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It's time to panic about climate change and there is no Plan B

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It's time to panic about climate change and there is no Plan B

  • There is no Plan B to save Earth's populations from the build-up of greenhouse gasses.
    Yu. Samoilov/Flickr There is no Plan B to save Earth's populations from the build-up of greenhouse gasses.

Let’s get this on the table right away, without mincing words. With regard to the climate crisis, yes, it’s time to panic.

We are in deep trouble.

To understand why, it is necessary to understand something about carbon budgets.

Some of the carbon dioxide added to the atmosphere by human activities such as fossil fuel burning is quickly taken up by the upper ocean and land ecosystems. Some of the rest is slowly absorbed into the deep ocean over the next millennium. However, a lot remains in the atmosphere, and it is only slowly removed by geological processes that take hundreds of thousands of years. Consequently, carbon dioxide accumulates in the atmosphere throughout the lifetime of the fossil-fueled economy, and it will not drop much even after we finally kick the carbon habit and cease our carbon dioxide emissions.

The situation is analogous to mercury accumulating throughout the lifetime of long-lived fish and the humans who eat them: It is cumulative exposure rather than the rate of exposure in any given year that determines the harm. Consequently, the longer the exposure persists, the closer one approaches a deadly accumulation.

So too with climate. Unlike conventional forms of pollution like those causing smog, which depend on local emission rates over the past week or so, the harm done to the climate by carbon dioxide emissions is determined by the cumulative emissions over spans of time measured in millennia. Since cumulative emissions by definition only go up, not down, the harm done by carbon dioxide emissions is, in effect, irreversible on time scales of importance to human societies. A corollary is that in order to halt global warming, it is necessary to bring net carbon dioxide emissions by the world economy to zero. There is no so-called “safe” level of carbon dioxide emissions. As long as we continue emitting any carbon dioxide, the world will continue to warm.

Barring technological breakthroughs allowing for the active removal of massive amounts of carbon dioxide from the atmosphere, the cumulative carbon we emit will determine the climate our descendants will have to cope with for at least the next 10,000 years, and probably much longer. Some calculations illustrating this point are detailed in a Nature article I was involved in, along with a cast of dozens.

Cumulative carbon is usually expressed in terms of the amount of carbon contained in the carbon dioxide added to the atmosphere by fossil-fuel burning, deforestation, and similar human activities. That’s because it is the carbon that is transferred to the atmosphere from long-standing reservoirs (primarily deeply buried fossil fuels) that we are concerned about; the oxygen in carbon dioxide was already in the atmosphere. A metric ton (“tonne”) of carbon dioxide, or about 2,200 pounds, contains a bit over a quarter-tonne of carbon, or about 550 pounds.

Anthracite coal is about 95 percent carbon, and gasoline and diesel fuel are about 86 percent carbon by weight, so completely burning a tonne of either fossil fuel adds roughly 950 kilograms (kg) and 860 kg to the stock of cumulative carbon for which humanity is responsible. (Other forms of coal may contain less carbon but are just as dirty because more must be burned to generate a given amount of energy. Bottom line: When it comes to climate, there is really no such thing as coal that can be called clean, no matter what the industry likes to claim.)

What does this all mean?

The upshot is that the total cumulative carbon allocation for humanity compatible with a 50–50 chance of keeping global warming under 2 degrees Celsius (3.6 degrees Fahrenheit) is, in round numbers, a trillion tonnes.

That’s it.


And of that trillion tonnes, we have already used up over 630 billion tonnes, leaving just 370 billion tonnes to go.

That might seem like a lot of tonnes, but at current emissions rate, we’d get there in just 37 years, or 2057. Up until 2016, there was reason to hope that perhaps the world emission rate had stopped growing and had leveled off; if the emission rate held steady at that level out to 2030, and thereafter trended linearly to zero by 2080, then with the help of the Paris climate accords we would have decarbonized without exceeding the trillion-tonne budget.

