For every degree C that Earth’s atmospheric temperature rises, the amount of water vapor in the atmosphere can increase by about 7%.
A warmer world is a one with heavier precipitation events, even in places where average rainfall may remain unchanged. www.carbonbrief.org/explainer-wh...
Same applies to the drivers of marine heatwaves, so I really doubt that climate models can do the job to simulate these changes, same as they can not simulate the increases in extreme precipitation which we recently observe which drive the moistening of the lower troposphere...
Source of the above assertion: "Systematic Occurrence Cycle of Typical RH-Profiles During the MJO: Evidence for Ubiquitous Pre-Moistening"; agupubs.onlinelibrary.wiley.com/doi/10.1029/... - fun fact the MJO cycle is speeding up...
Not that we will trigger it, but I'm quite curious what studies will find out on the sudden warming the last months of the whole tropical to subtropical Atlantic, as such a vast and sudden expansion of extreme SST's over large parts of an ocean basin was not projected...
What makes all this so interesting is, that with marine heatwaves in 2023 suddenly reaching a coverage of >40% of global oceans the above could be triggered by just the upper layer of the oceans heating faster than projected, as various feedbacks drive MHWs with one of them being water vapor.
"Transitions between these regimes occur via nonlinear atmospheric moistening, increasing relative humidity (RH)."
"A Satellite Climatology of Relative Humidity Profiles and Outgoing Thermal Radiation over Earth’s Oceans"; doi.org/10.1175/JAS-...
"Satellite observations over Earth’s oceans show two distinct regimes in the relationship between SST and outgoing longwave radiation (OLR): a temperate regime (OLR increases with increasing SST quasi linearly) and the super greenhouse regime (OLR decrease with increasing SST)."
"Observations of the tropical outgoing longwave radiation (OLR) show that above sea surface temperatures (SST) of about 295 K (21,85 °C), OLR decreases with increasing SST (contrary to its usual behavior), which is associated with nonlinear moistening processes in the atmospheric column."
"Water vapor is of particular importance for Earth’s energy budget due to its effective absorption of longwave radiation, yet its spatial and vertical distribution across Earth’s oceans is insufficiently characterized."
Just to be more precise: the non-linear increase was observed from 2012 to 2016 when global SST's made a jump - so what happened in the second half of 2023?
Another detail: tropical poleward moist air advection favors marine heatwaves by preventing latent heat release at the ocean surface...
But as they also write "Nonetheless, water vapor retrievals in this part of the atmosphere are also less accurate than in the free atmosphere and can cause anomalous trends" it could be wrong, but errors can go both ways...
Just thought it important that you know what we observe in the field...
Therefore the Clausius Clapeyron equation is misleading as water vapor increases can be much more than 7% per degree of warming in the real world where the atmosphere is not saturated.
In principle its simple: if mean RH levels increase from 50% to 60% in the lower troposphere (boundary layer) over a region of the oceans with one degree of warming, you get an increase in total water vapor content by 20% without any increase in temperature that comes on top.
"That all regions exhibit comparable RH increases in the marine boundary layer suggests that not only the underlying SST control the RH but also atmospheric dynamics, which might be the reason for the nonlinear decadal trends of RH at 925 hPa."
RH - relative humidity - "Geographically, the increase in marine boundary layer RH is observed over all oceans with the exception of regions with westerly offshore winds in the trade wind regions"
"Observed RH change at 925 hPa between 2012 and 2017 remains much larger than the expected 1% from climate projections. This result is consistent with findings by Borger et al. (2022), who also estimated the RH increase in the boundary layer to be much larger than the predicted 1% K−1"
What would interest me most is if we get a changing density gradient between the continents and the oceans - humidity increases more over the oceans than over the continents where relative humidity declines - moister air gets lighter - hope my suspicion is stupid but the main principle is clear...
Here you have the atmospheric profiles and the increases we observe in the field...
Source: "Increase in Tropospheric Water Vapor Amplifies Global Warming and Climate Change"; spj.science.org/doi/10.34133...
Source: "Changes in Relative Humidity Profiles over Earth’s Oceans in a Warming Climate: A Satellite-Data-Based Inference"; journals.ametsoc.org/view/journal...
First this one, as it is a main principle of global warming as it seems: "Globally, the marine boundary layer exhibits nonlinear moistening effects after about 2010, the end of the warming hiatus." till 2016 the increase happened - wonder how the increase was in 2023 - should have been enormous...
Nope! The Clausius Clapeyron equation is dead as it can only be applied in a steady state saturated system which is Earth seemingly not. Another critical model error one could say. Here is what happens in the real world: oops we missed the water vapor feedback! The observations in the comments...
