The time span of 20 years is still too short to be able to decide conclusively whether the current heating phase is a temporary or permanent development. In the former case, climate forecasts will have to be fundamentally revised. The physical mechanism that led to the cloud thinning is discussed differently in the literature. Vahrenholt: “The cloud changes can be caused by a decrease in aerosols, by atmospheric warming due to natural causes (e.g. the AMO or the PDO), by anthropogenic warming due to CO2, or by a combination of these individual factors. However, one thing can already be stated: the warming of the last 20 years has been caused more by change in the clouds than by the classical greenhouse effect.
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