Trump just betrayed the world. Now the world will fight back.

President Donald Trump has made a colossal mistake in deciding to withdraw from the Paris climate agreement. There is simply no case for withdrawal, other than a desire to double down on an ill-informed campaign promise, while the case for staying in is overwhelming. But damaging as it is, this decision is not the beginning of the end for efforts to contain climate change. The world decided in Paris to confront the climate threat, and it is not turning back.

Around the world, climate change is a metastasising danger, for some countries even an existential threat. It was understood in the years leading up to the Paris negotiation that the climate challenge could be met only with a new kind of agreement premised on concerted effort by all. That agreement - ambitious, universal, transparent, balanced - was reached in Paris, with the help of US leadership every step of the way.

Trump's decision will be seen as an ugly betrayal - self-centred, callous, hollow, cruel. The ravages of climate change have been on display in recent years in the superstorms, floods, rising sea levels, droughts, fires and killing heat waves that will only get worse as the carbon index mounts. Vulnerable countries will look at the United States, the richest power on Earth, the largest historic emitter of greenhouse gases, and think - even if they do not say - how dare you?

Former president Barack Obama once said to business leaders, in a Roosevelt Room meeting I attended, that climate change was the one threat, other than nuclear weapons, with the potential to alter the course of human progress. A near-consensus of major US companies urged the Trump administration to stay in the agreement because they know climate change is real, that the Paris agreement is a good and balanced deal, that their own concerns on matters such as intellectual property and trade will only be defended if US negotiators are at the table and that turning the United States into a climate-change pariah - will be bad for business, for access to markets and for investment. But our chief executive president decided to leave US business in the lurch.

All this is more than disappointing. And watching the so-called internal battle on this issue play out between determined antagonists on the one side and diffident, sotto voce defenders on the other was downright depressing.

But let's be clear: This is not the end of the line. This is a call to arms.

Countries won't follow Trump out of the Paris climate agreement and over a cliff. They won't give Trump the satisfaction of "cancelling" the agreement, as he promised during his campaign. They will want to show that they can carry on without the United States. And they know too well that climate change is real and that if the Paris regime fell apart, you'd just have to build it again. They will hold on to the hope that the current administration will be a one-term wonder. It is true that, in the longer run, it would be difficult for the Paris regime to produce accelerated action at the level that is needed without the United States. But other countries will probably bet that the United States will come back.

Progressive US states and cities also have a crucial role to play, not only in extending the good work they are already doing on climate change, but also by sending a clear and resounding message to the global community: that while Trump's Washington may have gone dark on climate change, inspired centers of innovation and commitment are lighting the way forward all over the country. In states such as California and New York, Washington, Oregon, Minnesota, Illinois and North Carolina, and in New England; in cities such as New York, Chicago, Los Angeles, Houston and New Orleans, among many others. These entities account for a sizable chunk of both US gross domestic product and carbon emissions. They may not be able to get the United States all the way to our 2025 Paris emissions target, but they have the potential to go far.

Private companies, too, have been instrumental in driving the clean-energy revolution, pursuing the massive economic opportunities presented by the need to decarbonise our energy system. And consumers are increasingly demanding that companies not only provide desirable products or services, but stand as a good corporate citizen.

Finally, for citizens, it is time to hold our leaders accountable at all levels of government. Protecting our nation, our children and our American heritage should not be optional for an elected leader. Nor should preserving America's singular standing in the world.

This is not a good day for climate change, and it is not a good day for the United States. Nothing we say now can change that. But it is a day that needs to be remembered as the visible moment the rear-guard opposition went too far. It is a day to spark action and resolve. It is a day that needs to count.

Todd Stern, a visiting lecturer at Yale Law School, was US special envoy for climate change from 2009 to 2016.