Sadly, those hopes have proved forlorn. While it is hazardous to draw conclusions about trends from just a few years of data, our recent carbon dioxide emissions record is gloomy; we are still on track for a perilous exponential growth rate. World emissions rose 1.5 percent in 2017, and an estimated 2.7 percent in 2018. For a time, US emissions continued to decline modestly despite the Trump administration’s environmental vandalism; the inexorable forces of the market meant that aging coal-fired power plants continued to be replaced by cheaper, cleaner, newer, and more efficient plants powered by natural gas and renewables. But growing carbon dioxide emissions due to industry and transportation have more than offset this progress, leading to an estimated 3.4 percent growth in US emissions in 2018. Chinese emissions went up nearly 2 percent in 2017 and 4.7 percent in 2018 – even while China put into place aggressive domestic energy policies in the past few years which may, eventually, bring down their national emissions. In addition, their “Belt and Road” – involving the creation of a vast, $1.3 trillion network of railways, energy pipelines, power plants, highways, and border crossings that seeks to create a China-led trading bloc involving two-thirds of the world’s population – is also funding a great deal of harmful fossil-fuel development, including $20 billion in funding for coal plants around the world.

Even in the European Union, which has expressed a strong commitment to decarbonization, emissions were up 1.8 percent in 2017. and down 2.5 percent in 2018, resulting in little progress toward decarbonization. Every year that passes where emissions fail to decrease puts the goal of staying under a trillion tonnes farther out of reach.

With continued 2.5 percent compound growth, we hit our trillion-tonne limit in under 27 years. And if the trend continues beyond that time, the dark magic of exponential growth brings our planet to two trillion tonnes in 50 years (4 degrees Celsius of warming, or 7.2 degrees Fahrenheit) and three trillion tonnes (6 degrees Celsius warming, or roughly 10.8 degrees Fahrenheit) just 86 years from now. Just 2 degrees Celsius of warming would have been bad enough; 4 degrees Celsius of global warming would be “cataclysmic,” said a report by the World Bank – hardly a bunch of radical environmentalists. The impacts are familiar: increased forest fires, drought in some places but deluges in others, loss of Arctic sea ice, increase in deadly heat waves, increased food insecurity, sea level rise, and biodiversity loss, among many other impacts – and we know for certain that the hotter it gets, the worse it gets.

And land warms more than the global average, and Arctic warming is even more amplified than land warming. An additional consideration is that there’s a 50–50 chance that the warming is worse than these mid-range forecasts, perhaps much worse. Heat stress could make half the planet uninhabitable for mammals outdoors.

That’s all unquestionably bad news. The question is not whether to panic, but how to respond constructively to the entirely justifiable anxiety about the climate disruption we are bringing upon ourselves.

A great deal of confusion has been caused by a misreading of the recent Intergovernmental Panel on Climate Change report on the benefits of halting warming at 1.5 degrees Celsius instead of the more usual target of 2 degrees Celsius. Of course, the carbon budget compatible with holding warming under 1.5 degrees Celsius is lower than a trillion tonnes. Once we allow for the warming caused by human-caused greenhouse gases such as methane and nitrous oxide, some estimates put the threshold low enough that in order to have a reasonable chance of avoiding it, carbon dioxide emissions would have to start declining right now. In one scenario discussed in the report, carbon dioxide emissions would have to decline by about 50 percent in just 12 years, and fall to zero not too long afterward.

This has led to headlines such as “We have 12 years to limit climate change catastrophe” in The Guardian. Rep. Alexandria Ocasio-Cortez (D-NY), in launching her largely worthy version of the Green New Deal, incorrectly stated that human-caused climate change will “destroy the planet” if action is not taken within 12 years – symptomatic of the misperception of the situation in many quarters. Statements like this fail to recognize the meaning of a warming target such as 1.5 degrees Celsius or 2 degrees Celsius.

