Climate Change Wet Bulb Temperature 35 Degrees Celsius

A climate change term we may all come to know well.

Peter Miles
Feb 16 · 5 min read
Animal carcass. Image — Pixabay Creative Commons.

An aspect of climate change not often discussed is the direct impact on humans and mammals of heat stress. Temperature and humidity are rising (Bellprat, et al., 2019; Willett, et al., 2007) and at a wet bulb temperature of 35 degrees Celsius, people’s bodies can’t dissipate metabolic heat, they then suffer from hyperthermia, overheating.

A wet bulb temperature is measured with a standard thermometer covered in a wet cloth while well ventilated, indicating the temperature at 100% humidity. Wet bulb or Temperature Wet TW is a measure of temperature and humidity combined.

Humans maintain an internal body temperature of 37 degrees Celsius, with a skin temperature kept at 35 degrees C or below. With the skin cooler than the internal core temperature heat can be lost to the skin. Heat from metabolism is lost from the body and skin by heat conduction, evaporative cooling and infrared radiative cooling (Sherwood & Huber, 2010).

The wet bulb temperature of 35 degrees Celsius is the temperature and humidity at which humans and mammals will become overheated, with potential death at 42 to 43 degrees internal body temperature. Conduction and evaporation cooling can’t occur as a result of the temperature and humidity respectively being too high (Sherwood & Huber, 2010).

Wet Bulb Globe Temperature, WBGT, is another index for measuring heat stress, it is often used in industry and includes the other factors of the amount of physical activity, the environment characteristics eg sun angle, cloud cover, and the clothing worn. Tw has been chosen here because it establishes a limit at which these other factors included in WBGT are ineffective (Sherwood & Huber, 2010; Willet & Sherwood, 2012).

The highest wet bulb temperature reached anywhere on earth is about 30 degrees C, this is probably because of a convective instability mechanism, that can occur with high temperature and humidity, which result in storm activity that cools air near the surface, but many areas of the earth have very low storm activity and low rainfall.

A climate change increase in air temperature of 7 degrees is possible by 2100, pushing the wet bulb temperature to 35 (Sherwood & Huber, 2010) while Sokolov, et al. (2009) projects 5.4 degrees air temperature rise by 2091 to 2100. Warming will continue to increase past 2100 if emissions of carbon dioxide continue.

Texas Military Department Heat Warning. Image — Flickr Creative Commons.
Map B of Tw max 30 degrees 1999 to 2008. Image — (Sherwood & Huber, 2010).

Many tropical, subtropical and some desert areas are likely to be affected by increasing Tw, with areas around the world being made uninhabitable.

One example is the Arabian Gulf region, the source of much of the world’s oil and gas, it is likely to have conditions approach and exceed the wet bulb 35 degree C limit of survivability for more than 6 hours, under the Intergovernmental Panel on Climate Change, IPCC, Representative Concentration Pathway, RCP trajectory, RCP8.5, by 2071 to 2100.

Specific areas predicted to be affected are the low coastal parts of the Arabian Sea, the Red Sea and the Persian Gulf. In the boreal summer, July, August, September, warm north westerly winds from Turkey and Iraq blow across the gulf gaining moisture and increasing the Tw in many Gulf cities, Abu Dhabi, Dubai, Doha, Dhahran and Bandar Abbas.

Oil has brought wealth to the region which can pay for electricity and air conditioning but under these extreme Tw conditions, it makes the reliability of electricity supply life threatening. Other countries are not so wealthy with many poor not able to afford air conditioning, such as in the Yemen coastal region and the cities of Al Hudaydah and Aden. They are expected to reach Tw of 33 degrees in extreme years, which could lead to death in children and the elderly (Pal & Eltahir, 2016).

Regions vulnerable to increasing temperature and humidity include South East Asia, South Eastern USA, Northern Australia, Southern China, Eurasia, Southern Europe, Central Africa and Latin America under the IPCC RCP 8.5 emissions scenario by 2081 to 2100 with air temperature rise of 2.6 to 4.8 C (Newth & Gunasekera, 2018; Mora, et al., 2017).

A high temperature and humidity, Tw, in regions may be detrimental to human health in summer and will certainly affect social and economic activities, and will be a lot worse in those countries not able to afford to adapt to the climatic changes.


Bellprat, O., Guemas, V., Doblas-Reyes, F., & Donat, M. G. (2019). Towards reliable extreme weather and climate event attribution. Nature communications, 10(1), 1–7.

Mora, C., Dousset, B., Caldwell, I. R., Powell, F. E., Geronimo, R. C., Bielecki, C. R., … & Trauernicht, C. (2017). Global risk of deadly heat. Nature climate change, 7(7), 501–506.

Newth, D., & Gunasekera, D. (2018). Projected changes in wet-bulb globe temperature under alternative climate scenarios. Atmosphere, 9(5), 187.

Pal, J. S., & Eltahir, E. A. (2016). Future temperature in southwest Asia projected to exceed a threshold for human adaptability. Nature Climate Change, 6(2), 197–200.

Sherwood, S. C., & Huber, M. (2010). An adaptability limit to climate change due to heat stress. Proceedings of the National Academy of Sciences, 107(21), 9552–9555.

Sokolov, A. P., Stone, P. H., Forest, C. E., Prinn, R., Sarofim, M. C., Webster, M., … & Jacoby, H. D. (2009). Probabilistic forecast for twenty-first-century climate based on uncertainties in emissions (without policy) and climate parameters. Journal of Climate, 22(19), 5175–5204.

Willett, K. M., Gillett, N. P., Jones, P. D., & Thorne, P. W. (2007). Attribution of observed surface humidity changes to human influence. Nature, 449(7163), 710–712.

Willett, K. M., & Sherwood, S. (2012). Exceedance of heat index thresholds for 15 regions under a warming climate using the wet‐bulb globe temperature. International Journal of Climatology, 32(2), 161–177.

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Peter Miles

Written by

Peter Miles B.Env.Sc. 45 years in Environmental Science, specializing in Wildlife and Conservation Biology. Writes about Animals, Revegetation & Climate Change.

Age of Awareness

Stories providing creative, innovative, and sustainable changes to the ways we learn

Peter Miles

Written by

Peter Miles B.Env.Sc. 45 years in Environmental Science, specializing in Wildlife and Conservation Biology. Writes about Animals, Revegetation & Climate Change.

Age of Awareness

Stories providing creative, innovative, and sustainable changes to the ways we learn

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