Question

The tilt of the Earth changes over very long time scales. Every ~20,000 years, the tilt slowly increases from 22° to 24.5° and then decreases back to 22° over another ~20,000 years. We are currently at a tilt of 23.5° and about half-way through the decreasing phase (heading back to 22°). Assuming no other changes to Earth’s climate, would you expect Northern Hemisphere mid-latitude summers (for example at 45° N) to be warmer, cooler, or the same 1000 years from now compared to today? Why?

Answer 1

The mid-latitude summers will be hotter than now in a thousand years time. The whole process of changing the angle from 22^o to 24.5^o takes about 20000 years. So, each half of the journey takes about 10000 years. As it is in decreasing phase now, in a 1000 years time the value will decrease by (2.5^o / 10000) * 1000 = 0.25^o . So, in a 1000 years time, the angle will be 23.25^o . So, the incidence from the sun on the earth's surface will be a lot more normal(i.e perpendicular) than now. So, the effective incident energy per unit area on the Earth's surface will be a lot higher. So, the temperature will be higher.