Ocean temperatures have been rising steadily for decades, with our seas having absorbed much of the excess atmospheric heat generated by our relentless burning of fossil fuels. But in March 2023, almost overnight, they suddenly skyrocketed. Temperatures have since remained well above normal, reaching “hot tub” levels in some places, with disturbing consequences that suggest we have pushed ocean ecosystems to breaking point.
As we report on “How climate change has pushed our oceans to the brink of catastrophe”, the rapid rate of these changes and the severity of the havoc they are causing have taken scientists by surprise. But it should also serve as a stark reminder that the impacts of climate change won’t necessarily be slow, predictable declines but sudden cascades with grave consequences, many of which we don’t fully understand.
Consider the world’s coral reefs, which have suffered their fourth global bleaching event on record this year. At a certain point, possibly within a few years, a series of marine heatwaves will probably kill off most of the world’s corals. Their demise will spell catastrophe, both for marine life and the people who depend on reefs for food, coastal protection and income.
Warmer water brings the world closer to other tipping points too. It laps at the edges of melting ice sheets and slows the circulation of ocean currents, for instance. Once these systems collapse, there is no going back.
Yet we fail to heed the warnings. As greenhouse gas emissions creep slowly upwards, it is all too easy to believe the impacts will be similarly gradual. The past 18 months have demonstrated how swiftly systems can break down when exposed to new extremes.
Our response is already long overdue. Cutting greenhouse gas emissions to net zero as quickly as possible is the only way to restore equilibrium in the long term. That will sound familiar. But when you consider the crisis playing out in our oceans, it is hard to imagine more compelling evidence of what we will be facing if we don’t take drastic action.
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