IPCC Fifth Assessment Synthesis Report

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The UN’s Intergovernmental Panel on Climate Change (IPCC) released the final installment of its massive fifth assessment report on Sunday.  It synthesizes the reports from each of its three working groups – physical science, impacts and vulnerabilities, and mitigation.

Here are some the key findings:

  • “Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, and sea level has risen.”
  • “Human influence on the climate system is clear, and recent anthropogenic emissions of greenhouse gases are the highest in history. Recent climate changes have had widespread impacts on human and natural systems.”
  • “Ocean warming dominates the increase in energy stored in the climate system, accounting for more than 90% of the energy accumulated between 1971 and 2010 (high confidence) with only about 1% stored in the atmosphere.”
  • “Over the period 1901–2010, global mean sea level rose by 0.19 [0.17 to 0.21] m.  The rate of sea-level rise since the mid-19th century has been larger than the mean rate during the previous two millennia (high confidence).”
  • “Surface temperature is projected to rise over the 21st century under all assessed emission scenarios. It is very likely that heat waves will occur more often and last longer, and that extreme precipitation events will become more intense and frequent in many regions. The ocean will continue to warm and acidify, and global mean sea level to rise.”
  • “Increasing magnitudes of warming increase the likelihood of severe, pervasive, and irreversible impacts for people, species and ecosystems. Continued high emissions would lead to mostly negative impacts for biodiversity, ecosystem services, and economic development and amplify risks for livelihoods and for food and human security.”
  • “Adaptation can reduce the risks of climate change impacts, but there are limits to its effectiveness, especially with greater magnitudes and rates of climate change.”
  • “Without additional mitigation efforts beyond those in place today, and even with adaptation, warming by the end of the 21st century will lead to high to very high risk of severe, widespread, and irreversible impacts globally (high confidence).”
  • “There are multiple mitigation pathways that are likely to limit warming to below 2°C relative to pre- industrial levels. These pathways would require substantial emissions reductions over the next few decades, and near zero emissions of CO2 and other long-lived GHGs by the end of the century.”
  • “Effective adaptation and mitigation responses will depend on policies and measures across multiple scales: international, regional, national and sub-national.”

This synthesis report will be used as a guide for the policy makers attending the UN Global Climate Summit scheduled for December 2015 in Paris. Any treaty agreed to there will take effect in 2020.