Instead, such targets are just guideposts as to how bad things get for various levels of warming. A 1.5 degrees Celsius warmer world is going to be pretty bad – but it is distinctly better than a 2 degree Celsius warmer world.

But if we do blow past the 2 degrees Celsius target, however, there is still a great deal to be gained by averting the arguably existential risks that come with a 4-or 6- degree Celsius warmer world. My colleague Myles Allen has more to say about the fallacy of the “12 years to doom” meme in The Conversation.

Solutions? Or false premises?

And that brings us around to the basket of attempted climate fixes loosely, if inappropriately, referred to as “geoengineering,” and specifically to schemes to cool the Earth by increasing its reflection of sunlight back to space (otherwise known as its albedo).

This sort of climate intervention is usually referred to by its boosters as “solar radiation management” or “solar geoengineering,” but regardless of which term is used, they both give the false impression of a comforting level of precision in knowing the outcome – something that is wholly inappropriate in the face of the substantial uncertainties surrounding it. We simply do not know the way the climate will respond to these novel forcings, or how our social and political systems will respond to these disruptive and possibly ungovernable technologies. In the US National Academy report on the subject, we adopted the rather wonky term “albedo modification” to describe these proposed interventions. But personally I prefer a term inspired by science writer Eli Kintisch’s take on the subject: “albedo hacking.” At present, it looks like the most feasible means of albedo hacking, from a purely technical standpoint, is the injection of substances into the stratosphere that lead to the formation of tiny aerosol particles that effectively reflect sunlight.

Albedo hacking has been touted as a sort of Plan B to make up for the world’s failure to make a responsible start on decarbonization of the economy. This is the scenario envisioned in an editorial by the noted atmospheric chemist Paul Crutzen in 2006, and it has tended to dominate the perception of the role of albedo hacking ever since.

But of all the possible scenarios in which albedo hacking would be deployed, using it to make up for a failure to decarbonize is the most nonsensical. Carbon dioxide accumulates in the atmosphere, but stratospheric aerosols do not. Therefore, albedo hacking as a response to failure to decarbonize requires injecting ever-increasing amounts of chemicals into the stratosphere, up to the point where the physical limits of the technique are reached or unanticipated adverse consequences become unbearable.

The excess carbon dioxide that human activities inject into the atmosphere has a warming effect that extends essentially forever, whereas the stratospheric aerosols meant to offset that warming fall out of the atmosphere in about a year. It’s just a matter of gravity – stuff denser than its surroundings falls – aided a bit by atmospheric circulations that enhance the removal. This is why the cooling effects of even a major volcanic eruption like Pinatubo dissipate after two years or so. Hence, whatever level of albedo hacking is needed to avoid a dangerous level of warming must be continued essentially forever.

Otherwise, an abrupt termination would catastrophically unleash pent-up warming in a matter of a few years – a snapback known as Termination Shock – and the magnitude of this potential climate shock would increase, the longer that albedo hacking is used to offset our failure to decarbonize. Deployment of albedo hacking does not in any way “buy time” to get carbon dioxide emissions under control, since once emitted, carbon dioxide cannot to any significant extent be unemitted with known economically feasible technology; if albedo modification becomes necessary, it must be maintained essentially forever. The problematic need to continue albedo hacking essentially forever, if it becomes necessary at all, is called the problem of Millennial Commitment.

This time commitment is an important point that seems to be easily glossed over in discussions about this technology: Once it is underway, and we have committed the planet to albedo hacking, we would soon be in a position where we would need to continue hacking the albedo essentially forever (at least in comparison to the time scales normally considered to be relevant to human societies).


Think of what that word means: We would be committing generations yet unborn to continuously run a mechanical process, over a time-span longer than the age of the pyramids, longer than the estimated 5,000 years that Stonehenge has been in existence, longer than the 12,000 years that have passed since the Neolithic invention of agriculture, and longer than the tens of thousands of years that engineers hope that their proposed deep underground storage centers can house nuclear waste.

