Abstract

Possible factors contributing to global warming during the last 100 years - the greenhouse effect, natural climatic variability, variations of solar activity, and cosmic ray fluxes as well as anthropogenic changes in land-cover are described. It is shown that currently it is very difficult to estimate even the relative role of each of these factors in global warming due to our still inadequate knowledge of them as well as discrepancies between different key data sets. It is shown that despite some successes and tremendous efforts in the fields of both climatology and paleoclimatology our knowledge of the Earth’s past climate is still lacking.