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Insects face calamitous habitat loss

23 May 2018
Photo of Tattoo Jep hornets
Tattoo Jep hornets: almost half the world’s insects could face habitat loss. (Courtesy: Kalamazadkhan CC BY-SA 4.0 via Wikimedia Commons)

Habitat loss may soon mean half the world’s insects, and many plants and animals as well, could find themselves without their familiar home ranges.

Right now, climate scientists warn, global planetary temperatures are on course to rise 3.2 °C above the average for most of human history. They have already risen by about 1 °C in the last 100 years.

And if they do, then 49% of insects, 44% of plants and 26% of vertebrates could lose more than half of their ranges.

If the 195 nations that agreed in Paris in 2015 to take steps to restrict global warming to a target of 1.5 °C keep their pledges, only 6% of insects, 8% of plants and 4% of vertebrates will experience severe reductions in their ranges. Even half a degree makes a huge difference.

“Insects are particularly sensitive to climate change. At 2 °C warming, 18% of the 31,000 insects we studied are projected to lose more than half their range. This is reduced to 6% at 1.5 °C. But even at 1.5 °C, some species lose larger proportions of their range,” said Rachel Warren of the University of East Anglia, who led the study.

“The current global warming trajectory, if countries meet their international pledges to reduce CO2, is around 3 °C. In this case, almost 50% of insects would lose half their range.”

These figures are projections based on a sample of animal and plant studies: the sample is however one of the largest undertaken.

Professor Warren and colleagues from Australia report in the journal Science that they studied data involving 34,000 insects and other invertebrates, 8000 birds, 1800 reptiles, 1000 amphibians and 71,000 plants, and took into account the capacity of each species to move to new habitat as the world warms.

Pattern of alarm

Such studies build on evidence assembled piecemeal, sometimes over many decades, about the impact of humanity on its fellow citizens of the planet. This evidence confirms a consistent pattern of alarm.

Researchers have established repeatedly that ecosystems already under pressure from human invasion are made more vulnerable by global warmingand climate change. More precisely, German scientists have established that the sheer numbers of insects that used to make a living around European farmlands have fallen dramatically, and even those insects that seem to survive almost everywhere could be under threat.

The new study found that a small number of species will extend their range in a warming world. Most will not. Many will have fewer places to go.

“This is really important because insects are vital to ecosystems and for humans,” said Professor Warren. “They pollinate crops and flowers, they provide food for higher-level organisms, they break down detritus, they maintain a balance in ecosystems by eating the leaves of plants, and they help recycle nutrients in the soil.”

Options narrowing

And, writing separately in the same journalGuy Midgley of Stellenbosch University in South Africa warned that the options for humanity are becoming severely restricted.

Humans depend on plants, insects and other animals to deliver water quality, soil conservation, flood prevention, crop pollination and natural pest control. All this is now threatened, not just by the clearing of forests and the growth of the cities, but by the profligate use of fossil fuels which release greenhouse gases such as carbon dioxide into the atmosphere, to drive global warming.

Researchers know, through a detailed study of the geological past, what higher concentrations of carbon dioxide can do to global climate. “There is way too much debate about the issue of climate change and whether or not it is real. What we really need to be doing is debating how we solve this problem,” said Professor Midgley.

“Those very high CO2 concentrations could well change the ecosystems of the world irrevocably. If we increase CO2 to over a thousand parts per million, over the next 50 to 60 years, which we are quite capable of doing if we fail to reduce our dependence on fossil fuels, we could literally move the world back 20 to 30 million years in the space of a century. It is like moving ecosystems backwards in time at the speed of light.”

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