From the outset, we knew that the Paris climate summit wasn’t going to be the end of the ongoing challenge to avert dangerous climate change. As we learned through the first 20 years of U.N. negotiations, it’s extremely difficult to get the nearly 200 countries of the world to come to agreement on anything, much less something as challenging as the transformation of our global energy economy. So, negotiators started out with what was practical, realising that if each country comes forward with its own plan, based on what’s possible instead of what’s ideal, an agreement could likely be reached.

Though the resulting agreement is modest in scale, by bringing the world together, it sends a clear signal to global energy markets: The age of fossil fuels is ending, and a new clean global energy economy is taking its place. While past agreements left the door open for continued reliance on fossil fuels by emerging economies like those of China and India, the Paris agreement makes it clear that we must all join together in a common goal — averting dangerous climate change.

Finally, global energy policy is beginning to reflect the clear message of climate change research. We have only one atmosphere, shared by developed and developing countries. We have only one planet, and the steady upward march in greenhouse gas concentrations and the consequent warming of the planet and attendant rise in sea level, expansion of drought and increase in destructive extreme weather events will spare none from its impacts. With the Paris summit, we finally have an agreement that holds all countries accountable for taking action on climate.

That said, not all countries are making the same commitments. But that’s okay. By keeping the goal of limiting warming to 2 degrees Celsius, but also acknowledging that 1.5 degrees would be even better, the agreement provides a starting point for action while encouraging those who can to do even more to protect the most vulnerable.

There will always be leaders and laggards, and like with other technological advances, the leaders will reap the benefits of the clean energy revolution while the laggards will be left to play catch-up. It’s not important that there remain vestiges of denial, beholden to fossil fuel funders and left to make silly arguments (e.g. that a snowball somehow disproves climate change).

By securing an agreement with almost every nation on Earth, the Paris summit takes the promise of clean energy and gives it room to grow. Even states that profit tremendously from what former President George W. Bush called our “addiction to fossil fuels,” like Saudi Arabia, can no longer argue against the inevitability of clean energy. Even they have submitted a plan to reduce emissions and grow their clean energy portfolio.

Not long ago, most people would consider the odds of Saudi Arabia agreeing to reduce emissions about as good as a snowball’s chance in … Saudi Arabia. Yet it too has now begun the transition to a clean energy economy.

That’s the power of Paris.

One cannot understate the importance of the agreement arrived at in Paris. For the first time, world leaders have faced up to the stark warnings that climate scientists have been issuing for years, instead of shrinking away with denial and delay. So, while the commitments made in Paris aren’t on their own enough to stabilize greenhouse gas concentrations at safe levels, they are enough to begin bending the emissions curve towards a safe climate. Paris is a beginning of a process. It provides a framework for continued progress toward the goal of averting dangerous interference with our climate.

Put into more technical terms, the Paris agreement gets us roughly halfway to where we need to be. A future path of business-as-usual carbon emissions would likely warm the planet about 5 degrees Celsius (9 degrees Fahrenheit). The reductions agreed upon in Paris reduce that to about 3.5 degree Celsius (6.3 degrees Fahrenheit), i.e. halfway down to limiting to 2 degrees Celsius (3.6 degrees Fahrenheit) warming, the level of warming that many scientists studying the impacts of climate change consider to be unsafe.

Different groups have come up with slightly different numbers than these, but the end result is the same: Paris doesn’t get us to a safe climate, but it does get us a substantial way there, close enough that we can now envision, in subsequent conferences, reaching an agreement for more stringent reductions that get us all the way there.

Now is not a time to rest on our laurels. There is a great amount of work that remains to be done if we are to avert dangerous and irreversible climate change. But there is light now at the end of the tunnel and hope that we not only can but indeed already are rising to the challenge.

This article was written by Michael Mann and first published on the Huffington Post online.