Speaking to a voter at a recent campaign stop in New Hampshire, former Vice President Joe Biden said of Sen. Bernie Sanders’s climate change plan: “Not a single solitary scientist thinks it can work.”

Less than a week later, the Sanders campaign released a statement signed by 57 science professors and researchers across the country, declaring that his plan “is not only possible, but it must be done if we want to save the planet for ourselves, our children, grandchildren, and future generations.”

The plan’s policies, the letter says, “are realistic, necessary, and backed by science.”

NEW: More than 55 scientists sign letter supporting @BernieSanders' climate plan #GreenNewDeal pic.twitter.com/xfRvjei7st — People for Bernie (@People4Bernie) January 28, 2020

I’m sorry, but this is wrong-headed — what Biden said, the response, the whole debate. The wisdom of a climate plan is not climate scientists’ to decide. It’s like asking physicists to judge a dance competition and hearing that one of the dancers is “backed by physics.”

Climate scientists are not prophets or priests. They cannot lay hands on a plan and bless it as feasible unto us. They are not the arbiters of what is or isn’t feasible for the US in 10 years, because that question involves 1,000 other questions about demographics, economics, politics, technology, social change, justice, and equity, and climate scientists are not experts on any of those things. They are experts on climate science.

Don’t get me wrong. There’s nothing wrong with climate scientists weighing in on a climate plan. They are concerned citizens like anyone else — probably more concerned, all things considered — and deserve to have their voices heard. But on complicated matters of politics and practicability, they have no special authority.

Science has a long and vexed history at the heart of climate politics. Conservatives have attacked it from the beginning, and as part of their defensive crouch, climate advocates (including many climate scientists) have adopted some rhetorical habits that do not serve them well.

I’ll focus on two of those bad habits here: using science as a moral shortcut and treating scientists as all-purpose experts.

Science does not say we should do things

The recent IPCC report concluded that, for any hope of limiting global temperature rise to 1.5° Celsius, net greenhouse gas emissions must fall 50 percent by 2030 and to zero (and below) by mid-century.

As that conclusion filtered out to climate activists, it became some version of “science says we have to cut emissions in half in the next 10 years.”

What the science says is crystal clear: we have to reduce our emissions extraordinarily rapidly. We must halve them by 2030 and get to net zero between 2040 and 2060 to have half a chance of keeping warming to 1.5 degrees (figure from https://t.co/nbP6gByRuK). 2/ pic.twitter.com/Z9EXkvPk1l — Profette Of Doom (@JKSteinberger) October 15, 2019

Technically, though, it’s not true. Science does not say things like that.

Climate scientists study biophysical systems and how they work. They can, based on the rules and regularities they have observed, predict how those systems will react to the introduction of, say, megatons of greenhouse gases. In fact, the models they have built have performed extraordinarily well at that task.

What climate scientists can say about the future is in the form of a conditional: if emissions are X, biophysical systems will respond like Y. They can describe the many subsystems that feed into climate change, how they have operated in the past, and predict what will happen if those subsystems change in various ways. Climate science might say, for instance, “If greenhouse gases continue on their current trajectory, the future will contain many more heat waves, storms, famines, conflicts, and migrations, which will cost humanity an estimated kajillion dollars.” (Here’s a peer-reviewed paper on possible economic damages to the US through 2090 under various scenarios.)

What climate science cannot tell us is what level of future climate impacts is “acceptable” or what level of present-day resources it is worth spending to avoid them. That is a prudential and moral judgment, about which climate science has no opinion. It can only tell us what might happen, not what should.

When people say “listen to the science,” what they really mean is that the moral and prudential implications of the science are so obvious as to go without saying. To them, the fact that GHG emissions are putting us at greater risk obviously means we must reduce GHG emissions.

But it’s worth remembering that consciousness of climate change was born in, and grew in, a particular set of tribes and identities, among a particular kind of people. Specifically, scientists, academics, researchers, policy analysts, and environmentalists all tend to rank high in what psychologists call “openness to experience.” They are inclined toward non-zero-sum, internationalist, cosmopolitan thinking.

Such people, confronted with a collective problem, reach naturally for cooperative, mutually beneficial solutions. It feels natural to them to do so; they assume everyone will.

But people with a more conservative temperament do not like that kind of thinking or those kinds of solutions and if they are told that certain facts make those solutions inevitable, they will resist the facts. That, in a nutshell, is the source of conservative resistance to climate science. It’s not about the science itself, it’s about the fact that the science comes packaged with what they see as a liberal policy program.

And just as conservatives often use climate science as a proxy to fight liberal policy solutions, liberals often use it as a proxy to support them. People on the broad left, including in science, research, and advocacy circles, are forever claiming that science backs their political and policy preferences. “Science says” we must decarbonize by 2030, or that it’s not possible; that decarbonization must involve nuclear, or that nuclear doesn’t pencil out; that getting off oil is necessary, or that it will never happen.

