DW: Professor Achim Bauer, you are an expert on the influence of solar activity that's happened in the past - specifically 2800 years ago is what your study is focussing on.

Achim Brauer: Actually what we are doing is we are looking at natural archives, that means lake deposits and tree rings and we try to find out in times when humans could not measure temperature and precipitation how the sun was affecting the climate.

So how exactly do you do that? You study lake sediments and somehow or another come to the conclusion that it didn't..

Okay, from the lake we could do both actually. We have new isotopes where we can see the direct traces of the sun so we know that 2800 years ago there was long period, 150-year long period, of a very weak sun and at the same time we can look at the compostion of these layers, these seasonal layers, which are milimeter-thick so we look in the microscope and then we can find out about seasons and climates and the seasons and what we've got from that is that especially the spring seasons were very windy so we had an increase in wind activity, so changes in atmospheric circulation at around the time when the sun was weak.

How far can you go back?

In principle, we can go back 10,000, 11,000 years, so as long as the present warm period was.

Well then let's go back then to the more distant past, the Little Ice Age, which started in the 16th century. It is said that this change of climate had nothing to do with solar activity, but rather volcanic activity. How do you feel about that?

Partly agree and partly disagree because we know that there were a number of strong volcanic eruptions.. what we know from our investigation is that the climactic effects of these eruptions did not last longer than three or maximum four to five years so that would not explain a really extended period of cold climate which we had during the Little Ice Age and actually that was the reason that we went to look at another period of solar mimima 2800 years ago becasue there were not so many volcanic eruptions.

Now we cannot control volcanic activity, we cannot control the sun, but what about ourselves and curbing CO2 emissions?

I mean if you just would like to discuss a little bit about what this is meaning for the future we could say that we know that this has been happening in the past, that the sun has a very strong impact on the climate. What is in the future we do not know because of these greenhouse gas emissions and so we have two different effects. And I think it's very important to reduce these emissions to keep system in a natural state.

How optimistic are you that we're going to be able to limit our CO2 emissions?

As a person who likes to learn from the past.. If I look back in the last 15 years, I can say that it was not really successful. A lot of people would like to have reduced their emissions but at present we are at a stage where we have CO2 emissions as high as never before, so I think we should look really to alternative ways as well and I think if the energy change in our country will be successful, this might be a signal for other countries aswell, so that I say I am carefully otimistic that we can change something in the future.

Carefully optimstic. Achim Brauer, thanks very much for joining us.

You're welcome.

(Interview: Anne O'Donnell)