better predict its changes in the future. This study focuses on the carbon impacts of urbanization in China where the share of the urban population has increased from 18% in 1978 to 59% in 2017 and the growing will continue in the coming decades. Our results show that China's TCS decreased at an accelerating pace over the past three decades with an average reduction of 0.72TgC/y in 1980-1990 and 8.72TgC/y in 2000-2010, mostly due to conversion from cropland and woodland to urban land. Through simulating urban expansion under four scenarios from 2010 to 2050, we found a potential increasing trend in land conversion from woodland to urban land. This conversion trend would result in carbon storage loss at an average rate of 9.31TgC/y ∼ 12.94TgC/y in 2010-2050. The increasing trend in both land conversion and carbon storage loss is especially visible in the population centers of the Yangtze River Delta and the Pearl River Delta. Considering that the indirect emission effects of urbanization, such as farmland displacement, population migration, and land degradation, may be much larger, the overall emission impact of forthcoming urban expansion in China would increase the uncertainty of the nation's carbon emissions and potentially undermine China's targets as committed in the Paris Climate Agreement.

Approaching the potential of model-data comparisons of global land carbon storage

Carbon storage dynamics in vegetation and soil are determined by the balance of carbon influx and turnover. Estimates of these opposing fluxes differ markedly among different empirical datasets and models leading to uncertainty and divergent trends. To trace the origin of such discrepancies through time and across major biomes and climatic regions, we used a model-data fusion framework. The framework emulates carbon cycling and its component processes in a global dynamic ecosystem model, LPJ-GUESS, and preserves the model-simulated pools and fluxes in space and time. Thus, it allows us to replace simulated carbon influx and turnover with estimates derived from empirical data, bringing together the strength of the model in representing processes, with the richness of observational data informing the estimations. The resulting vegetation and soil carbon storage and global land carbon fluxes were compared to independent empirical datasets. Results show model-data agreement comparable to, or even better than, the agreement between independent empirical datasets. This suggests that only marginal improvement in land carbon cycle simulations can be gained from comparisons of models with current-generation datasets on vegetation and soil carbon. Consequently, we recommend that model skill should be assessed relative to reference data uncertainty in future model evaluation studies.

Increased Global Land Carbon Sink Due to Aerosol‐Induced Cooling

AbstractAnthropogenic aerosols have contributed to historical climate change through their interactions with radiation and clouds. In turn, climate change due to aerosols has impacted the C cycle. Here we use a set of offline simulations made with the Organising Carbon and Hydrology In Dynamic Ecosystems (ORCHIDEE) land surface model driven by bias‐corrected climate fields from simulations of three Coupled Model Intercomparison Project Phase 5 (CMIP5) Earth system models (ESMs; IPSL‐CM5A‐LR, CSIRO‐Mk3.6.0, and GISS‐E2‐R) to quantify the climate‐related impacts of aerosols on land carbon fluxes during 1860–2005. We found that climate change from anthropogenic aerosols (CCAA) globally cooled the climate, and increased land carbon storage, or cumulative net biome production (NBP), by 11.6–41.8 PgC between 1860 and 2005. The increase in NBP from CCAA mainly occurs in the tropics and northern midlatitudes, primarily due to aerosol‐induced cooling. At high latitudes, cooling caused stronger decrease in gross primary production (GPP) than in total ecosystem respiration (TER), leading to lower NBP. At midlatitudes, cooling‐induced decrease in TER is stronger than that of GPP, resulting in NBP increase. At low latitudes, NBP was also enhanced due to the cooling‐induced GPP increase, but precipitation decline from CCAA may negate the effect of temperature. The three ESMs show large divergence in low‐latitude CCAA precipitation response to aerosols, which results in considerable uncertainties in regional estimations of CCAA effects on carbon fluxes. Our results suggest that better understanding and simulation of how anthropogenic aerosols affect precipitation in ESMs is required for a more accurate attribution of aerosol effects on the terrestrial carbon cycle.

