What is a heatwave?
It’s hot. Very hot. Hotter than it should be. It’s not for too long, just a few days or weeks, but everyone feels it, and everyone talks about it. We don’t give it fancy names, like we do with hurricanes, but you hear about it in the news. Or not.
The problem with heatwaves is that they are very relative. It’s not the same to register 30 ºC in the summer or in the winter. And it’s not the same to register 30 ºC in Greenland or in the Middle East. Each place has its average temperature for each time of the year. We call it a heatwave when a particular region goes well above that average for a number of days. How much above it, and for how long, varies from region to region. In many parts of the world, these events are already increasing in frequency, duration and intensity, and will increase even more as a result of the climate crisis.
The silent killer
Unlike more spectacular climate impacts such as tropical storms, floods or wildfires, heatwaves come up without a bang. For most people, heatwave days are just annoyingly hot and media sometimes even portrays them as something nice. But, actually, heatwaves are as dangerous a climate impact as it gets.
According to a recent academic study, heatwaves killed at least 157,000 people between 2000 and 2020 (only storms are deadlier, with around 200,000 victims). However, the authors of the report warn that this figure is very likely underestimated: many countries don’t monitor heatwaves and some times don’t even have a definition for them. To illustrate that point, only 6.5% of those casualties were registered in Asia, Africa, the Caribbean and South and Central America, despite those regions concentrating 85% of the global population.
Heat can be behind a number of health conditions. The most concerning is heat stroke, which occurs when the body is too hot and loses its ability to cool down. Children, the elderly and low-income communities are more vulnerable to heat stroke, as are people with chronic diseases, pregnant women and outdoor workers. The poorer a community is, the less access to cooling it has, which exacerbates inequality and injustice. Heatstroke is more likely in high humidity conditions.
More than just heat strokes
The dangers of heatwaves, however, go way beyond heat stroke. High temperatures are associated with lower air quality, which causes and aggravates respiratory diseases such as asthma. They are also related to cardiovascular and kidney diseases.
Extreme temperatures affect agriculture, stunting plant growth or directly killing them. Livestock is also affected, as animals can also see their growth, milk production and reproduction rates reduced. These impacts disproportionately affect communities who depend on agriculture for survival and don’t have any other social safety nets, which increases climate injustice. Heatwaves also affect infrastructure such as airports, roads and bridges, and any economic activity that requires outdoor work.
Is it hotter?
Heatwaves are a statistical occurence. They are relative to the average conditions, so by definition we can find it in any time and any place in history. But that doesn’t change the fact that climate change is making them worse in absolute and relative terms. Or, in other words: yes, it’s hotter than ever, more often, and yes, it will get hotter. Scientists have concluded that it is virtually certain that global heating drives that increase in the duration and intensity of heatwaves at a global level. That means, in climate science terms, above 99% certainty.
Heatwaves happen when a mass of high-pressure air remains stationary (still) for long enough to get warmed up by the sun. Greenhouse gases such as CO2 have the capacity to absorb heat, so a stationary mass of air will get warmer in the same amount of time if it contains a higher concentration of these gases. These phenomena are geographically uneven and their likelihood at a specific location depends on many factors, such as orography, tree cover, aerosol pollution, soil moisture or distance to the sea.
According to the IPCC, the average temperature of the extremely hot days in land will increase by 3ºC if we contain global warming under 1.5ºC, and by 4ºC if we stay under 2ºC. Keep in mind that this is an average! Some areas are already becoming uninhabitable during heat waves within this century.
The climate footprint
Heatwaves are one of the deadliest expressions of the climate crisis. We are seeing how they increase in frequency and intensity as the concentration of greenhouse gases mounts. And it is the greed of the fossil fuel industries and its allies what is pushing that increase. Let us retrace their steps.
Global heating is caused by an increase in the concentration of greenhouse gases, mostly (but not only) CO2 and CH4. These are found naturally in the atmosphere, but since we started massively burning fossil fuels, the concentration has been growing exponentially.
The increase in concentration of CO2 is linked to fossil fuels. There isn’t any other possible source (not volcanos, not clouds, not solar cycles, nothing). CH4 is also massively linked to fossil fuels and land use change. Studies and data have widely proven that: the debate is over.
The coal, oil and gas industries have massively profited from it and they continue to profit from an economic model that forces people to use fossil fuels. Reports have proven that they knew the damage they were causing since at least the 1970s, and that, instead of abandoning their business model, they actively worked to disinform the public. They still do. We keep burning fossil fuels because they choose (and they chose then) to use their power for that purpose.
But even if we cannot stop heatwaves completely, we can stop the fossil fuels industry. People around the world have been fighting to keep coal, oil and gas in the ground, to cut the financial flows that allow this industry to still exist and to push for a more equitable and clean future. If you haven’t yet, join us!