The simple answer is nothing. These climate accords aren't worth the paper they're printed on. A lot of that has to do with the fact that people wanted something on paper, even if it was meaningless (note that this is talking about the Lima conference that preceded Paris, and that the same basis was used there)
The strength of the accord — the fact that it includes pledges by every country to put forward a plan to reduce emissions at home — is also its greatest weakness. In order to get every country to agree to the deal, including the United States, the world’s largest historic carbon polluter, the Lima Accord does not include legally binding requirements that countries cut their emissions by any particular amount.
Instead, each nation will agree to enact domestic laws to reduce carbon emissions and put forth a plan by March 31 laying out how much each one will cut after 2020 and what domestic policies it will pass to achieve the cuts.
“If a country doesn’t submit a plan, there will be no punishment, no fine, no black U.N. helicopters showing up,” said Jennifer Morgan, an expert on climate negotiations with the World Resources Institute, a research organization.
Instead the architects of the plan, including top White House officials, hope that the agreement will compel countries to act to avoid international condemnation.
“It relies on a lot of peer pressure,” Ms. Morgan said.
Unsurprisingly, this produces weak accords
From a political perspective, perhaps this outcome represents “victory” for environmental activists launching their next fundraising campaign or for a president building his “legacy.” But it comes at the environment’s expense. A system of voluntary, unenforceable pledges relies on peer pressure for ambitious commitments and the “naming and shaming” of countries that drag their feet. In this context, true U.S. leadership and environmental activism require the condemnation of countries manipulating the process. Instead, the desperation to sign a piece of paper in Paris has taken precedence over an honest accounting. And once the paper is signed, any leverage or standing to demand actual change in the developing world will be weakened further.
As such, the US plan from Paris was largely Obama trying to lead by example and executive order (i.e. the Clean Power Plan). It was only enforceable as long as he was in office.
