President Trump is weighing two legal paths for withdrawing from the Paris climate change agreement, where the easiest road to leave the deal could take three to four years.

The multi-year path is the route that experts think is the best one to take politically, even though it may not be the most direct action as it would require a three-four year process.

"Even if the U.S. isn't officially out for three years, it wouldn't really matter as a practical matter," said Jeff Holmstead, former Environmental Protection Agency air chief under President George W. Bush and a partner at Bracewell law firm. Holmstead had been in the running to be Trump's pick to head the EPA before he chose former Oklahoma Attorney General Scott Pruitt.

"Even if the U.S. is technically subject to the Paris Agreement for three more years, the Trump administration isn't going to do anything to implement it during that time," Holmstead said.

The second option that Trump is looking at to leave the deal would be a flat out "mistake," Holmstead said.

The second path is to leave the UN Framework Convention on Climate Change, which the U.S. entered into under a Republican administration. The UNFCCC is the agency by which the U.N. negotiates and finalizes all global climate agreements.

"I do think that withdrawing from the UNFCCC would be a mistake since it was signed by George H.W. Bush," Holmstead said. "It doesn't really require anything meaningful other than doing a periodic inventory of U.S. [greenhouse gas] emissions." The Paris agreement is legally non-binding, except for the emission reporting requirements.

The Paris deal also sets up a Green Climate Fund to funnel more than $100 billion to small, developing countries to help them combat the effects of climate change. The GOP had criticized the measure in the waning days of the Obama administration but failed to stop two tranches of money sent to the fund equaling $1 billion. The second $500 million was sent three days before Trump was sworn in as president.

The Republican leadership has been silent on the green fund in recent months, focusing more on how the Paris deal bolsters legal arguments for the Obama administration's climate rules, such as the Clean Power Plan.

Other experts think Trump could be weighing a third option in addition to the two main paths. Trump could send the Paris agreement to the Senate for an up-or-down vote on ratification, where it almost certainly would fail in the Republican-controlled chamber.

"They could send it to the Senate and then, failing ratification, alert the UNFCCC that the United States did not in fact consent to the agreement," said conservative energy strategist Mike McKenna, who had been close to the administration during the transition.

The Obama administration negotiated the agreement to be non-binding, specifically so it could avoid having the deal go to the Senate where it would have stalled, or voted down.

In the weeks before Trump's meetings with leaders at the Group of Seven summit last weekend, his advisers had been weighing a way to redo the U.S.'s commitments under the Paris deal, referred to as Intended Nationally Determined Contributions, or INDCs. But under the agreement, the policies to meet the emission cuts can only be increased, not relaxed or cut, as the administration would have liked.

"The problem is that there is no way to change the relative contributions of nations," McKenna said. "So changing our INDCs doesn't really solve the problem of China and others gaining some definitive advantages." Republicans had argued that China's commitment to begin cutting its carbon dioxide emissions in 2030 was irrelevant when considering that the U.S. would have to begin cutting its emissions under regulations imposed by the Obama administration much sooner.

That scrapped the INDC strategy from the list of options and made clearer that withdrawing from the agreement was the only likely option.

Republican state attorneys general, led by coal state West Virginia, advised Trump in a letter last week that not withdrawing from the deal would raise "litigation risks" for the administration's deregulation agenda. More than 20 Republican senators echoed the same warning in a separate letter to the president last week.

They say that keeping the climate deal in place would allow environmentalists to use the courts to defend key regulations, such as the Clean Power Plan, and try to block Trump's efforts to eliminate them.

The Clean Power Plan and a number of other regulations are key pieces of the U.S.'s commitment to meeting the emission reduction targets under the Paris agreement.

The 2015 climate deal went into effect in November. It was signed onto by 197 countries that agreed to reduce greenhouse gas emissions beginning in 2020. The goal of the deal is to slow the Earth's temperature from rising 2 degrees over the next two decades.

Many scientists blame the burning of fossil fuels for causing the Earth's temperature to warm, resulting in sea-level rise, ocean acidification, more severe weather, drought and flooding.