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.”

���ܰ��DZ��’s most extreme heatwave so far may have killed between 17,000 and 25,000 people, according to an early estimate based on past deaths from heat in the region.

“These numbers are preliminary,” says at Indiana University. “But they highlight the need for rapid adaptation investments to avoid these impacts in the future.”

Callahan’s estimate is based on . “We’re taking data on temperature and mortality across Europe, and we are correlating how high temperatures relate to excess mortality rates,” says Callahan. “We then use that relationship to infer how a given heatwave affects mortality over a region like Europe.”

Callahan’s conclusion is that the heatwave in Europe from 22 to 28 June 2026 killed approximately 20,390 people, including 5210 in France, 4543 in Germany, 3163 in Spain, 2709 in Italy and 862 in the UK. These numbers are much higher than the direct counts announced so far, but this isn’t surprising because it takes time for data on deaths to be collected and analysed.

“This figure is a modelled estimate rather than a final count, and it will be some months before the true toll is confirmed, in part because heat rarely appears on a death certificate,” says at the University of Warwick in the UK.

For instance, on 28 June, the head of the World ��ҹ����1000���� Organization, Tedros Adhanom Ghebreyesus, said so far. This number is largely based on reporting around 1000 more deaths in the country than expected from 24 to 26 June.

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However, that statement made it clear that this number is based on a computerised death certificate system that is far from complete. It records 80 per cent of hospital deaths, 45 per cent of deaths in long-term care facilities and 25 per cent of deaths at home. “Mortality will consequently be higher than these initial figures suggest,” the statement said.

Even so, other experts think Callahan may have overestimated the numbers. “Twenty-thousand for a single week seems very large,” says at the University of Bristol in the UK. “We’d have to look into details of the modelling to be more sure.”

While Callahan’s method is sound, the main issue is that he used data from 2015 to 2019 to calculate the relationship between heat and deaths, says at Poznań University of Medical Sciences in Poland. People may now be less vulnerable due to ongoing adaptations, such as increased access to air conditioning, . Walkowiak’s back-of-the-envelope calculation is that if this is taken into account, the actual number of deaths would be around 15,000.

Callahan is sticking to his guns. “We don’t have very strong evidence that the relationship between temperature and mortality dramatically changed over time,” he says. “So it’s not obvious it’s different now than it was 10 years ago.”

“In general, we find that our sort of broader statistical estimates give higher numbers than direct reporting on the ground, because that direct reporting can often miss people who die from heat where it’s not obvious that heat was the cause,” he says.

On the flip side, Walkowiak says that Callahan hasn’t taken into account the fact that heatwaves of the same temperature are more deadly in early summer than in late summer. “In late summer, part of the especially vulnerable population is already long gone,” he says.

Mitchell also says the kind of approach used by Callahan also counts only the immediate deaths. There can be longer-term impacts, such as more deaths from domestic violence, suicides and kidney failure. “The impacts of heat on health vary a lot across timescales,” he says.

What matters most is avoiding further deaths as the planet warms further and heat becomes more extreme, says Nunes. “The signal is clear: heat is now the deadliest weather hazard we face, and the majority of these deaths are preventable,” she says. “We can now forecast these events with considerable accuracy; what we have not done is build the systems, across health, housing, social care and transport, for example, that translate an accurate forecast into actual protection. Adaptation is not keeping pace with the risk.”

A line that runs through Africa, Europe, Alaska and both poles divides Earth into two halves that reflect the same amount of light – and this newly discovered symmetry may play a critical role in the planet’s climate.

It was previously known that the northern and southern hemispheres have almost equal reflectivity, or albedo, but at the National Oceanic and Atmospheric Administration in the US and his colleagues have now uncovered a second line of symmetry along the 27° east and 153° west meridians.

The hemispheres separated by this line are nearly equal in three respects: their albedo in clear skies, the reflectivity of clouds and the fractions covered by ice-free oceans. This symmetry has persisted throughout 25 years of satellite observations analysed by Zhang and his colleagues.

At first, Zhang thought it must be a coincidence. “What convinced me that the east-west symmetry is not trivial are three features: its uniqueness, its persistence and what we call the triple symmetry feature,” he says. “Finding one division with equal total reflection might be expected. But finding a persistent, unique east-west division that also balances land-ocean distribution, clear-sky reflection and cloudy-sky reflection is much less trivial – especially given how variable and dynamic clouds are.”

While the east-west symmetry is centred near 27° east when averaged over the 25-year satellite record, in any individual year, the exact line of symmetry shifts slightly. The team found that these small year-to-year shifts are strongly related to the phase of the El Niño-Southern Oscillation (ENSO), a global climate phenomenon related to fluctuations in sea-surface temperatures in the Pacific Ocean.

“In other words, the symmetry may not simply be a geometric accident,” says Zhang. “It may be connected to one of the most important modes of climate variability on Earth. ENSO may act as a large-scale adjustment mechanism that helps keep the long-term east-west symmetry centred near 27° east.”

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at the Centre for International Climate Research in Oslo, Norway, who wasn’t involved in the study, says he doubted the discovery at first.

“I was a bit sceptical of an east-west symmetry separated at around 27 degrees east, which intuitively seems much less obvious than a separation at the equator, and I wondered if it could be a coincidence.”

However, Hodnebrog says he now agrees it is likely a “robust feature, and potentially another fascinating property of the Earth”.

The connection to ENSO may also be significant, says Hodnebrog. Unlike the north-south symmetry, which appears to be weakening due to the effects of climate change on sea ice and clouds, the east-west symmetry is currently stable, though models suggest it could weaken in future. “A potential future asymmetry could be an indication of changes in the atmospheric circulation,” he says.

at the University of New South Wales, Sydney, says there is a high potential that the east-west symmetry is a coincidence.

“Earth’s weather and climate communicate easily across longitudes,” says Jucker. “This is due to Earth’s rotation, which creates bands of circum-global easterly and westerly winds, and atmospheric perturbations preferentially propagating in the east-west direction as well.”

If there are mechanisms that maintain the east-west symmetry, it could have implications for geoengineering schemes, Zhang says. For example, attempts to increase the albedo of one hemisphere might be negated by a global-scale feedback loop.

“Before making confident claims about the effects of geoengineering, we need a stronger understanding of how clouds, circulation, precipitation and planetary reflectivity respond across the coupled Earth system,” says Zhang.