Five Things You Need to Know About the IPCC Fifth Assessment Report

Last Friday, the Intergovernmental Panel on Climate Change (IPCC), the world’s foremost authority on climate change, released the first segment of its Fifth Assessment Report on the state of the earth’s climate. The group brought together more than 830 scientists from 85 countries to review the body of published, peer-reviewed scientific reports on the earth’s climate in order to draw conclusions, make predictions, and set a certain level of confidence for each prediction. The report also received over 136,000 review comments from experts around the world. It’s important to remember that the IPCC is not doing research of its own: collaborators assess and aggregate the findings of other published research into a single report. This is the first major report by the organization since the landmark Fourth Assessment report in 2007, which earned the group (along with Al Gore) a Nobel Prize for raising public awareness of climate change. So, what do you really need to know about this report? Here are the five most important takeaways:
 

  1. The Earth is warming at an unprecedented rate. The Summary for Policymakers finds that “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, sea-level has risen, and the concentrations of greenhouse gases have increased.” Although the IPCC and climate scientists have been providing evidence of warming for decades, this report has the strongest evidence yet that each of the last three decades has been successively warmer than any preceding decade since 1850.
     
  2. It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century. The IPCC’s certainty that the warming of the Earth is predominantly caused by humans has been growing with each report published. This fifth assessment reports a 95% certainty that human influence is the dominant cause of the observed warming, up from 90% in 2007 and 66% in 2001. Evidence of human contribution to warming is seen in the “warming of the atmosphere and ocean, in changes in the global water cycle, in reductions in snow and ice, in global mean sea-level rise, and in changes in some climate extremes.”
     
  3. The slight decrease in warming rates over the past decade can be attributed to ocean warming and other natural phenomena. Much of what climate deniers have been jumping onto in this report is the plateau in warming over the past 15 years. The IPCC does identify an observed reduction in the warming trend from 1998-2012, but clarifies that reduction is due to some of the earth’s natural processes coinciding to temporarily reduce atmospheric warming. The report specifically points out a disproportionate amount of warming in the oceans as opposed to the atmosphere (more than 90% of energy accumulated between 1971-2010 has been stored in the oceans), volcanic eruptions that reflect heat back into space, and the downward phase of the 11-year solar cycle. As these processes phase out, we will again see the warming rate rise. And the signs of climate change aren’t pausing altogether: the increase in melting glaciers and sea ice shows that heat getting trapped in the oceans can be just as dangerous as in the atmosphere.
     
  4. The world’s coastlines are at risk. There is high confidence that the rate of sea-level rise since the mid-19th century has been larger than the mean rate during the previous two millennia. This report raised the previous predictions for sea-level rise by the end of the 21st century to anywhere from 10 inches to 2.7 feet. Scientists are predicting that up to 70% of the world’s coastlines will be affected by rising sea levels over the next century.
     
  5. Global mean surface temperature is likely to exceed 2°C by the end of the century. Previous IPCC reports have focused on a “safe climate target” threshold of 2°C in temperature increases before significant effects of climate change are experienced. The new report states that, given the amount of greenhouse gases that we are expelling into the atmosphere, certain models already find it likely that we will surpass this target, and one model finds it “about as likely as not” that we may exceed 4°C by 2100. This puts significant pressure on the international community to continue to limit greenhouse gas emissions going into negotiations for a new climate agreement in 2015.
     

This first summary, which covers the physical science findings, will be followed by three more reports released over the course of the next year covering the impacts of climate change and opportunities for adaptation (March 2014), mitigation opportunities (April 2014), and a final synthesis report in October 2014 to complete the Fifth Assessment Report. Overall, most of what has been released in this summary provides further evidence and higher levels of certainty for the findings of the Fourth Assessment Report. Bolstered by increased confidence about the human influence on climate change, will this report prompt states to increase the urgency of climate policies? Will these findings be sufficient to support a new international climate agreement in 2015? The impact that this report will have on climate policies is still an open question, but we’ll have our eyes on it. Stay tuned to Sense & Sustainability for further updates on the impacts of the IPCC Fifth Assessment.

 
Image Credit: Collection of Dr. Pablo Clemente-Colon, Chief Scientist National Ice Center

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