ALBERT

Description: Uncertainty in the response of terrestrial carbon sink to environmental drivers undermines carbon-climate feedback predictions Scientific Reports, Published online: 6 July 2017; doi:10.1038/s41598-017-03818-2

Description: The terrestrial biosphere can release or absorb the greenhouse gases, carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), and therefore has an important role in regulating atmospheric composition and climate. Anthropogenic activities such as land-use change, agriculture and waste management have altered terrestrial biogenic greenhouse gas fluxes, and the resulting increases in methane and nitrous oxide emissions in particular can contribute to climate change. The terrestrial biogenic fluxes of individual greenhouse gases have been studied extensively, but the net biogenic greenhouse gas balance resulting from anthropogenic activities and its effect on the climate system remains uncertain. Here we use bottom-up (inventory, statistical extrapolation of local flux measurements, and process-based modelling) and top-down (atmospheric inversions) approaches to quantify the global net biogenic greenhouse gas balance between 1981 and 2010 resulting from anthropogenic activities and its effect on the climate system. We find that the cumulative warming capacity of concurrent biogenic methane and nitrous oxide emissions is a factor of about two larger than the cooling effect resulting from the global land carbon dioxide uptake from 2001 to 2010. This results in a net positive cumulative impact of the three greenhouse gases on the planetary energy budget, with a best estimate (in petagrams of CO2 equivalent per year) of 3.9 +/- 3.8 (top down) and 5.4 +/- 4.8 (bottom up) based on the GWP100 metric (global warming potential on a 100-year time horizon). Our findings suggest that a reduction in agricultural methane and nitrous oxide emissions, particularly in Southern Asia, may help mitigate climate change.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Tian, Hanqin -- Lu, Chaoqun -- Ciais, Philippe -- Michalak, Anna M -- Canadell, Josep G -- Saikawa, Eri -- Huntzinger, Deborah N -- Gurney, Kevin R -- Sitch, Stephen -- Zhang, Bowen -- Yang, Jia -- Bousquet, Philippe -- Bruhwiler, Lori -- Chen, Guangsheng -- Dlugokencky, Edward -- Friedlingstein, Pierre -- Melillo, Jerry -- Pan, Shufen -- Poulter, Benjamin -- Prinn, Ronald -- Saunois, Marielle -- Schwalm, Christopher R -- Wofsy, Steven C -- England -- Nature. 2016 Mar 10;531(7593):225-8. doi: 10.1038/nature16946.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉International Center for Climate and Global Change Research, School of Forestry and Wildlife Sciences, Auburn University, Auburn, Alabama 36849, USA. ; Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Iowa 50011, USA. ; Laboratoire des Sciences du Climat et de l'Environnement, 91191 Gif sur Yvette, France. ; Department of Global Ecology, Carnegie Institution for Science, Stanford, California 94305, USA. ; Global Carbon Project, CSIRO Oceans and Atmosphere Research, GPO Box 3023, Canberra, Australian Capital Territory 2601, Australia. ; Department of Environmental Sciences, Emory University, Atlanta, Georgia 30322, USA. ; School of Earth Sciences and Environmental Sustainability, Northern Arizona University, Flagstaff, Arizona 86011, USA. ; School of Life Sciences, Arizona State University, Tempe, Arizona 85287, USA. ; College of Life and Environmental Sciences, University of Exeter, Exeter EX4 4RJ, UK. ; NOAA Earth System Research Laboratory, Global Monitoring Division, Boulder, Colorado 80305, USA. ; Environmental Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA. ; College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter EX4 4QF, UK. ; The Ecosystems Center, Marine Biological Laboratory, Woods Hole, Massachusetts 02543, USA. ; Institute of Ecosystems and Department of Ecology, Montana State University, Bozeman, Montana 59717, USA. ; Center for Global Change Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. ; Woods Hole Research Center, Falmouth, Massachusetts 02540, USA. ; Department of Earth and Planetary Science, Harvard University, 29 Oxford Street, Cambridge, Massachusetts 02138, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26961656" target="_blank"〉PubMed〈/a〉

