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The Green New Deal is presenting climate scientists such as me with a dilemma. At long last, some politicians (other than retired ones) are taking seriously both the importance and the challenge of dealing with climate change. But many of us are also uncomfortable with the rhetoric of “climate emergency,” and the implication that “the science dictates” a very specific policy response.

I was one of the authors of the Intergovernmental Panel on Climate Change (IPCC) Special Report on a Global Warming of 1.5°C, widely cited as saying “We have 12 years before we reach 1.5 degrees Celsius, if we fail to act now.” (Or, on your side of the Atlantic, 2.7 degrees Fahrenheit.) This is often conflated as “We have 12 years to act if a warming of 1.5 degrees Celsius is to be avoided.” Both sound bites are misleading, in potentially dangerous ways.

What our report actually said was that global warming has reached 1 degree Celsius (plus or minus two-tenths of a degree), increasing at 0.2 (plus or minus 0.1) degrees Celsius per decade, and would likely reach 1.5 degrees Celsius sometime between 2030 and around 2050 if the current rate of global warming continues. So while it would be irresponsible to discount the possibility that we are already at 1.2 degrees Celsius and warming at 0.3 degrees Celsius per decade, thus reaching 1.5 degrees Celsius by 2030, it is equally irresponsible to suggest that this figure is what the IPCC predicts. This is an important distinction; many of the critics of the Green New Deal would be all too happy to shout “IPCC doomsday forecast out by a factor of two” if global warming is still “only” around 1.25 degrees Celsius in 11 years’ time.

What about “We have only 12 years to act”? Emission scenarios that have a better-than-even chance of limiting warming to 1.5 degrees Celsius without resorting to massive—and potentially unfeasible—levels of carbon dioxide removal involve something like a halving of global emissions by 2030. However unlikely it sounds, this appears to be a relatively robust result (meaning that all available evidence agrees): The fastest rate at which emissions decline in all current computer models of the global economy is around 2 billion tons of carbon dioxide (2 gigtons of carbon dioxide) per year per year. (Yes, you read that right: It’s a deceleration, so it’s “per year per year.”) Try to make annual carbon emissions decline any faster than that, and the models just can’t keep the lights on.

These models have been widely criticized for making too-conservative assumptions about future technologies—but most are also designed with very optimistic assumptions about future policies, such as the immediate introduction of a global carbon price. No one knows if it is really possible to hit the brakes on global emissions that hard, but it would be brave to assume we can brake any faster.

Consequently, given that current emissions are over 40 gigatons of carbon dioxide per year, it would take more than 20 years to reach net zero even if we start reductions immediately—longer because the pace of reductions is expected to slow once we have dealt with the easy stuff. And because carbon dioxide accumulates in the climate system like lead in the bloodstream, warming will continue at least until net global carbon dioxide emissions reach zero.

So imagine we get to 2022, mid-way through the next US presidential term: Global emissions still haven’t peaked and it is clear there is no way of halving them by 2030. Will it then be “too late to prevent climate catastrophe”? It all depends what you mean by catastrophe: It might well be too late to limit warming to 1.5 degrees Celsius by emission reductions alone, but there will be plenty of things left worth saving. The danger with the word “catastrophe” is its finality: once catastrophe is inevitable, there seems little point in doing anything about it.

This 20- to 30-year “braking time” in the IPCC scenarios means we may well already be committed to 1.5 degrees Celsius, even if we reduce emissions immediately as fast as possible. So every year in which global emissions are not reduced (and they rose last year) is another 40 billion tons of carbon dioxide that we are committing our children to scrub back out of the atmosphere if they want to return global temperatures to 1.5 degrees Celsius sometime in the future. Given the scale of this challenge, the Green New Deal’s insistence on using only “low-tech” methods of carbon dioxide removal such as reforestation and soil restoration is worrying: It is not at all clear that measures like these can possibly remove enough carbon dioxide on the necessary global scale. Historically high historical emitters like the United States and the United Kingdom have the resources (and arguably the responsibility) to ensure that the world has other options available.

So what would I do? As Benjamin Franklin put it: “Any fool can criticize, condemn and complain, and most fools do.” I would like to see politicians debate something much more clearly focused on climate change—while the Green New Deal packages climate action with a host of other initiatives, like universal health care and employment. While these are worthy causes (and may be good politics), their presence makes it all too easy for its detractors to oppose the Green New Deal without addressing the fundamental climate issue—which, after all, is supposed to be its very reason for being. I’m not the only one calling for a much more focused Deal, such as the Washington Post’s proposal for an economy-wide carbon price. But again, this anchors climate action to a specific policy with a very mixed record thus far (as the Postacknowledges). I wonder what would happen if a much shorter and more policy-neutral bill were introduced, like the following:

Whereas the global temperature has reached 1 degree Celsius above its preindustrial level; that temperatures will continue to rise as long as global carbon dioxide emissions into the atmosphere continue; and that US carbon dioxide emissions from fossil fuel combustion remain over 5 billion tons per year; therefore be it resolved that the Federal Government will take all measures necessary to ensure that US carbon dioxide emissions from fossil fuel combustion are reduced, on average, by 1 billion tons per year for every tenth of a degree of global warming from now on.

You don’t need to be a mathematical genius to work out that this means that US fossil fuel carbon dioxide emissions would reach zero by the time global warming reaches 1.5 degrees Celsius. So opponents of such a measure would have to either argue that global warming has not actually reached 1 degree Celsius yet, or that fossil carbon dioxide emissions do not have a cumulative warming impact, or that US carbon dioxide is somehow special in not causing global warming. These are not points I hear very often, even from the most strident critics of climate action.

Alternatively, opponents would have to argue that they are comfortable with the United States continuing to cause global warming past 1.5 degrees Celsius, which would no doubt open some interesting conversations with farmers, fishermen, owners of coastal property, and others hit with the consequences. And the Chinese Hoax brigade would have no reason to oppose such a measure, because according to them global warming stopped in 1998 anyway. (Or was it 2016?)

Environmentalists might worry that this only addresses fossil fuel emissions: What about emissions from agriculture, refrigerants, and so on? I accept that this wouldn’t solve all aspects of global environmental change, and it certainly wouldn’t address healthcare or inequality. But if the United States was to lead on this and the rest of the world were to follow, this would “only” solve the problem of climate change caused by fossil-fuel carbon dioxide emissions.

I’ll take that.

One final point, from a fractious country on the far side of the pond: The United States did not get to the moon by starting with a 14-page plan. Kennedy set out the destination and the deadline, and left it to the collective genius of American enterprise and public servants to work out how to get there.

You can do it again.