This is the first in a four-part series on the relationship between global climate change and mass extinction. I wrote it for the old iteration of this blog, on the Climate Emergency Institute’s website, and I’m re-posting it here. Stay turned for the other three parts of the series, though be aware I probably won’t post them all back to back, as current events may require our attention, too.
According to one groundbreaking study published in 2004, in the next forty years climate change could commit over a third of all species to extinction.
It is important to understand what this means—and what it doesn’t mean. Future articles in this series will explore in more detail how predictions of this type are made, how climate change causes extinction, and how climate change interacts with other environmental problems to put stress on vulnerable species. For now, we will focus on a couple of take-home messages from the current research.
First, the numbers themselves are approximations because scientific knowledge is limited, yet this limitation of knowledge does not constitute a sort of generalized fuzziness. A good analogy might be short-term weather prediction. Weather predictions are sometimes wrong, but they are not randomly wrong. Instead, the factors which meteorologists are sure about form a kind of frame of certainly within which some details can shift across a known and limited range, like a door swinging inside its frame.
Even if the door swings open unexpectedly, it isn’t going to get up and walk off down the hall.
By the same token, when an ecologist says that anywhere from fifteen to thirty-seven percent of species are likely to go extinct, and then other ecologists come up with different predictions by using different models, that does not mean their warnings shouldn’t be taken seriously. The solid frame of their certainty is that we are in trouble.
And it’s worth noting that so far, when climatologists and ecologists studying the effects of climate change have been wrong, it’s because they have underestimated the speed and severity of change.
Second, the paper uses the phrase “committed to extinction,” which sounds scary but vague to a non-specialist’s ear. What this phrase means is that extinction is a process, not an event, and a species can sometimes go on existing for decades while this process plays out. In the same way, we might say that someone falling from a great height is committed to death. Yes, it is sometimes possible to save a falling person (we can suppose a lucky interception by a skilled sky-diver with a spare parachute), but barring intervention, the person will die. The falling person is still alive, but there is no sitting back and hoping for the best on the way down.
The authors of the study did not mean that a third of all species could be extinct in forty years; they meant that if we keep causing more climate change, then in forty years the conditions that these species need to maintain themselves will no longer exist. They will be in ecological free-fall. How long it will take after that for the last individuals of these species to actually die is hard to say, and until that final thud intervention may still be possible. However, we are currently engaged in a process that, if we don’t stop, will soon render a mass extinction as certain as gravity.
Third, this study makes clear that global warming is not a simple, on-or-off event, like someone flipping a switch. We have already warmed the planet considerably, and some further warming is already certain because of the greenhouse gasses we have already put into the sky. However, how much further warming there will be depends on how humanity behaves going forward. The 37% extinction prediction is based on a worst-case scenario of uninhibited greenhouse gas emissions (though the history of climate modeling suggests that if this scenario plays out reality will be far worse than the prediction). Reducing emissions to the point where the extinction risk is much smaller, around 15% of species lost, is not only still possible, it might be politically in reach. That is, we are already committed to disaster—we are falling. Yet the scope of the disaster is still under our control; the degree of our losses will be proportionate to our apathy now, and any improvement on our part will yield a corresponding cushion, small or large, to our fall.
To recap, global warming stands to disrupt the conditions that allow today’s animals and plants to survive. Therefore, some number of species alive today will likely be lost. At least a few species have been lost to global warming already. This is in addition to the wave of extinctions being caused by other factors, which has already reached geologically significant proportions; only five other times in the four billion year history of the earth has an extinction event occurred on this scale. The most famous of the previous extinctions caught the dinosaurs. Scientists can predict the extent of global warming-related extinctions for different climate scenarios by using a variety of means. Although there are still too many unknowns to be able to say exactly what is going to happen, scientists are sure of two things: human behavior is causing a major extinction event and the severity of this extinction, how many species die, can be directly affected, for better or worse, by the choices we make now.