Climate Letter #2056

The November issue of Scientific American magazine contains a lengthy article about rapidly rising precipitation written by Jennifer Francis, one of the world’s most prominent atmospheric scientists.  It is available to all readers online at this link:  https://www.scientificamerican.com/article/vapor-storms-are-threatening-people-and-property/.  It’s worth a close reading, as a source of information about current changes in the climate and also about how today’s top scientists are thinking about the causes.  Her views about why we are getting so much precipitation, and why it is being distributed unequally over certain parts of the globe in such extreme ways, are generally supportive of the conclusions drawn by atmospheric river (RA) researchers that were reported in recent letters.  She goes on beyond their work with commentary about how these rivers add to temperatures in the atmosphere as well as to precipitation, which I found especially interesting—mainly because it manages to avoid any discussion of greenhouse energy effects or the pure exchanges of radiation that are fundamentally involved in greenhouse production. Dr. Francis is more interested in discussing what happens to the latent heat that is released whenever vapor condenses into a liquid state.

This is in fact a good subject to think about, and to become familiar with, because the amount of energy released in this way is relatively large and possibly unusual.  I have always thought that much of this energy was converted directly into lightning and thunder, or to the forces behind the destructive power of high winds.  Heat formation due to condensation is most certainly possible, but how and where is it stored after formation, and how long does it last?  I don’t think Dr. Francis gives us a full set of answers in this article but she does open several doors to things worth considering.  She also has quite a bit to say about the impact of abnormally high nighttime temperatures and their possible causes, but leaves open any really convincing reasons for why daytime temperatures have not warmed up just as much.  Is humidity in the specific (or absolute) sense actually greater at night than in daytime?  We know relative humidity grows as temperatures cool down, approaching the point needed for condensation into dew or fog. Is the latent heat released by this condensation great enough to have a meaningful effect at night, but not normal in daytime?  Or, does the higher evaporation rate in daytime produce enough surface cooling to counteract the high air temperatures that cause the evaporation, in a meaningful way? Are these effects great enough to cause much of the anomalous disparity that has grown between night and day, while the globe as a whole grows warmer?

More generally, I am not ready to get used to the idea that heat is somehow trapped and then stored in a purely gaseous atmosphere. Gases are nothing but molecules, and molecules are not known for having an ability to store heat.  They can trap radiation, in the form of photons, in their own very limited way, and then respond by releasing a new photon, with no delay whatsoever.  The new photon may reverse the direction of the one trapped, which sensors made of solid materials will record as increased heat, but how will molecules by themselves, not densified into solids or liquids, be able to “store” their energy exchange activity in the way solids and liquids do, by means of their highly packed molecular interiors?  Maybe cloud droplets can store small amount of heat in their interiors in the way oceans do it, on a much smaller scale of course, but we need to ask some questions.  How much are they able to store when there is so much surface area on a droplet relative to the amount of interior space?  As for tiny little molecules, there is simply no interior space, or space content, suitable for any kind of storage activity.  Molecules can perform a quick energy turnover, vibrating for a split second, but then must be ready to repeat the same action at any instant.  Clear skies can be filled with radiation, which any sensor can pick up, but where do they gain the capacity to collect and store energy as heat in the way the sensor does, or any similar material?

The article contains a chart that shows something I would not have expected.  It is the lower one of the pair of charts labeled “Wetter World,” where we see the total volume of water vapor in a steadily rising trend since the beginning of this century, but not before. By contrast, the trend after 1980 was more of a downward thing.  Global temperatures have been in a steadily rising trend for over 45 years, since 1975, but apparently with no help at all from increases in the greenhouse energy produced by water vapor for the first 25 of those years—if the chart is right.  What did cause the sudden upturn after 1975, with all the greenhouse gases aside from water vapor just plodding along at their usual (relatively) slow and steady pace?  All I can think of at the moment goes back to what James Hansen says about the campaign that was starting to clean up the notorious sulfur emissions from burning coal and oil. This effort successfully cleared away a good share of the sulfate aerosols that were brightening cloud tops in a significant way and thus adding to the solar albedo.effect.  The sharp increase in water vapor could then account for the temperature acceleration in recent years, but what caused such a large shift creating the increase?  A rapidly growing volume of content held by overhead atmospheric rivers comes to mind as a possibility, but I have nothing in hand to show right now in the way of historical records. 

Carl