And if our offspring don’t (or simply can’t) do so at some point in the future, then they will suffer the consequences of an unimaginably huge climate shock, accumulated over vast amounts of time.

The physical basis of these concerns is not in doubt, and no amount of further research on albedo hacking can remove them.

Unfortunately, even the Environmental Defense Fund, or EDF – an unquestionably worthy environmental organization – has evidently bought into the fallacy that albedo hacking may be necessary as a “Plan B” for dealing with climate change. Their chief scientist, Steve Hamburg, stated in the organization’s 2011 press release “International Groups Call for Coordinated Oversight of Geoengineering Research” that “Solar Radiation management could be a Plan B. But more recently, the EDF seems to have gone beyond figuring out how to safely conduct research and moved into the area of promoting outdoor experimentation in real time – the first step to wholesale tinkering with the entire atmosphere. The EDF has publicly stated that it favors what it terms “small-scale field research” in their document titled “Our Position on Geoengineering” and accessed on July 25, 2019.

As can be seen from these two examples, there is some waffling here, but it is apparent that over time, the Environmental Defense Fund is gradually becoming, at the very least, a partner in a governance initiative that, in my view, has taken it as a foregone conclusion that outdoor experimentation at some scale will happen – and that the only question is how to govern it so it takes place in a so-called safe way. The governance initiative fails to ask the deeper question of whether it is wise at this point to engage in research that could facilitate the deployment of a technology that may well prove ungovernable.

The trouble with hacking

Dozens, and perhaps hundreds, of papers have been published on this topic since I first engaged with it, and they have not changed the basic nature of the key problems one iota.

I, myself, have contributed to the discussion of termination shock and millennial commitment in the National Academies report. As a scientist, I viscerally dislike repeating myself; I like to think that once the truth is out there, it will somehow win out and it is not necessary to belabor the point. But basic truths keep getting forgotten, particularly in the form of breathless press coverage of albedo hacking that is fatally attracted to the subject because it is perceived as boldly breaking down taboos – taboos that I would argue are there for a good reason. And so, once more into the breach.

Millennial commitment imposes an unprecedented burden on future generations. Boosters of albedo hacking point out the many technological dependencies human society already has, such as the Haber Process, which enables us to feed a population nearing 8 billion people by drawing nitrogen out of the air to make the primary ingredient in fertilizer. However, albedo hacking imposes an obligation that extends over millennia – while humanity has no experience of cooperating on maintaining any complex technological infrastructure for more than a century or two. An awful lot can happen over 10,000 years, and it would be a mistake to assume that human society would even be able to maintain its economic growth and technological capability without interruption over all that time. And failure to maintain the modification of albedo would have not just a local effect, but would drastically affect every square inch of the globe.

If we ever were to get into the Plan B scenario – where massive carbon emissions are offset by massive deployment of albedo hacking – humanity would be living under a terror that is hard for current generations to conceive. Imagine living in a world where the very habitability of large parts of the planet was dependent on maintaining a flimsy stratospheric shield that could disappear suddenly if there were a failure in the technological infrastructure that maintained it. This situation would be more like living under a plastic dome in the harsh vacuum of the Moon than living on our green and pleasant Earth. Those of us who lived through the daily fear of thermonuclear death from the skies during the depths of the Cold War have some inkling of what this would be like, but at least there was an exit strategy for the Cold War through negotiated nuclear disarmament. With known current technology, there is no exit strategy from Plan B.

Geoengineering boosters tend to counter that albedo modification would be so beneficial, compared to the alternative, that nobody would do something so crazy as to let the intervention terminate. But our current political world is rife with examples of irrationality and acts of national self-harm, so it is impossible to have confidence that it will treat albedo hacking with any more rationality than other contentious issues.

