Of the 197 arguments against climate change tracked by climate scientist John Cook on skepticalscience.com, this is the one most frequently invoked. The intended inference we are to draw is that because climate has changed before, blaming the current rise in temperature on human activity is incorrect.

The earth has gone through seven glacial cycles in the last 650,000 years and most of the climate changes over that period have been attributed to small changes in the earth’s orbit. The amount of variation since the end of the Little Ice Age in the mid-19th century is far too great to be assigned to variations in the earth’s orbit. In the 21st Century, global temperatures have been warmer than at any time in more than 10,000 of the past 11,300 years. By the end of this century, the Intergovernmental Panel on Climate Change (IPCC) projects the warmest temperatures ever over the past 11 millennia.