In 2015, representatives from 196 countries met for the Paris Climate talks, setting greenhouse gas emissions targets for the year 2025. As part of this agreement, the US has set what are called "intended nationally determined contributions," which are planned reductions in carbon emissions. A recent paper in Nature Climate Change examined the current federal policies and determined that it is unlikely the US will meet its own targets as things now stand.

The paper attempted a comprehensive evaluation of historical and projected greenhouse gas emissions in the US, and it put a particular emphasis on the most influential policy years. These were 2005 (the year the Kyoto Protocol went into effect and the Montreal action plan was developed) and 2025 (the date for reaching the targeted goals of the Paris climate talks). Researchers built a model that included historical and projected estimates of both climate data and energy use. The team then used the model to test the potential effects of several different pieces of climate policy that have been proposed or passed in recent years.

They found that the EPA’s Clean Power Plan would be the largest contributor to greenhouse gas emissions reductions, producing an estimated drop of 221 to 267 million tons of CO 2 equivalent. However, the team did find that an earlier, more ambitious version of the Clean Power Plan would have had an even larger effect.

Five other pieces of policy would have effects ranging from 36 to 146 million tons of CO 2 equivalent reductions. These include the EPA’s Significant New Alternatives Policy, the Montreal Protocol amendment, and a variety of gas and emissions targets set in the state of California.

The US has pledged a 28 percent reduction from the 2005 greenhouse gas emission level by 2025. But even the most robust reductions possible given current and proposed emissions policies would only produce roughly a 4.8 percent reduction in emissions. This would leave a 24.4 percent gap between the goals and the most optimistic projections of the effect of current policies.

The authors write that if the US were to adopt an aggressive phase-out of coal and natural gas generation, with accompanying increases in renewable energy and the adoption of electric vehicles, it is possible that a more robust emissions reduction could be made. Similarly, the conversion of oil- and gas-based heating systems to electric could result in considerable greenhouse gas reductions. Other gains could be made through policies that encourage people to use public transit and ride shares.

Though this paper presents some discouraging news on the US’ emissions reductions goals, it also presents several options for more aggressive pursuit of this goal. But all of the options involve changes in various transit, energy, and public works policies, which would be extremely difficult to enact.

Nature Climate Change, 2016. DOI: 10.1038/NCLIMATE3125 (About DOIs).