Out of sight shouldn’t be out of mind

In Clear the Air, May 20244 MinutesBy Lindsay WoodJune 15, 2024

Really big climate stuff happens in the oceans … In this first of a two-part analysis, we look at sea-level rise and how warming oceans buffer us from the worst of climate change.

We might imagine that overheated air, drenching storms and parched or swamped land epitomise the climate emergency. But the places we see least, the vast expanses and depths of the oceans, are almost ground zero (water zero?) for climate impacts.

Although the climate emergency concerns rising temperatures, because less heat escapes into space, we rarely hear about ‘stored heat’. Where does that extra heat actually go?

NASA can answer: “About 90% of global warming is occurring in the oceans.” Wow! And it seemed the atmosphere was doing the heavy lifting. NASA then explains the extra heat in the oceans is an eyewatering “360 zettajoules since 1955. A zettajoule is a sextillion joules or 1021 joules.”

Got that? Me neither! But I figured out that to heat the sea that much since 1955, we’d need 300,000 Benmore Hydros running full bore, 24/7. Eyewatering on steroids.

Regardless of the numbers, we should be seriously worried and profoundly grateful. Our home planet would be unliveable if that heat had gone straight into the air. “The top few metres of the ocean,” NASA adds, “store as much heat as Earth’s entire atmosphere.”

But that doesn’t make it okay; it just buys precious time (time we’re busy squandering). And hotter oceans cause enough problems as it is, such as escalating “ocean heatwaves” that stress ecosystems everywhere – like killing countless penguins in Northland, millions of farmed salmon in Marlborough, and bleaching sponges in Fiordland.

“If sea-surface temperatures … are warmer than normal,” says heatwave expert Luke Harrington, “that will generally increase the risk [of severe weather].” Hotter seas make for hotter air and wetter, wilder weather.

So when we’re next at the beach and find the sea nice and warm, let’s remember there’s a big price tag attached.

Another price is sea level rise (SLR). As glaciers and ice caps melt at record rates, they release vast quantities of water that had been safely locked away. Lynley Hargreaves, in Vanishing Ice, describes New Zealand glaciers melting a staggering seven times faster than at the start of this century. Really? Seven times faster than 20 years ago? “Every 500m we drive,” she reports, “melts a kilogramme of glacier ice.” Gulp.

Meltwater deepens the oceans by about 2mm per year. Factor in that water expands as it heats, adding 1mm-plus per year, and the current SLR exceeds 3mm annually.

And SLR brings other consequences – for example, saltwater intrusion into aquifers, groundwater and low-lying horticultural land. And, incredibly, the redistribution of vast volumes of meltwater is affecting the Earth’s rotation, and distorting its crust.

And talking of distorting the crust, New Zealand’s SeaRise programme created waves with the above map. In places, coastal land is rising and counteracting SLR (brown). But, in a double-whammy, most of it is sinking (blue) at rates that effectively double SLR or worse.

Out-of-sight oceans offer heaps of food for thought, and next month, we’ll explore more when we dive into freezing water and acid seas to explore two super-important but less-discussed changes to our oceans.