How will U.S. withdrawal from Paris accord impact global climate?

The U.S. is the world's second-largest emitter of carbon behind China, so what impact will President Trump's decision to withdraw from the landmark Paris climate accord have on global climate?

Scientists say Earth is likely to reach more dangerous levels of warming sooner as a result of the president's decision because America contributes so much to rising temperatures. Calculations suggest withdrawal could result in emissions of up to 3 billion tons of additional carbon dioxide in the air a year -- enough to melt ice sheets faster, raise seas higher and trigger more extreme weather.

According to researchers at Climate Interactive, reductions pledged by the U.S. prior to its withdrawal were expected to account for 21 percent of the total estimated global reduction.

"If we lag, the noose tightens," Princeton University climate scientist Michael Oppenheimer, co-editor of the peer-reviewed journal Climatic Change, told the Associated Press of the immediate threat climate change poses.

That being said, China, India and other nations are expected to overperform on their Paris accord commitments, which could "significantly outweigh" the U.S. dropping out of the agreement, according to an analysis by Climate Action Tracker.

Experts and advocates have pointed out, however, that climate-conscious legislation at the state and local level could make up for national withdrawal from the Paris accord. The Sierra Club, an environmental advocacy organization, predicts that 60 percent of reductions needed to meet the Paris agreement could be implemented below the national level, largely through the replacement of coal-fired power plants and investments in energy efficiency at the local level.

In the wake of Trump's announcement, mayors from more than 60 American cities -- including Houston -- pledged to uphold Paris climate agreement commitments in their jurisdictions.

"We are increasing investments in renewable energy and energy efficiency. We will buy and create more demand for electric cars and trucks. We will increase our efforts to cut greenhouse gas emissions, create a clean energy economy, and stand for environmental justice," the mayors, all members of the Mayors National Climate Action Agenda, wrote.

Internationally, walking away from the agreement could also distance the United States from its allies in the developed world. In the weeks leading to Pres. Trump's anticipated withdrawal, China, Russia, Germany and other nations reaffirmed their climate commitments.

The United States joins Syria and Nicaragua as the only developed nations in the world not participating in the Paris accord.

The Associated Press contributed to this report.

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