State of the Planet

News from the Columbia Climate School

Who cares about the Southern Ocean?

Scientists are often asked to explain why their work is important. I have been asked this question several times since the publication of a paper entitled “Wind driven upwelling in the Southern Ocean and the deglacial rise in atmospheric CO2” (Science, 13 March, 2009).  I’m going to try to answer it here.

In the paper my colleagues and I describe evidence for an increase in the vertical mixing, or overturning, of the ocean around Antarctica, also known as the Southern Ocean, during the period when Earth was coming out of the last ice age (roughly 17,000 to 10,000 years ago).  We link this increased overturning to the rise in atmospheric CO2 that occurred at that time.  We further suggest that the mechanism behind the increased overturning and release of CO2 from the ocean to the atmosphere involved a reorganization of Earth’s wind systems in response to severe cold winter conditions in the North Atlantic region at the time.  Evidence used to reach these conclusions, and the underlying principles supporting the interpretation, are described in the paper.  Here I want to address “Who cares?”

As many people know, carbon dioxide is a greenhouse gas. CO2 concentrations are rising today due to to human activities, burning of fossil fuels (e.g., coal, oil and gas) and changes in land use.  There is widespread concern that future changes in Earth’s climate may be caused by rising levels of CO2 and other greenhouse gases. Therefore much effort is devoted to developing models to predict the future climate impacts of increased atmospheric greenhouse gases.

Our recent study is one of many investigating the processes that regulated the CO2 content of the atmosphere in the past. We hope to understand the tight correlation between Earth’s climate over the past 800,000 years and the CO2 content of the atmosphere (for a graphic representation of this correlation see below as well as Lüthi et al., Nature, 15 May, 2008) as seen through the study of ice cores from Antarctica.

CO2 and temperature are tightly correlated through the ice ages. From Petit et al, 1990, taken from

The correlation in the past is robust, but correlation alone does not identify the processes responsible.  Neither does it indicate the sensitivity of Earth’s climate to changes in the CO2 content of the atmosphere.  These relationships must be worked out by independent methods.

Scientists often use models to understand past and present climate dynamics.  Models are the only tools we have to quantify these processes for the future. However, models cannot encompass the full complexity of Earth’s climate system.  For example, models cannot include all the factors that come into play nor can they resolve all desired spatial and temporal scales.  In some cases assumptions are made about unconstrained factors, while in other instances models use approximations for processes that cannot be represented explicitly in model codes.

Many scientists believe that understanding “why” changes in Earth’s climate were coupled so tightly with CO2 throughout the time period covered by the ice core records will help improve the models used to predict future climate change.  Thus, one way to improve models is to incorporate basic principles that are derived through research on past climate change.  Basically, the better scientists understand the processes regulating Earth’s climate, the greater the chance of making accurate predictions of future climate conditions.

We hope that our work helps clarify one of the fundamental mechanisms underlying the tight coupling between climate and CO2 in the past.  This one study does not provide the complete story, but it provides an important piece of the puzzle that will aid scientists in filling in the rest of the picture.

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15 years ago

To quote a scientist who’s opinion I greatly respect “so much to learn”. We know we are in deep trouble, we just don’t know how deep.

Each piece of the puzzle is important. The Southern Ocean has many secrets, some of them will be very important.