Albedo hacking is itself destabilizing, in the sense that its effects on regional climate, particularly with regard to precipitation versus temperature, are disparate. A contentious world is likely to get embroiled in disputes over which climate is right for which country, but in a deeply interconnected system like the climate system, it is impossible to solve one country’s problem without making different problems for another country. For example, what if Russia actually prefers a more ice-free Arctic? What if the albedo modification deployment that saves Beijing from killer heat waves causes failure in the Indian monsoon? For these things to be problems, it is not even necessary for feared effect to be real – if some climate-related damage is merely perceived to be the effect of albedo hacking, it will be a cause for contention, since the current state of climate modeling and the international justice system would make it exceedingly difficult to adjudicate such issues.

In the debate over the risk of abrupt termination, the availability of easy countermeasures that a dissenting country could deploy against albedo hacking facilities has been largely ignored. The two main proposed means of injecting aerosol-forming substances into the stratosphere make for easy and high-profile targets. Lumbering high-altitude aircraft would be ripe pickings for fighter jets or surface-to-air missiles, and the political consequences of shooting them down would be reduced by the fact that they would most likely be drones operating over international waters in the tropics.

Another seriously proposed scheme employs a hosepipe reaching from the ground to the stratosphere, suspended by balloons – a 16-kilometer high floppy tower, in effect. Imagine what an attractive target that would be for geoengineering dissenters, or even for apocalyptic terrorist groups aiming to just create chaos for human society. And there are other kinds of countermeasures. If Russia doesn’t like the restoration of Arctic sea ice by albedo hacking, all it has to do is to pump massive amounts of the potent and long-lived greenhouse gas sulfur hexafluoride into the atmosphere – or simply just dig up and burn more coal. The increased greenhouse effect would have to be countered by increased albedo hacking, and you can guess where that might end. To the resurgent terror of nuclear war, we would be adding the new terror of climate wars.

There are many additional problems with albedo hacking, including the primitive state of modeling the response to realistic aerosol injection, the production of climate states that have no real analogue to any time in Earth history, great uncertainties in the operation of key climate processes that govern climate response, and inadequacies in our current ability to monitor the Earth’s energy budget with the required accuracy, among many others. Active outdoor experimentation cannot address the most important questions short of an experiment so extensive as to count as deployment; for the most part, small-scale outdoor experimentation would serve to develop the technologies needed for deployment without providing the most important information bearing on whether it would ever be safe to do so. Consequently, in my view, the conjoined problem of termination shock and millennial commitment precludes albedo hacking from playing more than (at most) a very minor role in the portfolio of solutions to the climate crisis.

And to be clear, let it be noted here that I am not against benign, failure-tolerant, supplementary approaches to dealing with climate change, such as planting massive numbers of trees to help remove more carbon from the atmosphere – I just think that such so-called “natural” solutions have been oversold by the mass media. Their contributions, while useful, will be minor. And the copious and extravagant attention given to them by the popular press runs the risk of making us lose sight of the real goal: to cut down on the huge amount of carbon dioxide emitted into the atmosphere every year.

Where do we go from here?

The first order of business is to double down on efforts to decarbonize.

There is still time to turn that around – and if we don’t, any attempt to patch the climate using albedo hacking will only make the problem worse through the ever-increasing risk of termination shock.

To decarbonize, however, requires building a political movement that regards the climate crisis as a top priority. The Extinction Rebellion movement in the United Kingdom and the “Skolstrejk” actions led by young Greta Thunberg have helped to create a justified sense of urgency, and there are signs of an awakening in the US Democratic Party in the form of the push for a Green New Deal

The United Kingdom, despite a conservative government and a dysfunctional Parliament tied in knots over Brexit, has managed to make a legally enforceable commitment to achieve net zero carbon emissions by 2050, and has made significant progress towards that goal.

