But couldn't those clouds be a negative feedback?

Denver Weather Examiner: NASA: Global warming allegedly to increase severe storms

For every degree Centigrade (1.8 degrees Fahrenheit) increase in average ocean surface temperature, the team observed a 45-percent increase in the frequency of the very high clouds. At the present rate of global warming of 0.13 degrees Celsius (0.23 degrees Fahrenheit) per decade, the team inferred the frequency of these storms can be expected to increase by six percent per decade.

Climate modelers have long speculated that the frequency and intensity of severe storms may or may not increase with global warming. Aumann said results of the study will help improve their models.