Bill McGuire

Another week – another bombshell; this time exploding out of the world’s oceans. Covering more than seventy percent of our world’s surface, the oceans form an integral part of the climate system, interacting in many and complex ways with the atmosphere and cryosphere (polar ice). Because they are so closely aligned with the atmosphere they are also intimately linked to climate breakdown and increasingly impacted by it.

More than anything else, as the world has warmed, the oceans have protected us from overwhelming heat that would – by now – have otherwise likely wiped us out. The results of a study published in January reveal that, over the last 150 years, the oceans have absorbed a staggering 90 percent of the heat arising from increasing concentrations of greenhouse gases in the atmosphere. This is the equivalent of the energy produced by between around 1.5 Hiroshima-sized atomic bombs exploding every second over the entire period. Impressive enough; recently, however, the rate of heating has climbed to the energy equivalent of between three and six Hiroshima detonations a second. Another way of looking at it, is that over the last century and a half, the oceans have taken up about one thousand times the annual energy use of global society.

The huge quantities of heat sucked up by the oceans leave just a few percent to heat the land, atmosphere and ice caps – which is very lucky for us. The bad news is that the warmer oceans are starting to drive more powerful, and potentially more destructive, hurricanes and typhoons. Furthermore, ocean heating also drives rising sea levels as the warmer waters expand.

Another study, the results of which were published just this week paints a terrifying picture of the devastating impact of ocean heating on marine life. The authors of this latest study describe ocean heatwaves spreading like the wildfires that, on land, take out vast tracts of bush. In the oceans, instead, great swathes of coral reef, seagrass meadow and kelp forest are being wiped out – along with the sea-life that depends and thrives upon them. Following a similar trend to heatwaves on land, ocean heatwaves have tripled in frequency in just the last couple of decades, raising huge concerns about the survival of marine ecosystems as further heating occurs. Fish stocks, in particular, already seem to be suffering, with global stocks down by at least four percent since 1930, and by as much as 35 percent in some parts of the world.

The bottom line is that, while the oceans are shielding us from the worst of the heating caused by human activities, they can’t continue to do this forever. In addition, as they absorb more and more heat, so the life they contain is coming under increasing pressure. If we continue with business as usual, we will be left with oceans hugely depleted of life, and menus from which fish are permanently excluded. Yet another reason – as if we need one – for net zero emissions by 2025. Let’s do it.

Bill McGuire is Professor Emeritus of Geophysical & Climate Hazards at UCL and author of Waking the Giant: How a Changing Climate Triggers Earthquakes, Tsunamis and Volcanic Eruptions. He was a contributor to the IPCC 2012 report on Climate Change & Extreme Events and Disasters.

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