What to expect from the IPCC in its new climate science Assessment Report

Blog - Sept. 24, 2013 - By John Stone

This is a guest blog from Dr. John Stone, a longtime contributor to the Intergovernmental Panel on Climate Change and a board member of the Pembina Institute.



By the end of September, the Intergovernmental Panel on Climate Change (IPCC) will finalize the first instalment of its Fifth Assessment Report (AR5). This will focus on the physical science basis for the threat of climate change. Some of the conclusions have already been leaked and have been the subject of divergent media stories.

Many of the stories highlight the conclusion that the climate continues to change: temperatures are increasing, oceans are warming, sea-levels are rising, ice in the Arctic and elsewhere is melting, and extreme weather events are becoming more severe. These stories also add that we humans are responsible for most of the changes. What is of more concern is that some of these changes seem to be accelerating.

Other stories have emphasised the “hiatus” in warming of the Earth over the past decade or so suggesting that the worry of climate change has evaporated. Such stories are often intended to sow doubt and confuse. The purpose of this blog is to provide a guide to help understand the IPCC Report when it is released.

The role of the IPCC

The IPCC was created in 1988 to provide governments with accessible, balanced and authoritative assessments of the state of knowledge regarding climate change — what we know, what we don’t know and what are the uncertainties. The IPCC is an interesting social innovation, bringing together the scientific and government communities on what the UN Secretary General has referred to as the "greatest collective challenge we face as a human family.” The IPCC does not do research; rather it brings together teams of scientists, who work without payment, to assess the current literature — covering all relevant disciplines and in all the major languages.

People paddle down the streets of Calgary flowing a flood in June 2013.There are three Working Groups: the first deals with the physical science, the second with the impacts and adaptation, and the third with mitigation (what we can do to tackle the threat). A full assessment has been done every five to seven years. Drafts are produced and reviewed by other scientists and by governments in a fully transparent manner — all comments have to be properly considered and the responses recorded.

The full reports from each of the Working Groups are weighty tomes – each some 1000 pages long. In order to make them more digestible, the scientists also prepare short Summaries for Policymakers (SPM). These are considered at a formal meeting of scientists and governments. Nothing is included that the scientists do not consider as being scientifically sound. However, it allows governments a hand in making sure the information is understandable and balanced. In the end, governments “own” the science as much as the scientific community.

The SPM of the IPCC’s first Working Group will be released at the end of September. While the exact wording has yet to be finalized, some of the conclusions can be anticipated from the leaks and recent scientific literature.

The AR5 will build on and strengthen the confidence in many of the findings of previous Assessment Reports. A reason for this is that we now have longer and more reliable data sets that allow us to not only detect climate change but also attribute it to human activities — primarily the burning of fossil fuels. In addition we have improved our models of the climate system, although making predictions at a regional level still remains a challenge.

Highlights of this fall’s report

Some of the Report’s findings that are likely to receive considerable attention include:

  • IcebergThe IPCC will report that the Earth has warmed by almost one degree over the last century or more, and that the recent few decades have likely been the warmest for several centuries. However, while this warming trend is unambiguous, it has not been smooth. There have been periods when the temperature did not rise for a decade or so. We are experiencing such a hiatus now. Several reasons have been proposed to explain this, but a scientific consensus has yet to be reached.
  • Some of the greatest changes we have observed to date have been in what is known as the cryosphere, which includes snow and ice in Polar Regions as well as glaciers and ice-sheets. Everywhere one looks there have been significant changes. Of particular concern for Canadians is the dramatic decline of Arctic sea-ice, which threatens wildlife and the well-being of residents.
  • Some of the most damaging impacts of climate change include extreme weather events. While reliable observations are often limited to the last half century or so, droughts, heavy rainfall and heat waves have all increased in frequency.
  • One of the more contentious conclusions of the last IPCC Report in 2007 concerned the frequency and strength of hurricanes. Comprehensive records only became available with satellites observations and a complete understanding of how hurricanes are formed and sustained in still lacking.

Increasing evidence, increasing risk

In 1995 the IPCC’s Third Assessment Report stated that: “The balance of evidence suggests a discernible human influence on global climate”. This statement has been strengthened over time and is expected to be given an even greater level of confidence in this Report and be extended to include not only temperatures but also other climate variables such Arctic sea-ice.

Our emissions of greenhouse gases, which are the principle driver of recent climate change, continue to grow at a rate as large as the most extreme scenario envisaged by the IPCC. Further warming is now unavoidable. The exact magnitude depends on the actual emissions and on a factor that measures the sensitivity of the climate system. A more sensitive Earth will have a more rapid temperature change. This factor has been the subject of considerable scientific discussion and a reassessment is expected in this IPCC Report.

While some uncertainties remain in our understanding of the climate system, the evidence of the threat of climate change is clear. We have known enough to act for several years. This latest IPCC Assessment Report leaves little doubt that time is running out if we are to avoid dangerous consequences.


John Stone

John Stone is an adjunct research professor in the Department of Geography and Environmental Studies at Carleton University, and is widely regarded as an expert on climate change and international affairs. He serves as Secretary of the Pembina Institute's Board of Directors.


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