The new IPCC report (AR6) – an introduction

The IPCC is one of the world’s biggest scientific projects, with thousands of scientists in dozens of countries collaborating since 1988 to produce a series of reports. Its Sixth Assessment Report (AR6) is in three parts. Working Group 1 released Climate Change 2021: The Physical Science Basis last August, and WG2 has just released Climate Change 2022: Impacts, Adaptation and Vulnerability which “assesses the impacts of climate change, looking at ecosystems, biodiversity, and human communities at global and regional levels,” to quote its home page. Part 3 and a Summary will appear later this year.

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The IPCC Fifth Assessment Report: what does it say?

I don’t often run two climate-related posts in succession but can’t help myself this time, because the IPCC report is too important to ignore. The main themes of informed responses to it are that this Fifth report confirms and extends the Fourth (2007), that the nature of the problem has changed very little but the window of opportunity to avert disaster is relentlessly closing, and that sceptical responses to the report are financially and politically motivated disinformation.

The ABC’s Drum has a piece by Will Steffen of the (new, crowd-funded) Australian Climate Council which spends a fair bit of time demolishing the sceptics’ myths before summarising the true state of affairs thus:

What actually are the key messages of the IPCC Fifth Assessment Report?

  1. There is stronger evidence that the Earth’s climate is warming – rising air and ocean temperature, loss of mass from glaciers and ice sheets, and rising sea level.
  2. Scientists are more certain than ever that most of the warming since 1950 has been caused by human activities, primarily the emission of carbon dioxide from fossil fuel combustion.
  3. A warming climate is influencing the frequency and severity of many extreme weather events and is changing rainfall patterns, creating risks for human well-being, the economy and the environment.
  4. Stabilising the climate system will require substantial and sustained reductions of carbon dioxide emissions, and those of other greenhouse gases.

Climate State presents a crisp video summary, while Greg Laden gives us The IPCC Report in Pictures, presenting the key graphs with concise comments, e.g. “Most of the sea level rise over recent decades has been from the ocean getting warmer. But in the future expect the larger proportion to be from glaciers melting.” Both are well worth a look, since a picture is worth at least a thousand words. (Some of the comments on Laden’s blog are good, too.)

RealClimate gives, as we would expect, quite a technical review of the Report. One of its take-away messages is that, “The new IPCC report gives no reason for complacency – even if politically motivated “climate skeptics” have tried to give this impression ahead of its release with frantic PR activities. … Many developments are now considered to be more urgent than in the fourth IPCC report, released in 2007. That the IPCC often needs to correct itself ‘upward’ is an illustration of the fact that it tends to produce very cautious and conservative statements, due to its consensus structure – the IPCC statements form a kind of lowest common denominator on which many researchers can agree.”

A related point is that the IPCC has a cut-off date after which no new research can be considered, meaning that it excludes some highly significant newer studies. Thus, for instance it (only) says, “The last 30 years were probably the warmest since at least 1,400 years. This is a result from improved proxy data. In the 3rd IPCC report this could only be said about the last thousand years, in the 4th about the last 1,300 years,” since it  hasn’t looked at the Marcott study which pushes that climate record back ten times as far.  Similarly, disturbing recent work on Arctic methane and the instability of the Greenland ice sheet suggests that the IPCC’s projections again hug the lower edge of the real range.

Michael Mann, of hockey-stick fame, says on Live Science (cross-posted to The Guardian) that, “Climate-Change Deniers Must Stop Distorting the Evidence” and gives details of how, where and why they are wrong before closing with:

Don’t be fooled by the [deniers’] smoke and mirrors and the Rube Goldberg contraptions. The true take-home message of the latest IPCC report is crystal clear: Climate change is real and caused by humans, and it continues unabated. We will see far more dangerous and potentially irreversible impacts in the decades ahead if we do not choose to reduce global carbon emissions. There has never been a greater urgency to act than there is now. The latest IPCC report is simply an exclamation mark on that already-clear conclusion.

Stefan Rahmstorf (yes, you saw that name in my previous post), writing for Project Syndicate, focuses on a related point: that the bulk of climate science is very well established and that legitimate debate about what is still unknown is no reason to argue that “the science is not settled” and (crucially) delay action to mitigate disaster:

But our solid understanding of the fundamentals of global warming – the base of our knowledge of climate science – should provide reason enough to press on with the implementation of carbon-free energy technologies. With a rapid reduction in emissions, it is still possible to keep warming within safe bounds (estimated at below 2ºC); but the task is becoming increasingly difficult. Failure to act quickly and globally will leave our children and grandchildren struggling to adapt to rapidly rising seas and devastating weather.

What is our best mechanism of action, then? Rajenda Pachauri, chairman of the IPCC, says on The Independent that the financial markets are humanity’s only hope:

Dr Pachauri warned that unless a price could be put on carbon emissions that was high enough to force power companies and manufacturers to reduce their fossil-fuel use, there seemed to be little chance of avoiding hugely damaging temperature increases.

“An extremely effective instrument would be to put a price on carbon. It is only through the market that you can get a large enough and rapid enough response,” he said.

Perhaps someone should tell our Mr Abbott.