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As scientists have long predicted, warming is making heatwaves more deadly

Posted on 20 July 2021 by dana1981

This is a re-post from Yale Climate Connections

In its 2001 Third Assessment Report, the Intergovernmental Panel on Climate Change (IPCC) foresaw that global warming would lead to increasingly deadly heatwaves. “More hot days and heatwaves are very likely over nearly all land areas,” the world’s top climate scientists warned. “These increases are projected to be largest mainly in areas where soil moisture decreases occur.” 

 “The greatest increases in thermal stress are forecast for mid- to high-latitude (temperate) cities, especially in populations with non-adapted architecture and limited air conditioning,” they wrote at the time. “A number of U.S. cities would experience, on average, several hundred extra deaths each summer.”

Sound prescient? And familiar?  All too much so.

Twenty years later, it seems as though these climate scientists were gazing into a crystal ball rather than computer monitors. At the end of June 2021, the normally temperate Pacific Northwest experienced a record-shattering heatwave. The village of Lytton, in British Columbia,  set a new all-time Canadian temperature record of 49.6 degrees Celsius (121.3 degrees Fahrenheit) and was largely destroyed by a wildfire soon thereafter. Quillayute in the northwest corner of Washington, shattered its previous high temperature record by a full 11°F.

At least 800 deaths have so far been attributed to the extreme heat, and experts say they expect the final mortality tally to be considerably higher. Because of the region’s historically temperate weather, many homes lack air conditioning; residents were enveloped by temperatures well in excess of 100°F.

University of British Columbia marine biologist Christopher Harley estimates that the heatwave also caused over a billion marine wildlife deaths, as shells of dead mussels and clams coated rocks along the Pacific seashore.

Climate change made the heatwave more deadly

Contributing to the World Weather Attribution project, 27 scientists worked around the clock for a week immediately after this extreme event to determine the role played by climate change. The team used published peer-reviewed methods, comparing numerous model simulations of two scenarios: the “world as it was” when the event occurred, and a counterfactual “world that might have been” had humans not altered Earth’s climate by burning fossil fuels over the past 150 years.

The results are striking. The authors concluded that a heat event so extreme was “virtually impossible without human-caused climate change.” While it’s difficult to quantify the rarity of such unprecedented weather, their best estimate was that it was a 1-in-1,000-year event. Without human-caused climate change, such an extreme event would be at least 150 times rarer, and the heatwave was about 3.6°F hotter than it would have been naturally.

But continued climate change will make these extreme events much more common. If global warming breaches the Paris Climate Agreement guardrail of 2°C (3.6°F) above pre-industrial temperatures (compared to today’s 1.2°C, or 2.2°F higher), the scientists estimate that an event like this “would occur roughly every 5 to 10 years.” As study co-author Dim Coumou of the Potsdam Institute for Climate Impact Research suggested, “we may have crossed a threshold in the climate system where a small amount of additional global warming causes a faster rise in extreme temperatures.”

Heatwave climate connections

In fact, a 2020 analysis by Columbia University climate scientists James Hansen and Makiko Sato found that what was considered extreme Northern Hemisphere summer heat in the 1950s to 1980s is about 200 times more likely to occur today as a result of shifting temperature patterns.

Frequency of occurrence graphic

Frequency of occurrence of Northern Hemisphere land temperatures in 2009–2019 relative to the 1951–1980 average in green. From Hansen and Sato (2020).

But one question the new attribution study’s authors were unable to answer involves whether the June 2021 event was simply a case of “really bad luck” – just a natural extreme heatwave amplified by global warming – or whether climate change has loaded the dice in favor of this type of extreme heatwave in other ways.

For example, higher temperatures also draw more moisture out of the soil and vegetation and into the atmosphere, thus tending to exacerbate droughts. The region between southern British Columbia and California has been anomalously dry this year, with below-normal soil moisture since the beginning of April 2021 as a result of low precipitation. With less soil moisture available to evaporate, there is more heatwave energy available to raise air temperatures, as the 2001 IPCC report alluded to.

In short, it’s possible that climate change will worsen droughts in western North America, which will in turn worsen heatwaves.

Another possible factor involves a slowing jet stream resulting from  human-caused changes in the Arctic. The June heatwave was characterized by an atmospheric heat dome trapped by an omega blocking pattern, so-called because the shape of the jet stream current resembles the Greek symbol Ω. Authors of a 2018 study in Science Advances concluded that climate change is making these sorts of jet stream patterns occur more frequently in the Northern Hemisphere summer. But in the June 2021 event, the rapid attribution study concluded that – unlike the record temperatures on the ground – the jet stream circulation pattern was not particularly exceptional.

Those researchers were able to rule out a common suspect often posited by those described as climate deniers – ocean cycles. The El Niño cycle was in a neutral phase leading up to the heatwave, and the authors concluded “it had no influence on the occurrence of the heatwave.” Another ocean cycle called the Pacific Decadal Oscillation was found to “slightly favor cooler conditions for this region” at the time.

What makes extreme heat especially  deadly?

The combination of rising heat and humidity is especially dangerous, as Texas A&M climate scientist Andrew Dessler explained in a Twitter thread. The human body generates heat, and at temperatures above around 82°F, the surrounding air no longer carries away enough heat to keep the body cool. The remaining options to avoid a dangerously overheating body involve air flow across the skin (for example from wind or a fan) or evaporating sweat. And as climate change draws more moisture from the soil into the atmosphere, thus increasing humidity, sweating offers less relief. At 100% relative humidity, the body can’t evaporate any sweat (hence ‘dry heat’ is less uncomfortable because of the body’s ability to cool itself by sweating).

