Southern ocean close to acid tipping point: 450 ppm too high
November 11th, 2008 by Jim JustScientists have discovered that the tipping point for Southern Ocean acidification caused by human-induced CO2 emissions is much closer than first thought. The results are published in the Proceedings of the National Academy of Science.
The “tipping point” of acidification – when the acidity of the ocean reaches a level where the shells of calcareous marine creatures start to dissolve – had been predicted to occur when atmospheric CO2 levels hit 550 parts per million, around the year 2060.
The new research shows levels of the carbonate that these creatures need to build and maintain their shells drops naturally in winter, due to natural variations in factors such as ocean temperature, currents and mixing, and pH. This means the tipping point is likely to be reached at far lower atmospheric CO2 levels – around 450 ppm – which also happens to be the current target set by the IPCC for stabilization of CO2 emissions. This concentration is forecast to be reached by around 2030.
Ocean acidification could lead to large scale ecosystem changes, affecting not just plankton at the base of the food chain but other marine life higher up the food chain including fish, whales and dolphins.
The new findings provide additional evidence that 350 ppm should be the maximum target for atmospheric CO2 levels if we are to avoid catastrophic feedback processes that would mean the end of the Holocene era.
The Holocene began around 10,000 years ago. Human civilization – including the invention of agriculture and the domestication of farm animals – dates almost entirely within the Holocene. We may have already entered what might be called the Anthropocene – the “era of man” – characterized by significant human impacts on the Earth. There’s no precedent in human existence for what we have yet to experience.
We do know Earth’s climate system has still to respond fully to the rapid increase in greenhouse gases already in the atmosphere – much more warming is already in the pipeline. But already we’re seeing stunning consequences, including species extinctions at a rate unseen in the last 65,000,000 years, unprecedented disappearance of sea ice, and unprecedented droughts, for example in Australia.
450 ppm isn’t a realistic target if we’re to avoid tipping points beyond which there’s no return. We have to aim to get back down to 350 ppm, and the sooner the better.