President Donald Trump crashed the UN Climate Action Summit late Monday morning, along with Vice President Mike Pence, even though they weren't invited to attend.

The US commander-in-chief dropped in for about 10 to 15 minutes before departing the General Assembly hall. A Business Insider reporter there saw him sit with pursed lips in the US's seat, flanked by Pence, with Secretary of State Mike Pompeo and Mick Mulvaney, the acting chief of staff, behind him.

He stayed for speeches by Indian Prime Minister Narendra Modi and German Chancellor Angela Merkel. Trump clapped for the former politician's remarks, though seemingly not for the latter's.

Trump and his vice president were at the UN building in New York to speak at the Global Call to Protect Religious Freedom, which was happening simultaneously.

According to CNN's Jim Acosta, when asked why he attended the UN summit after all, the president responded: "I'm a big believer in clean air and clean water, and all countries should get together and do that, and they should do it for themselves. Very, very important."

The US was one of several countries not invited to speak at the summit

Over 100 world leaders — including Merkel, Modi, and French President Emmanuel Macron — attended the UN summit in New York, held ahead of the UN General Assembly meeting on Tuesday.

UN Secretary-General António Guterres organized the summit to pressure countries to slow the effects of climate change, according to the Financial Times.

Guterres plans to get countries to agree to stricter standards, citing the Paris climate agreement as a benchmark. In December 2015, world leaders pledged that their countries would act to prevent global temperatures from rising by more than 1.5 degrees Celsius (2.7 degrees Fahrenheit) and well under 2 degrees C (3.6 degrees F).

"I am appealing for leadership from politicians, from businesses and scientists and from the public everywhere," Guterres said. "We face a direct existential threat. Climate change is moving faster than we are."

Countries that didn't have a climate action plan prepared for the summit — including Japan, South Africa, and Australia — were encouraged not to speak. Others like Saudi Arabia and Brazil chose not to take part whatsoever.

"Only the boldest and most transformative actions [will] make the stage," Amina Mohammed, the UN deputy secretary-general, told the Financial Times. "We will see on Monday who is stepping up."

Climate activist Greta Thunberg gave an impassioned speech

Though the US was represented at the event by a diplomat, Trump had made it clear that the US has no intentions of making long-term commitments to lower its carbon footprint.

In June 2017, Trump announced that he would pull the US out of the Paris agreement, citing concerns that lowering fossil-fuel consumption would take a toll on the US economy.

Last Friday, millions of demonstrators gathered in cities around the world for a global climate strike, protesting inaction on climate change. The catalyst for the demonstrations was Greta Thunberg, 16, a Swedish climate activist known for her direct, outspoken manner. Thunberg sailed across the Atlantic in a zero-emissions sailboat (Thunberg says flying has too big a carbon footprint) to attend the summit, among several other events, including New York's climate strike.

At Monday's summit, Thunberg gave an impassioned speech on the dangers of climate change, telling world leaders, "You have stolen my dreams and my childhood with your empty words."

"The eyes of all future generations are upon you," she added. "And if you choose to fail us, I say we will never forgive you."