Extreme Temperature Diary- Saturday May 30th, 2020/ Main Topic: New Study Indicating That Dangerous Humid Heat Extremes Are Occurring Decades Earlier Than Expected

Saturday May 30th… Dear Diary. The main purpose of this ongoing blog will be to track United States extreme or record temperatures related to climate change. Any reports I see of ETs will be listed below each days climate, weather and environmental news section. I’ll refer to extreme or record temperatures as ETs (not extraterrestrials).😉

Main Topic: New Study Indicating That Dangerous Humid Heat Extremes Are Occurring Decades Earlier Than Expected

Dear Diary. This month we learned that yet another scientific study indicates that deadly climate change is occurring now, not decades in the future. That old adage of “we should be changing for our grandchildren’s sake” does ring true, but we should be decarbonizing for our own well being, as well, because a dystopian future is now.

Here is that new study as presented by Desdemona Despair:

Dangerous humid heat extremes occurring decades earlier than expected – “We are already locked in to large increases in the frequency and intensity of extreme humid heat events, and the risk is much larger than most people appreciate”

Map showing observed global extreme humid heat. Color symbols represent the 99.9th percentile of observed daily maximum TW for 1979–2017 for HadISD stations with at least 50 percent data availability over this period. Marker size is inversely proportional to station density. Graphic: Raymond, et al., 2020 / Science Advances
Map showing observed global extreme humid heat. Color symbols represent the 99.9th percentile of observed daily maximum TW for 1979–2017 for HadISD stations with at least 50 percent data availability over this period. Marker size is inversely proportional to station density. Graphic: Raymond, et al., 2020 / Science Advances

8 May 2020 (NOAA) – Oppressively hot summer days often evoke the expression, “it’s not the heat, it’s the humidity.” That sticky, tropical-like air combined with high temperatures is more than unpleasant — it makes extreme heat a greater health risk.

Climate models project that combinations of heat and humidity could reach deadly thresholds for anyone spending several hours outdoors by the end of the 21st century. However, new research says these extremes are already happening — decades before anticipated — due to global warming to date.

The study, “The emergence of heat and humidity too severe for human tolerance,” published today in Science Advances shows for the first time that some locations have already reported combined heat and humidity extremes above humans’ survivability limit. Dangerous extremes only a few degrees below this limit have occurred thousands of times globally — including in parts of the southwestern and southeastern United States — and have more than doubled in frequency since 1979.

“I believe that humid heat is the most underestimated direct, local risk of climate change,” said Radley Horton, a Columbia University professor and lead of NOAA’s Urban Northeast RISA team who co-authored the study. “As with sea level rise and coastal flooding, we are already locked into large increases in the frequency and intensity of extreme humid heat events, and the risk is much larger than most people appreciate.”

High humid heat defeats the body’s cooling system

The researchers conducted the most rigorous analysis yet using an index called “wet-bulb temperature” based on weather station temperature and humidity data. Wet-bulb temperature, the reading from a thermometer when covered in a wet cloth, is related to how muggy it feels and represents how effectively a person sheds heat by sweating.

Sweating alone does nothing to cool the body unless the water evaporates. Around a wet-bulb temperature of 95°F (35°C), human’s survivability limit, evaporation of sweat is no longer enough for our bodies to regulate their internal temperature. But serious impacts occur at values as low as 79°F (26°C). 

“When wet-bulb temperatures are extremely high, there is so much moisture in the air that sweating becomes ineffective at removing the body’s excess heat, like what happens in a steam room,” said Colin Raymond, the study’s lead author who conducted work at Columbia University and is now a postdoctoral scientist at NASA’s Jet Propulsion Laboratory. “At some point, perhaps after six or more hours, this will lead to organ failure and death in the absence of access to artificial cooling.” 

The authors’ survey of weather station data from 1979-2017 identified over 7,000 past occurrences of wet-bulb temperatures above 88°F (31°C) and over 250 above 91°F (33°C) around the world, as well as two stations that reported multiple daily-maximum wet-bulb temperatures above 95°F. These extremes occurred for 1-2 hours in parts of coastal southwest North America, including southeastern California and southwestern Arizona, South Asia, and the coastal Middle East. 

The southeastern United States, especially along the Gulf of Mexico, had multiple incidences of wet-bulb temperatures at or above 88°F; specifically, in east Texas, Louisiana, Mississippi, Alabama, the Florida Panhandle, Arkansas and North Carolina. Parts of India, Pakistan, northwestern Australia, the coast of the Red Sea, and areas along the Gulf of California in Mexico saw even higher extremes. 

Global trends in extreme humid heat. (A to D) Annual global counts of TW exceedances above the thresholds labeled on the respective panel, from HadISD (black, right axes, with units of station days) and ERA-Interim grid points (gray, left axes, with units of grid-point days). We consider only HadISD stations with at least 50% data availability over 1979–2017. Correlations between the series are annotated in the top left of each panel, and dotted lines highlight linear trends. (E) Annual global maximum TW in ERA-Interim. (F) The line plot shows global mean annual temperature anomalies (relative to 1850–1879) according to HadCRUT4 (40), which we use to approximate each year’s observed warming since preindustrial; circles indicate HadISD station occurrences of TW exceeding 35°C, with radius linearly proportional to global annual count, measured in station days. Graphic: Raymond, et al., 2020 / Science Advances

Global trends in extreme humid heat. (A to D) Annual global counts of TW exceedances above the thresholds labeled on the respective panel, from HadISD (black, right axes, with units of station days) and ERA-Interim grid points (gray, left axes, with units of grid-point days). We consider only HadISD stations with at least 50% data availability over 1979–2017. Correlations between the series are annotated in the top left of each panel, and dotted lines highlight linear trends. (E) Annual global maximum TW in ERA-Interim. (F) The line plot shows global mean annual temperature anomalies (relative to 1850–1879) according to HadCRUT4 (40), which we use to approximate each year’s observed warming since preindustrial; circles indicate HadISD station occurrences of TW exceeding 35°C, with radius linearly proportional to global annual count, measured in station days. Graphic: Raymond, et al., 2020 / Science Advances

These hot spots were primarily concentrated in coastal areas near high ocean surface temperatures and intense continental heat — a recipe for extreme humid heat.

