The start of a process by the United States to withdraw from the 2015 Paris climate accord is "very disappointing," Environment Minister Shinjiro Koizumi said Tuesday.

"Creating a decarbonized society is a pressing issue and (the U.S. move) is very disappointing," Koizumi told reporters.

"It'd be impossible to urge President (Donald) Trump to reverse the decision," Koizumi said.

Chief Cabinet Secretary Yoshihide Suga also expressed disappointment over the U.S. exit, saying the international community as a whole needs to tackle global warming.

"In view of the (Group of 20) Osaka summit declaration, we will explore ways to cooperate with the United States to address the issue of climate change," the top government spokesman said at a news conference.

The United States, the second-largest emitter of carbon dioxide, said Monday it has formally notified the United Nations of its withdrawal, initiating a yearlong process to pull out of the landmark pact intended to fight global warming.

Trump announced in December 2017 his decision to exit the pact adopted at a U.N. conference on climate change in Paris, saying that it is unfair to his country.

In June, the G20 summit in Osaka saw a rift over climate change, with the United States reiterating its intention to leave the accord, while the other members pledged to work toward its full implementation.

The Paris agreement, the successor to the 1997 Kyoto Protocol, aims to keep rising global temperatures to "well below" 2 C higher than preindustrial levels, so as to limit the occurrence of droughts, floods, melting glaciers, rising sea levels and other results of global warming.