Steam billowing from the cooling towers of Vattenfall’s Jaenschwalde brown coal power station behind wind turbines near Cottbus, eastern Germany, Dec. 2, 2009. (Pawel Kopczynski/Reuters)

When it comes to combating climate change, many scientists and policy makers focus on one major goal: cut carbon emissions enough to keep the planet’s average surface temperature from rising more than 2 degrees Celsius above its pre-industrial level. But a new analysis, published on Monday by the Grantham Research Institute on Climate Change and the Environment, said we’re still falling short of the mark.

For years, the 2-degree target has been touted by experts as a kind of climate threshold: By staying within its confines, many argue, we can keep the planet in relatively stable condition and avoid the most dire effects of global climate change.

Currently, world leaders are developing concrete emissions reduction goals in preparation for this December’s U.N. climate change conference in Paris, where they’ll ultimately draft an international agreement to combat climate change with the goal of staying within the 2-degree mark. By contrast, if world nations were to do nothing — in other words, if we stuck to a “business as usual” trajectory — experts believe our climate could warm more than 4 degrees by the end of the century.

Three of the most heavy-hitting emissions reduction targets have already been declared by the United States, the European Union and China. The United States has resolved to reduce its carbon emissions by 26 to 28 percent below its 2005 emissions levels by 2020, and the European Union has vowed that by 2030 it will collectively cut its emissions by 40 percent compared to its 1990 levels. Meanwhile, China has claimed its carbon emissions will peak by 2030.

But according to the Grantham report, these resolutions, combined with the rest of the world’s projected future emissions, will probably not be enough to keep Earth within the 2-degree boundary.

“In thinking about where we’re going, it’s important to have an assessment now of what the sum total of those commitments might add up to,” said co-author Nicholas Stern, chair of the Grantham Research Institute on Climate Change and the Environment and president of the British Academy.

Stern and his co-authors Rodney Boyd and Bob Ward, also of the Grantham Research Institute, calculated what global greenhouse gas emissions will be in 2030 based on the announced targets from the United States, the European Union and China, as well as energy use estimates for the rest of the world published by the International Energy Agency (IEA). Then, they compared these calculations with a report from United Nations Environment Programme (UNEP) describing the kinds of emissions pathways that might allow the world to reach its 2-degree target.

The authors found that if the United States, the European Union and China stick to their resolutions, their combined emissions in the year 2030 will be between 20.9 and 22.3 gigatons of carbon dioxide equivalent. (A gigaton is a billion metric tons.) And their estimate for the rest of the world’s emissions came to about 35.4 gigatons, meaning total global greenhouse gas emissions in 2030 could exceed 57 gigatons.

But according to the UNEP report the authors used for comparison, global emissions in 2030 must be below 48 gigatons if we want even a 50 percent chance of hitting the 2-degree mark. (What matters is not precise emissions in 2030, but rather what emissions pathway the world is on by then, with emissions in 2030 taken as a representation of that.)

In other words, on our current trajectory, we’re unlikely to make it.

This means the world needs to step up its game, both leading up to the conference in Paris and afterward, Stern said. He and his co-authors laid out four potential steps in their analysis that could help world leaders get back on target. These include coming up with more aggressive emissions reduction plans; increasing investment and innovation in clean energy and land use; creating a mechanism in the Paris agreement that will enable participating countries to review their efforts and create better targets post-2030; and building strong foundations at home for a decarbonized society.

There’s still room for optimism, according to Stern. There are some uncertainties in the analysis that could lean in a positive direction. For instance, China has vowed to cap its emissions by 2030, but they could still peak earlier than that — perhaps by 2025 or even sooner, Stern said. Improvements in our clean energy technology are also a possibility. “There’s uncertainty, on the positive side, that technical progress could be even faster than we thought,” Stern said.

He added that governments’ political will to take action is an uncertainty that could cut either way. He believed the key to political goodwill when it comes to climate action is remembering that growth and climate responsibility are not mutually exclusive. “I think the building of that political will depends critically that these two things can come together and support each other,” Stern said.

In addition to the four steps outlined in the paper, Stern said another key to effective climate action is increased cooperation between countries — particularly sharing ideas and paying attention to the methods other countries are using to achieve their goals. Paris should be seen as the beginning of an ongoing conversation about decarbonization — one that should challenge countries to set more aggressive goals for themselves.

“We should recognize that it looks as if Paris will take us half of the way between what might have been ‘business as usual’ and where we need to be to meet 2 degrees,” Stern said. “I would tend to take a glass-half-full approach to that and ask how we can fill the glass up.”