Large influence of soil moisture on long-term terrestrial carbon uptake.

The terrestrial biosphere absorbs about 25% of anthropogenic CO2 emissions, yet the rate of land carbon uptake remains highly uncertain, leading to uncertainties in climate projections1,2. Understanding the factors that are limiting or driving land carbon storage is therefore important for improved climate predictions. One potential limiting factor for land carbon uptake is soil moisture, which can reduce gross primary production due to ecosystem water stress3,4, cause vegetation mortality5, and further exacerbate climate extremes due to land-atmosphere feedbacks6. Previous work has explored the impact of soil moisture availability on past carbon flux variability3,7,8. However, the magnitude of the effect of soil moisture variability and trends on the long-term carbon sink and the mechanisms responsible for associated carbon losses remain uncertain. Here we use four global land-atmosphere models9, and find that soil moisture variability and trends induce large CO2 sources (~2–3 GtC/year) throughout the twenty-first century; on the order of the land carbon sink itself1. Subseasonal and interannual soil moisture variability generates a CO2 source as a result of the nonlinear response of photosynthesis and net ecosystem exchange to soil water availability and the increased temperature and vapour pressure deficit caused by land-atmosphere interactions. Soil moisture variability reduces the present land carbon sink while soil moisture variability and its drying trend reduce it in the future. Our results emphasize that the capacity of continents to act as a future carbon sink critically depends on the nonlinear response of carbon fluxes to soil moisture and on land-atmosphere interactions. This suggests that with the drying trend and increase in soil moisture variability projected in several regions, the current carbon uptake rate may not be sustained past mid-century and could result in an accelerated atmospheric CO2 growth rate.

Quantifying Human‐Mediated Carbon Cycle Feedbacks

AbstractChanges in land and ocean carbon storage in response to elevated atmospheric carbon dioxide concentrations and associated climate change, known as the concentration‐carbon and climate‐carbon feedbacks, are principal controls on the response of the climate system to anthropogenic greenhouse gas emissions. Such feedbacks have typically been quantified in the context of natural ecosystems, but land management activities are also responsive to future atmospheric carbon and climate changes. Here we show that inclusion of such human‐driven responses within an Earth system model shifts both the terrestrial concentration‐carbon and climate‐carbon feedbacks toward increased carbon storage. We introduce a conceptual framework for decomposing these changes into separate concentration‐land cover, climate‐land cover, and land cover‐carbon effects, providing a parsimonious means to diagnose sources of variation across numerical models capable of estimating such feedbacks.

Quantifying the Carbon Storage in Urban Trees Using Multispectral ALS Data

This paper presents a new method for quantifying the carbon storage in urban trees using multispectral airborne laser scanning (ALS) data. This method takes the full advantage of multispectral ALS range and intensity data and shows the feasibility of quantifies the carbon storage in urban trees. Our method consists of four steps: multispectral ALS data processing, vegetation isolation, dendrometric parameters estimation, and carbon storage modeling. Our results suggest that ALS-based dendrometric parameter estimation and allometric models can yield consistent performance and accurate estimation. Citywide carbon storage estimation is derived in this paper for the Town of Whitchurch–Stouffville, Ontario, Canada, by extrapolating the values within the study area to the entire city based on the specific proportion of each land cover type. The proposed method reveals the potential of multispectral ALS data in land cover mapping and carbon storage estimation at individual-tree level.

