Global warming-fuelled heat and drought is already hitting yields of maize, wheat and soybeans to the tune of $20 billion a year, a study has estimated. This could rise eightfold, to more than $160 billion by 2100, unless we slash emissions.

While the financial losses will be greatest for big producers such as the US, the impacts will be felt most in the lowest-income countries, where ,��������� at the International Institute for Applied Systems Analysis (IIASA) in Austria. “If you look at the least-developed countries in Africa, the impact is much bigger.” This could lead to social unrest and increased migration, she warns.

There is great uncertainty about these kinds of projections, not least because so much depends on how farmers respond and adapt to a continually changing climate, for instance, by switching to different crops or adopting irrigation where it is possible. In fact, the whole point of this study is to raise awareness and encourage adaptation, to help ensure these projections turn out to be overestimates, says team member , also at IIASA. “This is the entire mission of climate scientists: we make these cases for people to react, so our projections turn out to be wrong.”

The researchers started by gathering data on the yields per country of maize, wheat and soya from the UN Food and Agriculture Organization (FAO). Next, they took past climate data and calculated the drought level, using a standard approach that estimates soil moisture levels from rainfall and evaporation levels.

Past heat extremes and drought levels were then compared with the yields from 1974 to 2004 to estimate the impact of heat and drought. They then used these statistical correlations to estimate crop losses from 2007 to 2019. Their results suggest that increases in heat extremes and drought have caused a 3.5 per cent decline in yields relative to the 1974 to 2004 baseline. “Three per cent or so might not sound like much, but this is a major impact [on] the global food market, which regionally can trigger a severe crisis,” says Kornhuber.

The researchers then calculated the economic losses, based on FAO data showing how much farmers would have been paid for their produce at the time. Finally, they used the same approach to project future losses in several different emissions scenarios, assuming that some adaptation takes place.

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In a high-emissions scenario, known as SSP3-7.0, global yields will fall by around 35 per cent by 2100, with annual losses rising to more than $161 billion. “The production losses caused by heat and drought are around 855 million tonnes a year,” says Hwong, who presented the results at a meeting of the European Geosciences Union in Vienna in May. “I think that is equivalent to what around 2 billion people consume over a year.”

This could be an underestimate of the full impact of climate change for a number of reasons: it’s just three crops, and it doesn’t include flood, storm or rain damage, or the possibility that shortages could lead to big price increases, as is already happening with some other crops such as coffee and cacao.

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at Columbia University in New York says the study’s reliance on the statistical relationships between yield losses and extreme heat and drought could result in it overestimating the impacts by 2100. “Statistical yield models are great for explaining what’s happening now, and in the near past [or] future, but they are inherently unreliable when pushed into vastly different environmental regimes, such as high-emission climate scenarios by the end of the century.” Computer models of how plants are affected by rising CO2 and temperatures are better for projecting what will happen by the end of the century, he says.

at the University of Queensland, Australia, makes the same point. “Although models are not perfect, they are better suited for this type of extrapolation.” However, her team recently released a , which hasn’t been peer-reviewed, showing that two widely used models for wheat make large errors and are especially poor at forecasting the combined effects of extreme heat and drought.

But Kornhuber has defended his team’s use of statistical methods. “The models are remarkable tools, but some of the validation papers have suggested that they might not be super responsive to extremes,” he says. “In our project, extremes were the main focus, so we decided to establish these relationships directly through statistics.”

A heatwave in May set monthly temperature records across Europe; a heatwave in June became the hottest ever observed in western Europe. Now, in July, yet another heatwave is developing. Just 50 years ago, the June heatwave would have been virtually impossible. But global warming is making heatwaves more frequent, longer and more intense.

Worldwide, heat is the deadliest type of weather, killing more than each year. The number will increase, since even if we reached net zero tomorrow, the carbon dioxide we have already emitted will keep raising temperatures.

“This is just the start,” says at University College London. “Things are unfolding in a very, very major way now, because this isn’t just about it [being] too hot in London, and the long-term effects are going to be savage.”

Outside the tropics, the time of the year in which temperatures above 32°C occur has lengthened by 12 days in the past half-century. In Europe, the fastest-warming continent, the season of strong heat stress now starts on average in June and continues until almost September. Sometimes, like this year, it starts in May.

