By combining global temperature estimates from geological data with estimates of tropical temperatures obtained from oxygen isotope studies, it is possible to produce an estimate of the global average temperature for any time in the past. The modern global average temperature is 14.5˚C. The average global temperature for the last 540 ga is 20˚C, but the temperature has fluctuated between 25˚C (hothouse) and 10˚C (icehouse). During the Permo-Triassic Extinction, the global temperature spiked above 28˚C. Most of the time, the global temperature gently rises and falls in response to gradual changes in orbital and solar parameters, ocean currents, sea level, atmospheric chemistry (greenhouse gases), and other factors. These changes occur over millions of years. Rarely, there is a drastic change in one of these factors resulting in either rapid global warming (Kidder–Worsley events) or rapid global cooling (Stoll-Schrag events). These abrupt climate excursions take place over 1000s of years, rather than millions of years.

the world was colder than today only 2% of the time in the last 540 ga.

• Uncategorized