The impacts of climate change on animals are not uniform, nor are they simple. The magnitude of heatwaves, for example, varies among the world's climate zones. Similarly, the susceptibility of animals and plants to global warming differs among species and among regions. Because our predictions of Earth's future are often clouded by uncertainty, how can we best figure out who will carry on and who will go the way of the dinosaurs? An answer could lie in using broad ecological patterns, identified by combining detailed information on the biology of as many species as possible, to improve conservation practice and policy.
Malin Pinsky, from Rutgers University, USA, and a team of researchers from the USA, Norway and Canada assessed the vulnerability to climate change of animals living in two very different environments: on land and in the ocean. Specifically, they studied ectotherms – animals whose body temperature is directly influenced by environmental temperature (‘ecto’=outside, ‘therm’=heat), such as insects, reptiles, fish and molluscs. Extreme temperature not only negatively impacts individuals, but also whole populations, so the researchers wanted to find out how often these animals live under physiologically stressful conditions. They calculated the ‘thermal safety margin’ – the difference between the highest temperature a critter can withstand before it dies and the highest body temperature it will reach in its habitat – for more than 400 species, under current and predicted future warming conditions. They reasoned that the narrower the thermal safety margin, the more likely an animal was to be adversely affected by climate change.
The team found that the thermal safety margins of land-dwelling ectotherms are narrowest in regions midway between the equator and the poles, whereas marine species are most vulnerable at the equator. They also discovered that marine species have narrower thermal safety margins in general, leaving them more open to heatwave hardship. Additionally, the size of the thermal safety margins under a high greenhouse gas emissions scenario tighten to half the size of those under low emissions for both animal groups. On land, if animals lose the shade needed to avoid extreme temperatures, their chances of survival will all but vanish.
The authors suggest that the narrow thermal safety margins of marine ectotherms may have already caused local extinctions (the die-out of a species in a specific area). In fact, they estimate that twice as many local extinctions have occurred on the warmer edge of marine species’ ranges than for terrestrial species. It is possible that available habitat is key in mitigating the effects of climate change on land and underwater. If marine species are able to successfully move out of uninhabitable areas and colonise new locations, the team expects higher levels of local population extinction, but lower levels of global extinction, in marine versus terrestrial ectotherms. Land animals are not able to move as far to avoid warming temperatures, so access to protective thermal refuges – hideaways from the heat – will be critical.
The authors’ take-home message is that fish, lobsters, abalone and other ectotherms living in the ocean are highly vulnerable to global warming and it will not take much more heat to send populations crashing into the abyss. They emphasise that the collapse of marine ecosystems will have dire economic and nutritional consequences for humans, and the best way to avoid this catastrophe is to reduce our greenhouse gas emissions. The human race is shooting itself in the foot because climate change begins, and ends, with us.