Interview with Prof Eystein Jansen, director of the Bjerknes Centre for Climate Research and Lead Author of the IPCC AR5 report.
By Jill Johannessen (Translation by Sverre Ole Drønen and Beatriz Balino)
- If we are to stay below the "2-degrees" target, we must start transforming into an energy-renewable society now.
This is the clear message from Prof. Jansen upon the release of Fifth Assessment Report (AR5) from the Intergovernmental Panel on Climate Change (IPCC). AR5 provides the most updated and comprehensive knowledge of changes to the climate system and creates the scientific basis for climate policy over the next six years, both in Norway and internationally. The Bjerknes Centre is responsible for the development and implementation of the Norwegian Earth System climate model, which provided global projections to the report.
- A very important discovery is that the footprint of humanity’s greenhouse gas emissions is very evident in the climate system, he adds. Prof Jansen was Coordinating Lead Author of the chapter 7 "Palaeoclimates" in the previous IPCC report (AR4) published 2007.
Impact of human activities are clearly evident now
AR5 presents an extensive list of human impacts on the climate system. In the previous report, however, the human component could only be detected in the development of the temperature of the northern hemisphere.
- The IPCC now firmly concludes not only that the human impact upon temperature development is clear in every continent, except Antarctica, but also in a number of factors such as: rise in sea level, the chemical composition of ocean (e.g acidification and salinity), alternations in the ice/snow conditions (e.g. melting of glaciers, retreating sea ice in the Arctic, snow cover on land in the northern hemisphere), heat waves, changes in the ozone layer, and changes in precipitation patterns (significant increase in precipitation and of extreme precipitation events in the northern hemisphere).
Global warming in a 2000-year perspective
The inclusion of major reconstructions of past climates from a wide variety of sources (e.g. tree-ring dating, stalagmites, sediments from lakes and the seabed, and ice cores) is also novel in the present report. This enabled scientists to identify the human component of global warming on major continents such as Asia and South America.
-Past climate reconstructions in all continents, with the exception of Africa, clearly show that today’s global warming is unique in a 2,000 year perspective.
Sea level rise revisited
The IPCC has also revised estimates of global rise in average sea levels. If greenhouse gas emissions continue at present levels then it is expected that sea level will rise almost one meter this century. And even if emissions are reduced to meet the 2-degree target, sea level will still continue to rise, mostly likely more than 50 cm, by the end of the century.
- This report shows that what we have seen so far is just the beginning of a long-term rise in sea level which, in a time scale of centuries, will reach several meters. There is clear evidence of buy studying the climates of the past times similar to the present.
For instance, 3 million years ago it was almost 3 degrees higher than pre-industrial records and the CO2 concentration in the atmosphere was similar to what we expect to reach in the near future. Back then, sea level was 10–20 metres above current levels. Jansen explains that the processes affecting sea level (increase in temperature, both air and ocean interior, and melting of large ice sheets in Greenland and West Antarctica) are inherently sluggish, i.e. it takes a long time to provoke a response, of the order of hundreds of years to be noticeable.
-Studies of past climates give us some idea of the end results if there is a change of 2-3 degrees in temperature. What we don’t know is how long it will take for these ice sheets and the sea to reach a new point of equilibrium. Still, it is an indication of the gravity of the situation, even more now than six years ago.
There is a great responsibility resting on the shoulders of our generation
Today, the pace of temperature change is 20 times faster than anything previously recorded in nature. The planet is under a major pressure never before experienced in the time humankind has existed as a species. There is nothing in the past comparable to the present situation.
- The choices we make in the next couple of decades will determine how much risk we impose on future generations. It will require vast resources if humanity must adapt to a climate in constant flux.