Our Threatened Oceans: Q&A with Dr. Stefan Rahmstorf

Apr102009

Written by Ava

Dr. Stefan Rahmstorf has a lot to be thankful for. As an oceanographer and physicist with a love for the ocean, he's combining elements of two passions into one. With a new book, Our Threatened Oceans, he's letting the world know first-hand through his research that we should recognize how important the ocean is to our lives. At the same time, he's also worried that the climate issue (as well as other problems) factor heavily into the change in the ocean and that we all must start working on fixing these concerns.

Stefan, at least, is already figuring out how to do so. With his work on the role of ocean currents in climate change, he was awarded the $1 million Centennial Fellowship Award of the US-based James S McDonnell foundation and since the year 2000, he is teaching Physics of the Ocean as a professor at Potsdam University. Perhaps it will be Stefan who will lead the next future climate scientist to make a difference, just as he has. Here's what Stefan has to say about what we can do to help remedy the current dilemma facing our oceans.

You’re a physicist and oceanographer by training, how did you get into the field?

Already as a child I loved the ocean; I grew up in Holland near the North Sea, actually living below sea level. I also had an interest in physics. So combining these two passions to become a physical oceanographer seemed a great idea – and I’ve never regretted it once.

How did you move from general relativity theory to working on climate issues?

This may seem strange, but I did my first physics thesis on general relativity theory precisely because I wanted to become a physical oceanographer, and this was the closest that my university in Konstanz had to offer. The thesis work was actually in relativistic hydrodynamics. After that, classical hydrodynamics seemed easy in comparison...

What are some of the things you teach your students about physics of the ocean as a professor at Potsdam University?

I teach courses on ocean circulation theory – how you can explain the main observed features of ocean circulation, like the huge wind-driven subtropical gyres, from the basic hydrodynamic equations. I also teach courses in paleo-climatology – covering some of the amazing climate shifts in Earth’s history like the Dansgaard-Oeschger events, which can be explained by instabilities in the ocean circulation.

What is the role of the oceans in climate change?

Our planet should really be called ‘Ocean’ rather than ‘Earth’, since oceans cover 71% of its surface. That’s why most of the sun’s energy which drives the whole climate system gets first absorbed in the ocean waters. The oceans store this heat, move it around with the currents and release it later elsewhere. Just look at the difference between the seasons. In continental interiors, average summer temperatures are up to 44 ºC warmer than winter temperatures in Canada, and even up to 56 ºC in Siberia. Over the ocean and in coastal areas, the difference between summer and winter is typically just 8 ºC, because of this heat buffering effect.

And of course the oceans provide the ultimate water source for rain and snow, and hence the glaciers and ice sheets. The ocean is also a big sink for carbon dioxide, it has absorbed between a third and half of the extra CO2 that humans have blown in to the atmosphere from fossil sources. There is no way we could understand the climate system without understanding the oceans.

What is happening to our oceans?

With climate change, the oceans are getting hotter, turning sour and rising higher. Global warming is first affecting the surface waters, which have warmed on average by 0.6 ºC over the past hundred years. But in some places warming can be measured down to over a thousand meters ocean depth by now. Sea level has risen 20 cm since 1880, and the rise is accelerating. Global satellite measurements began in 1993: they show sea levels rising at a rate of 3.4 cm per decade (that’s the linear trend up to the end of 2008).

But there is other threats unrelated to climate change as well, some of them very immediate: overfishing, pollution, destruction of coastal habitats by development of industry and tourism.

You handle this in your new book, “Our Threatened Oceans”, right? Tell me about the book.

I wrote the book, which was published a few weeks ago, together with marine biologist Katherine Richardson. Scientific understanding of the oceans has advanced greatly, and we wanted to give a first-hand account of this knowledge for the average person in the street – or should we say the average person on a beach. We wanted to describe the fascinating world of the oceans, the riches of sea life and how it all works together. And we discuss the threats, of course, in order to show what we need to do to maintain the health and beauty of our seas.

What is the message you are trying to convey with the book?

We are in the midst of massive changes to our Earth, including the oceans. Humans have become a geological force changing our planet’s chemistry, thermodynamics and coastlines. On many fronts – from local politics to the global climate negotiations which will culminate this December in Copenhagen – decisions are taken now that will determine the fate of the oceans for millennia to come, in often irreversible ways. Let me sum up our message with the final sentence from our book: “We hope that this book will help to ensure that the crucial decisions we are all taking affecting the future of the oceans – whether we like it or not – are based on a realistic understanding of how the oceans work and how fragile they are.”

What is your take on ocean acidification?

The CO2 uptake by the oceans is on one hand a bonus – without it, CO2 levels in the atmosphere would be rising much faster still. But on the other hand it is a major threat to marine life. More CO2 in the ocean water makes it more acidic, that’s basic chemistry and a measured fact. If it gets too acidic, then coral reefs, sea shells and microscopic plankton at the basis of the oceanic food chains will not be able to function properly any more – they can’t build their calcium carbonate structures any more. If we continue with our fossil emissions, we’d reach this point in about fifty years. To me, this threat to the functioning of our oceans is by itself enough reason to drastically cut our CO2 emissions – even if CO2 was not also a greenhouse gas which heats up our climate.

What can someone like me do to provide more awareness of the dire situation of the ocean?

Knowledge is the key to good decisions. So running a blog bringing together interested people to discuss and exchange information is already an excellent thing to do. I think what is very important is to not get lost in a vague feeling of things being dire, but to clearly identify the threats and discuss the practical solutions.