How we're killing the oceans detailed in devastating new climate report

The oceans have helped buffer us against the worst effects of climate change, but they're really starting to suffer, a new report has found.

Scientists from the United Nations' Intergovernmental Panel on Climate Change (IPCC) released its Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) on Thursday. It confirms that sea level rise is accelerating thanks to humanity's increasing greenhouse gas emissions, but that's not all.

"What this report tells us is the oceans are getting warmer, they're losing oxygen, they're getting more acidic," Greenpeace oceans campaigner Jessica Desmond told The AM Show.

"We're seeing sea level rise, and we're seeing coastal wetlands, reefs and natural protections from extreme weather events breaking down all around us."

According to scientists, as the ocean warms its layers of water don't mix - warm water rises - which reduces the flow of oxygen and nutrients for marine life. 

The cryosphere encompasses parts of the world typically covered in ice. 

"We can now say with some confidence that Arctic sea-ice decline is unprecedented in at least 1000 years, which is some of the clearest evidence yet that human impacts on climate already dominate over anything natural," said Prof Steven Sherwood of the University of New South Wales Climate Change Research Centre.

"Also, this report examines expected changes out to the year 2300, when sea level rise is projected to be three to four metres without mitigation efforts, but could be kept under one metre with strong mitigation efforts."

The ocean plays an important in protecting us against temperatures getting even higher than they already are.

"The IPCC SROCC report confirms that the oceans provide us with an amazing buffer against climate change," said University of Otago and NIWA expert Prof Cliff Law, who contributed to the report as a reviewer.

"By absorbing 20 to 30 percent of the [carbon dioxide] we've released and an incredible 90 percent-plus of the additional heat retained in the global climate system, it's prevented the planet overheating."

Jessica Desmond.
Jessica Desmond. Photo credit: The AM Show

But warm water takes up more room than cold, so as the ocean warms it expands - add melting ice on top of this, and there are fears much of the damage has been done, regardless of what actions we take.

"The best available computer models suggest the threshold for large, irreversible change is nearby - somewhere between 1.5C and 2C global mean warming," said University of Otago's Prof Christina Hulbe.

"So while there is certainly change locked in, it may still be possible to avoid some of the largest consequences of global warming."

Temperatures are now about 1C warmer than in pre-industrial times. The report -which had more than 100 contributors from 36 countries - says since 1993, the rate of warming in the ocean has doubled. The seas rose 15cm in the 20th century, but now - less than two decades later - they're already rising twice as fast.  

"There is some change that is locked in, but what it tells us is that if we act now, we can drastically reduce the impacts that we're going to see over time," added Desmond. 

"We need to put 30 percent of the ocean off-limits to human activity. We've done a model of what that might look like, but most of the ocean is international waters - so we can put large swathes of international waters off-limits to exploitative activities, like fishing and seabed mining."

She said currently less than 1 percent of international waters are off-limits. 

IPCC Working Group II co-chair Debra Roberts says preventing the worst of climate change will take "unprecedented transitions in all aspects of society, including energy, land and ecosystems, urban and infrastructure as well as industry".

"The ambitious climate policies and emissions reductions required to deliver the Paris Agreement will also protect the ocean and cryosphere - and ultimately sustain all life on Earth. The more decisively and the earlier we act, the more able we will be to address unavoidable changes, manage risks, improve our lives and achieve sustainability for ecosystems and people around the world - today and in the future."

Desmond says even our Government, for all its talk, isn't doing enough. 

"They've done some good things... but there has to be much more action. It's not enough. We've known for a long time about climate change and successive Governments have let us down. But they know what the solutions are."