New Guidance on Dangerous Climate Change: IPCC “Reasons for Concern”
New data and a better understanding of vulnerability lead scientists to estimate greater damages from climate change impacts.
To provide insight into what impacts of climate change might be considered dangerous human interference with the climate system, authors of the 2001 Third Assessment Report (TAR) of the Intergovernmental Panel on Climate Change (IPCC) identified five different categories of impacts they judged to be of special concern with regard to potential danger to society and/or nature. The relationship between impacts for the “reasons for concern” (RFCs) and increases in global mean temperature (GMT) were portrayed in what has come to be called the “burning embers diagram” (see figure below). The five RFCs are:
• Risk to unique and threatened systems (e.g., coral reefs, tropical mountain glaciers, endangered species, etc.)
• Risk of extreme weather events (e.g., heat waves, floods, droughts, wildfires, hurricanes)
• Disparities of impacts and vulnerabilities (e.g., disproportionate harm to developing countries and the poor in developed countries)
• Aggregate damages (i.e. net global market damages)
• Risks of large-scale discontinuities (e.g., rapid sea-level rise, ocean acidification, and strong amplifiers of warming)
In a peer-reviewed paper published in the Proceedings of the National Academy of Sciences, authors of the 2007 IPCC Fourth Assessment report have revised the sensitivities of the RFCs to increases in global average temperature based on a more thorough understanding of the concept of vulnerability that has evolved over the past decade. Compared to results reported in 2001, smaller increases in global average temperature are now estimated to lead to significant or substantial consequences for the five RFCs (see figure). These results indicate that the risks of climate change may have been underestimated in the past.
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Source: Assessing dangerous climate change through an update of the Intergovernmental Panel on Climate Change (IPCC) ‘‘reasons for concern’’ (February 2009)