An important question for humankind is if storms are getting worse in a changing climate? Can it be proved that man is to blame for any one storm? The IPCC makes many important statements on these questions.

As far as blaming humans for any one storm the IPCC makes it clear it is impossible to discover the cause of any one extreme weather event, including from greenhouse gases for two reasons:

1) “extreme events are usually caused by a combination of factors”.

2) “a wide range of extreme events are a normal occurrence in an unchanging climate”. (AR4 FAQ 9.1 Page 696) 

On number 1 or combination of events the IPCC gives an example here of the extremely hot summer seen in Europe during 2003, the IPCC explains “a persistent high-pressure system that was associated with very clear skies and dry soil” as all this heated the surface even further. (AR4 FAQ 9.1 Page 696)

The IPCC goes on here to point out many things are needed to cause storms with some man-made affect while others are not. For example, storms are affected by jet streams, ocean temperatures, atmosphere changes, on and on. (AR4 FAQ 9.1 Page 696)

The IPCC states clearly “it is not simple to detect a human influence on a single, specific extreme event” (AR4 FAQ 9.1 Page 696)

The IPCC tells us improvements are needed towards understanding storms by gaining more data about them from the past and present.

For example, the IPCC admits a great deal of data is lacking by stating here there is “low confidence in observed trend in small-scale severe weather phenomena such as hail and thunderstorms because of historical data inhomogeneities and inadequacies in monitoring, systems.” (AR5 Section 2.6.2.4 Page 216)

Not only are there questions about small-scale severe weather events like thunderstorms and hail, but even bigger questions with large storm fronts, cyclones and hurricanes. These are very important negative feedbacks as they remove energy from the system in the form of wind and waves. The IPCC admits models have a very hard time accounting for such large unpredictable storms.

The IPCC notes atmospheric flows create systems that can be 1000s of kilometers large like cyclones and frontal systems. They note models have a difficult time with these, but they state they are making progress. (AR5 Section 7.2.1.1 Page 579)

IPCC states they continue to have “low confidence” in their understanding of long-term tropical cyclones on the 100-year scale. (AR5 Section 2.6.3 Page 217)

The IPCC has “low confidence of any trend or long-term change in tropical or extratropic storm frequency or intensity in any ocean basin”. (AR5 Section 3.7.5 Page 290)

They note the North America Monsoon Systems (NAMS) has strong influence on moisture seen Mexico and the southwestern USA, but admit it is very difficult to model. (AR5 Section 14.2.3.1 Page 1233)

The IPCC has “low confidence of any trend or long-term change in tropical or extratropic storm frequency or intensity in any ocean basin”. (AR5 Section 3.7.5 Page 290)

Rainfall, Droughts, Dryness, and Evaporation

There are other important questions related to the subject of clouds and water vapor in the areas of rainfall, droughts, dryness, and evaporation. For example, the IPCC notes there are differences in global studies on dryness or drought in some regions, with agreement in other regions. Here are the regions mentioned:

• IPCC notes “medium confidence” in regards of drought trends in East Asia (AR5 Section 2.6.2.3 Page 215)
• IPCC has “high confidence” of more drought in the Mediterranean and West Africa. (AR5 Section 2.6.2.3 Page 215)
• IPCC notes “high confidence” of less drought central North America and north-west Australia. (AR5 Section 2.6.2.3 Page 215)

When it comes to frequency and intensity of drought the IPCC notes the following regions.

• It is “likely that the frequency and intensity of drought has increased in the Mediterranean and West Africa.” (AR5 Section 2.6.2.3 Page 215)
• Shows a decreased in frequency and intensity of drought in central North America and north-west Australia since the 1950s.” (AR5 Section 2.6.2.3 Page 215)

The IPCC admits “AR4 conclusions regarding global increasing trends in drought since the 1970s were probably overstated.” (AR5 Section 2.6.2.3 Page 215)

The IPCC goes on to summarize in AR5 they lack the data to have more than “low confidence” about drought or less rainfall globally since the 1950s. (AR5 Section 2.6.2.3 Page 215)

The IPCC details an important area lacking data is precipitation and evaporation. The IPCC admits measuring “precipitation and evaporation directly and globally is difficult”. The reason is most of this activity happens over the oceans or 70% of Earth’s surface. Today, they have land records. (AR5 FAQ 3.2 Page 269)

Last in this area the IPCC goes on to note irrigation or power plant cooling have little effect on the global climate. (AR5 FAQ 8.1 Page 666)

This concludes all the important questions I found in AR4 and AR5 regarding water vapor type questions.