In 2013, the United Nations-sponsored Intergovernmental Panel on Climate Change (IPCC) completed the review of all the new evidence from peer-reviewed literature on the subject of climate change.
It last did so in 2007 and, at that time, published its Fourth Report: “Climate Change 2007: The Physical Science Basis.”
On Sept. 27, 2013, the IPCC released a 36-page “Summary for Policymakers” of its Fifth Report. The summary is free and available online at www.ipcc.ch. In October, the full online version of the report became available; it contained more than 2,000 pages of data, graphs, charts, references and interpretations from the combined efforts of hundreds of climate scientists working in the field.
The IPCC is a consensus document and all 195 nations had to agree with every word in the findings. The summary, in part, is quite clear: “Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia.” The probability of certainty has increased from 66 percent in 2001, to 90 percent in 2007, to 95 percent in 2013.
The summary goes on to state, “Human influence has been detected in warming of the atmosphere and the ocean.” Also, “It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.”
Two of many climate assessment illustrations from the IPCC Report highlight the findings. The bar chart summarizes the average temperatures for each of the past 16 decades for which actual thermometer data are available. It is labeled “Average global surface temperature, with confidence range.” The data clearly shows each of the past three decades is warmer than the proceeding one.
The second illustration is titled “27 Years of Above-Average Temperatures.” The individual bars represent a year for each of the past 60 years. Again, the data clearly shows the upward global temperature trend since the 1950s.