Extreme Temperature Diary- Saturday May 22nd, 2021/ Main Topic: Study Indicates That Heat-stress impacts predicted to double by 2099 With Emphasis On The Heat Index

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 the main topic of the day. I’ll refer to extreme or record temperatures as ETs (not extraterrestrials).😉

Main Topic: Study Indicates That Heat-stress impacts predicted to double by 2099 With Emphasis On The Heat Index

Dear Diary. Every few months I see a new study indicating how bad heat problems will be during the summer months if we don’t reign in carbon pollution. The new one I am presenting today takes into account the heat index. This index has been around for as long as I’ve been a meteorologist. Here is a definition from Wikipedia:


The heat index (HI) is an index that combines air temperature and relative humidity, in shaded areas, to posit a human-perceived equivalent temperature, as how hot it would feel if the humidity were some other value in the shade. The result is also known as the “felt air temperature”, “apparent temperature“, “real feel” or “feels like”. For example, when the temperature is 32 °C (90 °F) with 70% relative humidity, the heat index is 41 °C (106 °F).

The human body normally cools itself by perspiration, or sweating. Heat is removed from the body by evaporation of that sweat. However, high relative humidity reduces the evaporation rate. This results in a lower rate of heat removal from the body, hence the sensation of being overheated. This effect is subjective, with different individuals perceiving heat differently for various reasons (such as differences in body shape, metabolic differences, differences in hydration, pregnancymenopause, effects of drugs and/or drug withdrawal); its measurement has been based on subjective descriptions of how hot subjects feel for a given temperature and humidity. This results in a heat index that relates one combination of temperature and humidity to another.

Because the heat index is based on temperatures in the shade, while people often move across sunny areas, the heat index can give a much lower temperature than actual conditions of typical outdoor activities. Also, for people exercising or active, at the time, then the heat index could give a temperature lower than the felt conditions.


The heat index was developed in 1979 by Robert G. Steadman.[1][2] Like the wind chill index, the heat index contains assumptions about the human body mass and height, clothing, amount of physical activity, individual heat tolerance, sunlight and ultraviolet radiation exposure, and the wind speed. Significant deviations from these will result in heat index values which do not accurately reflect the perceived temperature.[3]

In Canada, the similar humidex (a Canadian innovation introduced in 1965)[4] is used in place of the heat index. While both the humidex and the heat index are calculated using dew point, the humidex uses a dew point of 7 °C (45 °F) as a base, whereas the heat index uses a dew point base of 14 °C (57 °F). Further, the heat index uses heat balance equations which account for many variables other than vapor pressure, which is used exclusively in the humidex calculation. A joint committee[who?] formed by the United States and Canada to resolve differences has since been disbanded.[citation needed]


The heat index of a given combination of (dry-bulb) temperature and humidity is defined as the dry-bulb temperature which would feel the same if the water vapor pressure were 1.6 kPa. Quoting Steadman, “Thus, for instance, an apparent temperature of 24 °C (75 °F) refers to the same level of sultriness, and the same clothing requirements, as a dry-bulb temperature of 24 °C (75 °F) with a vapor pressure of 1.6 kPa.”[1]

This vapor pressure corresponds for example to an air temperature of 29 °C (84 °F) and relative humidity of 40% in the sea-level psychrometric chart, and in Steadman’s table at 40% RH the apparent temperature is equal to the true temperature between 26–31 °C (79–88 °F). At standard atmospheric pressure (101.325 kPa), this baseline also corresponds to a dew point of 14 °C (57 °F) and a mixing ratio of 0.01 (10 g of water vapor per kilogram of dry air).[1]

A given value of relative humidity causes larger increases in the heat index at higher temperatures. For example, at approximately 27 °C (81 °F), the heat index will agree with the actual temperature if the relative humidity is 45%, but at 43 °C (109 °F), any relative-humidity reading above 18% will make the heat index higher than 43 °C.[5]

It has been suggested that the equation described is valid only if the temperature is 27 °C (81 °F) or more.[6] The relative humidity threshold, below which a heat index calculation will return a number equal to or lower than the air temperature (a lower heat index is generally considered invalid), varies with temperature and is not linear. The threshold is commonly set at an arbitrary 40%.[5]

