Commonly referred to as AR6, the Sixth Assessment Report from the Intergovernmental Panel on Climate Change (IPCC) is little different from the previous five. Confounding evidence of warming with confirmation of impending disaster, the report adds more fog than clarity to the discussion of climate change and policy. It is yet another political statement from a nominally scientific committee.
As with the previous reports, AR6 shows no significant long-term trends for the most worrisome extreme weather events. There have been no significant worsening trends for hurricanes, floods, tornadoes, or hydrologic and meteorologic droughts. Nevertheless, the IPCC makes dire forecasts about future extreme-weather trends. This is also a pattern consistent with previous assessment reports.
Though the report was issued with much fanfare and media coverage, most of the chapters will not be in final form until next year. That has not stopped the IPCC from issuing the Summary for Policy Makers of the findings of Working Group I and its associated headline statements. Some of these headline statements are very misleading, especially Headline Statement A.3:
“Human-induced climate change is already affecting many weather and climate extremes in every region across the globe. Evidence of observed changes in extremes such as heatwaves, heavy precipitation, droughts, and tropical cyclones, and, in particular, their attribution to human influence, has strengthened since the Fifth Assessment Report (AR5)”
The various assessment reports are consistent in showing long-term increases in average world temperature. These increases are uneven and moderate, and are not, themselves, proof for the scarier assertions of increasingly more dangerous weather.
A case in point is the analysis of heat waves. The definition of heat wave is a period of at least five days where the maximum temperature exceeds the average high temperature for those days by at least nine degrees Fahrenheit (five degrees Celsius). A small increase in average temperatures can lead to a larger increase in heat waves as many warm spells that went uncounted as they peaked just below the nine-degree threshold, exceed that threshold with the addition of one or two degrees of warming. For instance, a five day stretch where the temperatures would have been 95 degrees now could be 96.5 degrees. If the average high temperature for the period and location were 87, then the 1.5 degrees of warming turns a hot week of 95-degree weather (eight degrees above the average high temperature) into an official heat wave with 96.5-degree weather (9.5 degrees above the average high). Indeed, an analysis of the data shows that the larger number of heat waves is not due to average weather turning into very hot weather, but, instead, it is due to what would have been very hot weather turning into slightly hotter official heat waves.
The assessment reports have long highlighted an increase in heavy rainfall events. This often leaves the impression that there has been an increase in flooding. As with past reports, however, AR6 does not find an overall increase in flooding.
There is another bit of misdirection in this headline statement with respect to “Evidence of observed changes in extremes such as… tropical cyclones.” There is no reliable upward trend in tropical cyclones (known as hurricanes in the Atlantic and as typhoons in the Pacific) for the past century. Digging into the not-yet-official Chapter 11 shows that for a more recent period, models and synthesized storm histories indicate a variety of impacts on tropical storm characteristics. On the other hand, actually counting the storms does not show significant trends. Previous assessment reports and multiple independent studies confirm a lack of upward trend in hurricanes over the past century. For a comprehensive analysis of tropical cyclone trends see the work of Ryan Maue.
Previous assessment reports noted no overall increase in droughts. AR6 splits droughts into four categories and finds no increase in hydrologic and meteorologic droughts but slight trends in agricultural and ecological droughts. Whatever increases there may be from agricultural drought, it didn’t stop world agricultural output from more than doubling over the last four decades.
Though we now have a thirty-year-long history of IPCC assessment reports not finding scary trends in extreme weather, each of the reports predicts imminent catastrophic changes. These projections are repeated so dutifully by sympathetic politicians and media, that an echo-chamber effect creates the popular perception of worsening trends not actually found in the reports.
Rewinding to 1990 we read in the First Assessment Report, “Increases in atmospheric concentrations of greenhouse gases may lead to irreversible change in the climate which could be detectable by the end of this century.” Of course, they were talking about the last century.
The report also speculated that countries such as Brazil and Peru would suffer reduced agricultural production. Both countries (like the world as a whole) have, instead, seen increased agricultural production, due, in part, to the beneficial impact of CO2 fertilization.
The media and non-governmental organizations that depend on projections of catastrophe hold up the new assessment report as proof of an existential threat from climate change—just like they did the last five times.
