The heat waves we are experiencing now pose a serious threat to vulnerable groups such as the elderly, the sick and those in financial distress. The heat wave of 2003 was a bitter reminder of how devastating such events can be. Temperatures rose to 47.5 degrees Celsius in Europe during this time, leading to one of the most devastating natural disasters in recent history with an estimated death toll of between 45,000 and 70,000 in just a few weeks.
In addition to human losses, environmental and economic losses were also significant. Forests burned, crops in the fields dried up, city ambulances were operating at maximum capacity. Global financial losses amounted to approximately 13 billion US dollars. Despite this, the public is less aware of the risks of heatwaves than other extreme climate events.
That’s a problem, according to a study published in the journal Nature Communication. Heat waves like the one we saw in 2003 could become the new norm in years to come.
Combining epidemiology and climate modeling
Researchers from the ETH Zurich Institute for Environmental Solutions collaborated with an international team of epidemiologists on the research. Since 2013, they systematically collected data on daily deaths from extreme heat for 748 cities and communities in 47 countries in Europe, Southeast Asia, Latin America, the United States and Canada.
The researchers used this dataset to calculate the relationship between mean daily temperature and mortality for all 748 locations. From here they were able to determine the ideal temperature for each location where excessive mortality was lowest. For example, in Bangkok this value is 30 degrees Celsius, in Sao Paulo – 23, in Paris – 21 and in Zurich – 18 degrees Celsius.
Simulated physically reasonable extreme weather conditions
Every tenth above this ideal increases the extreme mortality rate. “Not all heat is created equal,” explains Samuel Luthi, a doctoral student under the supervision of David Bresch, lead author of the study and professor of weather and climate risk. “The same temperature has an entirely different effect on heat-related excess mortality in the population of Athens and Zurich.”
It depends not only on temperature, but also on physiology (climatisation), behavior (long sleep in the middle of the day), urban planning (green spaces vs. concrete), demographics of the population and the local health system.
Using this ideal value, the researchers calculated how extreme mortality rates would develop if global average temperature increases were 0.7 degrees (2000 values), 1.2 degrees (2020 values), 1.5 and 2 degrees. They used five particularly powerful climate models known as SMILE (large collection of initial conditions with a single model).
“We ran the same model up to 84 times with slightly different weather conditions on each lap. This gave us many possible weather systems that could occur if there is a certain amount of CO2 in the atmosphere,” explains Luthi. The researchers then combined this data with an epidemiological model to calculate temperature-related deaths.
Previous estimates of heat-related mortality were mostly based on calculations using a single climate model over a period of time.
“Our method allows us to quantify the extremes in the climate system much more efficiently and reduce the uncertainties arising from the characteristics of certain models.” Using supercomputers, Luthi calculated the effects of physically probable weather events on heat-related deaths for over 7,000 years. The size of the corresponding data set exceeds 1 terabyte.
15 percent of deaths are due to heat
The results show that the risk of heatwaves with high death rates has already increased significantly over the past 20 years. “Excessive mortality rates in a hot summer like 2003 were previously considered an extraordinary event in a century. This is now every 10 to 20 years, or every two to five years in many places in a 2°C warmer world, Lüthi said. He says we are waiting for it to happen.
Heat-related mortality rates, which are unlikely in 2000 (every 500 years), will occur 14 times in 100 years under the 2 degree scenario. Assuming an inability to adapt to the heat, the odds of dying in these extreme heat waves will increase 69 times.
Regions particularly at increased risk of heatwaves include the US Gulf and Atlantic coasts, the Pacific coast of Latin America, the Middle East, Southeast Asia and the Mediterranean region. Even in temperate climate scenarios, hot summers in these regions can account for ten percent of heat-related deaths in the country. Paris was particularly affected by the heat of 2003.
At that time, the figure was around five to seven percent; This means that in the French metropolis alone, the heatwave has caused about 2,700 people to die prematurely from dehydration, heat stroke and heart attack.
“Our calculations suggest that 15 percent of future deaths in Paris could be due to heat,” Lüthi says. Europe, especially Southern Europe, is one of the hot spots. Two factors are at work here: Temperatures here are rising at twice the rate of the global average, and the population is disproportionately older.
An alarming possibility
“The results scared me,” says the 30-year-old climate scientist. “While working on the research, I have always tried to look beyond the numbers and see the real lives of the people affected by the changes. This is worrying.”
He particularly points out that the assumptions underlying the modeling are actually conservative. The study suggests that the global average temperature will rise by a maximum of 1.5 to 2 degrees Celsius, but with greenhouse gas emissions at current levels, that figure will be 2.6 degrees Celsius.
Future scenarios, on the other hand, do not take into account the projected population growth, migration to cities and increasing numbers of elderly people; These are all factors that will further increase the extreme death rate due to heat. The study also lacked epidemiological data on Africa and India, hit hard by the climate crisis and poverty.
The results highlight the urgency of action, according to the researchers. Luthi argues that the most important step, at least to stem the escalating heatwaves, is to phase out fossil fuels as soon as possible. The study shows that although the risk is already high at 1.5 degrees, it is significantly lower than at 2 degrees. But society can also partially adapt to higher temperatures to mitigate the impact of future heatwaves. “We must now prepare for and manage the inevitable, avoiding the unmanageable at all costs,” advises Luthi. Source
Source: Port Altele
