Although there is no standard definition of a heat wave, it’s a phenomenon that everyone understands. We all have a general sense of what the term means. It’s not just that it’s hotter than normal for the time of year: the heat keeps going for several days, the temperature hardly falls overnight, and for most people, the hot weather is close to unbearable. When some people actually die of heatstroke and exhaustion during this period, there is no disputing the term. It’s a heatwave.
Heatwaves have been around for a long time: they are not events that have suddenly appeared since scientists started worrying about climate change and global warming. The first well-documented case may be the extreme heat that settled over London in 1858. The River Thames at the time was little more than a massive and foul sewer carrying the human waste of more than two million people slowly out to sea. Since the river is tidal in central London– most of the filth came back again. The smell was bad enough in the winter, but in the summer heat of 1858 the stench was intolerable. Since drinking water came from ground water sources outside the city but also contaminated by human waste, cholera was a constant threat.
The abominable stench from the River Thames in the mid 19th Century finally resulted in government action to build a sewerage system that still operates today.
There is a lesson to be learned from this event in Britain (which is not the obvious one that seemingly only catastrophic events lead to any real government action); it is that heat waves make all the other environmental problems and health issues that are present at the time much, much worse.
Heat waves occurred regularly throughout the 19th and 20th Centuries. Among the most well-documented heat waves in the United States are those that occurred in 1980 (St. Louis and Kansas City, Missouri), 1995 (Chicago, Illinois), and 1999 (Cincinnati, Ohio; Philadelphia, Pennsylvania; and Chicago, Illinois). The highest death rates in these heat waves occurred in people over 65 years of age .
But since the year 2000, there have been some extreme events. In 2003, a record heat wave over western Europe resulted in the deaths of tens of thousands of people, mostly in France. The young, the sick, and the elderly were most affected. Some estimates run as high as 80,000 deaths. For the period 2000-2106, at least 136,000 fatalities were recorded in Europe due to heat-related health complications, which represents more than 87% of all disaster-related deaths in that region .
In July 2006, heat waves again suffocated Europe and North America—where over 200 people died in the US. Temperatures in South Dakota reached 54°C; in California the heat rose to 50°C. A year later, Europe again experienced sustained temperatures over 45°C. This pattern has continued every year since.
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The most extreme recent event is reckoned to be the Russian heat wave of July 2010—when thousands of people died: the exact number is unknown. Scores of people reportedly drowned while swimming drunk!.
In the summer of 2011, a heatwave in Texas produced temperatures over 45°C. The associated drought and record wildfires cost an estimated $12 billion .
2015 was an extreme year for heatwaves. In Egypt temperatures reached 45°C—over 60 people died. This was followed by extreme temperatures in Iran which were reported as a heat index of 73°C! Then Pakistan was scorched in June by 49°C heat that left 1200 dead; almost 2000 were hospitalised for dehydration and heat stroke. The month before in India, over 2500 people succumbed to the overpowering heat.
In 2016, the hot weather continued its assault. In southern Africa at the beginning of the year an extreme heatwave set in–exacerbated by the continuing drought. Many places broke records in early January–records that had been set only weeks earlier in late 2015. The first week of January 2016, the temperature reached 42°C in Pretoria and almost 39°C in Johannesburg, both of which were 3°C or more above previous records.
Extreme heat also suffocated South and South-East Asia in April and May 2016 prior to the start of the summer monsoon. The extreme heat was centered on Thailand, where a national record of 44.6°C was set at Mae Hong Son in April. Several records were broken in Malaysia in March and April, and in May temperatures rose to 51°C in Phalodi—the highest temperature ever recorded for India.
In the Middle East and northern Africa, temperatures were at record highs. The highest temperture was recorded at Mitribah in Kuwait in July 2016 where the mercury hit 54°C which, if confirmed, would be the highest temperature on record for Asia. The same month, temperatures rose to 54°C in Basra, Iraq and 53°C in Delhoran, Iran .
In early August 2016, a heat wave in Europe dubbed ‘Lucifer’ caused several deaths. As sweltering heat settled across western Europe, temperatures rose to 38°C in Italy, 40°C in France, and 44°C in Spain .
In the same year, several countries, including Mexico and India, reported record high temperatures while many other countries observed near record highs. A week long heat waves at the end of April over the northern and eastern Indian peninsular, with temperatures over 44°C, contributed to a water crisis for 330 million people and caused 300 fatalities.
The extreme heat seems to intensify every year. In 2018, 22,000 people were hospitalized in Japan because of the unrelenting heat. In Ouagla, Algeria, temperatures rose to 51.1°C, a new record for Africa. In Australia, bats dropped dead from the trees as temperatures rose to 46.1°C.
So are heat waves getting hotter? And are they becoming more frequent? The answer to both questions appears to be: Yes!
