THE Great Barrier Reef is already in a critical state. Rising sea temperatures are killing corals faster than they can recover. As temperatures continue to increase, more and more of the reef will die, along with the rich variety of life and the AUS$6 billion tourism industry that depend on it.

By Michael Le Page

It is one headline-grabbing example among many. The continued rapid warming of the planet would wipe out many species, even if it were the only change happening. As it is, a sixth mass extinction in Earth’s history is already under way as farms replace forests and factory ships overfish the oceans.

The heating of the planet will push many struggling species over the brink. Some will just have no place left to go. For biodiversity, climate change is, in military jargon, a threat multiplier. Worse still, measures to limit warming often don’t take biodiversity into account. Some, such as the push for biofuels, directly harm it.

Yet there is little that is inevitable about what happens next. We might not be able to save all the species under threat, but we can save an awful lot of them. “We could cut the number of extinctions in half,” says John Wiens at the University of Arizona. “I think that’s the biggest cause for optimism.”

But our chances are better if we think more smartly about the links between biodiversity loss and climate change, and tackle both of these issues together. Done right, a rescue plan for nature can be part of a plan for saving humanity from the worst of climate change – and vice versa.

“Many species are already moving to stay within their comfort zone”

The world has warmed around 1°C since pre-industrial times. That is already having a dramatic effect on wildlife. In the Arctic, for example, the loss of more and more sea ice each summer is affecting many animals, from walruses to polar bears.

Unique species

Polar inhabitants have nowhere colder to go, but many creatures elsewhere are already moving to stay in their comfort zone. Some marine species, including mammals, birds, fish and plankton, have shifted their ranges by hundreds of kilometres. Other effects are more subtle. Oceanic low-oxygen zones are expanding because oxygen is less soluble in warm water. This is forcing species such as blue sharks to stay closer to the surface, making them more likely to be caught by fishing boats.

Rising sea levels, meanwhile, could wipe out species as low-lying islands are inundated. Mainland species are also at risk, such as the few hundred Bengal tigers in the Sundarbans, a network of mangrove forests along the coast of Bangladesh and north-east India. The effects of habitat destruction and rising water levels mean there will probably be no suitable habitat left there for these tigers by 2070.

Not all of those threats are as gradual as the melting of ice caps and the rising of sea levels. Extreme weather, fuelled by climate change, is one example. Hurricane Dorian, one of the strongest Atlantic storms ever recorded, may have wiped out several bird species in the Bahamas, including the Bahama nuthatch and the Abaco parrot, when it hit the islands in 2019. Warming-fuelled wildfires could also take out species with smaller populations. In 2015, for instance, fires in Western Australia burned much of the remaining habitat of Gilbert’s potoroo, one of the world’s rarest mammals.

A warming world isn’t bad news for all species. Some, especially small, highly adaptable and fast-reproducing ones, are thriving. But these tend to be things we regard as weeds, pests or unwanted invaders, such as mosquitoes, bark beetles and jellyfish.

So far, few species have been conclusively driven to extinction by climate change. The most clear-cut case is the loss of the Bramble Cay melomys (Melomys rubicola). This rat-like rodent was found only on its namesake island home, a tiny, low-lying Australian cay on the northern edge of the Great Barrier Reef. It died out some time after 2009 as rising sea levels led to the island being inundated during storms. Warming may have contributed to other extinctions as well. For example, climate change is thought to have aided the spread of a fungal disease called chytridiomycosis that has wiped out nearly 100 amphibian species.

So far, Earth hasn’t warmed much beyond the bounds of natural variations experienced over the past few million years. But many slower feedbacks, such as the melting of permafrost and the Antarctic ice sheet, have barely begun to kick in, so this will change.

We are heading into this with wildlife already devastated by our activities. Humans have altered three-quarters of all land and two-thirds of the oceans, according to a major 2019 report on biodiversity. More than a third of land and three-quarters of freshwater resources are devoted to crops or livestock.

It is in our own interests to turn things around. The “ecosystem services” that nature provides for free are worth trillions of dollars and underpin many livelihoods. For instance, hundreds of millions of people depend on coral reefs for tourism and the fish stocks they support, says Ove Hoegh-Guldberg at the University of Queensland in Australia. “This is an issue of people as much as it is about ecosystems and biodiversity,” he says.