Description: The contemporary Arctic carbon balance is uncertain, and the potential for a permafrost carbon feedback of anywhere from 50 to 200 petagrams of carbon (Schuur et al ., 2015) compromises accurate 21st-century global climate system projections. The 42-year record of atmospheric CO 2 measurements at Barrow, Alaska (71.29 N, 156.79 W), reveals significant trends in regional land-surface CO 2 anomalies (CO 2 ), indicating long-term changes in seasonal carbon uptake and respiration. Using a carbon balance model constrained by CO 2 , we find a 13.4% decrease in mean carbon residence time (50% confidence range = 9.2 to 17.6%) in North Slope tundra ecosystems during the past four decades, suggesting a transition toward a boreal carbon cycling regime. Temperature dependencies of respiration and carbon uptake suggest that increases in cold season Arctic labile carbon release will likely continue to exceed increases in net growing season carbon uptake under continued warming trends.

Description: Scientific understanding of the global carbon cycle is required for developing national and international policy to mitigate fossil fuel CO2 emissions by managing terrestrial carbon uptake. Toward that understanding and as a contribution to the REgional Carbon Cycle Assessment and Processes (RECCAP) project, this paper provides a synthesis of net land–atmosphere CO2 exchange for North America (Canada, United States, and Mexico) over the period 1990–2009. Only CO2 is considered, not methane or other greenhouse gases. This synthesis is based on results from three different methods: atmospheric inversion, inventory-based methods and terrestrial biosphere modeling. All methods indicate that the North American land surface was a sink for atmospheric CO2, with a net transfer from atmosphere to land. Estimates ranged from −890 to −280 Tg C yr−1, where the mean of atmospheric inversion estimates forms the lower bound of that range (a larger land sink) and the inventory-based estimate using the production approach the upper (a smaller land sink). This relatively large range is due in part to differences in how the approaches represent trade, fire and other disturbances and which ecosystems they include. Integrating across estimates, "best" estimates (i.e., measures of central tendency) are −472 ± 281 Tg C yr−1 based on the mean and standard deviation of the distribution and −360 Tg C yr−1 (with an interquartile range of −496 to −337) based on the median. Considering both the fossil fuel emissions source and the land sink, our analysis shows that North America was, however, a net contributor to the growth of CO2 in the atmosphere in the late 20th and early 21st century. With North America's mean annual fossil fuel CO2 emissions for the period 1990–2009 equal to 1720 Tg C yr−1 and assuming the estimate of −472 Tg C yr−1 as an approximation of the true terrestrial CO2 sink, the continent's source : sink ratio for this time period was 1720:472, or nearly 4:1.

Description: Rising atmospheric carbon dioxide (CO2) concentrations, primarily due to fossil fuel emissions and land-use change, are expected to continue to drive changes in both climate and the terrestrial and ocean carbon cycles. Over the past two-to-three decades, there has been considerable effort to understand how terrestrial and oceanic systems behave (in response to rising atmospheric CO2 and changing climate conditions), quantify the dynamics of system responses to environmental change, and project how the ocean and terrestrial carbon cycle will interact with, and influence, future atmospheric CO2 concentrations and climate. In this presentation, we will summarize key findings related to projected changes to the North American carbon cycle and drivers and associated consequences of these changes, as reported in Chapter 19 of the Second State of the Carbon Cycle Report (SOCCR-2). The findings not only capture projections of emissions from fossil fuel and changes in land cover and land use, but also highlight the decline in future carbon uptake capacity of North American carbon reservoirs and soil carbon losses from the Northern high-latitudes. Such a discussion of future carbon cycle changes is new in SOCCR-2, yet timely. It underlines the progress made since the release of the First State of the Carbon Cycle Report (SOCCR-1) in 2007 in identifying the vulnerability of key carbon pools and their co-evolution with changing climatic conditions. We will also discuss key knowledge gaps and outline a set of future research priorities, including both monitoring and modeling activities, that are necessary to improve projections of future changes to the North American carbon cycle and associated adaptation and resource-management decisions.