Going, Going, Gone?
It does not take a crystal ball to understand how momentous tipping points can be in natural systems that affect our welfare. Tipping points in climate can presage catastrophes on a planetary scale, even threatening civilization.
Think of what would happen if the Gulf Stream, the great Atlantic Ocean current that helps determine the weather in Northern Europe, decided to go on strike. (More on that later.) Or what a mass dieback in the Amazon basin that turns hundreds of thousands of square miles of tropical forest into grasslands would mean for the global environment. Or what would happen if the vast West Antarctic ice sheet disintegrated and tumbled into the ocean, raising global sea levels and flooding coastal cities.
Small and Large
As Malcolm Gladwell explained in his best-seller, The Tipping Point, small changes can make big differences. Indeed, the Merriam-Webster definition of a tipping point comes down to just that:
The critical point in a situation, process or system beyond which a significant and often unstoppable effect or change takes place.
The origin of the term is instructive, too. First uses date back to industrial engineering in the late 19th century: think of rail cars full of coal tipping over in a Yorkshire foundry, or the v-shaped cup that’s part of a tilting water meter. An initial small push – a nudge of the rail cart, or the addition of a few more ounces of water – and the avalanche begins. A similar logic applies to climate tipping points.
They represent large-scale, “nonlinear” shifts in the system that regulates the Earth’s weather. Tim Lenton, a climate scientist at the University of Exeter, has made a career of drawing attention to the importance of such phenomena. He would also be the first to point out that the Gulf Stream is but one part of the much larger, more critical Atlantic Meridional Overturning Circulation. AMOC has been slowing down noticeably, leading the Intergovernmental Panel on Climate Change to warn of its shutdown – though it has long called a full collapse in the 21st century “unlikely.” A recent analysis is not as hopeful, estimating the AMOC tipping point could occur mid-century.
One consequence of AMOC closing up shop would be a frigid Europe. The Gulf Stream delivers warm Caribbean waters to the North Atlantic, leaving London winters (merely) cold and rainy, and northern Europe rather more habitable than equivalent longitudes in Canada. After all, London is north of Calgary, yet January temperatures in London rarely fall below freezing, while residents of Calgary consider 30 degrees Fahrenheit in January a heat wave. All that makes the effect of climate change on AMOC both vital and complex. Just how should one think about such massive, disruptive changes like rapid cooling in Europe, especially in light of the sauna-like temperatures of recent European summers and lack of snow in the winter?
Another complicating factor: the time scales involved. One of the harder characteristics of climate change to wrap one’s mind around is its long-term nature. Today’s actions may or may not cause havoc far down the line, making inaction today all the easier to rationalize.
Slow and Fast
The consequences of AMOC or any other element of the Earth’s system approaching its tipping point would not be felt immediately. The Gulf Stream would not shut down overnight. Amazon dieback, too, would play out over decades, and sea-level rise due to a polar ice melt would take even longer to run its course. The West Antarctic ice sheet would not disappear overnight, even if the processes that make the breakup almost inevitable are already underway. Sea levels might ultimately take millennia to find their new equilibrium state.
This also makes the detection of tipping points difficult. For that matter, how do we know that any of these tipping points have not been crossed already?
Take sea-level rise. There is no doubt that the oceans are both warming and rising and – since warmer water takes up more space – that the former has been a key contributing factor to the latter. Indeed, thermal expansion has been among the most predictable drivers of global average sea-level rise. A second factor is the melting of the great inland glaciers left over from the last ice age. Most of them are doomed anyway, so adding up their contribution to sea-level rise is relatively easy. But that leaves the polar ice caps, where things get choppy.
Antarctica is home to enough water in the form of ice to raise global average sea levels by almost 60 meters (about 190 feet, no misprint) if it drained into the ocean. Fortunately, that awesome number is hardly relevant to us or to our children – or for that matter, multiple more generations to come – because the ice is probably not going anywhere for centuries. But another number is all too probable: the potential for up to 5 meters linked to melting of the West Antarctic ice sheet.
