Climate change is an existential threat to the human race. This may seem an absurd or alarmist statement, since we have been conditioned by unparallelled growth to expect that there are no catastrophes that are insurmountable. Even apocalyptic science fiction deals with bands of survivors who have, by definition, survived. And we always imagine ourselves as among the survivors.

But the threat is real. The latest report of the Intergovernmental Panel on Climate Change tells us that there are only a dozen or so years in which to change our economies radically if we are to keep the effects of the warming already under way to manageable proportions. That would require the countries of the world to live up to the most ambitious of the goals of the Paris climate change agreement, and keep the rise in average global temperatures to 1.5C above preindustrial levels. A rise of even half a degree above that, to 2C, will have effects that are very much worse. Already this seems much more likely. All corals will disappear, as will many insects and plants.

The disappearance of plants, and in particular the deforestation of tropical regions, is doubly dangerous, because it converts carbon sinks (which living trees are, because they absorb carbon dioxide) into producers of carbon. That is only one of the many possible tipping points which may lead to a sudden and violent escalation of the rate of change as malign feedback loops are formed.

All these risks make it quite credible that we will end with a warming of 3C, 4C or even worse – and the consequences will be globally terrible, and everywhere unavoidable. Hundreds of millions of people may die through droughts on land, and flooding at the coasts, through the loss of marine species due to acidification of the oceans, and probably through the disruption of long-term weather patterns around which the world’s agriculture has been shaped. These victims will not passively await their fates. Among the tipping points that we cannot foresee in any detail is the prospect of historically unprecedented refugee migrations as whole populations who have no choice but to starve or move set out for land where they can live. The political and indeed the military consequences are unlikely to be small.

None of this will only be the product of vast impersonal forces, any more than our present crisis is. There are always political and economic choices that explain our actions. A recent study identified 90 different organisations, ranging from states to private companies, that were between them responsible for nearly two-thirds of carbon emissions since 1864. They all behaved as rational, profit-seeking actors without any external responsibilities, and so brought us to the brink of catastrophe. This kind of twisted rationality exacerbates the dangerous physical effects of climate change.

The election of Jair Bolsonaro as president of Brazil now seems overwhelmingly likely, and he is committed, like Donald Trump, to withdrawing his country from the Paris accords. His policies in the Amazon basin will greatly accelerate deforestation. In Australia, the government of Scott Morrison must deal with the reality of climate change in the form of droughts and wildfires, but is at the same time denying any responsibility for the effects of its own actions when they worsen the situation.

This kind of short-term selfishness can’t be overcome only by appeals to unselfishness or to solidarity. Only long-term self-interest can be stronger: perhaps the fear that international anarchy must ultimately lead to international war in an age of nuclear and biological weapons.

It is not the direct effects of climate change alone but their indirect effects on the political and economic structures of the world that make it a genuinely existential threat. As individuals in the rich world, we should all eat less meat and use less fossil-fuel energy. But individual action will never be enough. We must also work to strengthen the kind of political structures that will enable, and if needed compel, the cooperation that is the only alternative to destructive anarchy.