In this new study, scientists used the largest available database of past temperature reconstructions extending back 12,000 years to carefully investigate the geographic pattern of temperature change during the Holocene. Olivier Cartapanis and colleagues find that, contrary to previously thought, there is no globally synchronous warm period during the Holocene. Instead, the warmest temperatures are found at different times not only in different regions but also between the ocean and on land. This questions how meaningful comparisons of the global mean temperature between reconstructions and models actually are.
According to the lead author Olivier Cartapanis, “the results challenge the paradigm of a Holocene Thermal Maximum occurring at the same time worldwide”. And, while the warmest temperature was reached between 4,000 and 8,000 years ago in western Europe and northern America, the surface ocean temperature cooled since about 10,000 years ago at mid-high latitudes and remained stable in the tropics. The regional variability in the timing of maximum temperature suggests that high latitude insolation and ice extent played major roles in driving climate changes throughout the Holocene.
Lukas Jonkers, co-author of the study and researcher at the MARUM – Center for Marine Environmental Sciences in Bremen, Germany, says “Because ecosystems and people do not experience the mean temperature of the Earth, but are affected by regional and local changes in climate, models need to get the spatial and temporal patterns of climate change right in order to guide policy makers”.
Thus, the new work by Cartapanis and colleagues presents a clear target for climate models as the ability of climate model to reproduce Holocene climate variations in space and time, will increase confidence in their regional projections of future climate change.