A study published recently in the journal Science goes some way toward answering a critical but open question about the Earth's hydrological (water) cycle in a warming world. Here's the abstract.

Fundamental thermodynamics and climate models suggest that dry regions will become drier and wet regions will become wetter in response to warming. Efforts to detect this long-term response in sparse surface observations of rainfall and evaporation remain ambiguous. We show that ocean salinity patterns express an identifiable fingerprint of an intensifying water cycle. Our 50-year observed global surface salinity changes, combined with changes from global climate models, present robust evidence of an intensified global water cycle at a rate of 8 ± 5% per degree of surface warming. This rate is double the response projected by current-generation climate models and suggests that a substantial (16 to 24%) intensification of the global water cycle will occur in a future 2° to 3° warmer world.

And in plain English in Global water cycle is revving up from the Nature blog—

The laws of physics — namely vapor pressure dependence on temperature — dictate that a warm atmosphere can hold much more water vapor than a cold atmosphere. As global temperature rises, so will evaporation, atmospheric moisture content and precipitation. At the same time, global atmospheric circulation models suggest that the distribution of rainfall will change along a pattern that will dry subtropical areas and increase precipitation at higher latitudes. As the world has already warmed around half a degree Celsius since 1950 the predicted changes should already be observable — except that there are not enough reliable measurements over land to confirm them without ambiguity. But in the oceans, which receive around 80 percent of global rainfall, their fingerprint is clearly visible. Analysing some 1.7 million measurements of ocean salinity made between 1950 and 2000, Paul Durack a climate researcher at Lawrence Livermore National Laboratory in California and colleagues, found that relatively fresh ocean regions have got notably fresher, while regions already saltier than average got even saltier. [My note: Fresher ocean regions received more rainfall, while saltier regions had more evaporation.] What’s more, the team found that the acceleration of the global water cycle proceeds much faster than current-generation climate models have been predicting. Changes since 1950 in ocean surface salinity suggest that the global water cycle speeds up at a rate of around 8% per each degree [centigrade] of warming — nearly double the average response seen in models. By 2100, when the world will likely have warmed another 2-3 degrees, the water cycle might intensify by 16-24 %, the scientists conclude.



Changes in salinity, from the Nature blog

Changes in salinity (saltiness) of ocean waters tell us how much evaporation and rainfall is typically taking place over time, and is thus a proxy measurement of changes in the intensity of the water cycle.

I would like to call the reader's attention to the phrase "the laws of physics" in the Nature text above. In the general case, you are allowed to have an opinion about baseball players, TV celebrities or politicians—these are all the same thing—government policies, economic frameworks, and all kinds of other things. You are not allowed to have an opinion about the laws of physics.

This relates to climate models in a straightforward way. Unlike economic models, which are mostly a make-it-up-as-you-go-along affair, climate models include those non-negotiable laws of physics. I talked about economic models in Economics — So Much Heat, So Little Light. Climate models can be wrong, for they are far simpler than the Earth's climate system they attempt to describe.

In this case, those models have underestimated changes in the Earth's hydrological cycle as a function of surface warming according to the salinity measurements of the Lawrence Livermore researchers. Thus climate researchers must go back to the drawing board and figure out what's going on here. In addition, these salinity measurements will be confirmed or disconfirmed by future data from satellites.

If everything goes according to plan, our understanding of this planet's climate and our effects on it should be nearly perfect on or about that future day when the Earth becomes almost uninhabitable for big-brained primates like us

Intensification of the hydrological cycle portends big changes in extreme weather events, in this case droughts and downpours. In short, there will be more and them, and they will be more intense. I had to laugh when I saw this widespread canard in the Nature blog post.

Perhaps the most inconvenient thing about global warming is that mainly the poor will have to carry the can. While, for example, the amount of rainfall at wealthy and relatively freshwater-blessed mid and high latitudes is likely to increase as the climate warms, drought-prone regions such as the Sahel zone will likely get even drier.

What's this? Do the "wealthy" people living at mid and higher latitudes think they are somehow immune from the larger effects of global warming and the other big disasters (e.g. in the oceans) we humans are bringing about? Apparently some of them do. I've seen this nonsense repeated many times before. Drought is a killer, but so are "hundred-year floods" which occur every other year. And when has it ever been the case that the poor didn't bear the brunt of some disaster, whatever it is?

This time around, as time goes on in the 21st century, nobody will be immune from the harmful effect of human meddling with the Earth's natural systems. And no amount of money is going to buy you a get-out-of-jail card.