SpaceX CEO Elon Musk tweeted that he spoke to President Donald Trump about the Paris climate accords three weeks ago and is now “cautiously optimistic” about the impending decision over whether to pull out. One of Trump’s campaign promises was to leave the climate accords, a landmark agreement that commits almost every country in the world to reducing greenhouse gas emissions.

The Paris deal was seen as a major victory because it included countries like China and India, which pollute heavily but have not signed on to climate deals before. Still, even if fully implemented, the plan would still only reduce emissions by half as much as necessary to prevent a global temperature increase of 3.6 degrees Fahrenheit, according to scientists. (It is considered crucial to avoid the 3.6 degree temperature increase in order to protect the planet.)

In recent weeks, the Trump administration has been in turmoil over whether to go through on its promise and pull out of the accord. The decision has already been postponed until June, after Trump returns from his foreign trip. Advisers have been lobbying the president that he would benefit from staying with the agreement, according to The Washington Post. Foreign leaders — including Germany’s Angela Merkel, Canada’s Justin Trudeau, and France’s newly elected Emmanuel Macron — have also stressed the importance of the accords in meetings with the president.

Musk has been part of Trump’s advisory council since December. In February, he defended this choice by saying that he doesn’t necessarily agree with the administration’s actions but believes that “engaging on critical issues will on balance serve the greater good.” (The Verge has reached out to Elon Musk for comment regarding today’s tweet and will update if we hear back.)

Let’s hope that Musk was right in February, and has used his influence with the president for the greater good: staying with the Paris accords.