The Guardian view on climate science: warming oceans are a warning of the chaos ahead

What was long predicted is now happening. Earth’s weather systems are increasingly disrupted and destructive, as a consequence of the amount of carbon dioxide and other greenhouse gases in the atmosphere. In addition to devastating heatwaves in the northern hemisphere, and their role in igniting forest fires, high sea temperatures over recent months have led scientists to reiterate their warnings that we are moving fast into uncharted, dangerous territory.

Climate models have always allowed for uncertainty. For decades, scientists have been certain of the direction of travel: towards increased heat, risk and instability. But how precisely the crisis would manifest, in what order systems would break down, and how the knock-on effects would unfold, remains a subject for research and discussion. Currently, there is a debate between experts about whether the pace of global heating is accelerating or stable. The likelihood of vital ocean currents, known as the Atlantic meridional overturning circulation, collapsing this century is also contested. One new study has suggested that a tipping point could be approaching, and that the analysis of the Intergovernmental Panel on Climate Change has, in this respect, been too conservative.

The causes of record-breaking ocean temperatures are also being investigated. While an El Niño weather event was expected this year, it is not regarded as a sufficient explanation of the ocean temperature rises recorded since April. Heat is also thought to be causing oceans’ colour to change from blue to green, due to increased plankton. The situation is particularly concerning because we have relied on the oceans to absorb 90% of the heat trapped by greenhouse gases. Dr Bernadette Sloyan, a marine scientist in Australia, has compared their role to that of an air conditioner.

Warmer seas present specific dangers, both to human and marine life: melting ice sheets; sea level rises (because water expands when heated); coral bleaching; more intense storms; lower oxygen levels causing fish to die. But they are also an indication of the overall pressure that global heating is placing on nature. The Earth’s capacity to stabilise the amounts of energy entering and leaving the planet’s system is reaching its limits for current patterns of existence.

For many of those focused on what is happening – including activists, scientists and politicians – the inadequacy of national and international responses to the emergency is disorienting as well as disturbing. Despite decades of pledges made under the auspices of the UN’s climate process, global emissions are at an all-time high. It is hard to fathom what further evidence is needed to persuade governments that a drastic change of course is the safest option.

But it is clear that the countries and businesses that are most strongly reliant on fossil-fuel profits will not willingly give them up. Whether and how they can be convinced or compelled to do so is the existential question of our times. Last weekend the G20 bloc of nations – which produce 75% of global greenhouse gas emissions – failed to reach agreement on phasing down fossil fuels. This November’s round of UN talks, Cop28, is being held in the United Arab Emirates and led by Sultan Al Jaber, who also heads his country’s national oil company. As forests burn and the sea turns green, the necessity of confronting vested interests – including energy-intensive western-type lifestyles as well as the corporations that depend on fossil fuels for profits – becomes more desperate by the day.

cover photo:Bleached coral, caused by rising sea temperatures along Australia’s Great Barrier Reef. Photograph: Helmut Corneli/Alamy