Global average sea-level rise has long been progressing at a pace best measured in millimeters: an average of one to two millimeters per year. But the change is far from linear with respect to time. In the past decade, the pace has more than tripled, to around four to five millimeters per year. The acceleration alone is worrisome, and it does not include contributions from the passage of any tipping points. Not yet, anyway.
Climate scientists David Pollard and Robert DeConto made quite a splash 15 years ago when they modeled the evolution of the West Antarctic ice sheet (which covers a third of the continent to an average depth of over 3,000 feet) over the past five million years. Their conclusion: the processes leading to the eventual collapse of the entire ice sheet may already be in motion. Translation: enjoy that Florida beachfront home while you can.
Alas not so fast – because Earth-system tipping is anything but. Gladwellian tipping points don’t just share the characteristic of little steps triggering massive changes – a little more, a little more, a little more and then goodbye New York City. They also come with a second key characteristic: the large changes that follow the small changes happen quickly. And how one ought to cope with the uncertainty of what will happen and on what time scale is difficult to say, as I detail in a technical paper with climate scientist Bob Kopp and colleagues.
First, preliminary changes taking centuries “may push the consequences of a tipping point beyond the time horizon of socioeconomic relevance.” Even 2 degrees Celsius (3.6 degrees Fahrenheit) of global average warming above pre-industrial levels would eventually increase sea levels by around six to nine meters (20 to 30 feet). But rightly or wrongly, society discounts such effects almost completely – rightly because it is true that there are more pressing environmental and social issues on today’s agenda, wrongly because we could make a big difference by acting now.
An all-star team of sea-level rise scientists, led by DeConto and including both Pollard and Kopp, argues convincingly that with emissions on their current path of generating around 3 degrees Celsius of warming, the rates of average global sea-level rise we’re experiencing today due to Antarctic ice loss alone would jump tenfold to around two inches per decade. By contrast, limiting emissions in line with 2 degrees of warming would keep Antarctic’s contribution at close to today’s levels, with total global sea-level rise considering all factors of around those two inches per decade.
But there’s another issue here – another tipping point with a scarier dynamic. Indeed, it largely explains why scientists are so worried about the unpredicted runaway ocean warming of the past few years. What if all this means that the floating ice shelves offshore Antarctica will disintegrate much faster than anticipated?
Your first reaction may be “so what?” For as every grade school science class is taught, when ice floating in a bowl of water melts, the water level more or less stays the same. But the overwhelming bulk of the ice in Antarctica sits on land. Here’s the catch: The floating ice shelf protects this landlocked ice from sliding into the sea. Thus, as the floating ice thins, huge quantities of overland ice may well end up in the water, accelerating sea-level rise accordingly.
A Technofix?
The most pernicious property of tipping points is that we can’t know for sure where the point is until we have passed it. And once passed, there may be no winding back the clock. That is, if the turning point in atmospheric temperature rise is reached, a high-tech fix – say, one that employs thousands of machines to suck carbon out of the atmosphere in order to get temperatures back into the comfort range – would be too slow to stop the ice sheet from sliding into the ocean.
But also note my carefully chosen reference to one particular form of “geoengineering” fix: carbon dioxide sequestration. It is distinct from potentially problematic solar geoengineering interventions (like attempting to mimic volcanoes by deliberately putting small reflective particles into the upper atmosphere) that do not address the root cause of too much CO2 directly, but may indeed be fast enough to spare the West Antarctic ice sheet.
That issue of timing may be particularly relevant for a third type of intervention, glacial geoengineering – that is, interventions directly aimed at preserving polar glaciers. The idea here is to either block warm water from melting glaciers from undermining the sea ice buttressing the ice on land, or to support ice shelves directly, perhaps with massive underwater dams.
Neither solar- nor glacial-geoengineering would provide any kind of assurance of stopping warming or its consequences. Nor should the potential for geoengineering be any kind of excuse to ease up on global emissions cuts. If anything, the apparent need to even consider such interventions should prompt all of us to push for more CO2 emissions cuts faster.
