Title: New paleoclimatic perspectives on the future of terrestrial systems: bigger change, higher confidence?
Prof. Jonathan Overpeck, The University of Arizona
Numerous assessments of future freshwater and terrestrial system change have highlighted the potential for unprecedented change in the 21st century given continued emissions of greenhouse gases (GHGs) to the atmosphere; the risk to biodiversity is also believed to be high. The basis for these assertions are strengthened by recent observed ecosystem change, as well as by a new global compilation of climate and vegetation change over the last deglaciation indicating that most, if not all, dominantly natural landscapes on the planet are at high risk of significant transformation given the projected magnitude of warming that is likely in the future absent major reductions in global GHG emissions. At the same time, new paleoclimatic results indicate that the Amazon forests may be more resilient to future change than previously thought, whereas the risk of human deforestation associated with multi-year “megadrought” might be higher than previously believed. A growing body of literature highlight that drought and megadrought risk around the globe is going to be a bigger problem than widely thought. We know with great confidence that warming will continue as long as GHG emissions continue, and this means more drying of terrestrial systems is likely over much of the planet. As a result, droughts will become more severe, longer and frequent as long as GHG emissions are not reduced significantly. The ability of precipitation increases to mitigate the ecological and hydrological impacts of continued warming is especially diminished in the many regions of the globe where multi-decadal megadrought is likely, an assessment made more challenging by the growing realization that that state-of-the-art climate models may underestimate the risk of future megadrought. Existing global climate change assessments may thus be underestimating the challenges to terrestrial water and ecoystems under continued climate change.