From Icehouse to Coolhouse

Post #1049

According to the best data series available, Earth is currently in the coldest of four historic climate states:

The right edge of blue shading at right represents current global temperatures in relation to the mean temperature from 1961-1990. After coming out of the last ice age, — and then entering the final blue shade at right on the graph — there is a point about 7,500 years ago (7.5 kyr Before Present) when Earth was warmer than it is now.

That purple shade was the last ice age, and just after exiting it, you find a temperature that was about 1 degree Celsius warmer than the 1961-1990 average. For most of the 66 million years that show up in the graph, Earth was hotter than it is now. The Representative Concentration Pathways (RCP lines) are purely speculative.

Those RCP lines presume that different atmospheric concentrations of greenhouse gases are going to warm the Earth, but that conjecture has not been confirmed by hard data regarding the temperature trend in the greenhouse gas layer which is 3-6 miles above the surface of the Earth. Evidence suggests that climate sensitivity is pretty low.

Reference

[66 million years of climate data] — https://scitechdaily.com/66-million-years-of-earths-climate-history-uncovered-puts-current-changes-in-context/