What to Know About the Paris Climate Agreement

President Donald Trump has long threatened to pull the U.S. out of the Paris Climate Agreement. After making it a campaign promise, he’s wavered on the issue but plans to announce his decision scheduled at 3 p.m. ET on Thursday.

The prospect of withdrawing from the agreement has met opposition from policymakers, corporations, other countries and concerned citizens. As Trump prepares to address the public, here’s what you need to know about the deal itself.

What is the Paris Climate Agreement?

Participating countries agreed to the landmark Paris Climate Agreement in December 2015 with an overarching mission: fighting climate change with the goal of keeping worldwide temperatures from rising more than 2°C (3.6°F) by 2100, the amount deemed irreversibly risky in terms of severe weather damage. The accord’s more ambitious goal would keep that temperature increase below 1.5°C (2.7°F).

The deal was established as non-binding, and countries set their own goals to reduce their greenhouse gas emissions. The agreement was envisioned to derive its strength from the accountability countries would hold each other to — essentially, peer pressure — at the subsequent meetings.

Read More: What to Know About the Historic ‘Paris Agreement’ on Climate Change

The major requirement of the agreement is for countries to honestly report their progress towards their own goals every five years, when they must submit new ways to improve. The agreement also stipulates that, beginning in 2020, developed countries send $100 billion annually to developing countries that will be spent furthering progress in countering and adapting to climate change.

President Obama’s administration pledged to cut greenhouse gas emissions in the U.S. by 26–28% (based on 2005 levels) by 2025. The White House had also agreed to give up to $3 billion to less wealthy countries before 2020.

Which countries participate in the Paris Climate Agreement?

The massive size of the agreement is what makes its effectiveness possible. The 195 countries that supported the agreement included developed and developing economies, marking the greatest global effort to curb the effects of climate change.

The U.S. would be in the vast minority if Trump pulls out of the agreement — even conflict-torn or isolated countries such as Iraq and North Korea signed up. Only two nations are not a part of the accord: Nicaragua and Syria. Both countries produce far less greenhouse gas emissions than the U.S.

Nicaragua had, in fact, refused to participate because its envoys thought the voluntary participation and lack of consequences for not meeting goals did not go far enough in addressing the climate crisis. Syria, dealing with a civil war that has raged for seven years, was in the midst of considerably heavy fighting during the accord talks. Additionally, Syrian President Bashar al-Assad’s government was under sanctions from many participants at the time.

What happens if Trump pulls out of the accord?

Trump exiting the deal deliver a blow to its efficacy, as the U.S. is the world’s second-largest polluter. Other countries have pledged to adhere to their goals in any event, but some people worry that the U.S. withdrawing would relax the sense of urgency for participants.

Read More: 3 Major Costs of Withdrawing From the Paris Climate Agreement

Since the agreement itself is non-binding, nothing would actually happen to the U.S. in terms of official consequences. The accord has a formal withdrawal process that takes four years, and the government could re-join in the future if it wishes.

But the environmental and economic effects would be significant. The Rhodium Group predicts that Trump’s policies will cause U.S. emissions to end up around 15-19% below 2005 levels by 2025, instead of Obama’s accord pledge of a 26-28% reduction. Pulling from the accord could also lead the U.S. miss out on worldwide investment opportunities in clean energy as other countries develop new technologies and create new jobs.