Beneath the waves, out of our sight,disaster is in the making

Peter Boyer

warns that global warming has already caused a crisis in our oceans and seas

“THE great mother of life” was how Rachel Carson, author of the 1962 environmental classic Silent Spring, described the sea. Today the great mother of life is ailing, with a high fever.

Silent Spring was about bird-killing pesticides on land, but Carson’s main scientific focus was actually the sea.

If she were still alive and working now, she would be writing a story on a far bigger scale, about how human excess has blighted marine environments from the coast to the deep ocean.

As Carson and many others have pointed out, what happens under the sea’s surface is a mystery to landdwelling humans. But more sophisticated surveillance tools and more focused and finely tuned scientific observations give us unprecedented insight into its role in the planet’s ecosystem.

For the past 20 years or more we have been getting some unsettling signals about warming ocean waters and how a rising level of carbon dioxide in the air affects the ocean’s acid-alkaline balance.

Now those signals are so strong as to be undeniable. Marine scientists are uncovering something approaching a horror story, with outcomes that will make no one happy.

Nowhere on the planet is the damage to our marine environment so painfully clear than off Australia’s shores. From the Pilbara coast to the Coral Sea and south to Tasmania, ocean heatwaves have laid waste to species and habitats, leaving dramatically altered assemblages.

One of the world’s most persistent ocean-warming “hot spots” is off southeastern Australia and Tasmania. Over the past 100 years or so it has been warming at a rate four times the global average.

Redmap, a national citizenscience website for unusual sightings of marine species operated by the Institute for Marine and Antarctic Studies in Hobart, regularly records marine creatures previously found only rarely in Tasmanian waters, including tropical species like snipefish.

Getting a new species on the end of your line can be pleasing, but there’s no pleasure to be had from what some of them are doing.

For instance, warm waters and an invading sea urchin are together steadily destroying Tasmania’s highly productive giant kelp forests.

A similar scenario has been playing out off Western Australia, where a marine heatwave event in 2010 wiped out nearly half the kelp forests over more than 100km of rocky reefs. Recovery has been patchy, with most of the coldwater kelp being displaced by warm-water seaweed.

In the summer of 2015-2016 tropical Australian seas from the North-West Shelf to the Coral Sea warmed by over 2C for nearly four months – the most intense marine heatwave in the region in nearly 40 years of records.

The devastating impact of that event and a weaker warming the following summer is still being felt. The booming tourist trade across

tropical Australia, especially in northeast Queensland, is suddenly feeling threatened by unprecedented coral bleaching caused by warm waters.

A study published in the science journal Nature in April found the event had permanently transformed the ecology of the reef, severely enough to “cook” some northern reef corals, which will never recover.

Another bleaching event in 2016-2017 saw yet more severe bleaching in the CairnsTownsville region and reaching as far south as water off Mackay. That spells more trouble ahead for the tourism trade.

While that poses a big problem for the Queensland and Australian economies, from an ecological perspective that’s the least of our worries. A Nature Communications paper published last month shows that marine heatwaves are becoming both more frequent and more extreme.

The study, led by Eric Oliver of Canada’s Dalhousie University, looked at ocean surface temperature records dating back to 1925. It found that since then, the average number of marine heatwave days in a year has increased by 54 per cent and that the trend has accelerated since 1982.

That means, said Oliver, that a marine ecosystem which 90 years ago would average 30 days of extreme heat each year is now experiencing about 45.

Tasmanian marine biologist Alistair Hobday says such exposure to heatwaves causes extensive damage to ecosystems, affecting biodiversity, fisheries and aquaculture. It’s the speed of change that has Hobday and his colleagues worried. He is dismayed that changes which just 10 years ago scientists thought we would take the best part of a century to reach are already being observed.

The Federal Government’s fix for the Great Barrier Reef, addressing agricultural run-off and developing resilient corals, is a side issue. We have a crisis that can only be stopped at its source with a sustained bid to eliminate fossil-fuel emissions, here and everywhere. Peter Boyer, who began his journalism career at the

Mercury in the 1960s, specialises in the science and politics of climate change.