Why the US will probably fall short of its Paris Agreement emissions target

With the landmark climate agreement nearing ratification, scientists are investigating how likely nations are to fulfill their pledges. One study suggests the United States, for one, may have been overly optimistic.

First Look

The United States, which produces one-sixth of the planet's total greenhouse gas emissions, has volunteered to slash emissions by 26 to 28 percent of 2005 levels by 2025 as its contribution to the soon-to-be ratified Paris Agreement.

Many have voiced concerns about how achievable this goal is, and a new analysis of both adopted and proposed measures conducted by researchers at the Lawrence Berkeley National Laboratory and published in the journal Nature lends legitimacy to the skeptics, finding that a lack of data and insufficient policies could make it very difficult for the US to meet its goal.

"If the policies were locked today, there would be a low likelihood of meeting the target," Jeffery Greenblatt, co-author of the study, told The Guardian.

“I wouldn’t disparage the US’s efforts so far, but we need to do more as a nation and globally to reduce emissions," he added. "However we splice it, that’s hard to do. We can’t make small alterations to our economy – we need fundamental changes in how we get and use energy.”

The first major problem is that the 2005 emissions levels, on which the US policies are based, are not particularly clear. Dr. Greenblatt and his Berkeley Lab colleague Max Wei estimated that in 2005 the US emitted between 6.3 and 7.4 billion tons of carbon dioxide, a range that diverges by more than a billion tons.

In addition, methane gas is notoriously hard to estimate, possibly adding as much as 400 million tons of emissions some years, according to the authors. Additionally, the US policy relies heavily on carbon reuptake from forests, but estimates range widely on how much carbon forests can absorb.

To meet the emissions goal, the US would have to cut between 4.5 billion and 5.5 billion tons of total emissions annually. Greenblatt and Dr. Wei calculated that even if all proposed and approved plans were put into full effect, including the controversial Clean Power Plan (CPP), the US would still fall short without additional measures.

The CPP, the cornerstone of President Obama's proposal to achieve the emissions cuts, aims to curb the greenhouse gas emissions from coal-powered plants. However, it is currently facing an uphill battle in the US Court of Appeals for the District of Columbia Circuit. Twenty-seven states with investments in coal production have accused the Environmental Protection Agency (EPA) of overstepping its authority, and the CPP cannot go forward while the case is being tried.

"There is certainly need for further policy action," Greenblatt told The Washington Post. However, he added, "I think the US should be complimented. They set their own target and they set out a path to meet it as best they could. I think if they need to work a little harder, that's not an unexpected outcome."

With 31 countries joining the Paris Agreement in the past week, the accord is very close to being ratified. The increased interest in reducing climate emissions comes at what could be a vital turning point for climate change policy as the US chooses between Democratic presidential nominee Hillary Clinton, who has said she would continue Mr. Obama's mitigation efforts, and Republican nominee Donald Trump, who has frequently called climate change a hoax.

"It's true that other nations collectively emit much more than the US, but we are one of the world's biggest emitters, right behind China," Greenblatt told USA Today. "So reducing our emissions will have a material effect on global totals. Perhaps more important, however, is that our efforts to reduce emissions can motivate other countries to set similarly ambitious targets."