By intruding into wild areas and exploiting wildlife, we are also giving pathogens such as the virus causing the covid-19 pandemic more chances to make the jump into humans or domesticated animals. Warming is generally expected to make matters worse, for example by allowing disease-carrying tropical mosquitoes to spread more widely.

Overall, though, the populations of most plants and animals have been greatly reduced, and they are already in shrinking, often fragmented areas. One recent study looked at the effect of future climate change on 80,000 species in 35 of the most wildlife-rich areas, including the Amazon rainforest and the Galapagos Islands. With warming of 5°C by around the 2080s, half of these species would no longer be able to survive in these areas.

In many parts of the world, even if suitable habitat remains, many species may not be able to reach it, because their paths are blocked by cities, roads, farms and fences. The same study found that if animals were able to move freely, 2°C of warming would result in the loss of 20 per cent rather than 25 per cent of species.

One issue with studies of this kind is that they assume species can’t survive outside their current climatic range. But many are already evolving and adapting as their habitats warm. In Finland, for instance, tawny owls are turning brown as snow cover declines.

There is a limit to what evolution can achieve, though, especially in species that reproduce slowly. Not only is the climate starting to change much faster than it has during the past few million years, but many species have suffered huge losses of genetic diversity as their numbers have declined. This makes it much harder to adapt to a changing environment.

To get a better picture of how wildlife will cope, in a recent study Wiens focused on about 500 plants and animals worldwide, looking at where they have already become locally extinct as the world has warmed. His results suggest that what matters most is the maximum annual temperature, not mean temperature, as many other studies assume. “The most straightforward explanation is that it just literally gets too hot and they die,” he says.

Extinction debt

Despite this, his conclusions are similar to those of many other studies, suggesting that about a third of terrestrial species could be lost altogether by 2070. “That could be cut in half by following the Paris Agreement and keeping temperature below an increase of about 1.5°C,” says Wiens.

As dire as these forecasts are, they may underestimate future extinction risk. “There could be a lot more extinctions caused by things like sea level rise,” says Wiens. “There’s a whole bunch of other threats.” It can take hundreds or even thousands of years for the full effects of changes such as habitat loss to play out – a phenomenon called extinction debt. In Europe, for instance, the number of extinctions happening today is more strongly linked to what happened a century ago than to current events.

One reason is that populations can become unsustainable once they shrink beyond a certain point. And a decline in one species can have knock-on effects on many others, leading to cascading ecological effects. One New Zealand flowering shrub, Rhabdothamnus solandri, for example, is slowly declining in numbers after the loss of the birds that pollinated it.

Multiplying effects

Some threats to biodiversity can’t be forecast with any certainty. For instance, people forced from their homes by disasters or conflict can have a severe impact on biodiversity in the places they flee to, rapidly deforesting vast areas and greatly reducing wildlife populations. Floods and storms displaced 15 million people in 2018 alone, and these numbers will rise as extreme weather keeps on getting more extreme. For some, there will be no going home: sea level rise will force hundreds of millions of people to move out of low-lying areas over the coming decades.

The combined effect of all these threats can multiply and be worse than any one alone. “For example, corals recover from bleaching episodes more slowly when they suffer stress from pollution, or damage from coastal development or poorly regulated sport or commercial activities,” says Sandra Díaz at the National University of CÓrdoba in Argentina. Similarly, in tropical forests, unusually hot and dry years, combined with the creation of roads, greatly increase the chances of destructive fires, she says.

On the one hand, these multiplier effects mean we may be greatly underestimating our impact on biodiversity over the coming century. “Our best calculations and projections do not incorporate all the possible cascading and non-linear effects,” says Díaz. “They are on the conservative side.”

On the other hand, this shows the importance of protecting and restoring wildlife areas – and that the benefits of such actions could be even greater than we think. For instance, creating wildlife corridors or deliberately relocating species to more suitable areas may save those that would otherwise be doomed.

“Climate policies often show anything but joined-up thinking”

For all these reasons, there is growing awareness that climate change and biodiversity are inextricably linked, and that we need joined-up policies to tackle both. One consequence is that the separate UN conventions on biodiversity and climate change should be merged, says Eric Dinerstein of the environmental organisation RESOLVE in Washington DC.

