New synthesis of African paleoclimate reconstructions reveals climate models underestimate rates of deglacial and mid-Holocene warming Earth and Planetary Science Letters

Paleoclimate data-model comparison can constrain uncertainties in climate model projections of climate change by testing climate model fidelity to observed or recorded temperature changes. Transient models are particularly useful tools for understanding how climates evolve in response to changing boundary conditions. Most data/model comparison has happened at a global scale, or for the extra-tropics. Because of the general scarcity of temperature records for the African continent, transient simulations have not been evaluated against the thermal history of Africa. We here present a new synthesis of glycerol dialkyl glyccerol tetraether (GDGT) records from a suite of lakes and marine sediments that, taken together, record the evolution of temperature in Africa since the last glacial maximum (LGM, 21ky before present). We compare this synthesis to a collection of transient climate model simulations that span the deglaciation and Holocene, including single and additive forcing experiments. We find that the models capture the spatial pattern of warming recorded by proxies well, but there is significant disagreement regarding the rates and amplitudes of temperature change, especially during the late deglaciation and Holocene. In particular, proxies warm significantly more during the late deglaciation than transient models do, and there is a mid-Holocene thermal maximum present in the proxy record that models do not simulate. Model underestimation of the rate of temperature change in response to relatively slow deglacial forcing could indicate that projections of future warming in Africa - in response to much faster greenhouse gas boundary condition changes - are also underestimated.