Companies have long made commitments to cut their carbon emissions. But, until recently, many of these targets haven’t been grounded in science. Their announcement may have sounded impressive. But it may not have reflected the size of a company’s emissions, or been aligned with what scientists say we can safely put into the atmosphere. That’s changing as a result of the Science Based Targets initiative from the Carbon Disclosure Project, the UN Global Compact, the World Resources Institute, and the World Wildlife Fund. More than 150 companies have agreed to set targets that accord with the goal of keeping global temperature increases under two degrees Celsius. And 13–including NRG Energy, Dell, General Mills, and Sony–have already produced a target. “Some companies just make a stab in the dark,” says Cynthia Cummis, WRI’s deputy director for greenhouse gas protocol. “They decide to reduce emissions 20% by 2020 [for example] and it sounds credible. Other companies have all their energy-efficiency projects planned, and they say, ‘Let’s add those together and that will be our target.’ That’s not going to get us to the level of reductions we really need.” Scientists say we need to emit no more than about 1 trillion tons of carbon by 2045 to stay within the two degree limit. We’ve already emitted more than half of that. In signing up to the initiative, companies agree to calculate targets based on one of seven methods. These include reducing emissions in line with internationally agreed “pathways”–say, a 70% cut by 2050. Or it could be in terms of GDP: A company works out its percentage of global economic output and matches its target as a percentage of the total limit. The initiative shows how some companies are ahead of governments in their carbon reduction efforts. None of the country commitments to last year’s Paris agreement were conceived with an overall carbon budget in mind. In fact, even if governments follow through on their promises, it’s likely emissions will go well beyond the two degree threshold. Cummis hopes to sign up at least 250 companies by 2018 and for science-based targets to become standard practice. Already some investors are taking science-based targets, or the lack of them, into account when appraising companies. “This is a way [for companies] to differentiate themselves from their competitors and it’s becoming a growing expectation from their customers and investors,” Cummis says.