Collaborative Research: Understanding the Role of Coupled Chemistry-climate Interactions in Internal Climate Variability

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A great deal of past research has been directed at understanding how coupling between climate and chemical species such as ozone and water vapor influence the climate response to anthropogenic emissions of greenhouse gases and ozone-depleting substances. But the importance of such coupling for year-to-year and decadal-scale variations in climate represents a key gap in our current scientific understanding of the climate system. The project will fill this gap through analyses of both existing numerical experiments across a wide array of climate models, and from new numerical simulations explicitly for the current project. The outcomes of the project will lead to improved understanding of the role of chemistry-climate coupling in the climate system. The work has broad implications for our understanding of climate variability and change, and their related climate impacts at the surface. The project will provide new insights into the importance of coupled chemistry-climate interactions for climate variability in the tropics, midlatitudes, and polar regions, and at both troposphere and stratosphere. It will improve our understanding of the importance of including coupled chemistry-climate processes in designing and evaluating future large-ensemble climate simulations. In particular, it will provide a benchmark for quantifying the importance of model-to-model differences in chemistry-climate interactions in simulations of climate change. This would help establish the fidelity of the processes included in global climate models, and thus has implications for public confidence in climate models and understanding of climate science. The new knowledge about the role of coupled chemistry-climate interactions in uncertainty in climate change projections would have a range of potential implications for both society and ecosystems over various regions of the globe. The project will also provide mentoring for two graduate students from groups underrepresented in the atmospheric sciences. In the first part of the work, the investigators will quantify the effects of coupled chemistry-climate interactions on climate variability on year-to-year timescales. They will explore in both existing and targeted numerical climate model experiments: 1) the differences in climate variability between control simulations with and without coupled chemistry; 2) the influence of atmospheric dynamics on various chemical species; and 3) the effects of variations in chemical species on atmospheric dynamics. The second part of the work will explore the role of coupled chemistry-climate interactions in climate change as the world moves from the era of ozone depletion when ozone depleting substances increased (about 1980-1995), to ozone recovery (1995-future). The investigators will focus on 1) variability in future climate states, 2) surface climate trends on decadal timescales, and 3) uncertainty in projections of future climate changes in large-ensemble simulations of coupled chemistry-climate models.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.