Large but decreasing effect of ozone on the European carbon sink

Abstract. The capacity of the terrestrial biosphere to sequester carbon and mitigate climate change is governed by the ability of vegetation to remove emissions of CO2 through photosynthesis. Tropospheric O3, a globally abundant and potent greenhouse gas, is, however, known to damage plants, causing reductions in primary productivity. Despite emission control policies across Europe, background concentrations of tropospheric O3 have risen significantly over the last decades due to hemispheric-scale increases in O3 and its precursors. Therefore, plants are exposed to increasing background concentrations, at levels currently causing chronic damage. Studying the impact of O3 on European vegetation at the regional scale is important for gaining greater understanding of the impact of O3 on the land carbon sink at large spatial scales. In this work we take a regional approach and update the JULES land surface model using new measurements specifically for European vegetation. Given the importance of stomatal conductance in determining the flux of O3 into plants, we implement an alternative stomatal closure parameterisation and account for diurnal variations in O3 concentration in our simulations. We conduct our analysis specifically for the European region to quantify the impact of the interactive effects of tropospheric O3 and CO2 on gross primary productivity (GPP) and land carbon storage across Europe. A factorial set of model experiments showed that tropospheric O3 can suppress terrestrial carbon uptake across Europe over the period 1901 to 2050. By 2050, simulated GPP was reduced by 4 to 9 % due to plant O3 damage and land carbon storage was reduced by 3 to 7 %. The combined physiological effects of elevated future CO2 (acting to reduce stomatal opening) and reductions in O3 concentrations resulted in reduced O3 damage in the future. This alleviation of O3 damage by CO2-induced stomatal closure was around 1 to 2 % for both land carbon and GPP, depending on plant sensitivity to O3. Reduced land carbon storage resulted from diminished soil carbon stocks consistent with the reduction in GPP. Regional variations are identified with larger impacts shown for temperate Europe (GPP reduced by 10 to 20 %) compared to boreal regions (GPP reduced by 2 to 8 %). These results highlight that O3 damage needs to be considered when predicting GPP and land carbon, and that the effects of O3 on plant physiology need to be considered in regional land carbon cycle assessments.

Large sensitivity in land carbon storage due to geographical and temporal variation in the thermal response of photosynthetic capacity.

Summary Plant temperature responses vary geographically, reflecting thermally contrasting habitats and long‐term species adaptations to their climate of origin. Plants also can acclimate to fast temporal changes in temperature regime to mitigate stress. Although plant photosynthetic responses are known to acclimate to temperature, many global models used to predict future vegetation and climate–carbon interactions do not include this process.We quantify the global and regional impacts of biogeographical variability and thermal acclimation of temperature response of photosynthetic capacity on the terrestrial carbon (C) cycle between 1860 and 2100 within a coupled climate–carbon cycle model, that emulates 22 global climate models.Results indicate that inclusion of biogeographical variation in photosynthetic temperature response is most important for present‐day and future C uptake, with increasing importance of thermal acclimation under future warming. Accounting for both effects narrows the range of predictions of the simulated global land C storage in 2100 across climate projections (29% and 43% globally and in the tropics, respectively).Contrary to earlier studies, our results suggest that thermal acclimation of photosynthetic capacity makes tropical and temperate C less vulnerable to warming, but reduces the warming‐induced C uptake in the boreal region under elevated CO2.

Increased importance of methane reduction for a 1.5 degree target

To understand the importance of methane on the levels of carbon emission reductions required to achieve temperature goals, a processed-based approach is necessary rather than reliance on the transient climate response to emissions. We show that plausible levels of methane (CH4) mitigation can make a substantial difference to the feasibility of achieving the Paris climate targets through increasing the allowable carbon emissions. This benefit is enhanced by the indirect effects of CH4 on ozone (O3). Here the differing effects of CH4 and CO2 on land carbon storage, including the effects of surface O3, lead to an additional increase in the allowable carbon emissions with CH4 mitigation. We find a simple robust relationship between the change in the 2100 CH4 concentration and the extra allowable cumulative carbon emissions between now and 2100 (0.27 ± 0.05 GtC per ppb CH4). This relationship is independent of modelled climate sensitivity and precise temperature target, although later mitigation of CH4 reduces its value and thus methane reduction effectiveness. Up to 12% of this increase in allowable emissions is due to the effect of surface ozone. We conclude early mitigation of CH4 emissions would significantly increase the feasibility of stabilising global warming below 1.5 °C, alongside having co-benefits for human and ecosystem health.