Scientists combine measurements of heat and humidity through what are known as ‘wet bulb’ temperatures. Prolonged wet bulb values close to body temperature (98°F) are not survivable. A 2020 study in Science Advances found that areas near the equator like the Persian Gulf and portions of Central America, India, and Southeast Asia are already very close to this survivability limit, and that the limit will be regularly exceeded if global warming approaches 2.5°C (4.5°F) above pre-industrial temperatures, rendering these regions potentially uninhabitable.

“Our results provide a strong warning: Our rapidly warming climate is bringing us into uncharted territory that has significant consequences for health, well-being, and livelihoods,” the authors of the new attribution study concluded. “Greenhouse gas mitigation goals should take into account the increasing risks associated with unprecedented climate conditions if warming would be allowed to continue.”

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Comments 1 to 5:

  1. This blogpost by Clifford Mass of UoW has already attracted a lot of adverse comment on Real Climate, and elsewhere.

    Though more than one error has been pointed out e.g. Mass claiming no trend for increasing temperature records in the Pacific NW, when there clearly is a trend in the chart he shows, he has not modified the post in any way. 

    It is a dispiriting reminder that some scientists are still lending their credibility to climate change denial, whatever their intentions. I found mass being cited by the "uninformed" as an excuse for inaction.

    A more detailed refutation of Mass' post may be in order.

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    Moderator Response:

    [BL] Link activated.

    The web software here does not automatically create links. You can do this when posting a comment by selecting the "insert" tab, selecting the text you want to use for the link, and clicking on the icon that looks like a chain link. Add the URL in the dialog box.

  2. Although  his blog post does not refer directly to Clifford Mass, Tamino (who has participated in the discussion of this at RealClimate, has posted an analysis of the heat wave:

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  3. Recommended supplementary reading:

    Scientists are worried by how fast the climate crisis has amplified extreme weather by Angela Dewan, CNN, July 20, 2021

    An exceprt from the article:

    "Climate scientists have for decades warned that the climate crisis would lead to more extreme weather. They said it would be deadly and it would be more frequent. But many are expressing surprise that heat and rain records are being broken by such large margins.

    Since the 1970s, scientists have predicted the extent to which the world would warm fairly accurately. What's harder for their models to predict — even as computers get more and more powerful — is how intense the impact will be."

    A number of prominent climate scientists were interviewed for the article and are extensively quoted.

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  4. Scientists rarely question the fact of Climate Change. The question is why climate is changing, and the fellows of the carbon theory won the pot, contaminating every climate discussion with their "Bad Humanity" idea. And actually, all people solely think about CO2 and Greenhouse gas emission. No other idea has permission to be pronounced. Other opinions are judged as non-scientific and are demoralized. At the same time, people forget to think about the greenhouse effect of water, the most abundant substance on earth. It is the fact, that water cools the earth’s surface by evapotranspiration by making possible all living conditions in the biosphere. Even if carbon plays its role in global warming, the water’s cooling effect is much important for immediate corrective action, by massive reforestation in the tropics.
    The tropics distribute their energy by convection of water-vapor and cool the hemispheres by precipitation and washing out of carbon dioxide. Therefore, we should intensify research on the global hydrological cycle and stop immediately all deforestation in the tropics. Especially the Mangroves should be preserved, as we perceive looking to Somalia and the consequences of its prehistorical extinction. We argue that even the expansion of the Sahara desert is a consequence of deforestation an the western shore of the Red Sea.

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    Moderator Response:

    [DB] As constituted, your comment is a Gish Gallop of unrelated and uncogent claims.  Please first read the Newcomers, Start Here page and then the History of Climate Science and the Big Picture pages before commenting further.  If you still have concerns needing answers at that point, use the Search function in the Upper Left corner of any page here and place those concerns formatted as questions on the most appropriate page.  Thanks!

  5. Taken from Wiki:  "Mass maintains a popular weblog in which he posts regular articles on meteorology, Pacific Northwest weather history, and the impacts of climate change[8] written for the general public. According to Mass, "Global warming is an extraordinarily serious issue, and scientists have a key role to play in communicating what is known and what is not about this critical issue.[9]"

    Mass has stated publicly that he shares the scientific consensus that global warming is real and that human activity is a major cause of warming trend in the late 20th and 21st centuries.[10][11] He has been critical of the Paris Climate accord for not going far enough to address the negative impacts of climate change.[12]

    However, Mass is frequently critical of and has expressed concern that when media and environmental organizations make exaggerated claims about the current impacts of climate change, or cite climate change as the cause of specific weather events. He is concerned about misinforming the public about a key societal issue, distracting public and governmental attention from more immediate environmental concerns, and stifling opportunities for effective bipartisan policy-making to slow climate change and mitigate its effects.[13][14][15][16]

    His statements on the severity and progression of anthropogenic global warming have elicited condemnation from The Stranger[17] as well as members of activist environmental organizations[18] due to concerns that Mass's scientific approach to understanding and communicating the risks associated with global warming could result in public apathy or be used by climate change deniers to bolster their claims."

    I think Professor Mass is just typical of climate scientists giving  responses to their perceived inaccuracies in the increasing climate craziness reporting. What is different with this professor is he is more of a "personality". Possibly the second link from 2.Bob Loblaw at 22:18 PM on 21 July, 2021   disproves Mass' theory but the science though was beyond my understanding.

    The back and forth exchange between scientists peer reviewing "science" is what keeps us up to date and reliably informed. The fact Climate Change deniers can cherry pick a "headline" will never change.  I don't know whether to feel hopeful or nor when I read this either,

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