An open letter signed in 2009 by Donald Trump and other business leaders urging the US to enact climate-change legislation. Grist President Trump officially announced Thursday that he will pull the United States out of the Paris Climate Agreement, a landmark climate document signed by all but two countries (Nicaragua and Syria).

The move was consistent with Trump's recent statements on climate change — though at one point, it appears he was concerned about the issue.

Trump's history of commenting on climate change mostly begins in 2009, when he signed a full page ad in the New York Times directed at President Obama, urging him to take action on climate change.

Unless someone else signed his name for him, or he signed without reading the letter, it is safe to assume at that time Donald Trump believed in manmade climate change and its dangers.

According to Grist, which broke the news, "None of the signers that Grist interviewed this week could recall who had organized the letter or knew who had asked Trump to sign." It's unclear how big of a role President Trump had in the letter.

But things soon changed.

A 'hoax'

In November 2011, Trump insisted on Twitter that global warming wasn't real because it was snowing in New York City in October, a theme that has come up in his Twitter history many times over the years.

His first couple of tweets on climate change in 2012 criticized President Obama for spending billions of dollars on the issue, and the World Bank for "tying poverty to 'climate change'."

In 2013 President Trump moved on to comment on the popularity of referring to the issue as "climate change" instead of "global warming."

Then he came out with this statement in November 2012:

In fact, Trump has connected China and climate change quite a few times in his Twitter history. In April of 2013 he said: "The Chinese talk of climate change and carbon footprint but don't clean up their factories-but they sell us the equipment to clean up ours!"

In December of the same year, he tweeted "We should be focusing on beautiful, clean air & not on wasteful & very expensive GLOBAL WARMING bullsh-t! China & others are hurting our air."

Twice on December 6th, 2013, Trump declared global warming an "expensive hoax." This stance stands up pretty well to Trump's declaration on Thursday that the Paris Agreement "is less about climate, and more about the rest of the world gaining economic advantage over the United States."

Trump sarcastically tweeted about record setting low-temperatures across the US in December of 2013, saying it "must be global warming, I mean climate change!" He may not have realized the record-setting cold temperatures directly supports the climate change theory (climate change can lead to temperature swings in both directions).

In February 2014 he reiterated his annoyance with the so-called name change from global warming to climate change (In reality, global warming refers to the Earth warming, while climate change refers to changes in climate patterns.)

As of February 2015, President Trump seemed to still believe this, according to his tweet: "Among the lowest temperatures EVER in much of the United States. Ice caps at record size. Changed name from GLOBAL WARMING to CLIMATE CHANGE."

In May 2014, he linked global warming to nuclear weapons — it wasn't the only time he brought this topic up, either:

In 2015 he dedicated a few tweets to criticizing Obama for focusing on climate change while "ISIS and Ebola spread like wildfire."

2016 campaign

At the first presidential debate on September 26, 2016, Hillary Clinton brought up how her perspective on climate change differs from Trump's. Here's how the exchange unfolded:

CLINTON: Some country is going to be the clean- energy superpower of the 21st century. Donald thinks that climate change is a hoax perpetrated by the Chinese. I think it's real.

TRUMP: I did not. I did not. I do not say that.

CLINTON: I think science is real.

TRUMP: I do not say that.

As many news organizations pointed out after the debate, Trump tweeted in 2012 that "The concept of global warming was created by and for the Chinese in order to make US manufacturing non-competitive."

In response to a question about his views on climate change on ScienceDebate in September, 2016, Trump implied that the US shouldn't waste "financial resources" on climate change and should instead use them to ensure the world has clean water, eliminate diseases like malaria, increase food production, or develop alternative energy sources.

"There is still much that needs to be investigated in the field of 'climate change,'" he said. "We must decide on how best to proceed so that we can make lives better, safer and more prosperous."

President Trump

President Donald Trump announces his decision that the United States will withdraw from the landmark Paris Climate Agreement, in the Rose Garden of the White House in Washington, U.S., June 1, 2017. REUTERS/Kevin Lamarque

But then, in 2016, President Trump had a series of meetings with environmentalists, including actor Leonardo DiCaprio.

Business Insider asked the CEO of the Leonardo DiCaprio Foundation, Terry Tamminen, who was at the meeting, what that was like. Tamminen and DiCaprio presented Trump with multiple job-saving scenarios that the Paris Agreement could support.

"When we talked to him about the benefits to the economy of clean energy... in the US and energy efficiency and the various measures to tackle climate change, he was all in favor of those because they were good for the economy as well as the environment, and that's when he then said he would have an open mind about the Paris Agreement," Tamminen said.

While Trump may have had an open mind in December 2016, he ultimately chose to leave the agreement on June 1, 2017. In his speech, Trump said that "the United States will withdraw from the Paris climate accord ... but begin negotiations to reenter either the Paris accord or an — really entirely new transaction, on terms that are fair to the United States, its businesses, its workers, its people, its taxpayers."

In a briefing with reporters after Trump's speech, White House officials refused to answer if Trump believed in the overwhelming scientific consensus that humans are causing climate change.

The list of tweets is not exhaustive. You can read all of Trump's tweets that have mentioned "climate change" or "global warming" here.