Can animals and plants adapt to global warming?

At a glance

Just like “the climate has changed before”, this is another vague and unsubstantiated talking point. It is essentially meaningless because again it omits details – and details matter. Yes, some plants and animals can adapt – think of invasive plants like Japanese knotweed or annoying pests like rats. They seem to get on just fine under a wide range of conditions.

Other species, however, have evolved to fit into much narrower ecological zones. Think of Alpine plants: in a warming climate they may be able to extend their natural range uphill as the permanent snow-line retreats, but where can they go once they've reached the mountain-top?

On average, species that can migrate are moving some six kilometres polewards a decade, but such movements are not necessarily successful. For example, a butterfly may attempt to extend its range polewards, but if its food-plants do not grow in the territory it migrates to, then its caterpillars will have nothing to eat. Is that a recipe for success? Finally, whilst some species are capable of quickly migrating to places with more favourable physical conditions, others are not. A coral reef cannot simply pack up and move, can it?

We can clearly see how we've also made things more difficult for many species to adapt. One only has to consider the combination of a warming climate, gradually shifting Earth's climatic belts toward the poles and the amount of alterations we've already made to the planet's surface. Species run short of options. They can either interact with us to a far greater extent or they dwindle away until they are gone.

Another unwanted consequence of such changes is the emergence of zoonotic pathogens. These are things like viruses that have evolved to jump from other animal species to humans, bringing an increasing risk of pandemics. These are details that the person saying or writing, "animals and plants can adapt", is omitting from the conversation. Details always matter.

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Further details

The natural world has already been under attack for centuries. Since the discovery of agriculture, humans have massively transformed the globe through the expansion of civilization, to the detriment of Earth’s biodiversity. Great swathes of temperate forest in Europe, Asia and North America have been cleared for agriculture, timber, and urban development. Tropical forests in South America and Africa are now on the front line. Human-assisted invasions of pests, competitors, and predators are rising exponentially and overexploitation of fisheries and forest animals for meat have already driven many species to the point of collapse.

The ways plants and animals adapt to changes in their environment often involve migrating to areas with relatively favourable conditions (Bartley et al. 2019). But now, in order for many species to migrate large distances they would have to cross large areas of human influence. Mass migration in areas of large human population – entwined with crisscrossing, high-speed highways and polluted, dammed-up rivers – is self-evidently a challenging task.

Along with that, it has been shown that climate change has already had an impact on the environmental cues that animals use to determine the timing and navigation of their migratory patterns (Seebacher & Post 2015). Subsequently, these changes in animal migratory behaviour have also been shown to have a detrimental effect on the animal’s average lifespan and overall health.

There is much evidence that we are already on the brink of a mass extinction event. Because of human activity, the number of species on the planet is already decreasing. According to the Millennium Ecosystem Assessment (an international environmental report with the goal of assessing the impact of ecosystem change on human well-being), 60% of the world’s ecosystems are now degraded. The global rate of extinction is already at 100 to 1000 times that of the “normal” background rate on geological timescales. Mass-extinction events, marked in the fossil record, have typically taken place over a long time period compared to human history. But we can say one thing with certainty: rapid, anthropogenic climate change and environmental degradation is only making things worse for Earth’s biodiversity.

If we fail to prevent catastrophic climate change, there will be many regions of the world (some of which are highly populated) which will become uninhabitable to even us humans. This is based on human physiology and future temperature and humidity predictions under climate change. When temperature and humidity levels are too high – indicated by something scientists call a high “wet bulb temperature” – the human body is not able to cool itself by sweating. Extended periods of these high wet bulb temperatures, increasing the rate of heat stroke and death in humans are expected by later this century under medium to high emission scenarios (Newth & Gunasekera 2018), especially in tropical regions (fig. 1).

Fig. 1: Projected ten-year maximum monthly mean Wet-Bulb Globe Temperature by 2091-2100 under different Representative Concentration Pathway (RCP) scenarios. WBGT is derived from the Wet Bulb Temperature and near-surface air temperature as a proxy for globe temperature. Adapted from Newth & Gunasekera (2018).

Right now, only 1% of the Earth’s land is considered a “barely livable” hot zone, mainly within the Sahara and other desert regions. If emissions continue unregulated and climate change continues unmitigated, this fraction could increase to 19% by 2070. Billions of people live in these potential, future hot zones. Due to the current state of the global economy, many disadvantaged people residing in these potentially deadly places may not be able to move away or adapt.

In summary, the current outlook on Earth’s biodiversity is gloomy. We know that most mass extinctions in the fossil record have been triggered by the rapid onset of global warming due to an increase in carbon dioxide emissions to the atmosphere. In the past, these emissions were usually due to large, volcanic episodes which occurred over tens to hundreds of thousands of years. On a geological timescale, these changes occurred in the blink of an eye, and this is why they were so costly. The human-caused climate change that is occurring today is similar; since 1850, we have increased atmospheric CO2 levels to the highest they have been in the last 3 to 5 million years.

Even though all of this may be depressing, there is still hope. There is still time to reverse the worst effects of man-made climate change, and to do so we must reduce consumption, support conservation efforts and transition to renewable energy. For all of human history we have depended on Earth’s biodiversity, and it now depends on us to save it.

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