The latest intergovernmental report on climate change states that "human influence on the climate system is clear." Here's how the Intergovernmental Panel on Climate Change arrived at its conclusions.
Climate change is "unequivocal," "human influence on the climate system is clear" and limiting anthropogenic climate change will require "substantial and sustained reductions of greenhouse gas emissions." At the end of last week (30 January), the Intergovernmental Panel on Climate Change (IPCC) drew these conclusions in the finalized version of their Fifth Assessment Report, Climate Change 2013: The Physical Science Basis. Here are three important facts about the IPCC, their report, and how they arrived at these conclusions.
#1: IPCC reports are driven by significant amounts of data
The IPCC is an international scientific body that provides policymakers with an authoritative view on climate change, its causes, and its likely impacts. Through their assessment reports, the IPCC provides a scientifically comprehensive view of what is happening in our climate system. The reports are a critical tool for policy makers to make decisions regarding current and projected climate change. The IPCC has released five comprehensive assessment reports since its inception in 1988.
The IPCC does not conduct original scientific research. Instead, it develops reports and draws conclusions from the latest scientific literature on climate change from across the globe. In developing this report, Working Group 1 analyzed 9,200 peer-reviewed scientific publications.
IPCC reports are written based on the best available science. Each report bases its conclusions on the current scientific data, meaning that conclusions in each report evolve to take into account the latest scientific information. For example, while the previous Fourth Assessment Report, released in 2007, stated that "most of the observed increase in global average temperatures since the mid-20th century is very likely [>90% confidence in scientific parlance] due to the observed increase in anthropogenic greenhouse gas concentrations," the Fifth Assessment says: "It is extremely likely [>95% confidence] that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in greenhouse gas concentrations and other anthropogenic forcings together." The Fifth Assessment assigns an even greater confidence rating to human impact on the climate, even as it includes all human influences on the climate in this statement, including the cooling effect of aerosol emissions.
#2: The newly released Fifth Assessment Report is "the most comprehensive and authoritative synthesis" on climate change ever generated
The lengthy delay between reports is because the IPCC develops its conclusions from a rigorous scientific process. Each report is the result of worldwide scientific collaboration. The Fifth Assessment Report is over 1,500 pages long and includes over 2 million gigabytes of numerical data from climate model simulations. A total of 259 authors from 39 countries contributed to the report. 1,089 expert reviewers from 55 countries and 38 governments reviewed and commented on the report. President Obama's senior advisor on science and technology issues John Holdren said the report "represents the most comprehensive and authoritative synthesis of scientific knowledge about global climate change ever generated."
#3: The IPCC released its drafts and comments along with the full report -- interested readers can scrutinize the IPCC's extensive drafting process themselves
In addition to the release of the full physical science report, the IPCC also released extensive documentation of the assessment's drafting and review process last week. This included releasing the earlier drafts of the report that were subject to formal review, and all 54,677 written review comments by expert reviewers along with the responses by the authors to the comments. This means that anyone can scrutinize the IPCC's process, and look at the extensive peer reviews that resulted in such a comprehensive report.
Human induced warming of the climate system is real. Now, the debate should turn to how to translate this scientific reality into policy responses.