The heat index and its counterpart the humidex both take into account only two variables, shade temperature and atmospheric moisture (humidity), thus providing only a limited estimate of thermal comfort. Additional factors such as wind, sunshine and individual clothing choices also affect perceived temperature; these factors are parameterized as constants in the heat index formula. Wind, for example, is assumed to be 5 knots (9.3 km/h).[5] Wind passing over wet or sweaty skin causes evaporation and a wind chill effect that the heat index does not measure. The other major factor is sunshine; standing in direct sunlight can add up to 15 °F (8.3 °C) to the apparent heat compared to shade.[7] There have been attempts to create a universal apparent temperature, such as the wet-bulb globe temperature, “relative outdoor temperature”, “feels like”, or the proprietary “RealFeel“.

Meteorological considerations

Outdoors in open conditions, as the relative humidity increases, first haze and ultimately a thicker cloud cover develops, reducing the amount of direct sunlight reaching the surface. Thus, there is an inverse relationship between maximum potential temperature and maximum potential relative humidity. Because of this factor, it was once believed that the highest heat index reading actually attainable anywhere on Earth was approximately 71 °C (160 °F). However, in DhahranSaudi Arabia on July 8, 2003, the dew point was 35 °C (95 °F) while the temperature was 42 °C (108 °F), resulting in a heat index of 78 °C (172 °F).[8]

The human body requires evaporative cooling to prevent overheating. Wet-bulb temperature, and Wet Bulb Globe Temperature are used to determine the ability of a body to eliminate excess heat. A sustained wet-bulb temperature of about 35 °C (95 °F) can be fatal to healthy people; at this temperature our bodies switch from shedding heat to the environment, to gaining heat from it.[9] Thus a wet bulb temperature of 35 °C (95 °F) is the threshold beyond which the body is no longer able to adequately cool itself.[10]

Table of values

The table below is from the U.S. National Oceanic and Atmospheric Administration. The columns begin at 80 °F (27 °C), but there is also a heat index effect at 79 °F (26 °C) and similar temperatures when there is high humidity.

See the source image

For example, if the air temperature is 96 °F (36 °C) and the relative humidity is 65%, the heat index is 49 °C (120 °F)

Effects of the heat index (shade values)

26–32 °CCaution: fatigue is possible with prolonged exposure and activity. Continuing activity could result in heat cramps.
32–41 °CExtreme caution: heat cramps and heat exhaustion are possible. Continuing activity could result in heat stroke.
41–54 °CDanger: heat cramps and heat exhaustion are likely; heat stroke is probable with continued activity.
over 54 °CExtreme danger: heat stroke is imminent.

Exposure to full sunshine can increase heat index values by up to 8 °C (14 °F).[11]

For the formula and more read on using this link:


Now here is that article with a big warning concerning carbon pollution:

Heat-stress impacts predicted to double by 2099

By Kevin Wheeler May 20, 2021

A man wipes the sweat from his face in the scorching heat at a business district in Tokyo. (AP Photo/Koji Sasahara)

A man wipes the sweat from his face in the scorching heat at a business district in Tokyo. (AP Photo/Koji Sasahara)

As heat, humidity and populations rise by the end of the 21st century, so too will heat stress, researchers say, likely increasing the health risks of millions of people but also signaling another reason to reach important climate and emissions goals.

A paper published April 26 in Earth’s Future draws on many heat-stress variables, where other studies tend to focus on only one aspect, such as duration or temperature. The researchers found that the potential impact of heat-stress events lasting from one day to one week will double from 2060-99 across the U.S., with population growth on the East and West coasts accounting for much of the added stress.

“The heat-stress events that we are considering to be extremes in the past are likely to be more normal in the future,” said co-author Ashok Mishra, an associate professor of civil engineering at Clemson University. “Overall, we’re likely to see more extremes in the future.”

Heat stress is a major cause of mortality around the world, with low-income communities bearing much of the burden. The National Weather Service defines excessive heat exposure in terms of heat index, the “feels like” measurement that combines temperature and humidity. For the agency, excessive heat exposure, or heat stress, equals a heat index over 105 degrees Fahrenheit. 

