The word "detection" by climate scientists has been used to refer to the identification of the significant change in climate during recent times and its association with the enhanced greenhouse effect due to man-made greenhouse gas emissions. Although a global warming has taken place during the 20th century, we need to be sure that mankind, rather than some natural process, is responsible for it, before committing substantial resources towards tackling the problem.
The rise in global average surface temperature of about 0.6C in 100 years is consistent with the enhanced greenhouse effect theory. Nevertheless, the difficulty in "greenhouse detection" arises because there are numerous other natural causes of climatic variability, some operating over a similar time scale that can produce comparable changes to that of the enhanced greenhouse effect. In addition, the global climate can fluctuate quite randomly, warming or cooling by up to 0.3C per century.
The best way to see if global warming and the enhanced greenhouse effect are associated is to use computer models to simulate the likely climatic effects of the changing atmospheric composition, and to compare the results with observations. Such models have significantly increased confidence in the belief that current global warming is indeed due to greenhouse gas pollution. Whilst changes in the amount of sunlight received by the Earth may explain some of the short-term climate variability during the 20th century, in light of the most recent evidence, and taking into account the remaining uncertainties, most of the observed warming in the last 50 years is likely to have been due to the increase in greenhouse gas concentrations.