“The two are so interdependent and the solutions are interdependent,” he says. “We can’t save biodiversity without staying below 1.5 degrees, and we can’t stay below 1.5 degrees without saving biodiversity.”

In general, more has been done to try to tackle climate change than to stem biodiversity loss. Unfortunately, climate policies often show anything but joined-up thinking. Exhibit A are the various incentives or laws promoting biofuels because they are seen as “green”. “There is no doubt that the push for biofuels has seriously harmed biodiversity,” says Tim Searchinger at Princeton University.

Growing use of biodiesel is responsible for 90 per cent of the increased demand for vegetable oil since 2015, says Searchinger. In Europe, more than half of imported palm oil ends up powering cars, driving the destruction of wildlife and carbon-rich forests in South-East Asia for palm oil plantations. Europe is also fuelling deforestation elsewhere by importing wood to burn for energy, while still counting this as a means to reduce carbon emissions.

The fundamental issue that is overlooked is that land is limited. If existing farmland is switched to new uses such as growing bioenergy crops, more farmland is generally carved out of wild habitats elsewhere, destroying biodiversity and adding carbon to the air in the process. The situation is complex: a few biofuels, mainly those made from genuine waste, can be beneficial overall. But many policies wrongly treat any biofuel as green. With the aviation industry now eyeing biofuels as a way to claim it is limiting emissions, matters could get even worse.

If climate policies fail to take biodiversity into account, the reverse is often true, too. For instance, efforts to save the Iberian lynx are focused on the southern part of the Iberian peninsula, where conditions will become too dry for the cats this century.

Some measures really can help us preserve biodiversity and cut carbon emissions at the same time. In general, areas that are rich in wildlife also store lots of carbon, says Dinerstein. His team has mapped out what additional areas around the world, for example in the Amazon basin or on Madagascar and Borneo, need to be protected to help the greatest number of species and maximise carbon storage. Many other groups support this approach.

This could be done without taking existing farmland out of production and at a relatively low cost, says Dinerstein. In some places, tree planting with native species may be necessary, but often there is no need. “The most effective thing we can do is to allow degraded areas to grow back,” he says – rewilding and restoring ecosystems, in other words.

Preserving biodiversity isn’t just a fringe benefit of protecting carbon-storing trees, but is important to maximise carbon storage. In tropical forests, the largest trees typically have big seeds that are dispersed by animals, says Dinerstein – and they are the ones that are most valuable to loggers. “If we hunt them out, those massive, large-seeded trees are replaced with those with smaller seeds that don’t grow as tall, don’t grow as large and sequester much less carbon.”

Better future

At the same time, we need to slow and eventually halt the clearing of land for farms. Encouraging people to eat less meat would help enormously. If everyone shifted to a plant-based diet, we would only need a quarter of the farmland used now, while vastly reducing the greenhouse gas emissions associated with producing food.

But with meat consumption increasing rather than falling, it is vital to maximise yields on existing farmland. “The expansion of farmland and the associated habitat loss is still very ongoing,” says Emma Kovak at the Breakthrough Institute in California. “The intensification of farming can spare habitat for wildlife.”

A low-intensity organic farm might have more wildlife on it, but it produces less food, which means more farmland is needed elsewhere in the world, she says. Per unit of food, high-intensity farming has a much lower impact. Kovak has shown that if the European Union had embraced higher-yielding, genetically engineered crops, it would have led to a substantial reduction in greenhouse gas emissions via less land use.

Despite the dire outlook, many researchers remain optimistic. “I’m incredibly hopeful,” says Dinerstein. For a start, protecting more land would actually cost relatively little, he says. There is even hope for the coral reefs. “If we stabilise the climate, there is a very good chance that coral reefs will grow back over time,” says Hoegh-Guldberg.

Many initiatives and studies around the world show that we can protect biodiversity and tackle climate change while offering a better and fairer future for people, says Díaz.

“But these studies also show, very clearly, that this will only work with very fast, very deep, very bold changes in the way we consume, eat, trade and value,” she says. “The opportunity to shift gears and do what needs to be done for a better future will close soon.”

Rescue plan for nature
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About this feature

This is the fifth and final feature in our “Rescue Plan for Nature” series produced in association with the United Nations Environment Programme and UNEP partner agency GRID-Arendal. New Scientist retains full editorial control over, and responsibility for, the content