A “stressful” heat index not only induces heat exhaustion and heat stroke but can also exacerbate cardiovascular disease and possibly lead to heart attacks and strokes, according to the Environmental Protection Agency. People age 65 or older are also more susceptible to the dangers of heat stress.

Mishra and lead author Sourav Mukherjee, a Ph.D. student in water resources engineering at Clemson, began looking at heat stress after witnessing record-breaking heat waves in the Southeastern U.S. over the summers of 2019 and 2020.

To determine the potential impact of heat stress, the pair and colleagues first collected climate data, accounting for temperature and humidity from 1980 to 2019, and calculated heat stress from this period. Then, they projected these values into the near and distant future using projected climate and population datasets, developing a framework to examine the present and projected potential impact of heat stress. Crucially, the calculations account for humidity, which promotes heat stress. 

“If we are only considering the temperature, it is fine, but if you include the humidity that is done in this study, that has a significant impact on the health, because humidity prevents the body from cooling off,” Mishra said in an interview with The Academic Times

Population growth along the East and West coasts of the U.S. is expected to drive heat stress as urban populations grow and rural populations shrink. 

Heat stress is going to become even more dangerous because, since the 1960s, temperatures have not been rising in a linear fashion, according to Mishra. They’re rising with more variability, which makes them harder to adapt to. The researchers also accounted for these fluctuating, rapid changes in heat stress that shock the body, which prior studies have not done.

“Suppose I have acclimated to a temperature of 70 degrees Fahrenheit, and suddenly, for the next couple of days, there is 100-degree-Fahrenheit heat wave,” Mukherjee said. “That also gives the body a heat shock, and the body has to acclimate to that shock.”

A recent study on tobacco hornworm larvae confirmed some negative effects of heat stress, because larvae subjected to long heat waves did not grow as well as those experiencing shorter heat waves or none at all.  

For policymakers, Mukherjee said, the takeaway is “how they need to understand the implications of pinpointing the geographical region, which is likely to see aggressive potential impact of heat stress during aggressive emission scenarios without mitigation.” 

According to Mishra, effective mitigation could come through net-zero carbon initiatives that seek to drastically reduce and eventually eliminate greenhouse gas emissions that contribute to climate change. In April, the U.S. and Canadian governments jointly announced a new Greening Government Initiative, which seeks to make government facilities and activities emission-free by 2050. 

“We need to bring carbon emissions down globally by a factor of two within the next decade to avoid crossing the 1.5 Celsius warming threshold,” said co-author Michael Mann, a distinguished professor of atmospheric science at Pennsylvania State University. “The Biden administration has pledged to bring the U.S. in line with that commitment, but they need to work with Congress now in advancing a specific policy agenda, which includes measures such as carbon pricing and subsidies for renewable energy, that can meet that commitment.”

According to Mann, the 1.5 degrees Celsius threshold is significant because it is the point at which heat stress and other harmful climate impacts show a “marked” increase when exceeded. Limiting global temperature rise by that amount is also the more aspirational goal of the international Paris Agreement.

Mishra and Mukherjee are interested in expanding their heat-stress research to see what factors aside from temperature and humidity could contribute to heat stress. This could include soil moisture, because low-moisture soil absorbs less heat than high-moisture soil and contributes to higher temperature in the lower atmosphere, according to Mishra. 

The duo also believe the study opens new avenues to examine not just where heat stress is happening but also whom it hurts most. Access to air conditioning, for example, is less common in low-income communities. Mishra and Mukherjee envision future studies, potentially collaborating with social scientists to look at the disparity of heat stress within populations. 

The study, “Projected doubling of US heat stress by the late 21st century,” published April 26 in Earth’s Future, was authored by Sourav Mukherjee and Ashok Mishra, Clemson University; Michael E. Mann, Pennsylvania State University; and Colin Raymond, California Institute of Technology.

I’ll let my readers know when the next significant heat study comes out. Am hoping that these will become more regionalized with more specifics soon.

Here is one big “ET” from Saturday:

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.)

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

(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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