IS THE NEXT ICE-AGE ALREADY UNDERWAY?

A follow-up to Lubos Motl's observations...

The geological record certainly tells us we are overdue for an ice age. And 5,000 years ago the Sahara was green, which is what happens in warm periods, as warmer seas give off more evaporation to fall as rain. Deserts are a feature of ice ages. So the excerpt below from Pierre Jutras is interesting:

Greenhouse ages are characterized by an absence or quasi-absence of desertic conditions, which are a feature of ice ages....

"We are now in a period of global warming"

This is only true on a short time scale, such as the past 500 years or so. It is already not true at the scale of 5,000 years, when Earth's climate was considerably warmer, and it is certainly not true at the scale of five million years, which takes us out of the current ice age. The main control on large-scale carbon dioxide fluctuations, which ultimately control climatic fluctuations, is plate tectonics. When global plate tectonics are dominated by continental collisions, leading to the formation of supercontinents, the erosional rates of calcium and magnesium from continental crust increase. This leads to an increase in carbonate deposition (limestone and dolostone), which forms the main long-term storage of carbon away from the atmosphere....

We are now in the middle of the fourth ice age, and biodiversity has been shrinking very rapidly over the past two million years (i.e. since long before the time when anthropogenic activities became meaningful).

Due to orbital cycles, ice ages are affected by regular, second-order climatic fluctuations. We have gone through warm peaks for the three main types of orbital cycles over the past 5,000 years, and all these cycles are now on a cooling trend. It is predicted that ice sheets will start forming again in mid-latitudes in about 3,000 years, and that half of North America and Europe will be covered by kilometres of ice in 5,000 years. Hence, the present warming trend is just a small notch in an otherwise cooling trend.

In a nutshell, we are putting a lot of energy into preventing global warming, whereas the threat of global cooling should perhaps be our main concern. Who knows, maybe one day we will burn fossil fuels for the sole purpose of preventing global cooling. Geological history has proven that ecosystems thrive better with a higher carbon dioxide budget. Yet, we are trying really hard to keep them in their present state of starvation.

Source - Pierre Jutras is an associate professor of geology at Saint Mary's University in Halifax, Canada.