"The Ocean Waters in The Southern Oceans Have Become Less Effective in Drawing Down Carbon Dioxide from The Atmosphere"
8 Jun, 2007 04:14 pm
The British Antarctic Survey has been conducting studies on the ocean's role as a natural carbon sink and how that role has been affected due to human CO2 emissions. The Survey's Director Chris Rapely answers scitizen's questions.
Has the increase in CO2 in the atmosphere due to human activity had any impact on the ocean's capacity to absorb the additional gas ?First, I would like to say that this is work carried out by researchers at both BAS and at the University of East Anglia.
It seems so. There’s a chain of events that taking place. What we have found in the last few year is that the winds that run around the Antarctic have intensified. This can be attributed to human induced global warming and the presence of the ozone hole. This has had several effects. One has been to waft warmer wind over the Antarctic Peninsula and cause a strong warming there. The other effect, which is unanticipated, has been to cause the ocean waters in the southern oceans to become more mixed, and therefore less effective in drawing down carbon dioxide from the atmosphere.
What impact does this have on the biosphere ?
It is indeed a biological pump in the ocean. The small plankton that feed on the little phytoplankton in the ocean that act to process the carbon absorbed in the water. Their fecal pellets drop down to the bottom of the ocean, and the carbon is sequestered. So, indeed it is a pump. The issue is whether the oceans are helping by taking out some of the carbon dioxide that humans have put into the atmosphere by burning fossil fuels. Since the beginning of the industrial revolution humans have emitted 500 gigatons carbon equivalents of carbon dioxide through a mixture of burning fossil fuels, cement production, and clearing the land surface for agriculture-changing the mix of the terrestrial biosphere. The vegetation on land and in the ocean have reabsorbed about half of that, net. But there is evidence that in a warmer world both of those sinks will weaken, which was anticipated. What was not anticipated was that this southern ocean sink, a particularly important one, would have already weakened because of the effect of the strengthened winds and the increased overturning of the waters.
What does all of this mean in terms of Climate Change?
We just heard yesterday that the G8 are agreeing to targets or a process by which targets will be set to limit carbon dioxide emissions. The reason for doing this is try and stabilize the carbon dioxide content of the atmosphere at a level at which people consider acceptable, or beyond, which would become dangerous in the sense that parts of the Greenland ice sheet or the Antarctic ice sheet might melt, that the climate might change, and affect agriculture and water supplies. The generally accepted figure of global warming is about 2 degrees. The generally accepted figure to stabilize carbon dioxide in the atmosphere to achieve that is about 450 and 500 parts per million. Remember that were at 370 now. The emissions trajectory that you have to follow to achieve that -were currently at 7 gigatons per year- is to turn that over rather than let it continue to rise and bring it down to a region of a couple of gigatons a year or maybe less. If the oceans and terrestrial biosphere carbon sinks are weakened as they have been in the past or indeed if they were turned into sources, then that 2 gigaton limit per year would have to be even be lower.
Interview by: Christopher Le Coq
Chris Rapley is the Director of the British Antarctic Survey, a Fellow of St Edmund's College Cambridge, and an Honorary Professor at University College London and at the University of East Anglia.
