Sunday, 4 November 2012

Ocean Acidification, Corals and Ken Caldeira

Image credit: The International Geosphere-Biosphere Programme and Globaia
This is a spin-off post from the radio series for the BBC World Service I am currently producing, Discovery: The Age We Made.  Presented by science writer Gaia Vince, it consists four programmes looking at the notion that humans have launched a new geological time period on the planet, the Anthropocene.  

Further down,  I have posted the audio of a great interview we did with leading climatologist Ken Caldeira on the seemingly likely fate of the world's coral reefs, because of the geologically extraordinary alterations we are making to the Earth's atmosphere.

We talk to leading earth and environmental scientists about the changes to the global environment our species is making which are so profound that they will leave physical, chemical and fossil marks in the rock strata forming today.  Homo sapiends is creating an assemblage of geological evidence that would tell any geologist in the far flung future (millions of years from now) that something forced the Earth into a new state - or down "a different trouser leg of geological time," as one of our interviewees put it.

The second part of The Age We Made focusses on climate change and the other consequences of our fossil fuel emissions, notably ocean acidification and its likely impact on the world's reef building corals.

About one third of the 10,000,000,000 tonnes of carbon we now put annually into the atmosphere as carbon dioxide dissolves into ocean waters.  Simply put, it forms a weak acid, carbonic acid.  Humans have been building up to this 10 billion tonnes per year emission output since the Industrial Revolution.   The acidity of shallow seawater has been creeping up, in step.  The latest measurements show that ocean acidity in the top levels has increased by about 30% on the last one hundred years - apparently, the most rapid rise measurable in Earth history.

This is a grim development for corals, and the millions of fish and other marine species that live in the reef ecosystems which the colourful, mineralising ones build.  Coral organisms make their skeletons from minerals, also dissolved in seawater.  The more acidic the waters, the harder it is for them to do this.   Some reefs in the Great Barrier recently measured are actually dissolving, such is the pH of the water now.

The finding about the dissolving corals of Australia's Great Barrier Reef came up in one of the interviews we did with Prof Ken Caldeira of the Department of Global Ecology at the Carnegie Institute for Science at Stanford.  So too did the suggestion that coral reefs would not be sustainable anywhere in the global ocean by 2050.  Cramming everything we wanted to put in the broadcast radio programme was impossible, so here you can listen to part of Ken's conversation with Gaia at greater and compelling length.   Prof Caldeira puts our CO2 emissions (particularly the rate of them) and their effects on the oceans into a stark geological time perspective.

There's a couple of minutes towards the beginning in which Ken talks about the processes in the normal long course of geological time which have kept ocean pH levels relatively stable.  Stick with it!  Because it helps to explain why what's happening today is so "extreme" to quote Prof Caldeira.

The last time anything comparable happened to the planet's oceans was about 60 million years ago, during the Paleocene-Eocene thermal maximum.  It was such a long time ago, that back then, horses were like the little one on the right.

This Google Earth video tour of ocean acidification is also excellent, in part because it shows graphically how acidification has increased and is projected to rise over the next few centuries.   It also nicely explains some of the basic science neglected by me here.