WASHINGTON, June 4 (Xinhua) -- Former U.S. Secretary of State John Kerry on Sunday questioned U.S. President Donald Trump's sincerity to negotiate a better version of the Paris Agreement.

"Everybody knows he isn't going to do that because he doesn't believe in it. Because if he did believe in it, you wouldn't pull out of Paris (Agreement)," said Kerry in an interview with NBC.

"America has unilaterally ceded global leadership on this issue, which, for years, even Republican presidents, George H.W. Bush, you know, pushed in this direction," he added.

Trump on Thursday announced his decision to pull the United States out of the Paris Agreement on climate change, arguing that the international accord poses a threat to the U.S. economy.

Despite his decision to leave the deal, Trump would stick to the four-year-long withdrawal process stipulated by the agreement, which means that the U.S. withdrawal won't take effect till November 2020, about two months away from the end of his first term.

Trump also said the United States would begin negotiations to re-enter the Paris Agreement or make a new deal.

However, he indicated that re-entry may not be a top priority for his administration.

"If we can, great. If we can't, that's fine," said Trump, adding that the new agreement must ensure "fair" treatment to the United States, its businesses, its workers, and its taxpayers.

"There is a significant risk that the administration has underestimated the complexity of global climate negotiations," David Livingston, associate fellow in Carnegie Endowment for International Peace's Energy and Climate Program, told Xinhua in an email.

"The Paris Agreement was, practically speaking, more than a decade in the making," Livingston added.

Since the 1990s, the international community has been engaging in forging collective actions on climate change.

The Paris Agreement of climate change, agreed on by almost every country in the world in 2015 after lengthy negotiations, aims to tackle global warming by cutting greenhouse gas emissions and sets a global target of keeping the rise in the average temperature no higher than 2 degrees Celsius above pre-industrial levels.