Limiting global warming could preserve biodiversity

Australian and UK researchers are pushing for global warming to be limited to 1.5°C, claiming that such a limit could protect hundreds of thousands of insects, plants and animals.

Published in the journal Science, the study led by Professor Rachel Warren and her team analyses countries’ current emissions reductions pledges and compares them to the ideal of 1.5°C, as well as the earlier aspiration of 2°C. Unfortunately, current pledges are nowhere near that range — and that’s something of a problem for biodiversity.

“With current pledges, corresponding to ~3.2°C warming, climatically determined geographic range losses of >50% are projected in ~49% of insects, 44% of plants, and 26% of vertebrates,” the researchers wrote. “At 2°C, this falls to 18% of insects, 16% of plants, and 8% of vertebrates and at 1.5°C, to 6% of insects, 8% of plants, and 4% of vertebrates. When warming is limited to 1.5°C as compared with 2°C, numbers of species projected to lose >50% of their range are reduced by ~66% in insects and by ~50% in plants and vertebrates.”

But why would such losses occur in the first place? An article accompanying the study, written by Professor Guy Midgley from Stellenbosch University, explains that higher levels of warming would lead to systemic ecological simplification, a process where many “climate losers” are replaced by far fewer “climate winners”. Such a simplified ecological landscape could have impacts on ecosystem services such as water quality, soil conservation and flood prevention, Professor Midgley said, all of which are important for human wellbeing. Fewer insects also mean fewer pollinators, with associated implications for many plant species and related food production.

Furthermore, Professor Midgley stated that efforts to limit warming may require large tracts of land to be made available for capturing and storing carbon: some estimates are for up to 18% of the land surface or 24–36% of current arable cropland by the end of this century. And this expanding land use itself could threaten remaining habitats.

“So here is the irony,” Professor Midgley said. “In order to achieve the 1.5°C target, we may well damage many of the habitats that support biodiversity in order to achieve a target that will save biodiversity.

“We need to find the combinations of options that minimise conflicts between these competing demands. Only if we succeed in solving this nexus between climate security, land use and biodiversity conservation will we be able to ensure a sustainable future in the long term.”

Other researchers have been quick to comment on the news, with Dr Paul Read from the University of Melbourne describing Professor Warren’s paper as a “sober, careful analysis” that is also somewhat conservative, as it “doesn’t even begin to look at ecological interactions, natural disasters or tipping points”.

Dr Marissa Parrott, a reproductive biologist from Zoos Victoria, was particularly concerned by the potential impact global warming will have on Australia, noting that the land Down Under has “the worst recent extinction record of any country in the world” and is, according to the paper, “one of the countries most likely to be affected by increased global temperatures”.

“This is particularly concerning for animals restricted to Australia’s alpine region, like the critically endangered mountain pygmy possum, alpine she-oak skink and Guthega skink,” Dr Parrott said. “These species are highly adapted to colder environments and would be threatened by warmer temperatures, changes to food sources, encroachment from other species into their habitat and increased fire risk. The mountain pygmy possum, for example, requires a thick blanket of snow to safely hibernate and survive winter. They also rely on migratory Bogong moths as a key food source — the loss of invertebrates, as suggested by this new research, could be catastrophic.”

But Professor Ary Hoffmann from the University of Melbourne was sceptical about the inclusion of invertebrate data, noting, “Many invertebrates … have a substantial adaptive capacity and high inherent rates of increase, which can reduce impacts and increase the ability to counter climate change through evolutionary changes and through plastic changes in phenotypes, such as using diapause to avoid extreme events. There are also winners under climate change whose distributions will expand.

“And there are drivers other than climate change which will be important for invertebrates and other species,” Professor Hoffman continued. “For instance, the paper mentions a German study showing a decrease in insect biomass … of 75%. But in that paper the authors indicate that this decrease in biomass is potentially associated with habitat destruction and chemical use, not just climate change. So you can’t decide that one factor is a driver without considering all components.”

Professor Caroline Sullivan from Southern Cross University was more accepting of the idea that a 1.5°C restriction will reduce the risk of biodiversity loss, but feels this will be a “massive challenge, since we are already struggling to agree on how higher limits can be achieved”.

“Mitigation measures to reach these goals put a massive challenge on land-use actions, with vast areas of land dedicated to carbon capture likely to exacerbate any impact of warming on habitats and species,” she said, echoing Professor Midgley’s concerns.

“All of this indicates the need to recognise the urgency of the need for adaptation. We humans have to recognise that it is up to us to build the future we want. As the authors point out, biodiversity through insects, birds and microbes is what drives our food system, and if we don’t want to face global famine in the not too distant future, we must act now. This means we need to protect larger and more diverse areas of the planet and all its biomes if we are to ensure that the ecosystem services, which underpin our life-support system, are going to continue to be available for future generations.”

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