A global reconstruction of temperature changes at the Last Glacial Maximum

The Last Glacial Maximum (LGM, 19-23ka BP) represents the most recent interval when the global climate was substantially different to the present, and as such provides us with a key target in testing the response of climate models to large changes in radiative forcing. There is, however, significant disagreement even in such first-order diagnostics as the global mean temperature at that time, with estimates ranging from as much as 6C to as little as 3C colder than the pre-industrial climate, and this uncertainty limits our ability to critically assess climate model performance. Some recent comprehensive syntheses of proxy data both on land and ocean have provided a new opportunity for an improved assessment of the climatic state of the LGM. Here we combine these proxy data with the Paleoclimate Modelling Inter-Comparison Project ensemble of structurally diverse state of the art climate models to generate a spatially complete reconstruction of surface air (and sea surface) temperatures. Our reconstruction is significantly different to and more accurate than previous approaches and we obtain an estimated global mean cooling of 3.9 +/- 0.8C (95% CI).