The Pope gave Donald Trump a 192-page letter he wrote on climate change

Pope Francis gave Donald Trump a letter he wrote regarding climate change as a gift on the president's visit to the Vatican: EVAN VUCCI/AFP/Getty Images

Donald Trump was given a gift during his meeting with Pope Francis at the Vatican: a papal letter detailing why the world should fight against climate change.

Pope Francis issued the encyclical in 2015, just months before nearly 200 countries signed the historic Paris Agreement on climate change.

The agreement is considered a large part of President Obama's legacy, particularly his work on environmental issues like establishing a protected national park in Hawaii and passing legislation on clean energy.

The US is one of the largest emitters of carbon in the world and so its role is crucial to the success of the agreement along with China and India, also large carbon emitters.

The encyclical, titled Laudato Si or "Praised Be," essentially tied protection of the planet made by God to Catholics' faith in God.

In it he writes that climate change is a “global problem which has grave implications: environmental, social, economic, political, and for the distribution of goods.”

Mr Trump and his aides have often played up the president's business acumen and experience running a global company. Pope Francis addresses the ties between multinational corporations and climate as well.

"[T]he pollution produced by companies which operate in less developed countries in ways they could never do at home, in those countries in which they raise their capital: We note that often the businesses that operate this way are multinationals. They do here what they would never do in developed countries or the so-called first world."

He went on to write that “by itself the market cannot guarantee integral human development and social inclusion.”

Mr Trump has repeatedly called climate change a “hoax” perpetrated by the Chinese in the past - a stance which appears to have softened a bit after his face-to-face meeting with Chinese President Xi Jinping.

China has become a leader in renewable energy investments, which topped new money pouring into the oil and gas industry for the first time in 2015 to the tune of $350 billion.

He also appointed former Exxon CEO Rex Tillerson as Secretary of State and a known climate denier, Scott Pruitt, to lead the Environmental Protection Agency (EPA).

In his proposed federal budget, Mr Trump also plans to cut the State Department and EPA budgets - the agencies where much of federal climate change work is done - by nearly a third.

Climate change programmes across the whole federal government, but especially in the Coast Guard, the maritime security agency of the US which also does ocean and endangered species conservation work.

The president has also caused consternation for many countries in the group of seven (G7) for not making a decision on whether to keep the US in the Paris Agreement. The G7 has issued a cohesive statement on climate change until this year, where they cited the Trump administration's lack of clarity on their message as a problem.

Several alliances, including the 28-member military alliance North Atlantic Treaty Organisation (Nato) have declared climate change as a global security threat, especially in the Middle East where drought and famine are growing concerns.

The Vatican's Secretary of State brought up climate change during the meeting as well and encouraged Mr Trump to stay in the Paris Agreement. The White House said a decision whether to remain in the agreement would be made after the G7 meeting later this month in Sicily, Italy.