The US and Russia have recently agreed to hold talks on the New START Treaty, the only accord left regulating the two largest nuclear arsenals in the world. While this is undoubtedly good news, we must not allow it to lull us into complacency. Global events this year, most notably in Ukraine, have raised fears of a nuclear conflict to levels not seen since the cold war. There are more than 10,000 nuclear warheads remaining in the world, and the Kremlin’s language regarding weapons of mass destruction has became increasingly threatening in 2022.
    Beyond the horrible fates of victims in the strike zones, a large-scale nuclear exchange would profoundly alter the climate system as we know it, while more limited scenarios could have a devastating impact. An ever-growing body of work has shown that even a local nuclear conflict could usher in a climate catastrophe. As marine scientists, we have considered what this could specifically mean for the world’s oceans.

    Unfortunately, such “good news” never reaches Europe, as marine productivity remains compromised in the Arctic and north Atlantic relative to the rest of the world. This occurs because the new environmental state favours a different, larger, type of marine algae that can actually strip nutrients from the surface ocean once they die and sink, counteracting the physical surplus.

    Why would the ocean be so slow to recover from a nuclear conflict? Water heats and cools very slowly, and the ocean is strongly stratified with different water masses layered on top of each other. This gives the ocean a much longer “memory” than the atmosphere. Once disturbed, many changes are either not reversible on human timescales or are unlikely to return to their initial state.

    These findings add a new perspective on just how much humanity can affect the Earth system. While we are grappling with the fact that our greenhouse gas emissions can reshape the climate in a blink of geological time, it is worth remembering that nuclear arsenals remain large enough to fundamentally shift the Earth system in the blink of an eye.

    This logic comes with all the standard trappings of trying to do maths with morality, but it starts to make a lot more sense when you realise that the risk of an extinction-level event – and thus the chance we could avert it – isn’t actually unimaginably low.

    Even a more limited conflict could push our oceans into a fundamentally new state that lasts much, much longer than we would have expected. Understanding the length, and the weight, of these timescales should be forefront in our calculus of ongoing diplomacy.