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The reef report is in and ocean scientists are fearful

It’s a frightening time for ocean scientists. From a scientific perspective, humanity is conducting the largest uncontrolled experiment in its history on our only home, the planet. By continuously driving up carbon emissions, we have willingly steered ourselves into uncharted waters.

How do we know this? This week, Sydney hosts a meeting of the world’s leading paleooceanographers and climatologists; scientists who play a key role in revealing how the planet has previously adapted to changing CO2 levels. This conference focuses on studies of the oceans’ history that use ancient ice and sediment cores, fossils of corals and climate models.

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Ice cores tell us, with some certainty, that CO2 levels are currently rising at least 10 times faster than the highest known rate of natural increase prior to industrialisation. We also know that climate systems are highly sensitive, complex, and non-linear. Change may move slowly and steadily for a while, but then might reach a precipitous tipping point.

Sediment cores can take us back in the earth’s history to reveal earlier abrupt warming events. Around 55 million years ago, increases in CO2 levels pushed temperatures up, over the several thousand years, perhaps triggered by the release of methane hydrates from deep oceans or intense volcanic activity. The oceans warmed by 5 degrees C and acidified as they absorbed huge atmospheric loads of CO2, causing the largest known deep-sea extinction in the past 90 million years.

Today, much of our immediate future depends on our oceans. These are the planet’s biggest fluid systems. They play a critical role in determining our climate by absorbing or releasing carbon dioxide and heat, as well as driving weather patterns through evaporation and precipitation. Our oceans have, so far, done us a great service; absorbing one third of our industrial CO2 emissions since 1850, and more than 90 per cent of the Earth’s warming in the past 50 years, so cushioning the impact of climate change on land.

Marine biologist and UNSW Australia's research pro vice-chancellor and Emma Johnston.

Marine biologist and UNSW Australia’s research pro vice-chancellor and Emma Johnston.Credit:UNSW

But as CO2 and heat are absorbed, our oceans are changing, and so is their capacity to support ecosystems such as our Great Barrier Reef, and to continue to take up carbon dioxide into the future. Many big questions remain, especially as the most recent comparable atmospheric CO2 levels date back 3 million years.

As scientists, we are rarely 100 per cent certain about anything, but when we are sure of something it’s because there is a huge amount of evidence behind us. And we are sure that the greatest threat to the long term outlook of the Great Barrier Reef is climate change.

And we are sure that there is no time left to worry about “fake uncertainties” peddled by climate change doubters. We are already cataloguing climate-related ecological disasters such as the mass bleaching of our national living treasure, the Great Barrier Reef. There are more disasters on the horizon.

It is now a question of whether, and how, our ecosystems will adapt to such rapid changes, and whether, and when, our clever choices can slow those changes down.

Professor Emma Johnston is a marine ecologist, UNSW Dean of Science and President of Science and Technology, Australia. Professor Katrin Meissner is a physical oceanographer and climate scientist and director of the Climate Change Research Centre at UNSW.

The 13th International Conference on Paleoceanography opens at UNSW on Monday, September 2.

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