The Evidence

There is so much evidence for climate change that it’s hard to know where to start. And anyway there’s no point in overloading you with an endless series of graphs and charts.

The IPCC said “Warming of the climate system is unequivocal.”

That should be enough. But here are the basics.

This is a graph1 of historic CO2 levels.

The low part on the left is the last ice age.

The flat part on the right is the last 10,000 years during which time civilization developed and the near vertical line on the right shows CO2 levels spiking since the industrial revolution.

If we zoom in on the last few decades by looking at the “Keeling curve”2 we see the arc of CO2 levels getting steeper. The pace at which we’re adding to climate change is accelerating, not declining.

This is the graph you should care most about. It is this curve that all those international negotiations are aimed at making go the other way; down.3

What has it meant?

  • Here’s a curve of global temperatures. Up, up, up.
  • Here’s a graph of global sea level change; it’s accelerating too.
  • Here are comparative images of ice coverage in the summer in the arctic; one from 30 years ago, the other from 2007 but 2011 was just as bad.


1) This graph from Andrew Weaver’s Keeping Our Cool with a caption that reads:

Atmospheric carbon dioxide level over the past 21,503 years. The data from 1777 to 19,762 BC are from Monnin et al. (2004) while the data from 1832 to 1978 are from Etheridge et al. (1996). Both of these are from Antarctic ice cores. The data between 1959 and today are from the famous Mauna Loa record in Hawaii as archived by NOAA.

2) The Keeling curve is from NOAA and is public domain.

3) One big problem in making the Keeling curve go down is that even if we stopped adding new carbon dioxide to the atmosphere completely, this is the curve that shows what’s already up there. It will take a very long time to come down by itself.