Emergent Constraints on Climate-Carbon Cycle Projections

Earth System Models (ESMs) are designed to project changes in the climate-carbon cycle system over the coming centuries. These models agree that the climate will change significantly under feasible scenarios of future CO₂emissions. However, model projections still cover a wide range for any given scenario, which impedes progress on tackling climate change. Estimates of the Transient Climate Response to Emissions (TCRE), and therefore of remaining carbon budgets, are affected by uncertainties in the response of land and ocean carbon sinks to changes in climate and CO₂, and also by continuing uncertainties in the sensitivity of climate to radiative forcing. Over the last 7 years Emergent Constraints have been proposed on many of the key uncertainties. Emergent constraints use the full range of model behaviours to find relationships between measureable aspects of present and past climates, and future climate projections. This presentation will summarise proposed emergent constraints of relevance to future climate-carbon cycle projections, and discuss the implications for the remaining carbon budgets for stabilisation at 1.5K and 2K.