But both do deserve more study, especially with an eye toward their interaction with planetary-scale tipping points. Even if the world could live with Miami underwater, the trade-offs might become more urgent when looking at 100,000 square miles of the Eastern Seaboard engulfed, or when considering the fate of 100 million people who call the lowlands circling the Bay of Bengal their home.
Tipping Economics
Tallying the full economic costs of climatic tipping points is a formidable task. Instead of precise answers to narrow questions, it consists in part of speculative answers to broad questions. And the inherent conservativism of science necessarily leads to conservative answers. But, alas, the practical alternative to trying to make sense of the economic costs of tipping points is to write off the issue as if it didn’t matter. So try we did.
Three colleagues and I set out to quantify the economic impact of tipping points in a study spanning AMOC, the Amazon dieback, the West Antarctic ice sheet and five other potential mega-problems ranging from the Indian summer monsoon shutting down, to the sudden release of carbon and methane stored in permafrost covering the Arctic and its ocean equivalent, methane hydrates stored in deep ocean seafloors.
The ultimate metric of the cost of climate inaction is the social cost of carbon, the full cost of each ton of CO2 released into the atmosphere – in other words, the price every polluter should be paying for the privilege of using the atmosphere as a dumpster. The task, then, is to calculate the economic impact of each climatic tipping point on the social cost. Overall, our calculations put the impact at around 25 percent of conventional estimates of the social cost.
Reactions to that number have spanned the gamut, to put it politely. The responses ranged from “grim” on the one hand, to variations on “here they go again” on the other.
The latter reaction is best interpreted as a broadside against “standard,” neoclassical economics, or what some believe that standard economics says (or fails to say) about the urgency of climate action. I have some sympathy with skepticism of the relevance of neoclassical economics: The discipline does need a climate revolution. I would also argue that the 2018 Nobel Prize given to Yale’s Bill Nordhaus, while well deserved, ironically set the climate policy debate back by a decade or more. (In any case, the prize should have at least been shared with the late Martin Weitzman of Harvard, who sadly died in 2019.)
But these broadsides against the relevance of “standard” economics in formulating climate policy have indeed been just that – broad. The published reply to our study is co-authored by climate scientist Tim Lenton, lending the exercise some credibility. But it zeroes in on one number in our original analysis, a figure concluding that, at 6 degrees Celsius of global warming, tipping points would lower total consumption by around 1.4 percent.
Now, it’s easy to take that number out of context and make fun of it. How naïve must economists be to believe that climatic changes large enough to wipe out society as we know it – 6 degrees Celsius is a civilization-ending jump in global average temperatures – would lower GDP by only 1.4 percent!
The misunderstanding here is that our analysis uses a climate damage function that has civilization as we know it collapsing well before 6 degrees of warming. Loosely speaking, if everything is dead already at 4 or 5 degrees of warming, further tipping points don’t add much of anything. You can only die once.
Meanwhile, the “around 25 percent” figure referring to how much the potential for tipping points add to the social cost of carbon does indeed hide quite a bit. In short, that impact, too, has a long right tail. We estimate a 10 percent probability of tipping points not merely increasing the social cost by 25 percent, but doubling it.
All this raises the question whether making more precise estimates of the social cost of tipping points is all that fruitful. There is surely more work to be done focused on individual climatic tipping points – and especially on their potential interactions. Let me go out on a limb now and guess that the news won’t be good. Calculating the social cost of carbon is important, but doing so ought not detract from getting on with cutting climate pollution, and quickly.
Positive Tipping
There always seems to be news to lead one to believe that, for every two steps forward the world is taking toward the containment of climate warming, we are taking one step back. But perhaps the overarching and underappreciated storyline on the climate front is that climate technology, finance and public policy are moving very fast in the right direction.
To be clear, this is not to argue for laissez-faire, let-markets-fix-things-on-their-own naïveté. It is to acknowledge how much climate action has already achieved, and how much more is in the works. It is also to say that tipping, it turns out, is a two-way street.
