C-FORCE: Carbon-Cycle Feedbacks from Response to Carbon Emissions

The dominant driver of anthropogenic global warming is the increasing amount of the greenhouse gas carbon dioxide in the atmosphere. This is increasing because it is being emitted by the burning of fossil fuel, deforestation and cement making, with only ~45% staying in the atmosphere. The rest is stored in other reservoirs at or near Earth's surface including the ocean, trees, soils, permafrost and methane ice, as well as sediments and rock. Carbon flows naturally between the atmosphere and these reservoirs by processes like photosynthesis, decay, weathering, burial and ocean circulation. Collectively, the exchange of carbon between these reservoirs is termed the carbon cycle. One of the biggest uncertainties about future climate change is how the carbon cycle will respond to (or 'feed back' on) our warming planet. It is possible, for example, that if global warming exceeds a threshold, permafrost and methane ice stored at the seafloor will melt rapidly, adding further greenhouse gases to the atmosphere and accelerating the warming. It is very difficult to predict whether 'tipping point' behaviour like this will occur in the global carbon cycle.

C-FORCE will measure how the global carbon cycle responded from start to finish during a past period of global warming that was driven by emissions of carbon-based greenhouse gases to the atmosphere. The Paleocene-Eocene Thermal Maximum (PETM) is the largest natural climate change event of the last 65 million years, and the closest natural comparator to the modern rates of global warming and carbon greenhouse gas emissions. During the PETM, initial global warming of 4-5 degrees Celsius over a few thousand years was partially driven by carbon emissions from an unusually massive episode of volcanism, and the climate then gradually recovered to its pre-existing state over more than 100 thousand years.

C-FORCE will use a novel model of the global carbon cycle to compare the carbon supplied by volcanism with the total PETM...