“Wet-bulb temperatures above 86°F (30°C) are rare in the U.S. As wet bulb temperatures approach 95°F, even the healthiest people, relaxing in the shade without heavy clothing and with an endless supply of water, cannot prevent themselves from overheating,” Horton said. “Even at lower wet-bulb temperatures, like 79°F (26°C), those with pre-existing health conditions (like respiratory, cardiovascular, and renal disease), the elderly, as well as those performing strenuous outdoor labor and athletic activities, are at a high risk.”

The authors note, for example, that the 2003 European heat wave caused over 50,000 deaths at wet-bulb temperatures close to 79°F. In the United States where air conditioning is more widespread, the 1995 Chicago heat wave reached wet-bulb temperatures of 85°F and killed over 700 people.   

Extreme humid heat risk is imminent and increasingly severe

Though the reported extreme exceedances were brief and highly localized, a large number of locations, such as near the Persian Gulf and Red Sea, could surpass the 95°F threshold in just a few decades, much sooner than other studies have suggested, according to the authors. Many populous areas are close to the limit.

Horton believes more research is needed on the factors that generate extreme wet-bulb temperatures in different regions, as well as potential impacts on energy, food systems, and human security. 

“The deadly trends in recent decades toward increasingly extreme humid heat underscore a major societal challenge for the coming decades,” Horton said. “Advances in our understanding and appreciation of extreme humid heat risks have the potential to increase the economic productivity and livelihood of Americans and all people, while protecting the health of the most vulnerable.”

The study was supported by NOAA’s Regional Integrated Sciences and Assessments (RISA) Program.

Additional resources

Contact

  • Alison Stevens, NOAA Research Communications, at alison.stevens@noaa.gov.

Dangerous humid heat extremes occurring decades before expected


Projections of extreme humid heat exceeding the physiological survivability limit. (A) Shading shows the amount of global warming (since preindustrial) until TW = 35°C is projected to become at least a 1-in-30-year event at each grid cell according to a nonstationary generalized extreme value (GEV) model. In blank areas, more than 4°C of warming is necessary. Black dots indicate ERA-Interim grid cells with a maximum TW (1979–2017) in the hottest 0.1% of grid cells worldwide. (B) Total area with TW of at least 35°C, as a function of mean annual temperature change 〈T〉 from the preindustrial period. Red (green) vertical lines highlight the lowest 〈T〉 for which there are nonzero areas over land (sea)—the respective ToE. (C) Bootstrap estimates of the ToE. See text for details of this definition and calculation. Graphic: Raymond, et al., 2020 / Science Advances

Projections of extreme humid heat exceeding the physiological survivability limit. (A) Shading shows the amount of global warming (since preindustrial) until TW = 35°C is projected to become at least a 1-in-30-year event at each grid cell according to a nonstationary generalized extreme value (GEV) model. In blank areas, more than 4°C of warming is necessary. Black dots indicate ERA-Interim grid cells with a maximum TW (1979–2017) in the hottest 0.1% of grid cells worldwide. (B) Total area with TW of at least 35°C, as a function of mean annual temperature change 〈T〉 from the preindustrial period. Red (green) vertical lines highlight the lowest 〈T〉 for which there are nonzero areas over land (sea)—the respective ToE. (C) Bootstrap estimates of the ToE. See text for details of this definition and calculation. Graphic: Raymond, et al., 2020 / Science Advances

The emergence of heat and humidity too severe for human tolerance

ABSTRACT: Humans’ ability to efficiently shed heat has enabled us to range over every continent, but a wet-bulb temperature (TW) of 35°C marks our upper physiological limit, and much lower values have serious health and productivity impacts. Climate models project the first 35°C TW occurrences by the mid-21st century. However, a comprehensive evaluation of weather station data shows that some coastal subtropical locations have already reported a TW of 35°C and that extreme humid heat overall has more than doubled in frequency since 1979. Recent exceedances of 35°C in global maximum sea surface temperature provide further support for the validity of these dangerously high TW values. We find the most extreme humid heat is highly localized in both space and time and is correspondingly substantially underestimated in reanalysis products. Our findings thus underscore the serious challenge posed by humid heat that is more intense than previously reported and increasingly severe.

The emergence of heat and humidity too severe for human tolerance

Speaking of heat in the southeastern U.S. with possible tropical cyclone development in the Gulf for June, I’ll have more on that on the last day of May, which will be tomorrow. Stay tuned.

Here is more climate and weather news from Saturday:

(As usual, this will be a fluid post in which more information gets added during the day as it crosses my radar, crediting all who have put it on-line. Items will be archived on this site for posterity. In most instances click on the pictures of each tweet to see each article. The most noteworthy items will be listed first.)

Here is one big “ET” from the last couple of days:

And from elsewhere on the planet:

Now here are some of today’s articles and notes on the horrid COVID-19 pandemic:

(As usual, the most noteworthy items will be listed first.)

(If you like these posts and my work please contribute via the PayPal widget, which has recently been added to this site. Thanks in advance for any support.) 

Guy Walton “The Climate Guy”

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