This is part of Work Package 1 of NESSC (Netherlands Earth System Science Centre)
Ice core records give us highly detailed information of the earth for the last 800 thousand years, such as Antarctic air temperatures and composition of the atmosphere. But to speculate about the climate beyond that time, millions of years into the past, NESSC primarily relies on fossilized remains of organisms preserved deep in the earth. These remains are called proxies.
Well-developed proxies can tell us a lot about environmental circumstances in the distant past. For example, with the the ratio of magnesium and calcium in carbonized shells of fossilized planktonic foraminifera, we can predict the sea surface temperature with an accuracy of 1.5 degrees Celsius. But accuracy can be compromised by external factors like salinity or magnesium-calcium ratios in the sea, and for several important climate variables no proxies exist.
Currently the accuracy for seawater temperatures of the past million years is 2-3 degrees Celsius, and 3-5 degrees Celsius for the past hundred million years. Our ambition is to ultimately reconstruct seawater temperatures with an accuracy of less than 1 degree Celsius for the past million years, and less than 2 degrees Celsius for the past 100 million years. There is a continuous need for improving proxies and constraining uncertainties.