When we think about climate change, we should think about the Younger Dryas. You probably haven’t heard of the Younger Dryas, a cold period that started 12,900 years ago — at the end of the last glacial period — with a 10˚C cooling over two centuries, and ended 1,200 years later with a 15˚C warming over a few decades. (To appreciate the magnitude of these temperature changes, remember that 1.5˚C is the current scientific consensus for planetary warming that humanity can absorb without major upheaval.) The Younger Dryas was the last of around 25 violent temperature swings that occurred in the last glacial period. It’s named for the Arctic flower, the Dryas octopetala, that migrated far south as the polar tundra overtook forested land.
We should be asking whether a sudden upheaval in climate like the Younger Dryas could happen again. The Younger Dryas reminds us that the stability of the Holocene — the past 11,000 years of Earth history — belies the volatility Earth has experienced in the not-so-distant past. This planet’s climate systems are capable of transformations on far more rapid timescales than we myopic humans can imagine. Only when our conception of the possible includes climate change as abrupt as the Younger Dryas will we understand the risk we’re choosing to live with.
The scientific definition of abrupt climate change is a change that occurs when the climate system crosses some threshold, triggering a transition to a new climate state at a rate faster than the cause. The National Academy of Sciences offers this analogy: Imagine that you have a curved track balanced on a fulcrum. There are two curves, each on either side of the fulcrum, that form “cups” in which a ball can rest. A ball placed in either one of the curves is stable. If pushed, it will roll for a short time but return to its original position. A ball placed on top of the fulcrum is unstable. If pushed ever so slightly, the ball will fall into one of the cups, putting the system in a completely new state. This is an abrupt change.
Now imagine that you are in a dark room, unable to see what state the ball is in or what the device looks like. You have no idea how close the ball is to its tipping point, but you continue to push the ball. Sound short-sighted? Well, we’re playing this game now, with our Earth. We’re in a dark room, pushing our planet’s systems without being sure about how close we are to the runaway-greenhouse-warming or species-extinguishing tipping points. We know these tipping points exist because geoscientists have documented the effects of crossing them. Take, for example, the Permian Extinction, when abrupt carbon dioxide release 252 million years ago acidified the ocean and caused the extinction of 96 percent of marine life.
The geologic record teaches us that climate tipping points are real — but we never talk about them.
Most climate reporting that I see in the media describes global warming as a process of continuous deterioration. A quick skim of the stories the New York Times selected to represent the 2018 “Year in Climate Change” creates an image of a planet gradually becoming less hospitable. February 6, 2018: “Floods are Getting Worse, and 2,500 Chemical Sites Lie in the Water’s Path.” March 12, 2018: “Hotter, Drier, Hungrier: How Global Warming Punishes the World’s Poorest.” September 25, 2018: “Climate Change is Killing the Cedars of Lebanon.”
The operative verb tense in these titles is the present continuous. Climate change is killing, is eroding, is getting worse. A world getting hotter, drier, hungrier is a world that is frightening but still predictable. We think we will have time to respond. The Younger Dryas reminds us we may not have this time. No climate scientist would claim an ability to predict when the Younger Dryas would happen, only that it’s possible — and that’s why we need a Green New Deal.
We certainly need a Green New Deal — the resolution introduced by Rep. Alexandria Ocasio-Cortez (D-NY) and Sen. Ed Markey (D-MA) to mobilize the United States to reach zero emissions by 2030 — because of continuous climate change, because hurricanes are increasing in intensity and frequency and because the ranges of disease-carrying insects are expanding and exposing more people to Zika and Lyme. But we also need a Green New Deal because of abrupt climate change; because 12,900 years ago, the North Atlantic plummeted into the Younger Dryas; because 55.5 million years ago, a warming ocean triggered the release of frozen methane, raising global temperatures by 5-8˚C (and because the same methane deposits exist today, waiting to be destabilized in our warming ocean). We need a Green New Deal because humans could force another Younger Dryas, transforming society as we know it.
We have the technology to reach zero emissions today. We can build new solar arrays and windmills, we can invest in sustainable family farms, we can upgrade all buildings to maximize their energy efficiency — while creating well-paying jobs, cutting energy costs and cleaning up a history of environmental degradation in places where poor people and people of color live. We’ll still be operating in a dark room, but at least we’ll be less at risk of knocking the ball off its fulcrum.
The Green New Deal is a mobilization that will operate on the same timescale of abrupt climate change; that is, over decades. It’s easy for critics to say neither one — neither abrupt climate change nor the Green New Deal — can happen that fast. But both can. The Green New Deal is ambitious — some say too ambitious — but since it is the only policy on the table that sets its sights on zero carbon emissions, it is a policy worth pursuing.
As a science student, the potential for abrupt climate change drives me to the lab; as an inhabitant of planet Earth, it keeps me up at night; as a citizen, it compels me to support the policy proposals that will most immediately and most intensely reduce our carbon emissions. The Green New Deal, which demands an immediate move to zero emissions, is that policy.
Many scientists think the Younger Dryas began when meltwater from the Laurentide Ice Sheet, which covered half of North America at the end of the last glacial period, drained into the North Atlantic ocean. Because freshwater is less dense than salty water, this meltwater formed a “lid” that prevented saltwater from sinking, inhibiting the Atlantic Gulf Stream from carrying warmer water northward from the tropics, and causing abrupt regional cooling.
Right now, as we speak, the Greenland Ice Sheet is rapidly melting into the North Atlantic, nearly twice as fast as it did during the 1990s and 2000s. Of course, the context today is vastly different from that of 12,900 years ago — there was a lot more ice to melt at the end of the glacial period, and the warming then was natural, unlike the anthropogenic greenhouse warming we’re experiencing today. Will we see a Younger Dryas in our lifetimes? Who knows. But 12,910 years ago, hunter-gatherers probably didn’t think abrupt climate change was coming, either. And then it came.
Rachel Gold ’19 wishes everyone a Happy Earth Week and wants you to stop by the Main Green today to see her mud from the Younger Dryas. Please send responses to this opinion to
firstname.lastname@example.org and op-eds to email@example.com.