A tipping point in climate computer estimates is a threshold where large and perhaps irreversible changes occur. Some estimates are silly, 20 foot ocean rises, etc., but without data from recent times it is hard to make models more reliable. There was a period of high warming nearly 1,100 years ago and in 10,000 B.C. we were still in an ice age, but with only accurate temperature readings for the last 40 years, and formal observation at all only done for the last 150 years, the only way for climate models of the future to be calibrated is to 'predict the past.'

A new paper shows how knowledge of climate reconstructions from thousands of years ago can be used to fine-tune Earth System models to provide a more accurate understanding of climate system thresholds.

Observations of the past are not enough in atmospheric science any more than they are in medicine or physics. "Palaeoclimate records of abrupt climate changes from the deeper past allow us overcome this problem,” says senior author Dr. Peter Hopcroft of the University of Birmingham.

In their study the team focused on one key example, the ‘greening’ and subsequent rapid desertification of the Sahara, which took place in the mid-Holocene period, around 6,000 years ago.

By feeding data from fossil pollen and sedimentary records into a typical climate model, they were able to show how the model could then predict the Sahara’s transformation into a savannah, which was marked by increased plant coverage, expansion of lakes and most importantly increased rainfall.

The results were then independently compared with studies of marine sediment records from the region, showing how the model accurately captured a very rapid return to the desert conditions over the Sahara.

“We now need to apply these methods to other models to test how universal the results might be,” added Dr. Hopcroft. “But by demonstrating how paleoclimate information can be used to improve the way models can simulate past abrupt climate change, we hope that we can begin to increase our confidence in future projections of abrupt events.”