As scientific coordinator of the Tara Arctic Drift in 2007-2008, Jean-Claude Gascard gives us his perspective on the changes taking place at the North Pole.
Trained as an oceanographer, Mr. Gascard quickly began to study polar oceans and ice. He is currently working on a book about the European research program DAMOCLES, to which Tara Expeditions contributed. This publication will contain all the scientific articles produced thanks to observations made on board the schooner. A new Arctic drift is envisaged for the coming years.
What was your role during Tara Arctic?
At the time I was working at the University Pierre et Marie Curie in Paris, in the LODYC laboratory (pronounced “Odyssey) — Laboratoire d’Océanographie Dynamique et de Climatologie. Ten years before Tara Arctic, we had been in contact with Jean-Louis Etienne at the time when the boat was still called Antarctica. In 2005, in anticipation of the International Polar Year (2007-2008), we thought a collaboration with Tara should be established, knowing we had a mutual desire to conduct research in the far North. We decided to work with the European Union during the International Polar Year (2005 to 2010) on the DAMOCLES project. I coordinated the project about climate change in the Arctic, in connection with the spectacular retreating of glaciers observed in 2007.
What measurements were made on site?
Thanks to the schooner Tara, which is a unique research platform, we performed simultaneous observations in the atmosphere, ice and ocean. We employed several devices, such as radiometers and seismographs installed on the ice. Other instruments made atmospheric profiles measuring temperature, wind strength at various altitudes, and the level of humidity. We took measurements from an altitude of 1000 meters down to a depth of 1000 meters, and within the 2 meters of ice that separate the ocean from the atmosphere.
Our observations and the results of these studies are difficult to summarize in a few words. They are the subject of numerous scientific articles. We mainly worked on the dynamics of what happens in the atmosphere, in the ocean and sea ice, and the interactions between the three. In other words, what happens through the ice to transfer heat, or to insulate the ocean from the atmosphere when it is very cold or warmer.
Our observations allowed us to set up models to create better climate forecasts, taking into account physical factors, i.e. temperature transfers. We wonder how these thermal flow transfers are evolving, how they propagate through the atmosphere, through the ocean and through the pack ice.
We focused on what we call the number of Freezing Degree Days (FDD). For example, if it’s -20°C for 100 days, you multiply -20°C by 100 days yielding 2000 FDD. This corresponds to a production of about one meter of ice. By calculating these FDDs, which vary from year to year, we find that there are fewer FDDs and therefore less ice formation in the Arctic. For the last 30 years, we have lost about 2000 FDDs in winter or one meter less ice per winter. We should therefore not only be concerned about what happens in summer with melting ice but also in winter during the formation of sea ice.
In terms of volume, we have lost 10,000 km3 of ice between the 1980s and today. That is a meter of ice over 10 million square kilometers. In comparison, France is half a million square kilometers.
Is the impact of human activities one of the causes of this drastic melting?
Climates develop on the basis of physical relationships. By altering balances, for example by releasing carbon dioxide into the atmosphere, humans impact the climate. We try to measure the “anthropogenic forcing,” which describes the impact of human activities on the climate compared to its natural variability. Today there exists both anthropogenic forcing, as well as natural variability which no one disputes. 10 billion humans will inhabit the Earth at the end of the century and it’s quite normal to be concerned with this forcing effect originating from humans.
What we observe today in the Arctic is a fairly new phenomenon, and things change quickly. There is indeed a variability from year to year between the areas and ice concentrations that are influenced today by anthropogenic forcing in addition to natural forcing. For us, the effect of human activity is absolutely clear, because without it we could not explain such changes.
When we talk about climate warming, there are nuances to perceive and to understand. For example, we see more and more cold air descending to low latitudes, and warm air rising to the Arctic. We find ourselves in a situation where the Arctic is warming and our mid-latitudes are cooling. The Earth does not heat up everywhere in the same way. We are working on this schema, and our observations are intended to help us better understand the relationships of cause and effect.
You speak of “natural variability”. This summer Tara encountered a lot of ice on the east coast of Greenland.
The system reacts to various disturbances. When we say that ice is retreating in the Arctic, this includes the melting ice, but also the ice leaving the Arctic via currents, which then moves south into the North Atlantic. This is a net loss for the Arctic.
As an oceanographer, what do you expect of the next Climate Conference in Paris?
To get away from the current stagnation and incomprehension about the phenomenon! What are we talking about when we discuss climate change? I think there’s a problem of understanding. The information conveyed and the discussions all go in different directions. If there is clarification, decisions will be easier to make. This is what Tara Expeditions is trying to do by enlightening the choice of policy makers using proven scientific results.
Interview by Noëlie Pansiot
- Watch this animation representing the volume of ice in the Arctic: