Trump announced at the beginning of June his decision to withdraw the U.S. from the Paris climate agreement.
Trump cast the move as one that puts the U.S. first and called the Paris accord "very unfair at the highest level to the United States."
During his speech Monday, Obama also addressed North Korea.
"China is the one country North Korea does depend on to some extent and the elites depend on to access foreign currency, basic supplies that are important to the regime," the former president said, according to CNN.
"Pyongyang doesn't always listen to China. ... Unlike [Kim Jong Il], [Kim Jong Un] often times has engaged in fairly significant diplomatic insults of Beijing in a way we haven't seen before and in a way that surprised China," he added.
"You have a young man who is only interested in maintaining power and is willing to do anything to sustain that."
Trump last week said the United States’ “patience is over” with North Korea, calling for an aggressive international effort to curb the rogue state’s nuclear program.
“Together, we are facing the threat of the reckless and brutal regime in North Korea,” Trump said at the White House alongside South Korean President Moon Jae-in. “The nuclear and ballistic missile programs of that regime require a determined response.”
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