Constraining carbon cycle processes over the last glacial cycle

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Anthropogenic climate change is one of the greatest global environmental challenges we face. The emissions we generate from burning fossil fuels are changing the levels of greenhouse gases in the atmosphere and warming the Earth's climate. This is clear - yet there is still considerable uncertainty in how the Earth will react to these emissions over the longer term. One of the major sources of this uncertainty is how the carbon cycle will respond, both to higher levels of carbon dioxide and to the changing climate. Climate models are one of the most important tools we have for studying climate change, however, the climate system is complex and climate models are far from perfect. We can validate the modelled climate system response by comparing climate simulations to reconstructions of past climate and current observations. Over the long-term, some of the most important and reliable climate data reconstructions come from ice cores in Antarctica and Greenland. These ice cores record changes in greenhouse gases and proxies for climate over several glacial cycles. Recently developed complex climate-carbon cycle models and data reconstructions over the last glacial cycle provide a unique opportunity to quantify the importance of climate-carbon cycle feedbacks over very long time scales.A key goal of my research program is to understand these feedbacks and assess their relative importance in forcing past glaciations. Understanding the mechanisms behind the climate variations over a glacial cycle is a major scientific challenge. Complex Earth System Models have not been able to simulate the full magnitude and timing of glacial-interglacial carbon dioxide transitions thus far. Although the initial forcing is thought to be primarily from variations in the Earth's orbit, previous work with simpler models suggests that many other processes are involved and the importance of various carbon-cycle feedbacks is still widely debated. Research outlined in this proposal will utilize the only Canadian model, and one of the few models anywhere, that is capable of simulating the carbon cycle over a glacial cycle. This research will provide a methodical evaluation of carbon cycle feedbacks within a consistent modelling framework, utilizing state of the art land, ocean, ice sheet and carbon cycle components. Constraining the response of the carbon cycle will help reduce the uncertainty of the climate system response to anthropogenic emissions and will be of great utility to climate policy decision makers. The long-term consequences of anthropogenic emissions, such as shifts in ecosystems and sea level rise from ice sheet melt, may be particular severe. It is critical that we understand and quantify past carbon cycle processes to give us more confidence in projecting any future climate-carbon cycle response.