Ever since the Paris climate agreement was signed in 2015, there has been a sense of buoyancy in the environmental community. That optimism was shaken briefly when Donald Trump announced the US would pull out of the agreement, but then restored quickly as every other country in the world recommitted to the cause of keeping global average temperatures from rising by more than 2°C above pre-industrial levels or, better still, 1.5°C.

The optimism is kept aloft by some promising trends. The costs of renewable energy are getting lower and lower. Shareholders of oil companies are pressuring them to fess up to the climate risks inherent to the business. Investors are pouring ever-growing sums into green bonds. Countries are becoming more ambitious about climate goals: Some are planning to ban the use of petroleum-powered cars, while others are aiming to hit zero emissions within decades in all sectors, including transportation, power, and industry.

All this would make it seem we’re on track. But we are not. In 2017, the world set a new record high for greenhouse-gas emissions. What can we do to turn the tide?

In two separate analyses published this week in Nature Geoscience, Glen Peters and Oliver Geden, researchers at the Center for International Climate Research and the Max Planck Institute for Meteorology, respectively, argue the solution is to completely rethink the way we set the policies designed to push us towards climate goals.

Changing the status quo

To convert the Paris climate agreement’s temperature-based targets into achievable goals, scientists calculate something called a “carbon budget,” or the total amount of greenhouse gas that all countries together can put into the atmosphere without causing average global temperatures to breach the crucial thresholds.

All scientists agree the current pace of climate change is unprecedented, and that it’s largely the result of human activities. But they debate the value of carbon budgets. In 2017, the dispute got particularly heated after a group of respected climate scientists suggested in a study that the world could continue to emit greenhouse gases at the current rate for a lot longer than we thought previously.

These debates matter. Lawmakers, who are usually not trained to understand climate science, use carbon budgets suggested by scientists, like those in the 2017 study, to lay out policies to help their countries honor their Paris climate commitments. But lawmakers need to balance environmental concerns with economic ones. If, suddenly, scientists say we have more time in hand, policymakers are likely to respond with actions like delaying the date when all cars need to be electric.

The problem, Peters argues, is that that carbon budgets have so many uncertainties that it renders them useless to policymakers. In his analysis, Peters says it’s possible to make scientifically valid arguments for both a large carbon budget and a small carbon budget. That’s because these budgets are derived from climate models, which are themselves based on hundreds of variables, and any small change in a handful of variables can produce different results.

“The carbon budget is great for an elevator pitch,” Peters says. “But it does not really serve a useful purpose for policy.” A better target, he says, would be zero emissions. The zero-emissions goal is acknowledged in Article 4 of the text of the Paris climate agreement, though it doesn’t set a date for when the world should reach that target (it does say that rich countries need to get there sooner than poor ones). Most scientists agree that the zero-emissions target date for the world as a whole should likely be early in the second half of the century.

A zero-emissions target may seem inflexible, but it’s actually much more actionable than a variable and uncertain emissions budget. It is relatively simple for each country to set a target date to reach zero emissions, based on, say, how wealthy it is. Then, each greenhouse-gas emitting entity in the country can set its own goal to reach zero emissions and governments can lay out effective policies to help emitters get there by the target date.

Talking politics

Convincing politicians to commit to a zero-emissions goal won’t be easy, Geden says. That’s because, directly or indirectly, scientists have been giving politicians a false sense of hope with regards to climate change.

“For 30 years now, we’ve been hearing that it’s five minutes to midnight,” says Geden. It’s the doomsday analogy that warns us that climate catastrophe is coming soon. “But in that period we’ve continued to emit more and more greenhouse gases, [and] scientists still say it’s only five minutes to midnight. How can that be?”

Geden worries that scientists always say it’s feasible to hit climate goals under certain circumstances. His concern is not that this is false, but that politicians hearing the message will only take home it’s first part—that the goals are attainable—and ignore the section where the experts lay out the specific details necessary to reach those ends.

Scientists have good reason for employing positive rhetoric: they worry that if they say the goals are infeasible then politicians would give up on climate action. They are “constantly shifting and shaping their assumptions to keep their story alive, because they fear defeatism,” says Geden. It’s one reason there are so many different carbon budgets for hitting the same climate goals: they’re essentially offering up a sampler platter for policymakers to choose from, allowing them to pick whichever budget makes their political life easier.

For example, until 2007, the concept of negative emissions—which relies on developing technologies cheap enough to pull carbon dioxide from the air—did not feature in popular climate models. But because the world was continuing to emit more CO2 each year, it became clear that, to keep the 2°C goal feasible, scientists had to start including negative emissions in their climate models. Now it is widely assumed that, if we are to hit our Paris goals, we will need negative emissions at a large scale, capturing billions of metric tons of carbon dioxide each year by some time in the second half of this century.

Geden has a solution to the communication breakdown that currently exists between scientists and policymakers. Instead of saying “yes, we can hit climate goals if we do this, this, and this,” Geden argues, scientists need to change their communication and say “no, we cannot hit climate goals unless we do this, this, and this.” That, he argues, will encourage among lawmakers the urgency scientists feel, but have failed to articulate to date.