The global community signed an historic agreement at the Paris climate talks to tackle the threat of climate change and accelerate the shift to clean energy around the world. This is a momentous breakthrough. 185 countries have pledged to reduce their climate change pollution, strengthen their climate commitments every five years, protect people living on the front lines of climate impacts, and help developing nations expand their clean energy economies.

Most important, this agreement sets ambitious goals. It calls for holding global temperature rise to 1.5 degrees Celsius, with a first step of keeping us at no more than 2 degrees of warming.

Reaching the 2-degree target is essential to prevent catastrophic climate impacts, but scientists say it still leaves us open to dangerous levels of rising seas, food insecurity, and extreme drought. It would make the Marshall Islands and other island nations uninhabitable and expose countless vulnerable communities to deadly harm. Keeping the temperature rise at no more than 1.5 degrees will sustain these communities and create a brighter, more stable future for our children and grandchildren.

Seeing 185 countries commit to cutting carbon pollution, seeing some 2,400 mayors and city leaders devote their communities to clean energy, seeing thousands of business leaders and investors affirm that this is good for the economy—and furthermore, that we can’t afford the high cost of waiting—has left me with a real sense of hope about our collective future.

The climate talks also represent the moment when it became clear that our hope for the future has not been misplaced. Yes, this will be a long and difficult struggle. Yes, there’s still much more to be done. But so many moments in Paris helped demonstrate that victory is within our reach.