Heat, drought, fire, hunger: studies predict ‘fierce’ conditions as ecosystems evolve

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The hot weather hit India earlier than usual: temperatures of 44°C in April almost certainly dashed hopes for a bountiful wheat harvest in the subcontinent. Even before the end of the month, desperate citizens were yearning for dust storms to darken the skies and bring down the temperature.

Welcome to a modified future. Four new studies, each quite distinct, seem to confirm that large-scale heat, drought and hunger can only get worse as global temperatures rise. One of the most disturbing is a prediction that fierce summer temperatures and prolonged droughts are increasingly likely to occur simultaneously.

Heat and drought increase the risk of forest fires. A second study looked at the impact of wildfires — in 2021, those incinerated vast swathes of Siberia and the western United States — to conclude that they are actually intensifying Arctic warming: the ash of “brown carbon” from burning forests was probably double that of burning fossil fuels. More global warming means more heat and drought, which means more fire risk, which means even more warming.

A third research team has examined the combined impact of global warming and the constraints of modern agriculture to confirm that the global insect population toll is accelerating: the two factors combined have almost halved the number of insects. insects on agricultural land and reduces the number of species. in the sites examined by more than a quarter.

Biodiversity is a measure of the health of the planet: the richer and more vigorous the natural life, the better for everyone. The richest land habitats have always been large forests. But when these are degraded – by drought, by forest fire, by the axe, the farmer, the miner or the rancher – the consequences go far beyond the release of even more gas to greenhouse effect to further increase temperatures. The loss of forests, according to a fourth study, can seriously increase local temperatures, change wind patterns, change the reflectivity of local land surfaces, interfere with cloud composition and interrupt regional precipitation.

Which brings us neatly back to the challenge of heat and dryness. European scientists began by defining their double trouble as summers when the average temperature was more than 90% of the years between 1950 and 1980, and the precipitation was less than nine tenths of the same three decades.

Then, after counting the times when extreme heat and drought were recorded simultaneously, they simulated a future at least 2°C warmer than in pre-industrial times. They report in the journal Nature Climate Change that between 1950 and 1980, heat and drought only occurred together 3% of the time. In the warmer world of tomorrow, such double events become four times more likely.

How this plays out largely depends on local rainfall patterns: more heat can often mean heavier rainfall as well. For central Europe, even with more precipitation, this could mean simultaneous heat and drought every 10 years or, if conditions become drier, every four years. Central North America could be heading for such simultaneous events every six years in the worst case, every nine years if precipitation increases.

“Climate change may alter the distribution of precipitation in some regions,” said lead author Emanuele Bevacqua of the Helmholtz Center for Environmental Research in Leipzig, Germany. “Precipitation patterns depend on atmospheric circulation, which determines regional weather dynamics through numerous interactions over large parts of the globe.”

One such interaction has been at work in the Arctic, which is warming three times faster than the rest of the planet. Research in the journal One Earth clearly shows that wildfires far to the south contribute powerfully to this effect by filling the atmosphere with particles that absorb radiation and raise atmospheric temperatures.

In 2017, researchers aboard a Chinese icebreaker examined aerosols in the polar atmosphere. They concluded that brown carbon was an important factor and that the impact of brown carbon from blazing biomass – forest timber, foliage, undergrowth and peat – was responsible for at least twice as much warming as carbon. brown from fossil fuel exhaust and smokestacks. In the Arctic, the impact is almost one-third that of black carbon from burning fossil fuels. And, of course, more brown carbon means more warming, in a feedback loop.

“Increasing brown carbon aerosols will lead to global or regional warming, which increases the likelihood and frequency of wildfires,” said lead author Pingqing Fu of Tianjin University. “Increased wildfires will emit more brown carbon aerosols, further heating the earth, making wildfires more frequent.”

Global warming, too, is now believed to make insects less common. According to extensive research from 2017, insects “create the biological basis of all terrestrial ecosystems. They recycle nutrients, pollinate plants, disperse seeds, maintain soil structure and fertility, control populations of other organisms, and provide a “major food source” for other creatures. Life cannot function without them.

British scientists report in the journal Nature that they have reviewed 20 years of data on insect diversity and abundance, gathered in more than 750,000 records of nearly 18,000 species of insects – beetles, butterflies and moths of wasps, bees, ants, flies, grasshoppers, dragonflies, damselflies, and so on — between 1992 and 2012. They read 264 published studies from more than 6,000 sampled locations, in nearly every habitat in the world. And then they made comparisons.

In places where agriculture was most intensive and where the climate had also warmed considerably, the number of insects had dropped by 49% and the number of different species was 29% lower than in places still covered. of natural plants and without any significant signal recorded. warming up. In areas where agriculture was less intensive, but increasingly warm, the surviving natural habitat cushioned the losses. Where three quarters of the land was more or less wild, insect abundance was down only 7%; where the natural cover was only 25%, the fall was 63%.

“Our results underscore the urgency of action to preserve natural habitats, slow the expansion of high-intensity agriculture and reduce emissions to mitigate climate change,” said study leader Charlie Outhwaite. from University College London. “The loss of insect populations could be harmful not only to the natural environment, where insects often play a key role in ecosystems, but it could also harm human health and food security, especially with pollinator losses.

But forests do more than simply support animal life and store carbon: research by American scientists in the journal Frontiers in Forests and Climate Change now shows this very clearly. The foliage sends aromatic chemicals (scientists call them biogenic volatile organic compounds) into the atmosphere, where they play a role in cloud formation. They increase the concentration of water droplets in clouds, making them brighter so they reflect more energy back into space. If the forest is reduced, so are the cooling effects of the clouds above. And that’s not the only way forests help moderate local temperatures.

Rainforests help provide their own rainfall. “Once you cut the trees, you remove the pump that transfers water from the surface to the atmosphere, which affects downwind rainfall,” said co-author Louis Verchot of the International Center for tropical agriculture in Colombia.

Forests even control the wind, with tall canopies of trees carrying heat away from the surface and into the atmosphere. “Imagine a smooth surface, the wind is flowing straight, and the heat from the sun is going straight down. But with the canopy and its surface like a crown of broccoli, those air particles bounce around and the heat is dispersed,” said first author Deborah Lawrence of the University of Virginia.

“If we seek overall climate benefits, both local and global, we should work very hard to grow and nurture forests in the tropics and seek to sustainably manage forests outside the tropics.”