The Climate in Emergency

A weekly blog on science, news, and ideas related to climate change


The Fifth IPCC Report: Just the Facts, Ma’am

This is the second in a four-part series on the IPCC’s fifth Assessment Report, which has been coming out in installments since last year. The first article in our series provided an overview on what the IPCC is, how it is structured, and how and why it produces this reports.

This past weekend, the IPCC, or Intergovernmental Panel on Climate Change, released an official summary of the third installment of its report. Before we get in to talking about this latest document, I want to take a step back and discuss the contents of the previous installments, beginning with the first one, the report from Working Group I, which was published last year.

I will not do a detailed summary, because the IPCC has already done that; you can download their Summary for Policy Makers (SPM) yourself. However, even the summary is dozens of pages long and dry as toast. If you aren’t familiar with sorting through this kind of report, or even if you are, learning about the document through bloggers and journalists seems more appealing. Reading other people’s perspectives is indeed a good way to draw on the experience of others, who may have been following the issue longer, and at more depth, than you have. But the problem is that commentators disagree with each other a lot and it is very hard to sort through their conflicting interpretations if you do not have a baseline understanding of what the report says and what that means.

So here (with apologies to Joe Friday), are just the facts, a summary of the Summary for Policy Makers, of the report by the Working Group 1 of the IPCC, which covers the basic science of climate change.

After a brief introduction, the report summarizes the observed changes in several different parts of the Earth: air, ocean, cryosphere (ice), sea level, and the carbon and other biogeochemical cycles. There are no real surprises here, although some of the details have either changed or become more certain since the last report. The broad, take-home message is that the air and water have gotten warmer, precipitation patterns have changed, the ocean has become more acidic and the patterns of its varying surface salinity have changed (because of changing precipitation across the ocean surface), levels of various greenhouse gasses have gone up, and the sea level has risen. The report describes each change in crisp, dense detail.

A short section on the drivers of climate change follows. Again, the broad, take-home message is familiar, but the report does make clear a number of factors that don’t normally make it in to the public discussion. In essence, there are multiple factors that influence, or force, our climate, both globally and regionally, and part of climate science is the study of these factors and how they interact. The various greenhouse gasses humans release are an example of positive forcing, because they act to warm the climate, but there are also non-human sources of forcing. Likewise, certain types of particulate pollution, or aerosols, plus natural aerosols from various sources, provide negative forcing,  or cooling. Cloud patterns, and changes in solar output can also influence our climate. These factors do not all cause the same amount of forcing, and scientists do not understand them all equally well. One of the reasons that climate models are still not completely accurate is that scientists don’t yet fully understand how the interaction of aerosols with clouds influences the climate.

One thing they are sure of now is that human activity is the dominant influence and has been since the middle of the 20th century.

The report does address each known cause of forcing, positive or negative, separately, discussing both how strong its influence is and how much we know or do not know about it.

Then there is a section on the strengths and weaknesses of existing climate models (which mostly do very well, now) and how these have changed since the last IPCC report, the AR4. Also, the report discusses how climate responses are quantified, that is, what exactly scientists measure when they measure the climate.

Then the report details exactly what humans have been doing to the climate; how much of the observed changes can actually be attributed to us and how sure scientists are that the attribution is correct (they’re pretty sure).

Finally, the report presents its predictions for the future, for the atmosphere, the ocean the cryosphere, and so on. Again, there are no great surprises in terms of the take-home message; global warming will continue, and will get more severe if we do not stop greenhouse gas emissions. Even when emissions stop, warming will continue for some time because of the emissions that have already occurred, but we do still have some control over how severe that warming will be.

This last section is difficult to read, because the authors provide no real context for their predictions. That is, they do not say whether and how these climate changes will hurt, or who will be hurt. That, of course, is a subject for a later installment of the report. A reader can, of course, mentally put the context back in and can tell, for example, that increased monsoon precipitation means a lot more flooding, especially in certain developing countries. The picture presented by the report is thus a colorless, extremely academic view of a future none of us actually want to arrive. And yet, there are no truly catastrophic predictions; the possibility of our crossing some kind of thresh-hold beyond which climate change will suddenly begin tearing apart life as we know it is never addressed.

That doesn’t mean such thresh-holds are not a possibility, only that they are not predicted by the current mainstream of climate science. Of course, it is the nature of such thresh-holds to be unpredictable.

Criticism of the IPCC report covers the spectrum; they are variously accused of either they are accused of under-representing the danger we face, or of over-representing it. Often there is the further accusation, overt or implied, that their mistakes are deliberate, motivated by some personal or political bias. I will address that at greater length in a later post, but deliberate bias in either direction is unlikely.

The best evidence that the IPCC is not biased in favor of alarmism is simply that they have not raised much of an alarm. As dire a picture as this report paints, it is much less severe than many credible scientists think it should be. They also lack credible motive to gin up fear of climate change beyond what is appropriate; IPCC members serve without pay and in any case there is very little money in global warming mitigation. Anyone inclined to lie for a buck could do much better in a different field.

It is slightly more plausible that they have caved to political pressure, but again, if these people have lied for political reasons they have done a very bad job of it. There is plenty in their report to offend climate deniers. Instead, their failure to acknowledge some of the scarier possibilities for our future is probably due to two features of the IPCCs structure. First, their mandate is to summarize the entire body of science on climate change, so ideas that are plausible but not yet full accepted by the mainstream tend to get lost in the crowd. Second, when preparing a report, the IPCC reviews only work published before a certain cut-off date. The time it takes to publish scientific papers adds further delay, so that IPCC reports are actually several years out of date even on the day they are published. Since climate change has been getting worse over time, and since newer discoveries tend to be ever more dire and frightening, we should expect out of date news to be comparatively rosy.

Out-of-date news is better than no news, of course, and the IPCCs job is to compile reports for the rest of us, who cannot spend our time reading and analyzing thousands upon thousand of scientific papers.

A few things stand out that make the Summary for Policy Makers much more reliable and more nuanced than brief quotes may suggest.

First, the use of language is very precise and in some ways different from the way we ordinarily write. For example, some phrases, such as virtually certain, are actually quantitative. That is, they refer to specific, mathematically calculated probabilities, which you could check if you wanted to. They don’t lack confidence, they are just talking about statistics.

Second, even in the Summary, the authors include notes on how they arrived at their statements, what methods they used. These notes not only ensure transparency, they also provide a lot of important context that might be left out by a journalist’s quotes.

Third, there is a lot of detail and nuance that a casual glance might miss. For example, the authors state that “It is extremely likely that human influence has been the dominant cause of the observed warming since mid-20th century.” That doesn’t mean that they have just now decided that humans are causing global warming–that has been clear for a long time. The first estimates of human potential to influence climate were made in 1896, based on the discovery of greenhouse gasses in 1859.  No, the key word here is dominant. They mean they are now pretty sure that human influence is stronger than all of the other things that also influence climate–a much more disturbing announcement.

The bottom line is that the first installment, officially known as A5 WG 1, summarizes what most of us have been hearing for years but, because it gives a complete picture, a lot of the points that have been taken out of context to generate debate are now back in context and readily accessible.

And the bottom line below that is that we shouldn’t have needed a 5th Assessment Report to begin with. We should have fixed this problem already, and it has gotten worse because we didn’t. Can we make a commitment to not require a 6th?