An article in the New Scientist (No.3161) by John Pickrell, entitled “Too hot to handle”, discusses the increasing trend of heatwaves throughout the world, as a result of climate change.
Pickrell starts by discussing Australia, which had a heatwave in January 2017, with the hottest ever recorded temperatures in Sydney and Brisbane (Sydney had over 47 degrees). Large parts of the country had temperatures over 40 degrees C for weeks on end, as well as bush fires. Many of the unique species of wildlife common to Australia had to be rescued from fires and heat, many of them suffering from heat exhaustion, burns, dehydration and stress.
Temperatures of 50 degrees C are predicted by 2040 for Australia.
Pickrell then goes on to cite papers, which give statistics about fatalities during heatwaves, one from The Lancet which covered research by 26 institutions (including the World Health Organization).
The 2003 heatwave in France killed 70,000 people – but it would appear that the level of humidity is the crucial factor, as high levels of water in the atmosphere can reduce the body’s ability to cool down through sweating. To sweat effectively, you must maintain your blood volume, so dehydration can cause heat stress, followed by heat stroke, multiple organ failure and possible death. The elderly and children are at greater risk of heat stroke, as well as those on medication or with heart disease.
I came across another wordpress website, which gives a useful chart showing temperature against relative humidity and which combinations are lethal:
and below for the table (with acknowledgments):
The black crosses in the chart above show temperature and relative humidity during events that were lethal. The blue line shows the likely boundary between lethal and non-lethal events, and the red line is a 95% probability threshold.
According to The Lancet, global warming has reduced the workforce in India by 418,000.
An interesting map of the world is given in the New Scientist article to show the probability of deadly heatwaves for three global warming scenarios: 1.5 degrees C; 2 degrees C and 4 degrees C. This can be seen by clicking on the link below:
It shows that, even with an increase in global temperature of 2 degrees, many parts of the world will become uninhabitable, through rising temperatures: North West Africa, much of the Middle East, parts of Central and South America, India, Pakistan and Bangladesh and much of Australia. At four degrees the situation is dire throughout much of the tropical world.
The New Scientist article concludes with a list of advice on how to keep cool.
Another academic article on a similar subject has been published in the Proceedings of the National Academy of Science USA by Sherwood and Huber in 2010 (Vol 107, (21), 9552-5) entitled “An adaptability limit to climate change due to heat stress.” This article has been summarised in the Science & Technology section of the The Observer (10th Sept. 2017). This article gives a chart showing which species die at particular degrees of warming above pre-industrial levels. Amphibians will be the first to go (at 0.6 degrees+), followed by penguins, due to loss of food sources, as the krill populations dwindle. At 1.6 degrees+, the wooded tundra is lost, along with its inhabitants, moose, lynx and brown bears, followed by large African mammals, such as elephants, then rain forest dwellers (orangutans, jaguars, sloths) at 2.6 degrees+. At a warming of 4 degrees, 70% of species would be extinct, coral reefs dead and deserts would expand across the world. The fate of humankind would be dominated by mass migration, on a scale even larger than we see today, with water resources extremely limited, as we would have to abandon most of the Earth or live underground. The authors predict that, by 2050, temperatures will be in a range that nobody has experienced before.
It is interesting to note that the Australian town of Coober Pedy, a major site for opal mining, has already built an underground town, including hotels, for those times in the year when it is already too hot to live above ground.
2nd August 2018
Since this post was first written, time has now moved on into 2018 with heatwaves across much of the northern hemisphere (see other posts on this site for details). Even climate sceptics are now beginning to accept that climate change is with us, with the extremes of weather which accompany it.
A piece this week in The Guardian by David Carrington deals with the issue of human survivability during heat waves. I quote a short passage from him, in which he summarises scientific work on the issue:
“The new analysis assesses the impact of climate change on the deadly combination of heat and humidity, which is measured as the “wet bulb” temperature (WBT). Once the WBT reaches 35C, the air is so hot and humid that the human body cannot cool itself by sweating and even fit people sitting in the shade die within six hours.
He then goes on to discuss which parts of the world are most at risk of high WBT temperatures. This would appear to be the north China plain, with a population of 400 million people, most of them farmers. The scientists who produced the data have predicted that by 2070 to 2100, this area of the world will become uninhabitable. Other areas at risk are the Middle East, around the Gulf (particularly Dubai, Abu Dhabi, Doha and the coastal cities of Iran) and parts of South Asia (around the Indus and Ganges valleys).
For the full Guardian article, see:
The UK has experienced another heatwave period this summer, with record temperatures being reached in a number of countries. It was particularly humid in the UK, with weather forecasters predicting the humidity above 50%, a level which can prove fatal with temperatures above 25ºC, according to the graph shown above.
So its worth looking again at the relationship between WBT (wet bulb temperature) and death due to heat stress. The following can be found in Wikipedia:
“Living organisms can survive only within a certain temperature range. When the ambient temperature is excessive, humans and many animals cool themselves below ambient by evaporative cooling (sweat in humans and horses, saliva and water in dogs and other mammals); this helps to prevent potentially fatal hyperthermia due to heat stress. The effectiveness of evaporative cooling depends upon humidity; wet-bulb temperature, or more complex calculated quantities such as Wet Bulb Globe Temperature (WBGT) which also takes account of solar radiation, give a useful indication of the degree of heat stress, and are used by several agencies as the basis for heat stress prevention guidelines.
A sustained wet-bulb temperature exceeding 35 °C (95 °F) is likely to be fatal even to fit and healthy people, unclothed in the shade next to a fan; at this temperature our bodies switch from shedding heat to the environment, to gaining heat from it. Thus 35 °C (95 °F) is the threshold beyond which the body is no longer able to adequately cool itself. A study by NOAA from 2013 concluded that heat stress will reduce labour capacity considerably under current emissions scenarios.
A 2010 study concluded that under a worst-case scenario for global warming with temperatures 12 °C (22 °F) higher than 2007, the wet-bulb temperature limit for humans could be exceeded around much of the world in future centuries. A 2015 study concluded that parts of the globe could become uninhabitable. An example of the threshold at which the human body is no longer able to cool itself and begins to overheat is a humidity level of 50% and a high heat of 46 °C (115 °F), as this would indicate a wet-bulb temperature of 35 °C (95 °F).”