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A study points out that the number of deaths attributable to low temperatures in Europe is ten times higher, but researchers warn: climate change will reverse this relationship.
The cold wave that hit Brazil last week made civil society mobilize to help the homeless population, vulnerable to the most dramatic consequences of the drastic drop in temperatures. It snowed in dozens of cities in southern Brazil, there was frost in several other states, and the temperature was negative in the capital of São Paulo, in an atypical scenario, even in winter, for a tropical region. The scenes of Brazilian cities under a thin layer of ice contrast with the records of fires and extremely high temperatures in North America. Neither Brazil is prepared for a cold at this level, nor Canada for a melting heat. Nevertheless, the scenes spark public debate about the planet's emergency climate situation and beg the question: which is more dangerous, cold or extreme heat?
A study published in July in The Lancet Planetary Health, based on mortality data from 147 regions in 16 European countries (including Spain ), showed that deaths attributable to temperatures — both cold and hot — rose from 7% of total deaths in Europe between 1998 and 2012. Altogether, the survey estimates a staggering four million deaths related to temperature in these 15 years (about 270,000 deaths per year).
Currently, heat and cold do not have the same impact on mortality: low temperatures are related to 10 times more deaths than heat. But the report's authors warn that the climate crisis will change that situation. Cold-related deaths will decrease, while heat-related deaths will increase. And suppose humanity continues to overheat the Earth with its greenhouse gases at the same rate as it has done so far. In that case, the result will not be optimistic: the increase in heat deaths at the end of this century will outweigh the reduction in cold-related deaths in Europe.
Èrica Martínez Solanas, one of the article's authors and a researcher at the ISGlobal Climate and Health Program, explains that "in the short term, a reduction in deaths from heat is expected." However, the situation will change from the middle of this century: "There will be a tipping point of deaths attributable to heat, which will cause there to be more heat-related mortality than cold."
Martínez points out that some studies point to a balance and even a positive effect, about deaths, of the warming process that the planet is going through - this is one of the arguments used by defenders of fossil fuels and by those who do not wants drastic policies against climate change to be adopted. But the researcher maintains that “everything depends on the time horizon used.” In other words, if the increase in temperatures predicted in the different scenarios for the end of the century is taken into account, this positive effect on mortality is diluted, according to his study.
The authors made projections for several scenarios: a very optimistic one, in which greenhouse gas emissions would be reduced at high speed, in line with the Paris Agreement(which would cause, by the end of the century, the average temperature increase in Europe to be 1.67 degrees about pre-industrial levels); another that predicts a minor reduction in emissions and a 2.89-degree rise in temperature in 2100; and the last scenario in which emissions would continue as they are now, causing the average temperature to rise by 4.54 degrees. The study highlights that, by the end of the century, "it is expected that the increase in the fraction [of mortality] attributable to heat will outweigh the reduction in that attributable to cold, especially in scenarios that consider little or no mitigation" that is, in those where the increase in average temperature exceeds 2.89 degrees in Europe.
If the data are analyzed by region, the study points to a homogeneous decrease in deaths attributable to the cold across Europe in the coming decades due to climate change. However, this is not the case for heat deaths: a more significant increase in the Mediterranean area.
In the case of Spain, for example, deaths attributed to temperatures in the study for the period analyzed (1998-2012) are 5.32% of the total; 4.31% related to cold and 1.01% to heat. At the end of the century, in the most pessimistic scenario of global warming, deaths would reach 5.19%. Thus, those related to heat would rise to 7.37% of the total, while those about cold would fall 2.18%.
Hot and cold waves
To carry out their calculations, the researchers first established a “minimum mortality temperature,” which is “different for each region and country,” explains Martínez, who shares the principal authorship of the article with Marcos Quijal, also a researcher at ISGlobal, a promoted center by the La Caixa Foundation. Within Spain, for example, this minimum mortality temperature for the 15 years analyzed was 20.5 degrees in Catalonia, 22.8 in Madrid, and 23.9 in Andalusia. From there, the researchers calculate the excess mortality attributable to heat and cold.
But, as explained by Julio Díaz, from the National School of Health at the Carlos III Health Institute, deaths attributable to high or low temperatures are not the same thing as deaths caused by a wave of heat or cold. In this case, the situation is reversed: in Europe, many more people die from heat waves than from cold weather. In Spain, for example, 1,050 people die each year from cold waves and 1,380 from heat, recalls Díaz, who is not one of the authors of the article published in The Lancet, but is one of the country's leading experts in health and environment. Environment. This is simply because heatwaves — periods of more than three days with temperatures above the usual maximum — are more numerous than cold.
However, if only the minimum mortality temperature is used as a reference, the days when the thermometers are below this point are much more numerous than those above, says Díaz.
The health effects
But beyond the numerical ratio, why is heat more dangerous to health than cold? Díaz explains that the cold interacts with infectious diseases that aren't present in the summer months. These are diseases, respiratory, transmitted, and aggravated in winter, such as flu or pneumonia.
That doesn't mean that heat doesn't impact health either. María Neira, director of the Department of Public Health and Environment of the World Health Organization (WHO), points out that highly high temperatures cause an aggravation of respiratory and cardiovascular diseases, “especially in the elderly.” In addition, they provide an increase in ozone, which has adverse effects on human health, and pollen and other allergens, which cause more asthma attacks.
Neira recalls that studies predict an increase, in the coming decades, in mortality related to heat and other extreme phenomena linked to global warmings — such as floods or droughts that put food security at risk in many areas of the planet. And warns: "In no case will the damage to health caused by climate change be compensated by the reduction of mortality related to the cold."