Calfornia Governor Jerry Brown (D) and former New York City Mayor Michael Bloomberg (I) kicked off the Global Climate Action Summit in San Francisco on Thursday, beginning with Brown predicting how historians would remember President Donald Trump.
"When Trump says, in effect, ‘We like more methane going into the air,’ that is highly destructive," Brown said. "Very highly destructive."
When asked how Trump will be remembered by history, the governor did not mince words.
"A liar, criminal, fool," Brown responded. "Pick your choice," he added, referring to Trump's destructive record on protecting the environment.
Brown said that Trump's easing of regulations on methane emissions was on the doorstep of "not only on insanity but criminality."
Californians concerned with the health of the planet were elated by Brown standing up to Trump.
Some people thought Brown was being too generous.
On Tuesday, the EPA announced its intent to repeal Obama-era methane rules, which were put in place to curb greenhouse gas emissions in an attempt to slow the effects of human-caused climate change.
Methane is a greenhouse gas that is more than 20 times more powerful at trapping heat than carbon dioxide.
"This is insane – it borders on criminality," Brown tweeted. "It perhaps is the most obvious and dangerous and irresponsible action by Mr. Trump. And that’s saying quite a lot, because he has a whole list of them."
Trump pulled the United States out of the 197-country Paris Climate Accord last year, however American cities, states, and municipalities are still making concerted efforts to reduce greenhouse gas emissions.
In a report shared at the summit, Bloomberg highlighted the progress being made despite Trump's efforts to sabotage the legacy of Barack Obama and rescind basic environmental protections.
"Since 2000, the U.S. has reduced carbon emission more than any other large nation," Bloomberg said. "It is a process that has continued since the 2016 election."
The billionaire former mayor also noted that in spite of Trump's promises to "bring back coal," that industry is in steady decline.
"Last year, U.S. emissions fell to the lowest levels in 25 years. Coal plants continue to close despite the administration’s efforts to prop them up," Bloomberg said. "They are being closed a the same rate -- maybe even a touch faster under President Trump than they did under President Obama."
Brown emphasized the importance of making climate change a top priority, as rising global temperatures, acidifying oceans, and pollution present a threat to all of humanity - and the window of opportunity to mitigate the problem is rapidly closing.
"Climate change is still not at the top of the political issues I don’t think in any country," Brown said. "But we are putting it there. And we have to constantly raise our ambition. The threat of climate change is as real as any we deal with."
Earlier this week, Brown signed an executive order instructing California to have a zero-carbon footprint by 2045. He also signed SB100 into law, the goal of which is to have zero emissions from the state's electric supply by 2045.