Impact of Changes in Anthropogenic Forcing on the Terrestrial Carbon Budget through the Year 2300

Thursday, December 13, 2018 - 08:00
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Atmospheric carbon dioxide is modulated by sources and sinks of carbon, a third of which is absorbed by terrestrial ecosystems. Extreme climate and carbon cycle events have the potential to alter the strength of terrestrial uptake, affecting total carbon budgets; however, scientific understanding of these effects is still lacking. This uncertainty could alter the assessment of the rate of atmospheric CO2 increase and the intensity of associated feedbacks with the terrestrial biosphere. Anthropogenic activities change the carbon cycle by changing the atmospheric radiation budget, and through land use and land cover changes (LULCC). Over long timescales, the role of humans in modifying these extreme events is poorly understood. The carbon cycle beyond the year 2100 has thus far not been studied well in the current literature. Climate change projections through the year 2100 may miss biogeophysical and biogeochemical feedbacks that emerge after 2100 due to non-linear and cumulative effects of climate warming. This study uses simulations from a series of Earth system model scenarios for the years 1850 through 2300. To investigate the role of anthropogenic forcing in modifying extreme events, we consider the following scenarios: with and without anthropogenic atmospheric greenhouse gases and aerosols, and with and without LULCC. We hypothesize that after 2100, as land and ocean sinks weaken, anthropogenic emissions and land use change will increase the rate of intensity and frequency of negative carbon cycle extremes (NCCE) compared to those of positive carbon cycle extremes (PCCE). Our preliminary results have shown that changing patterns of extremes over time could be due to changing vegetation trends. For instance, the reduction of NCCE could be due to vegetation dieback and intensification of NCCE due to large increases in productivity. The results of this research provide insights into the contribution of human activities in altering carbon cycle extremes, quantifying implications for terrestrial carbon budgets, and informing future mitigation and adaptation policies.

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