What Does A Six-Degree Rise In Average Global Temperature Mean, Anyway?

When people talk about global warming, they say things like “models predict that Earth will warm between 2 and 6 degrees Celsius in the next century”. But what does that mean? I can’t tell the difference between 74° F and 76° F, or between 23° C and 25° C. Is a two-degree change in global temperature really that important?


We’ll look at two periods in time when the global temperature was within 10 degrees (Celsius) of what it is now – the Ice Age and the Cretaceous.

The Ice Age

Scientists can estimate global temperatures by examining ice cores taken from the South pole. They estimate that during the Ice Age, the Earth was 4 to 7 degrees (Celsius) cooler than it is today.

Here’s what that four to seven degree change in temperature gave us:

When the global temperature rose, glaciers in North America receded to form the Great Lakes and Niagara Falls. Animals that lived in tundra conditions could no longer survive in what is now Southern California.

Again: all of these changes were accompanied by a global rise in temperature of four to seven degrees Celsius. It’s a small enough change that I wouldn’t touch my thermostat.

The Cretaceous

The Cretaceous period, at its warmest, was 8 to 10 degrees (Celsius) warmer than today, and during more moderate periods was 6 to 8 degrees warmer.

During the Cretaceous:

The Cretaceous also had wildly different lifeforms than the modern Earth, but it is unlikely that climate change was the only reason they went extinct.


Given that efforts to stem climate change are severely underfunded, I recommend beating the rush and:

A six-degree change in global temperature is very, very bad.

  1. Or possibly very large jaguars.