We also need to educate foot-draggers about the success stories in progress toward decarbonization – such as Sweden, which reduced its carbon footprint dramatically by relying on a broad portfolio of policies. Some of these policies were market-oriented, while others involved direct regulation and government policies; between them, they enabled the creation of the infrastructure needed to decarbonize – a concept that is not strange even in the context of robber-baron American capitalism: Just think of the transcontinental railroad, electrification, the interstate highway system, and the creation of the Internet, to name a few examples. To be sure, the portfolio of policies involves energy efficiency and renewables, but depending on context it can also involve gas-fired power plants with carbon capture and storage (a neglected technology) and nuclear energy – though an expanded role for the latter requires the engineering research needed to get nuclear off its current negative learning curve.

Then, too, there is a potential role for the more benign forms of climate intervention, namely Carbon Dioxide Removal (CDR), which would actively remove carbon dioxide from the air and store it in some form or place from which it could not get back. CDR is benign, in the sense that it does not treat just the symptom of the climate crisis but its root cause, and it does not have the problem of termination shock or millennial commitment.

CDR may never be economically feasible, so it would be dangerous to count on it as a fix, but it would be a valuable element of the portfolio of responses if it ever became feasible; it deserves vastly expanded research funding relative to the trickle of funding it gets currently. If CDR ever proves feasible at sufficient scale, it could alleviate some of the millennial commitment problem entrained by albedo hacking – and to embark on a destabilizing program of albedo hacking research before achieving the necessary CDR capability would be foolish.

It should be cautioned, though, that the emerging fad for so-called natural approaches to CDR is largely wishful thinking, and can play only a minor role relative to decarbonization. For example, a recent study argues that theoretically a trillion trees could be planted, which at maturity would pull 200 billion tonnes of accumulated carbon out of the atmosphere – assuming climate change didn’t kill them off and burn them up.

In the context of our trillion-tonne limit, however, even this massive hypothetical scenario represents just a small dent in the carbon budget; the estimates of atmospheric carbon dioxide drawdown given in the paper also neglect the important fact that when carbon dioxide is taken out of the atmosphere, a lot of stored anthropogenic carbon dioxide degasses from the ocean (or equivalently, the rate of ocean uptake of carbon dioxide is reduced).

There is also a lot of hype surrounding the potential for improved agricultural practices to take carbon dioxide out of the atmosphere and store the carbon in soils. But carbon stored in soil is not separated from the oxygen that wants to recombine with it, and bacteria have had two billion years to get very good at extracting energy by metabolizing organic carbon. The relatively rapid turnover of soil carbon means that even with continued practices that pump carbon into the soil, the reservoir fills up rather quickly. In pasturelands, researchers have estimated that soils could take up at most 200 million tonnes of carbon per year, but the reservoir would saturate after a few decades, as the Food Climate Research Network noted in its report, “Grazed and Confused.” Even allowing for 50 years of storage, that amounts to a measly 10 billion tonnes of carbon – just about one year of current emissions.

There is simply no good fix if we fail to stop pumping carbon into the atmosphere. We are already suffering some of the harms due to human-caused climate disruption. The only question is how much we will ratchet up the toll of human suffering, and the destruction of the ecosystems with which we share the Earth, before we finally achieve net zero carbon emissions.

Raymond T. Pierrehumbert is the Halley Professor of Physics at the University of Oxford. This story originally appeared in The Bulletin of the Atomic Scientists. It is republished as part of’s partnership with Covering Climate Now, a global collaboration of more than 300 news outlets to strengthen coverage of the climate story. is proud to be a partner in Covering Climate Now, an international project by more than 300 of the world's finest news organizations — The Guardian and Bloomberg, BBC, CBS News, Christian Science Monitor, Daily Mirror, Daily Beast, New Republic, Scientific American, Vanity Fair, PBS NewsHour, and more, including reporting from Australia, Canada, United Kingdom, Ireland, Argentina, Bangladesh, Chile, India, Israel, Italy, Japan, Netherlands, New Zealand, Norway, South Africa, Sweden, Belgium, Brazil, Czech Republic, Egypt, Morocco, Germany, Turkey and elsewhere. Read's reporting on this topic, and selected stories from other outlets.

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