Get on the side of science. Get on the side of the people. Get on the side of the future. pic.twitter.com/jZC3KmNjvF — Jerry Brown (@JerryBrownGov) October 29, 2019

Again, it’s not true. Science doesn’t say things like that. It can and should provide the factual boundaries of debate, but it can not answer the plethora of questions within those boundaries, questions primarily about us, what we should do, what we’re capable of doing, who should benefit and who should suffer, and who owes what to whom. Science is, as the philosophers say, “necessary but not sufficient” for productive climate debate.

Both sides of the debate are using science as a proxy, drafting it in service of moral and prudential arguments that, for whatever reason, they are afraid to make directly. It’s not healthy. Those moral and prudential arguments need to be had. The case for action needs to be made on its own terms, not on science’s borrowed authority.

People often misunderstand this point, so let me emphasize: I believe that the case for ambitious climate action is overwhelmingly strong (which is why I’ve been making it my whole career) and that cooperative, non-zero-sum agreements and an aggressive, government-driven transition are the best and only way to protect the world’s most vulnerable people and species.

I believe that, as conservatives are forced to stop hiding behind lies about the science and make their moral and prudential case directly, on its own merits, they will find themselves in an increasingly untenable position. The reactionary approach to climate change — build higher walls, cut off refugee flows, get the fossil fuels while the getting is good — is selfish, myopic, even nihilistic. There’s no good case to be made for it.

That’s precisely why conservatives have so loved squabbling about science all these years. It allows them to hide from a debate they know they can’t win.

They are close to being pulled out into the open, but every time climate advocates get dragged into science debates, these macho partisan contests of whose list of scientists is longer, they are playing conservatives’ game. Every time they tell the public that “science says” we must, e.g., pass a carbon tax, or implement a Green New Deal, they are strengthening the conservative case that they are hiding policy and value judgments behind the cover of science.

There are policy and value judgments behind any climate plan. It is counterproductive to hide them or pretend that science settles them. They must stand on their own.

Expertise is not fungible

Democrats have adopted the goal of reaching net zero carbon emissions by 2050. Pulling that off will require rapid and fundamental changes to US politics, the economy, and values and norms. It will involve an endless series of difficult tactical and strategic choices, from the long-term to the immediate, e.g., how to get legislation past the filibuster in 2021.

Over and over again, advocates will face trade-offs between their ambitions and the limits of the political systems currently in place, even as they work to expand what is politically possible. Those decisions, which can be agonizing, cannot be made by science.

Climate science is helpful in making clear the consequences of various decisions, which is what led Democrats to adopt the goal in the first place. But there’s no reason to think that climate scientists’ understanding of biophysical subsystems translates to wisdom on social and political matters.

As it happens, there are entire research communities and academic disciplines devoted to studying politics, policy, and social change. Their expertise deserves respect too, and it is not interchangeable with climate science.

Seeking wisdom means hearing not just from climate scientists but from social scientists, economists, psychologists, and historians. Social change as sweeping, as what’s being contemplated, will require all the insight we can find, wherever we can find it.

Conservatives have attacked expertise and the institutions that produce it for decades. The way to defend it is not to invoke scientists like some sort of priestly class capable of settling disputes among mere mortals, but to respect the institutions, the rules that make them work, their specializations, and their limitations.

Ultimately, the big questions about how to decarbonize the US won’t be decided by experts. They will be decided by America’s imperfect democratic processes. Influence in those processes is won through money and organizing, not expertise. The backing of scientists is good for winning arguments among those already of a like mind, but a great deal more is needed to make progress on the ground.

Scientists cannot solve the crisis of authority

It increasingly seems that the US is composed of two warring tribes that lack a shared body of facts or any shared sources of authority. Consequently, they are unable to communicate or persuade one another of anything.

This gridlock benefits the party of the status quo — the GOP demographic that has a hold on power far beyond its shrinking numbers — but it is disastrous for climate change. It understandably has climate hawks in a state of high anxiety, casting about for anything that might break through the paralysis.

That urgency pushes them to reach for science, one of the few sources of authority that retains any cross-cultural power, more often than is healthy. They are loading more on climate science than it is meant to bear.

Whatever their differences on policy, Biden and Sanders are both guilty of this, wielding science like some sort of scepter that can grant or deny credibility on climate change. It’s a poor substitute for the debates they ought to be having over political strategy, priorities, and policy design.

All politicians and reformers should be informed and bound by science — no small caveat, given the fantasyland in which the GOP dwells these days — but science will always under-determine what they can or should do. They will need a moral and prudential case that is convincing on its own terms.

Preventing immense suffering and transitioning to a healthier and more equitable society are not scientific goals. But they are worthy goals nonetheless.