IPCC Synthesis Report: What’s Actually in It?

Published: 00:47 GMT le 16 novembre 2014

IPCC Synthesis Report: What’s Actually in It?

My series of blogs following the El Nino forecasts got a nice call out in Andy Revkin’s Dot Earth Opinion Piece. I’ll probably do one more update in a couple of weeks.


At the beginning of November, I wrote a piece at the release of the IPCC Synthesis Report. From the IPCC (Intergovernmental Panel on Climate Change) website, the “Synthesis Report (SYR) synthesizes and integrates material contained within IPCC Assessment Reports and Special Reports. The SYR should be based exclusively on material contained in the three Working Group Reports and Special Reports produced during the 5th or previous Assessment Cycles. It should be written in a ‘non-technical style suitable for policymakers and address a broad range of policy-relevant, but policy-neutral questions’ …” The intent of the IPCC reports is to assess the state of the science and provide translation of science-based knowledge to policymakers. The Synthesis Report has taken on a special emphasis because we are building up to the 2015 Conference of Parties in Paris.

In my earlier blog I expressed frustration with the language that the United Nations Framework Convention on Climate Change (UNFCCC) often placed on these documents. I also was writing in response to the press coverage that was coming out at the time of release.

For the past two weeks we have used the report in my current class on climate-change uncertainty in the context of decision making. (Eight students of varied backgrounds.) What struck me most about the report is how different the report is from what had been reported in the press. From the press reports, it sounded as if the document was still carrying forth the idea that dangerous irreversible climate change was all in the future and a variety of tipping points could be avoided with aggressive reduction of fossil fuels.

Whenever I have my class read one of the IPCC reports I ask them first the message of the report, who they see as the audience of the report, and if the communication was effective. Usually they provide mixed reviews, with statements that the language of the reports and the figures remains encumbered with the jargon and complexity that is inherent to the field. There is often the criticism that especially with the figures, there is an attempt to communicate too many ideas. The response to the text of the Synthesis Report’s Summary for Policy Makers was uniformly positive and enthusiastic. The authors of the report had communicated effectively and powerfully in a way that reached not only to policy makers but to a broader public.

The primary message:

climate change is here;

more is on the way;

we cannot avoid this;

we must adapt; and

to keep things manageable we must also reduce our greenhouse emissions to virtually zero – or remove carbon dioxide from the atmosphere.

If you look at the full Synthesis Report, 116 pages, and search for “irreversible,” then you find major conclusions:

* Warming caused by CO2 emissions is effectively irreversible over multi-century timescales unless measures are taken to remove CO2 from the atmosphere.

* Climate change will amplify existing risks and create new risks for natural and human systems. Risks are unevenly distributed and are generally greater for disadvantaged people and communities in countries at all levels of development. 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.

* Many aspects of climate change and its impacts will continue for centuries, even if anthropogenic emissions of greenhouse gases are stopped. The risks of abrupt or irreversible changes increase as the magnitude of the warming increases.

* Within the 21st century, magnitudes and rates of climate change associated with medium to high emission scenarios (RCP4.5, 6.0, and 8.5) pose a high risk of abrupt and irreversible regional-scale change in the composition, structure, and function of marine, terrestrial and freshwater ecosystems, including wetlands (medium confidence), as well as warm water coral reefs (high confidence).

* 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).

* Inertia in the economic and climate systems and the possibility of irreversible impacts from climate change increase the benefits of near-term mitigation efforts (high confidence).


The Synthesis Report makes it quite clear than irreversible warming and consequences of that warming have already occurred. In fact, the first bullet in the list above states that all of the warming associated with carbon dioxide increase is irreversible. Changes in ecosystems and extinctions related to warming, irreversible. Current and growing impacts of sea-level rise, irreversible.

It is also interesting to search the full report for dangerous; it only appears twice in the document. In neither case does the word dangerous occur in the context that dangerous climate change can be avoided. (I feel like I am doing a Common Core exercise.)

One part of the report that I especially like is the template (Box 2.4 in the document) which serves as a “starting point for evaluating dangerous anthropogenic interference with the climate system.” This relies on identification of “five reasons for concern:”

1) Unique and threatened systems

2) Extreme weather events

3) Distribution of impacts

4) Global aggregate impacts

5) Large-scale singular events

I include the text associated with “Large-scale singular events;”

“Large-scale singular events: With increasing warming, some physical and ecological systems are at risk of abrupt and/or irreversible changes (see Section 2.4). Risks associated with such tipping points are moderate between 0 and 1°C additional warming, since there are signs that both warm-water coral reefs and Arctic ecosystems are already experiencing irreversible regime shifts (medium confidence). Risks increase at a steepening rate under an additional warming of 1 to 2 °C and become high above 3°C, due to the potential for large and irreversible sea-level rise from ice sheet loss. For sustained warming above some threshold greater than ~0.5°C additional warming (low confidence) but less than ~3.5°C (medium confidence), near-complete loss of the Greenland ice sheet would occur over a millennium or more, eventually contributing up to 7 m to global mean sea-level rise.” (“Tipping points” only appears four times in the document, once to say there is little evidence of an Arctic sea ice tipping point.)

As we discussed the report in class, the message that emerged from the report is that if we do not reduce our carbon dioxide emissions by several 10s of percent, in the next 1 – 3 decades, then the warming and its impacts will become large enough that adaptation is not incremental; that is, adaptation will not, simply, be modifying what we know how to do. In some cases adaptation will not be possible – we will have to do something new, something different (something fantastic). It is also true that as the warming gets larger, we move outside of the range or parameters on which our models were trained. Therefore, model guidance becomes more unreliable.

I confess that the Synthesis Report extends further from the language of the Framework Convention than I expected. What is in this report is quite different than what was in the headlines. The responses from my students suggest that the written communication from the report is exceptional. The language is more dispassionate than grim or alarming. The report has had its flash in the press, now it is time for serious people to use it.

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Uncertainty Definitions (from Box.Introduction.2)

“The IPCC Guidance Note on Uncertainty (2010) defines a common approach to evaluating and communicating the degree of certainty in findings of the assessment process. Each finding is grounded in an evaluation of underlying evidence and agreement. In many cases, a synthesis of evidence and agreement supports an assignment of confidence, especially for findings with stronger agreement and multiple independent lines of evidence. The degree of certainty in each key finding of the assessment is based on the type, amount, quality, and consistency of evidence (e.g., data, mechanistic understanding, theory, models, expert judgment) and the degree of agreement. The summary terms for evidence are: limited, medium, or robust. For agreement, they are low, medium, or high. Levels of confidence include five qualifiers: very low, low, medium, high, and very high, and are typeset in italics, e.g., medium confidence. The likelihood, or probability, of some well-defined outcome having occurred or occurring in the future can be described quantitatively through the following terms: virtually certain, 99–100% probability; extremely likely, 95–100%; very likely, 90–100%; likely, 66–100%; more likely than not, >50–100%; about as likely as not, 33–66%; unlikely, 0–33%; very unlikely, 0–10%; extremely unlikely, 0–5%; and exceptionally unlikely, 0–1%. Assessed likelihood is typeset in italics, e.g., very likely. Unless otherwise indicated, findings assigned a likelihood term are associated with high or very high confidence. Where appropriate, findings are also formulated as statements of fact without using uncertainty qualifiers.”

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I'm a professor at U Michigan and lead a course on climate change problem solving. These articles often come from and contribute to the course.

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