26 research outputs found
Response to Comment on âMycorrhizal association as a primary control of the CO 2 fertilization effectâ
Norby et al. center their critique on the design of the data set and the response variable used. We address these criticisms and reinforce the conclusion that plants that associate with ectomycorrhizal fungi exhibit larger biomass and growth responses to elevated CO2 compared with plants that associate with arbuscular mycorrhizae
The global carbon budget 1959-2011
Accurate assessments of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere is important to better understand the global carbon cycle, support the climate policy process, and project future climate change. Present-day analysis requires the combination of a range of data, algorithms, statistics and model estimates and their interpretation by a broad scientific community. Here we describe datasets and a methodology developed by the global carbon cycle science community to quantify all major components of the global carbon budget, including their uncertainties. We discuss changes compared to previous estimates, consistency within and among components, and methodology and data limitations. CO2 emissions from fossil fuel combustion and cement production (EFF) are based on energy statistics, while emissions from Land-Use Change (ELUC), including deforestation, are based on combined evidence from land cover change data, fire activity in regions undergoing deforestation, and models. The global atmospheric CO2 concentration is measured directly and its rate of growth (GATM) is computed from the concentration. The mean ocean CO2 sink (SOCEAN) is based on observations from the 1990s, while the annual anomalies and trends are estimated with ocean models. Finally, the global residual terrestrial CO2 sink (SLAND) is estimated by the difference of the other terms. For the last decade available (2002â2011), EFF was 8.3 ± 0.4 PgC yrâ1, ELUC 1.0 ± 0.5 PgC yrâ1, GATM 4.3 ± 0.1PgC yrâ1, SOCEAN 2.5 ± 0.5 PgC yrâ1, and SLAND 2.6 ± 0.8 PgC yrâ1. For year 2011 alone, EFF was 9.5 ± 0.5 PgC yrâ1, 3.0 percent above 2010, reflecting a continued trend in these emissions; ELUC was 0.9 ± 0.5 PgC yrâ1, approximately constant throughout the decade; GATM was 3.6 ± 0.2 PgC yrâ1, SOCEAN was 2.7 ± 0.5 PgC yrâ1, and SLAND was 4.1 ± 0.9 PgC yrâ1. GATM was low in 2011 compared to the 2002â2011 average because of a high uptake by the land probably in response to natural climate variability associated to La Niña conditions in the Pacific Ocean. The global atmospheric CO2 concentration reached 391.31 ± 0.13 ppm at the end of year 2011. We estimate that EFF will have increased by 2.6% (1.9â3.5%) in 2012 based on projections of gross world product and recent changes in the carbon intensity of the economy. All uncertainties are reported as ±1 sigma (68% confidence assuming Gaussian error distributions that the real value lies within the given interval), reflecting the current capacity to characterise the annual estimates of each component of the global carbon budget. This paper is intended to provide a baseline to keep track of annual carbon budgets in the future
Impacts of global change on Mediterranean forests and their services
The increase in aridity, mainly by decreases in precipitation but also by higher temperatures, is likely the main threat to the diversity and survival of Mediterranean forests. Changes in land use, including the abandonment of extensive crop activities, mainly in mountains and remote areas, and the increases in human settlements and demand for more resources with the resulting fragmentation of the landscape, hinder the establishment of appropriate management tools to protect Mediterranean forests and their provision of services and biodiversity. Experiments and observations indicate that if changes in climate, land use and other components of global change, such as pollution and overexploitation of resources, continue, the resilience of many forests will likely be exceeded, altering their structure and function and changing, mostly decreasing, their capacity to continue to provide their current services. A consistent assessment of the impacts of the changes, however, remains elusive due to the difficulty of obtaining simultaneous and complete data for all scales of the impacts in the same forests, areas and regions. We review the impacts of climate change and other components of global change and their interactions on the terrestrial forests of Mediterranean regions, with special attention to their impacts on ecosystem services. Management tools for counteracting the negative effects of global change on Mediterranean ecosystem- services are finally discussed
Global carbon budget 2013
Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe data sets and a methodology to quantify all major components of the global carbon budget, including their uncertainties, based on the combination of a range of data, algorithms, statistics and model estimates and their interpretation by a broad scientific community. We discuss changes compared to previous estimates, consistency within and among components, alongside methodology and data limitations. CO2 emissions from fossil-fuel combustion and cement production (EFF) are based on energy statistics, while emissions from land-use change (ELUC), mainly deforestation, are based on combined evidence from land-cover change data, fire activity associated with deforestation, and models. The global atmospheric CO2 concentration is measured directly and its rate of growth (GATM) is computed from the annual changes in concentration. The mean ocean CO2 sink (SOCEAN) is based on observations from the 1990s, while the annual anomalies and trends are estimated with ocean models. The variability in SOCEAN is evaluated for the first time in this budget with data products based on surveys of ocean CO2 measurements. The global residual terrestrial CO2 sink (SLAND) is estimated by the difference of the other terms of the global carbon budget and compared to results of independent dynamic global vegetation models forced by observed climate, CO2 and land cover change (some including nitrogenâcarbon interactions). All uncertainties are reported as ±1Ï, reflecting the current capacity to characterise the annual estimates of each component of the global carbon budget. For the last decade available (2003â2012), EFF was 8.6 ± 0.4 GtC yrâ1, ELUC 0.9 ± 0.5 GtC yrâ1, GATM 4.3 ± 0.1 GtC yrâ1, SOCEAN 2.5 ± 0.5 GtC yrâ1, and SLAND 2.8 ± 0.8 GtC yrâ1. For year 2012 alone, EFF grew to 9.7 ± 0.5 GtC yrâ1, 2.2% above 2011, reflecting a continued growing trend in these emissions, GATM was 5.1 ± 0.2 GtC yrâ1, SOCEAN was 2.9 ± 0.5 GtC yrâ1, and assuming an ELUC of 1.0 ± 0.5 GtC yrâ1 (based on the 2001â2010 average), SLAND was 2.7 ± 0.9 GtC yrâ1. GATM was high in 2012 compared to the 2003â2012 average, almost entirely reflecting the high EFF. The global atmospheric CO2 concentration reached 392.52 ± 0.10 ppm averaged over 2012. We estimate that EFF will increase by 2.1% (1.1â3.1%) to 9.9 ± 0.5 GtC in 2013, 61% above emissions in 1990, based on projections of world gross domestic product and recent changes in the carbon intensity of the economy. With this projection, cumulative emissions of CO2 will reach about 535 ± 55 GtC for 1870â2013, about 70% from EFF (390 ± 20 GtC) and 30% from ELUC (145 ± 50 GtC)
Towards a unified theory of plant photosynthesis and hydraulics
The global carbon and water cycles are strongly governed by the simultaneous diffusion of CO2 and water vapour through the leaves of terrestrial plants. These diffusive fluxes are controlled by plantsâ adaptations to balance carbon gains and hydraulic risks. We introduce a trait-based optimality theory that unifies the treatment of stomatal responses and biochemical acclimation of plants to changing environments. Tested with experimental data from eighteen species, our model successfully predicts the simultaneous decline in carbon assimilation rate, stomatal conductance, and photosynthetic capacity during progressive soil drought. It also correctly predicts the dependencies of gas exchange on atmospheric vapour pressure deficit, temperature, and CO2. Consistent with widely observed patterns, inferred trait values for the analysed species display a spectrum of stomatal strategies, a safety-efficiency trade-off, and a convergence towards low hydraulic safety margins. Our unifying theory opens new avenues for reliably modelling the interactive effects of drying soil and air and rising atmospheric CO2 on global photosynthesis and transpiration
No support for carbon storage of > 1,000 GtC in northern peatlands.
Northern peatlands store large amounts of carbon: 500â±â100âGtC, according to a consolidated estimate from a diversity of methods1,2,3,4,5,6. However, Nichols and Peteet7 presented an estimate of 1,055âGtC, exceeding previous estimates of carbon stock in global peatlands2 and in northern peatlands by a factor of two. Here we argue that this is an overestimate, caused by systematic bias introduced by their inclusion of 14C dates from mineral deposits and other unsuitable sites, the use of records that lack direct measurements of carbon density, and the methodology issues. Furthermore, their estimate is difficult to reconcile within the top-down constraints imposed by ice-core and marine records, and estimated contributions from other processes that affected the terrestrial carbon storage during the Holocene epoch