Nature has published another major study confirming the impact of global warming, “Attribution of observed surface humidity changes to human influence” (subs. reqd.). Why is the study important?
Water vapour is the most important contributor to the natural greenhouse effect, and the amount of water vapour in the atmosphere is expected to increase under conditions of greenhouse-gas-induced warming, leading to a significant feedback on anthropogenic climate change.
The humidity level is also important because it affects the pattern of extreme storms. What did the study find?
[T]his study demonstrates that the observed increase in surface specific humidity is directly attributable to anthropogenic influence and is distinct from the predicted response to natural forcing….
Although radiative forcing of the climate is dominated by changes in the amount of water vapour in the upper troposphere, anthropogenic moistening of the surface and lower atmosphere is likely to have important implications for extreme precipitation, tropical cyclones and human heat stress.
In short, global warming is happening, humans are the cause, and it is going to lead to more severe hurricanes and rainstorms.