The global fight against climate change needs a leader. Step up, America.

For the first time in history, almost every independent country in the world has agreed to a bold climate policy target, and taken concrete steps toward it. This is a tremendous victory for humanity and the planet we live on.

The deal is a non-binding policy framework under which signatory nations agree to keep warming "well below" 2 degrees Celsius (ideally shooting for 1.5). Nations have submitted pledges to get some way toward this goal; world leaders will gather on April 22 for a signing statement. And though the policy pledges are not yet ambitious enough, this is by far the most successful international summit ever on the biggest threat to world civilization. The deal is also a big win for Secretary of State John Kerry, who is racking up an extraordinary series of diplomatic successes for President Obama's second term.

But a word of caution: Despite this historic agreement, actual policy success is not remotely guaranteed. Each nation is now going to have to follow through on its own. And for the deal to work, the United States must get out in front of the pack.

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Doing so would be relatively easy for the U.S. Though we have made much progress over the last decade or so, we've got a long ways to go to catch up to countries like Denmark and Germany — and because the U.S. is so big, decarbonization would mean a far larger absolute volume of reduced emissions anyway. And being richer than almost all European nations, we can also more easily afford aggressive policy.

Second, such a policy would have many ancillary benefits. Aside from causing climate change, oil and especially coal are dirty energy sources that kill thousands of Americans every year and sicken orders of magnitude more. Climate policy means fewer respiratory disorders and cancers, and longer, healthier lives for American citizens.

In addition, aggressive decarbonization will of necessity mean big social upgrades. Aside from airports and highways, our transportation infrastructure is generally lousy, even by middle-income nation standards. A low-carbon nation would simply have to have a decent electrified passenger rail system, for instance, as it's by far the most efficient way to move lots of people around at moderate to high speeds. Building one of these (only 40 years after Europe and Japan built theirs) would be a great boon for Americans.

Third, it's good diplomatic politics. The whole point of this exercise is to tackle climate change, and there is an unusually important role for activists and politicians to play moving forward. As Brad Plumer explains, the Paris deal is legally nonbinding — structured as a group of individual promises to reach a common goal rather than a top-down coercive framework (like the Kyoto agreement, which fell to bits). It's something like agreeing with a friend to help each other lose weight.

The Paris bargain contains an extremely aggressive overall target — limiting warming to 1.5 degrees Celsius — but the actual policy pledges are totally inadequate to reach it. We've already reached 1 degree warming; 1.5 is likely already locked in given past momentum (meaning reaching it would probably require removing carbon dioxide from the atmosphere).

It's critical for climate activists in each individual country to maintain political pressure to post additional emissions reductions wherever possible, ideally far beyond what has already been promised. It's both a good thing on its own terms and the only way the agreement will function. Decarbonization progress will strengthen the hand of future American climate negotiators, who will be able to point to concrete success. World progress is likely to be uneven, and somebody must set a good example. As the world's largest historical emitter, it's only natural that for the U.S. to take the lead.

So what does that mean?

For starters, implementing President Obama's Clean Power Plan, and building on it with a big price on carbon. Buildings would be better insulated and everything would become more efficient. Coal would be phased out, followed by oil and gas for most uses. Construction techniques and materials, particularly concrete, would be upgraded and streamlined. Basically, we'd be following in the footsteps of Germany, at least for the first decade or two.

This is not so much a way of coercing China and India to reconfigure their society against their own self interest as helping them achieve that self interest. As I have argued before, the key thing to remember about climate change is that it is primarily a threat to human civilization — and particularly developing nations. Either China or India alone could easily emit enough carbon to blow past 1.5 degrees warming. Cajoling and pressuring them into decarbonization and renewable-led economic development is more than anything helping them to save themselves.

In five years, the world's nations will meet again for another climate summit to compare results and strategies, and reconsider the overall policy framework. Let's have a big fat success to boast about when it comes along.