In their recent Science article, Marcott and colleagues present a reconstruction of Earth’s mean surface temperature over the last 11,300 years – the Holocene. Why is this important? It is the most comprehensive and inclusive reconstruction to date from which to assess how novel our current temperatures are compared with those in the recent geologic past. In other words, are we experiencing average temperatures that are essentially unprecedented over this timeframe?
The answer is yes. The authors show that following the Industrial Revolution, the average global temperature has risen from some of the coldest to warmest levels ever recorded in the past 11,300 years. This fast rate of warming essentially overturned a long term cooling trend that began 5000 years ago. This is solid evidence that we are experiencing abnormally rapid rates of temperature rise, and that temperatures have reached unusual levels.
The reconstruction is robust in a variety of ways. First, for the last 1500 years, it agrees with other published reconstructions. Second, it incorporates data from 73 different records, which on average, yield a temperature record every 120 years. Finally, it employs a number of statistical approaches to account for uncertainty from the data.
Marcott, S. A., J. D. Shakun, P. U. Clark, and A. C. Mix (2013) A reconstruction of regional and global temperature for the past 11,300 Years. Science, 339,1198–1201.