Week 2. 400ppm

Understanding past climate changes can be key to understanding the state of the climate in the future. On May 9, 2013, carbon dioxide levels in the atmosphere reached the level of 400 parts per million (ppm). The last time the Earth experienced this level of carbon dioxide was in the Pliocene about three to five million years ago. Investigate what the temperatures were during this time period and compare them to today. Using your knowledge from the course so far, what could explain the changes?

During the Pliocene CO2 levels were at a similar level of today. It is thought that a lot of the differences between the Earth then and now were due to the feedback loops discussed last week.

For example, there was significantly less ice both at the poles and on the mountain ranges. This ice albedo loop keeps the temperatures high.

The distribution of heat around the globe was very different. A few degrees shift in temperature has a great effect on the Earth’s oceans and the currents. The change in the sea surface temperature (SST) particularly affected the higher latitudes. These were much warmer than they are today, although the temperatures around the tropics were quite similar.

The comparison with the Pliocene is important because it is one of the few times we can compare climates (then and now) where there are similar taxa living. We can therefore derive some implications for consequences of increasing global temperatures today.