Over the last several decades, there has been an increasing number of high-humidity heat waves—characterized by the persistence of extremely high night-time temperatures. The combination of high humidity and high temperatures at night can have fatal consequences for the elderly. Extreme heat events are now responsible for more deaths annually than hurricanes, tornadoes, floods and earthquakes combined .
Across the globe, extremely warm nights that used to come once in 20 years now occur every ten years. And extremely hot summers (those substantially above the historical average) are now occurring across a larger swathe of the planet’s land area—as much as ten times larger than the period 1951-1980 . One indication of the changing climate can be deduced by comparing the number of record lows with the number of record highs. In the US about 60 years ago, the number of new record high temperatures recorded across the country was roughly equal to the number of record lows: a sign of the natural variability of weather patterns but nothing to suggest that the climate was changing. But since the beginning of this century, the number of new record highs recorded each year has been twice the number of new record lows. In early 2012, that ratio rose to over 7:1. The graph illustrates the observed trend since the 1930s .
So yes, heat waves are becoming hotter. And although graph shows the trend for the USA, there’s plenty of evidence to show that this is a global trend.
Extreme temperatures have killed at least 166,000 people in the last 20 years. During the last 10 years heatwaves overtook flooding to become the third highest cause of global disaster mortality. The incidence of extreme temperature also increased rising to 219 events in 2006-2015 up from 177 the previous decade .
In spite of the recent record-breaking temperatures, recorded deaths from heat waves has fallen since 2005, mainly due to lower mortality in Western Europe—where health impact-based weather forecasting was introduced following the 2003 heatwave, an example followed by several countries including India. However, the global numbers for deaths due to heatwaves are considered to be substantially under-reported. While in Western Europe, public awareness may have increased and there is now much better medical support, middle-income and developing countries in the tropics for the most part have not adopted these measures.
In North America, increasing access to air-conditioned spaces and greater awareness of the risks, has tended to reduce the number of fatalities resulting from heat waves over the last few years. But this form of adaptation, which depends on access to reliable electrical power, cannot be replicated everywhere. Across Asia, in the developing world, and everywhere families cannot afford air-conditioning, the impact of heat waves is deadly. In African and Asian villages without electricity there is no respite: the young, the elderly and those who because of illness are unable to cope with the heat, will die in greater numbers.
In the Middle East: across Iraq and Iran and over the Persian Gulf, summer temperatures are now regularly hitting 50°C or higher. The wealthy take refuge in the air-conditioned malls, cooled to less than half that temperature by electrical power generated by natural gas. But the region is home to a third of the world’s refugees, hundreds of thousands of whom live in tent cities. For these unfortunates, there is no escape from the insufferable heat.
For more information check out these sources:
 See : Analyses of the effects of Global change on human health and welfare and human systems. US Climate Change Science Program: Synthesis and Assessment product 4.6. September 2008. Washington DC.
 See : Heatwaves and health. CRED Crunch. Issue No. 46. Centre for Research on the Epidemiology of Disasters (CRED), Université catholique de Louvain, Brussels, Belgium. December 2016.
 See : Worst heatwaves in history: timeline. Accessed at //www.telegraph.co.uk/news/worldnews/northamerica/usa/8653974/Worst-heatwaves-in-history-timeline.html
 See : Heat waves and climate change: A science update from Climate Communication. Accessed at //www.climatecommunication.org/wp-content/uploads/2012/06/Heat_Waves_and_Climate_Change.pdf
 WMO statement on the state of the global climate in 2016. WMO -No. 1189. World Meteorological Organisation. Geneva, Switzerland.
 See : Deadly heat wave, nicknamed ‘Lucifer’ engulfs Europe. Accessed at //thinkprogress.org/europe-a-heat-wave-named-lucifer/?
 See: State of the climate in 2016, a 2017 report by the American Meteorological Society.
 See the article by Lugber G. and McGeehin M.: Climate change and extreme heat, in the American Journal of Preventive Medecine 35 (5): 429-435. 2008.
See : Heat waves and climate change: A science update from Climate Communication. Accessed at //www.climatecommunication.org/wp-content/uploads/2012/06/Heat_Waves_and_Climate_Change.pdf
 See the report of the US global change research program: USGCRP, 2017: Climate Science Special Report: Fourth National Climate Assessment, Volume I [Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart, and T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, 470 pp.
 See the 2016 report from the Centre for Research on the Epidemiology of Disasters (CRED) : Poverty & Death: Disaster mortality 1996-2015. Centre for Research on the Epidemiology of Disasters, Université catholique de Louvain, Brussels, Belgium.
See also: 2018–a year of climate extremes. //www.wri.org/blog/2018/12/2018-year-climate-extremes