These are some of the unexpected impacts of heatwaves

Record heatwaves in 2022 have affected millions of people across Asia, America, Europe, North Africa, Australia and the Pacific islands.

And extreme weather events including heatwaves are forecast to become more frequent and intense as the warming atmosphere drives climate change.

Wildfires and melting airport runways are the kind of impacts we might expect from heatwaves.

But extreme heat can also have unexpected consequences.

When the temperature rises, so does hate speech. Scientists in Germany found “marked increases” in hate tweets on Twitter of up to 22% at extremely hot temperatures of between 42°C to 45°C. Very cold temperatures of -6°C to -3°C also correlated with a 12·5% rise in hate tweets.

Hate speech online is a potential channel through which “temperature alters interpersonal conflict and societal aggression”, say the researchers at Potsdam Institute for Climate Impact Research.

Their study, published in The Lancet Planetary Health, used a dataset of four billion tweets from 773 cities across the United States between May 2014 and May 2020.

China experienced its worst heatwave and drought for 60 years this summer, which reduced water supply for hydroelectricity, the country’s second biggest source of power.

The country responded by mining and importing more coal, according to Canadian news channel CTV News.

The record heatwave dried up parts of China’s Yangtze River, affecting water supply for tens of thousands of people. Surging demand for air conditioning also put pressure on the electricity grid. In the first two weeks of August, China’s power plants burned 15% more coal than a year ago.

Record high temperatures in California on the US west coast are especially affecting Latino communities.

Many Latino immigrants work outdoors in jobs including farming and gardening, so are vulnerable to extreme heat, explains US news programme Eyewitness News. There are 20 times more heat-related deaths among farm workers than among civilian US workers, data shows.

Latino immigrants can also have pre-existing medical conditions and live in low-income communities that are often the hottest parts of cities because of a lack of green spaces, among other factors. These areas suffer from a heating phenomenon known as the “urban heat island effect”.

Separate research in the UK has found that people of colour are four times more likely than white people to live in neighbourhoods most vulnerable to extreme heat.

Record heatwaves and drought are causing trees to shed their leaves prematurely to save water and energy.

This ‘false autumn’ has arrived two to three months early in the UK, which reached record temperatures above 40°C this summer and had its driest July for 20 years.

Nature conservation charity Devon Wildlife Trust, which has seen false autumn signs across its 60 nature reserves, said prematurely brown leaves were a sign that “a tree is stressed and attempting to conserve water”.

Berries are also ripening early to help plants and trees save water, says UK woodland conservation charity, The Woodland Trust.

The growing number and intensity of wildfires in the US is exposing millions of Americans to air pollution, scientists say.

Over the last decade, there has been a 27-fold increase in the number of people in the US exposed to unhealthy levels of polluting particles in the air, a new study finds.

In 2020 alone, nearly 25 million people were exposed to high levels of smoke pollutants from wildfires for at least one day a year, reports the study published by the American Chemical Society.

Air pollution is growing fastest for higher income populations and mostly Hispanic populations, the researchers add.

In France, heatwaves have been linked with weight loss in heart failure patients, suggesting their condition is getting worse.

Weight loss in heart failure patients can lead to low blood pressure and kidney failure, which is potentially fatal, explains a report published in the European Society of Cardiology journal, ESC Heart Failure.

In hot weather, heart failure patients can lose more fluids than healthy people because of water pills known as diuretics that they take to eliminate waste from the body.

The research found a “very strong” link between temperature and body weight in 1,420 patients with chronic heart failure studied across two heatwaves in France in July 2019.

Emissions of carbon dioxide and other greenhouse gases caused by human activity are driving global warming and mean heat extremes are now three times more frequent, climate scientists say.

Countries have pledged to cut emissions to keep global temperature rises well below 2°C and below 1.5°C if possible, as agreed in the United Nations Paris Agreement signed in 2015.

Efforts are also underway globally to adapt places and infrastructure to climate change.

Cities are planting more trees and greenery to help them keep cool in heatwaves, for example.

Sydney, Australia, plans to plant five million more trees by 2030 and Seville, Spain, which regularly hits temperatures of 40°C in the summer months, is planting 5,000 trees a year. Seville is also the world’s first city to categorize heatwaves in a similar way to the ranking of hurricanes and typhoons in the US and Asia, according to Bloomberg.