This text was originally published in Spanish in Magazine 2023, now on sale. You can get a copy, in digital or paper, through our website.
When it comes to the climate crisis my friend and mentor the late Stephen Schneider used to say, «The ‘end of the world’ or ‘good for you’ are the two least likely among the spectrum of potential outcomes». Is that true? Can we rule out a worst-case scenario of human climate change-caused extinction? Or is it too late to prevent civilization-ending climate Armageddon?
In my forthcoming book Our Fragile Moment: How Lessons from the Earth’s Past Can Help Us Survive the Climate Crisis, I investigate Earth’s vast climate history for an answer to this and other critical questions about our climate future.
The lessons start early, and so do the mysteries. The great Carl Sagan recognized the paradox of the «Faint Young Sun». Early in Earth’s 4.54 billion year lifetime, our Sun was 30% less bright than it is today. Standard calculations indicate that the planet should have been frozen (and lifeless). But it was not. iI was warm enough to the support the liquid water believed to be required for life as we know it. Sagan recognized the solution was a greenhouse effect much stronger than today—probably because of high levels of carbon dioxide and methane.
Remarkably, as the Sun gradually grew dimmer over the ensuing billions of years, Earth’s greenhouse effect grew brighter. Does Earth have a «thermostat» that keeps the planet within habitable bounds? Such holds the ‘Gaia hypothesis‘ of James Lovelock and Lynn Margulis, name after the Greek Earth goddess. Over geologic time, the hypothesis appears to bear out. But there have been striking exceptions. When photosynthesizing life took off a little more than two billion years ago, the huge rise in oxygen scavenged much of the potent greenhouse gas methane, leading to a runaway «positive feedback» a vicious cycle, in this case, of cooling, and ice buildup that generated further cooling and glaciation. There’s evidence that Earth became entirely encased in ice. The episode even has a name —«Snowball Earth». Life on Earth was nearly snuffed off, and likely survived only by seeking refuge in warm environments such as hydrothermal vents in the deep ocean.
So which scenario applies as we warm the planet through our profligate burning of fossil fuels? A Gaian scenario of climate resilience? Or one ruled by ruthless runaway feedback processes? We can turn to other episodes in Earth’s history for answers. Let’s start with the greatest extinction event of all, at the boundary between the Permian and Triassic periods 250 million years ago.
For decades, there has been speculation that a massive release of methane stored under the sea floor might have triggered a devastating warming spike. Along with another natural episode of rapid (at least, on a geological timescale) warming that happened later, around 56 million years ago (known as the «PETM»), climate doomers insist this is an analog for a «methane bomb» we face today –a rapid release of methane frozen in the Arctic permafrost and coastal shelves– that has already been triggered by human-caused warming. Unstoppable runaway warming and human extinction, they say, is assured.
A review of the paleoclimatic evidence simply doesn’t support this narrative, however. With these past climate episodes, the main cause of the warming was carbon dioxide (CO2)—the same greenhouse gas that we are pumping into the atmosphere today from fossil fuel burning and other human activities. The best available science indicates that so-called «methane feedbacks» played at most a modest role. Indeed, as recently as 120,000 years ago, before the last ice age, temperatures in the Arctic were warmer than they are today, yet there was no massive release of methane.
That’s the good news. But there’s bad news too. Today we are increasing the concentration of CO2 in the atmosphere more than ten times faster than any known natural episode and that presents a monumental challenge to us and all other living things on this planet. If we do not reduce carbon emissions, then the paleoclimate record also tells us —quite clearly– that we will, within a matter of decades exceed levels of warmth not seen in millions of years.
In an odd way, we benefited from ancient climate episodes. The most famous extinction event of all was the asteroid that struck Earth 65 million years ago generating a planetary dust cloud that rapidly cooled the planet, killing off the dinosaurs (with the notable exception of their avian descendants). Their loss was our gain. It created a niche for the small mammals that would eventually evolve into primates. The drying of the tropics during the Pleistocene period created a niche 2 million years ago for early hominids, proto-humans, who could hunt prey as forests gave way to savannahs in the African tropics. The cooling episode known as the «Younger Dryas» 13,000 years ago as Earth was thawing out of the last Ice Age, spurred the development of agriculture in the fertile crescent. And sprawling city states —human civilization— emerged around 6,000 years ago as drying in the middle and near east necessitated early engineering projects, freeing up citizens up to perform other tasks such as construction, leading to the formation of the first true urban settlements.
So we see that natural climate change has at times created new niches that we or our ancestors were able to exploit, and challenges that have spurred innovation. But there’s a relatively narrow envelope of climate variability within which human civilization remains viable. We are rapidly leaving that envelope. The conditions that allowed us to live on this earth are fragile. Our own fragile moment is in jeopardy. The paleoclimate record is replete with examples of both winners and losers. And we stand to be the losers now.
The impetus for action doesn’t require implausible scenarios of runaway «methane bomb» driven warming. The truth is bad enough. In the absence of further climate policy, we will likely warm the planet 3C (5F) or more. And if we choose, worse, to abandon current policies and accelerate our extraction and burning of fossil fuels, we could warm the planet 4-5C (7-9F). That’s warmth we haven’t seen in tens of millions of years, and a rate of warming that has no precedent.
That’s a future of massive wasting of ice sheets, meters of sea level rise, inundation of the world’s major coastal cities, with half the planet unlivably hot, and heat waves, droughts, wildfires, floods and superstorms unlikely anything we’ve yet witnessed. Hollywood has provided us depictions of such a world and it’s not pretty.
It is incumbent upon us not to consign future generations to such a dystopian future. A recent peer-reviewed study in the leading journal Nature shows that we can keep warming below 2C, the level of planetary warming that the 2015 Paris agreement established as a safety limit, if the Glasgow pledges are kept and implemented on time. But limiting warming to 1.5C is preferable given the risk of escalating damage from extreme weather events and, in particular, the threat posed to low-lying island nations already threatened with inundation from melting ice and rising sea level. So more stringent policies are still needed, and it is up to us to hold the feet of politicians and other influential to the fire.
Now is not the time to give into climate fatalism, especially based on false pseudoscientific narratives of unavoidable extinction. Unlike the dinosaurs, we have agency. We see the metaphorical asteroid coming and we can still do something about it.
The text can also be read in Spanish here.
Michael E. Mann is Presidential Distinguished Professor of Earth and Environmental Science at The University of Pennsylvania. His newest book, Our Fragile Moment: How Lessons from the Earth’s Past Can Help Us Survive the Climate Crisis, is due out later this year.