When Goldman Sachs estimates that the climate measures in the U.S. Inflation Reduction Act of 2022 will trigger almost $3 trillion in total public and private spending over the decade while unleashing well over $10 trillion in total spending by mid-century, that is a reason to celebrate. The fact that deep-red Texas is moving past deep-blue California in total installed solar capacity is a reason to celebrate. The reality that solar panels have become the cheapest source of electricity is a reason to celebrate. And that’s just the tip of the iceberg.
Ironically, the latest policy concern around solar panels and electric vehicles is that they are too cheap – that the Chinese have become so efficient at making them that manufacturers in the U.S. and EU can’t compete without subsidies or tariff protection.
The news also points to the many positive tipping-like phenomena already underway. These positive social, political and technical feedback loops may not all meet the Gladwellian standard of a true tipping points, but they do so in spirit.
People are plunking down their own money for heat pumps, induction stoves and electric cars in part because they are fundamentally better technologies, and also because they will save them money. There are plenty of vested interests attempting to delay the inevitable, but delay is all they can do.
The name of the game is marshalling finance, technology and a host of other forces to turn the usual fears of tipping points on their head, and to move from avoiding negative climatic tipping points to harnessing positive socioeconomic ones. The world will be a cleaner, richer and more livable place for it.
But…
There is a risk in focusing on planetary-scale tipping points: They distract from the all-too-real economic shocks likely to be triggered by much smaller, more immediate climate changes.
Crop yields, for example, do not need Earth-system tipping to fall off their own cliff. All it takes is relatively small increases in global average temperatures that lead to local daily temperatures crossing thresholds of somewhere around 30 or 32 degrees Celsius (86 to 90 degrees Fahrenheit) for yields to collapse. For corn, the threshold appears to be around 29 degrees Celsius, for soybeans around 30 degrees, and for cotton around 32 degrees.
These temperature thresholds exist for crops and people alike. New York students taking the Regents Exams to graduate high school are 10 percent more likely to fail when the exams fall on a day above 32 degrees Celsius (90 Fahrenheit). Or that one – one(!) – additional day above 32 degrees Celsius in a year lowers annual payroll by 0.04 percent in the United States, and probably much more in poor countries lacking air conditioning.
Moreover, the effects don’t stop with less productive crops and sweatier brows. Hotter days lead to more road rage and car crashes on the one hand, and police aggression on the other. Not to mention more domestic violence and ethnic riots. They also show up some areas that may be relatively inconsequential but lead to inescapable conclusions. An analysis of almost 60,000 Major League Baseball games shows that pitchers will apparently hit opposing team batters to retaliate for earlier errant pitches more on hot days than on average ones.
All of this adds up to real economic impacts, as Jisung Park details in his book Slow Burn (excerpted in the Spring 2024 issue of the Milken Institute Review). Often it is not the dramatic tipping points but the small, sometimes hidden costs that hit hardest. Park has both conducted and collected a wealth of studies, zeroing in on daily temperature thresholds of around 30 to 32 degrees Celsius, above which bad things tend to happen.
None of this is to say that planetary-scale tipping points don’t matter. But the small, daily costs add up to quite a bit all by themselves. Crucially, these temperature thresholds are not tipping points in the Gladwellian or any other sense of the term. It merely takes a linear increase in temperatures to pass thresholds that cause crop yields, test scores or economic productivity to plummet.
One novel analysis by two young macroeconomists points to how these economic shocks add up to as much as 12 percent of GDP for as little as 1 degree Celsius of warming, between three and 10 times as much as prior estimates. And the big innovation here is both simple and striking: climate economists are typically looking for specific, identifiable links between temperatures and adverse events. Adrien Bilal and Diego Känzig do pretty much the same, but instead of linking local impacts to local temperatures, their data allow them to link local impacts directly to global average temperatures. The result: a social cost of carbon five times currently prevailing estimates.
Gernot Wagner is a climate economist at the Columbia University Business School. His most recent book is Geoengineering: the Gamble (Polity Press).
This essay was first published by the Milken Review under the title “Tipping Carbon” (24 July 2024). It is the second in a mini-series; the prior essay is titled “Taming Carbon” (23 October 2023).
Citation:
Wagner, Gernot. “Tipping Carbon.” Milken Review, 24 July 2024.