By measuring the ratios of different water isotopes in polar ice cores, we can determine how temperature in Antarctica and Greenland has changed in the past.
The oldest ice core we have was drilled by the European Project for Ice Coring in Antarctica (EPICA) from Dome C on the Antarctic plateau.
It extends back 800,000 years and shows a succession of long, cold ‘glacial’ periods, interspersed roughly every 100,000 years by warm ‘interglacial’ periods (of which the last 11,000 years is the most recent).
At this time, there was a huge ice sheet (the Laurentide) over northern North America.
Freshwater delivered from the ice sheet to the North Atlantic was able periodically to disrupt the overturning of the ocean, causing the transport of tropical heat to the north to reduce and then suddenly increase again.
While this mechanism cannot occur in the same way in today’s world, it does show us that, at least regionally, the climate is capable of extraordinary changes within a human lifetime – rapid switches we certainly want to avoid experiencing.
Ice cores provide direct information about how greenhouse gas concentrations have changed in the past, and they also provide direct evidence that the climate can change abruptly under some circumstances.
Slices of ice core, drilled from the depths of the Earth’s ice sheets, reveal details of the planet’s past climate.
Ice cores are cylinders of ice drilled out of an ice sheet or glacier.
However, ice cores have provided us with evidence that abrupt changes are also possible.
During the last glacial period, Greenland experienced a sequence of very fast warmings (see Fig. The temperature increased by more than 10°C within 40 years.
Ice sheets extended over North America as far south as Wisconsin, and over Britain to south of The Wash.