That increases people’s exposure to hot days and heatwaves. Parts of North America, Europe, South America and Africa now experience up to 50 more days of strong heat stress compared with the 1970s.

“If you’ve got heatwaves that last longer, and then you’ve got more heatwaves, people are going to be in that raised physiological state for longer,” says Neil Maxwell at the University of Brighton, UK. “That can lead to greater inflammatory marker responses, and that ultimately puts a greater stress upon individuals.”

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Strong heat stress almost never occurred at night before 1998. But now, nighttime temperatures in western Europe and other places are increasing at of global warming as a whole.

A drop in body temperature triggers sleep. If the environment is too hot, it is harder to fall asleep, as well as to enter a state of deep sleep. And loss of sleep over several nights in a row can hinder reaction time and boost anxiety and stress.

“If you don’t get cooling periods at night, which we define in this country as less than 20°C at night, sustained temperatures without cooling have worse impacts,” says Montgomery.

The hottest summer ever seen led to apocalyptic scenes in Europe in 2022. Wildfires broke out in France, Portugal and Spain. Italy’s longest river, the Po, ran dry in places, and wrecks of Nazi ships full of explosives were discovered as the Danube fell to record lows. In the UK, temperatures exceeded 40°C (104°F) for the first time.

More than 60,000 people died because of these baking temperatures. The highest mortality rates were in Mediterranean countries, which had some of the biggest temperature anomalies, with temperatures reaching higher than 40°C in Italy, Greece and Spain. These countries also have some of the , whose bodies aren’t as resilient to heat and who are more likely to have chronic illnesses.

“You also get inflammatory responses from heat, so heat exposure in itself triggers all sorts of bad biology in your body, basically, that is directly harmful… and in particular in people with diseases,” says Montgomery.

The frequency of a heat stress day followed by a tropical night of at least 20°C has increased 73 per cent in Europe since the 1970s. These are called “compound events” because the body isn’t able to cool down and recover at night, compounding the heat stress.

Europe has also seen prolonged periods of heat stress become more common. And Africa is now almost three times more likely to suffer hot spells lasting three-quarters of the year or more.

Leaders like US President Donald Trump have made pledges to plant millions of trees while increasing CO2 emissions. But in the case of urban heat, trees can make a big difference. They create areas of shade, and they also draw moisture from the soil, which then evaporates from their leaves, cooling the environment. Neighbourhoods with tree canopies can be as much as than similar places.

But although many cities have started planting trees to deal with heat, a recent found that many still have swathes of territory below the 30 per cent canopy cover that can reduce dangerous heat island effects. More than 90 per cent of the buildings in Paris and London fall below this threshold.

The heatwave that swept Europe last week saw many temperature records broken, leading people to ask if extraordinary June heat is the “new normal”. Unfortunately, the truth is that we are never going to have normal in our lifetimes again – just ever more extreme heat.

Climate scientists are continually warning of the need to prepare for hotter heatwaves, worse droughts, more flooding and rising seas. During heatwaves like the one just passed, the hottest and most humid ever seen in Europe, they might even get a little media coverage. But then the weather cools, the news agenda moves on and nothing is ever done.

We are currently on course for average global surface temperatures to rise by between 2.1°C and 3.3°C by 2100, and possibly even more. Even these alarming numbers are a little misleading because the oceans that cover most of the planet don’t warm as fast as the land. Average land temperatures are therefore going to go up by a lot more than the above numbers imply.

But what really matters to us is extreme weather, not the average. The projections for future extremes are already dire, and there are reasons to think that we are in for extremes even greater than those currently projected for a given level of warming. With uncertainties over the survival of the vital AMOC ocean current and the risk of a major glacier collapse, the only thing we really do know is that we must prepare for conditions far worse than Europe has just experienced.

We are on course for average global surface temperatures to rise by between 2.1°C and 3.3°C

It is possible to get through even worse heatwaves if all your infrastructure and systems are geared up to cope, but for most countries, this isn’t the case. The fact is, the world is changing fast and we need to change just about every aspect of our lives to adapt – our homes and offices, factories and schools, cars and trains, farms and gardens, and so on. But it isn’t happening. One day, after the tragic deaths grow too great to bear, we will ask why we did nothing to prevent them.