This is part of Work Package 2 of NESSC (Netherlands Earth System Science Centre)
Ice cores supply detailed information about the earth over the past 800 thousand years, such as Antarctic air temperatures and the atmosphere's composition. Yet, for information about the past climate of millions of years ago, we depend on the fossilized remains of organisms that have been preserved deep in the earth. Those remnants are called proxies.
A well-developed proxy can give us a lot of information about the climate conditions in the past. Thus, with the ratio of magnesium and calcium in the calcified skeletons of plankton fossils, we can accurately calculate the sea surface temperature to 1.5 ° C. However, the accuracy may sometimes suffer from other factors such as salinity or magnesium-calcium ratios in the sea. In addition, there are no proxies for many important climate variables.
The seawater temperature accuracy of the past million years is 2 to 3 ° C, and 3 to 5 ° C for the past hundred million years. Our ambition is to reconstruct seawater temperatures with a precision of less than 1 ° C for the past million years, and less than 2 ° C for the past hundred million years.
Thus, the need to improve proxies and reduce uncertainties only goes on.