IPCC Fourth Assessment Report
Climate Change 2007, the Fourth Assessment Report (AR4) of the United Nations Intergovernmental Panel on Climate Change (IPCC), was published in 2007 and is the fourth in a series of reports intended to assess scientific, technical and socio-economic information concerning climate change, its potential effects, and options for adaptation and mitigation. The report is the largest and most detailed summary of the climate change situation ever undertaken, produced by thousands of authors, editors, and reviewers from dozens of countries, citing over 6,000 peer-reviewed scientific studies. People from over 130 countries contributed to the IPCC Fourth Assessment Report, which took six years to produce. Contributors to AR4 included more than 2,500 scientific expert reviewers, more than 800 contributing authors, and more than 450 lead authors.
| The four SRES scenario families of the Fourth Assessment Report vs. projected global average surface warming until 2100 | ||
More economic focus |
More environmental focus | |
| Globalisation (homogeneous world) |
A1 rapid economic growth (groups: A1T; A1B; A1Fl) 1.4–6.4 °C |
B1 global environmental sustainability 1.1–2.9 °C |
| Regionalisation (heterogeneous world) |
A2 regionally oriented economic development 2.0–5.4 °C |
B2 local environmental sustainability 1.4–3.8 °C |
"Robust findings" of the Synthesis report include:
- "Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice and rising global average sea level".
- Most of the global average warming over the past 50 years is "very likely" (greater than 90% probability, based on expert judgement) due to human activities.
- "Impacts [of climate change] will very likely increase due to increased frequencies and intensities of some extreme weather events".
- "Anthropogenic warming and sea level rise would continue for centuries even if GHG emissions were to be reduced sufficiently for GHG concentrations to stabilise, due to the time scales associated with climate processes and feedbacks". Stabilization of atmospheric greenhouse gas concentrations is discussed in climate change mitigation.
- "Some planned adaptation (of human activities) is occurring now; more extensive adaptation is required to reduce vulnerability to climate change".
- "Unmitigated climate change would, in the long term, be likely to exceed the capacity of natural, managed and human systems to adapt".
- "Many impacts [of climate change] can be reduced, delayed or avoided by mitigation".