It is the first paper applying a "rigorous" method for distinguishing among the different factors that influence climate, such as greenhouse warming, aerosol cooling, and the influence of solar radiation. So it describes and applies a new technique to an exciting problem.

It is new in its application to the climate change problem. The technique itself is a well-known mathematical approach (multiple regression), but we have tailored it to the climate change problem in a novel way.

The paper tries to determine if greenhouse warming is apparent in surface temperature trends, and if, additionally, sulfate aerosol influence is obvious in the data. It also establishes if climate-model simulations are in agreement with the most important aspects of the observed temperature trends across the globe. The paper concludes that greenhouse warming is apparent in the data, that sulfate aerosols have an important contribution, and that solar effects by themselves or natural climate variability alone cannot explain the data. Our paper describes changes in climate, and shows that only the human-induced increase in greenhouse gases in the atmosphere combined with other anthropogenic influences can fully explain it.

I worked as a research scientist at the Max-Planck institute for Meteorology in Hamburg, which has an extensive modeling group and this gave me the opportunity to use the latest simulations for my research. I developed the method together with its director, Klaus Hasselmann, who is truly an outstanding scientist. My contacts to other modeling groups provided me with the opportunity to use more than one model's data while those with the observationalists helped me gather the latest observed data.