Climate mitigation pledges leave half of world’s insects at risk

If nations meet their current emissions reduction targets under the Paris Agreement, the resulting warming will sharply curtail the environment suitable for roughly half the world’s species of insects, a new analysis shows. Insect groups that pollinate flowering plants, on which much of agriculture depends, are at especially high risk.

The new study, published 17 May in Science, is the most extensive look yet at the projected effects of different levels of warming on species worldwide1. Researchers from the University of East Anglia in the UK and James Cook University in Australia analyzed the range maps of 115,000 species, including 71,000 species of plants, 31,000 insects, 8,000 birds, 1,700 mammals, 1,800 reptiles, and 1,000 amphibians.

They then calculated how those range maps might change in the future by outlining climatically suitable range for each species under different levels of warming, taking into account the ability of species to disperse to more favorable locations as the climate shifts.

“We measured the risks to biodiversity by counting the number of species projected to lose more than half their geographic range due to climate change,” lead author Rachel Warren of the University of East Anglia said in a press release. When a species’ geographic range shrinks, it becomes more vulnerable to extinction.

If countries meet their current pledges under the Paris Agreement and make no further emissions cuts, this is likely to lead to about 3.2 °C of warming (compared to pre-industrial temperatures) by the year 2100. Under 3.2 °C of warming, 49% of insects, 44% of plants, and 26% of vertebrate species would lose half their geographic range.

“This is really important because insects are vital to ecosystems and for humans,” Warren said. “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.”

If, instead, the nations of the world meet the overall goal of the Paris Agreement and hold warming to 2 °C then 18% of insects, 16% of plants, and 8% of vertebrate species will see their ranges shrink by half.

And if we can limit warming to 1.5 °C, the more ambitious goal of the Paris Agreement, then only 6% of insects, 8% of plants, and 4% of vertebrates will be at risk. The findings add to a growing body of research in favor of striving for the 1.5 °C goal.

“Overall, insects are exposed to greater potential climatic range loss than any other animal group, and also benefit the most if warming is constrained to 1.5 °C rather than 2 °C,” the researchers write. The half-degree difference between 2 °C and 1.5 °C of warming halves the risk to plants and vertebrates, and cuts the risk to insects by two-thirds.

However, the researchers’ analysis is likely to underplay the risks to biodiversity, they acknowledge, because it does not take into account how interactions between species could be disrupted by climate change, nor the effects of extreme weather events and fires that are projected to become more frequent and intense as the planet warms.

A further complication is that some species’ range maps are likely to expand with climate change, according to the analysis. “Might this imply the replacement of many ‘climate losers’ with far fewer ‘climate winners’ in a simplifying ecological landscape?” asks Guy Midgley, a professor at the University of Stellenbosch in South Africa, in a commentary on the research also published in Science2.

And paradoxically, some strategies for holding warming to 1.5 °C will raise other risks to biodiversity. A lot of scenarios for aggressive climate change mitigation call for bioenergy with carbon capture and storage, or BECCS, which involves growing trees or other biofuel crops in large plantations. That could lead to agricultural intensification and natural landscapes being converted to biomass plantations. So in highlighting the plight of insects and other biodiversity, the researchers bolster the case for making fast, steep emissions cuts, rather than relying on future technological workarounds, as the best strategy for fighting climate change.

Sources:

1. Warren R. et al. “The projected effect on insects, vertebrates, and plants of limiting global warming to 1.5°C rather than 2°C.” Science. 2018.

2. Midgley G. “Narrowing pathways to a sustainable future.” Science. 2018.

Image: Preying Mantis

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