Climate Expert: What The IPCC Actually Says About Extreme Weather

People are going absolutely nuts these days about extreme weather. Every event, anywhere is now readily associated with climate change and a portent of a climate out of control, apocalyptic even.

I’ve long given up hope that the actual science of climate and extreme weather will be fairly reported or discussed in policy — nowadays, climate change is just too seductive and politically expedient. [emphasis, links added]

But for those who want to know what research actually says on the relationship between extreme weather and climate change, that information is readily available.

Today I’ll share the excellent work of the Intergovernmental Panel on Climate Change (IPCC) summarizing what its most recent assessment says about various types of extreme weather and climate change.

When you read the below you will realize that the difference between what you see in the news (including statements from leading scientists) and what the IPCC has concluded could not be more different.

One day Ph.D. dissertations will be written about our current moment of apocalyptic panic.

Identifying the signal of human-caused climate change, according to the IPCC, refers to detecting and attributing a change in the statistics of a particular climate or weather variable.

The IPCC further defines the emergence of a signal of climate change :

In this Report, emergence of a climate change signal or trend refers to when a change in climate (the ‘signal’) becomes larger than the amplitude of natural or internal variations (defining the ‘noise’).

The IPCC further defines a concept called the time of emergence:

Time when a specific anthropogenic signal related to climate change is statistically detected to emerge from the background noise of natural climate variability in a reference period, for a specific region

The “time of emergence” is a key concept of the AR6 report and a focus of its Chapter 12.

It is important to note that just because a signal has not been detected, that does not mean that changes are not happening. However, as I have often said, the practical significance of a signal that can’t be detected cannot be large.

Before proceeding — A sidenote, perhaps telling about the state of climate research:

We (Ryan Crompton, John McAneney, and I) were the first to introduce the concept of time of emergence into the academic literature in 2011.

The IPCC instead references the concept to a 2012 paper that applied the same concepts and methods but failed to cite our work. I am used to such things!

But it is satisfying to know that our work helped to kick-start a major part of the IPCC AR6, which devoted an entire chapter to the topic. Now you know also.

Back to extreme weather — let’s take a look at what IPCC AR6 says about the time of emergence for various extreme events. Here are some direct quotes related to specific phenomena:

• An increase in heat extremes has emerged or will emerge in the coming three decades in most land regions (high confidence)
• There is low confidence in the emergence of heavy precipitation and pluvial and river flood frequency in observations, despite trends that have been found in a few regions
• There is low confidence in the emergence of drought frequency in observations, for any type of drought, in all regions.
• Observed mean surface wind speed trends are present in many areas, but the emergence of these trends from the interannual natural variability and their attribution to human-induced climate change remains of low confidence due to various factors such as changes in the type and exposure of recording instruments, and their relation to climate change is not established. . . The same limitation also holds for wind extremes (severe storms, tropical cyclones, sand, and dust storms).

The IPCC helpfully provides a summary table for a range of extremes, indicating for various phenomena whether emergence has been achieved with medium or high confidence at three points in time:

• to date (today), i.e., specifically when IPCC AR6 was completed in 2021,
• by 2050 under RCP8.5/SSP5-8.5, and
• by 2100 under RCP8.5/SSP5-8.5.

Those three dates are displayed as the three right-most columns in the table below.

A white entry in the table means that emergence has not yet been or is not in the future expected to be achieved.

The blue and orange entries represent the emergence of respectively increasing and decreasing signals at various levels of confidence.

Take a moment and look at the table carefully. Look especially at all those white cells.

The IPCC has concluded that a signal of climate change has not yet emerged beyond natural variability for the following phenomena:

• River floods
• Heavy precipitation and pluvial floods
• Landslides
• Drought (all types)
• Severe wind storms
• Tropical cyclones
• Sand and dust storms
• Heavy snowfall and ice storms
• Hail
• Snow avalanche
• Coastal flooding
• Marine heat waves

Furthermore, the emergence of a climate change signal is not expected under the extreme RCP8.5 scenario by 2100 for any of these phenomena, except heavy precipitation and pluvial floods, and that with only medium confidence.

Since we know that RCP8.5 is extreme and implausible, that means that there would be even less confidence in emergence under a more plausible upper bound, like RCP4.5.

The IPCC concludes that, to date, the signal of climate change has emerged in extreme heat and cold spells.

The IPCC states:

An increase in heat extremes has emerged or will emerge in the coming three decades in most land regions (high confidence) (Chapter 11; King et al., 2015; Seneviratne and Hauser, 2020), relative to the [preindustrial] period, as found by testing significance of differences in distributions of yearly temperature maxima in simulated 20-year periods.

In tropical regions, wherever observed changes can be established with statistical significance, and in most mid-latitude regions, there is high confidence that hot and cold extremes have emerged in the historical period, but only medium confidence elsewhere.

Clearly, with the exception perhaps of only extreme heat, the IPCC is badly out of step with today’s apocalyptic zeitgeist.

Maybe that is why no one mentions what the IPCC actually says about extreme events. It may also help to explain why a recent paper that arrives at conclusions perfectly consistent with the IPCC is now being retracted with no claims of error or misconduct.

Roger Pielke Jr. has been a professor at the University of Colorado since 2001. Previously, he was a staff scientist in the Environmental and Societal Impacts Group of the National Center for Atmospheric Research. He has degrees in mathematics, public policy, and political science, and is the author of numerous books. (Amazon).

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