Guest post by Willis Eschenbach
There’s a new study out from NOAA called “Probable maximum precipitation (PMP) and climate change”, paywalled of course, which claims that global warming will lead to a 20%-30% increase in “probable maximum precipitation”. The abstract says:
Probable Maximum Precipitation (PMP) is the greatest accumulation of precipitation for a given duration meteorologically possible for an area. Climate change effects on PMP are analyzed, in particular, maximization of moisture and persistent upward motion, using both climate model simulations and conceptual models of relevant meteorological systems. Climate model simulations indicate a substantial future increase in mean and maximum water vapor concentrations. For the RCP8.5 scenario, the changes in maximum values for the continental United States are approximately 20–30% by 2071–2100. The magnitudes of the maximum water vapor changes follow temperature changes with an approximate Clausius-Clapeyron relationship. Model-simulated changes in maximum vertical and horizontal winds are too small to offset water vapor changes. Thus, our conclusion is that the most scientifically sound projection is that PMP values will increase in the future due to higher levels of atmospheric moisture content and consequent higher levels of moisture transport into storms.
When I heard that number, a 20%-30% increase in maximum rainfalls, my urban legend detector starting ringing like crazy.
Figure 1. The authors’ guess at how much more rain will be falling by the end of the century.
So … why did my urban legend detector go off from this claim? It has to do with energy.
The press release quotes the authors as saying:
“We have high confidence that the most extreme rainfalls will become even more intense, as it is virtually certain that the atmosphere will provide more water to fuel these events,” said Kenneth Kunkel, Ph.D., senior research professor at CICS-NC and lead author of the paper.
Now, the increase in maximum rainfall is said by the authors to be due to the increase in water vapor in the air. It’s unclear if the 30% increase in maximum rainfall will be matched by a corresponding overall increase in rainfall. However, it is highly unlikely that an increase in water vapor will only increase maximum rainfall events. The authors themselves say that their projections show “a substantial future increase in mean and maximum water vapor concentrations”.
So to be conservative, let’s cut the 30% increase in maximum water vapor down to a 20% increase in mean water vapor, and see what that looks like.
I want to determine how much energy we’re talking about here. Suppose the rainfall were to go up (on average) by about 20% globally. Right now, the globally averaged rainfall is on the order of a metre of rain over the entire surface per year, a bit more or less depending on who is measuring. Twenty percent of that is 200 mm. So we need to evaporate an additional 200 mm over every square metre of surface to produce the stated increase in rain.
It takes 2260 joules of energy to evaporate a gram of water. For each square metre we need to evaporate 200 mm, or 200 kg of water. To evaporate that much water takes 4.52e+8 (452,000,000) joules of energy.
Now, a joule is a watt-second. We need 4.52e+8 joules of energy every year to evaporate the additional water, which is 4.52e+8 watt-seconds per year. Dividing that by the number of seconds in a year (3.16e+7) gives us the change in constant 24/7 watts needed to evaporate that much water. Remember, this is an increase in the constant watts of energy striking every square metre of the planet.
And that number, dear friends, the amount of additional energy needed to increase global evaporation and thus rainfall) by 20%, turns out to be 14.3 W/m2. That’s about the amount of energy increase from three doublings of CO2. Yes, CO2 would have to go from the current ~400 ppmv to about 3,200 ppmv to provide that much extra forcing …
So my urban legend detector is still working fine. There’s nowhere near enough energy available to power that claimed jump in rainfall.
Now, I could leave it there, since the energy necessary to make their claims possible doesn’t exist. But in order to confirm that finding, my plan of further inquiry was to see whether either the intensity of rainfall events or the mean rainfall has changed over the last century. People are always claiming that we don’t have any controls for our experiments when we study nature. But nature provides its own experiments. To start with, we have the warming since 1900. On land, according the Berkeley Earth Surface Temperature data, the temperature has gone up about a degree over that time … but did the rainfall go up as well?
Figure 2. Global precipitation over the land, in mm/day. Data Source 1901-2009: CRU TS 3.10.01 (land)
OK … no increase at all in global rainfall, neither in the monthly means nor in the maximums. So no support for their claims there.
So how about local maximum rainfall events? Are those going up?
For this, we can turn to the temperature and precipitation records of England. For the Central England region, we have daily temperatures and daily precipitation records since 1931. Since 1931, the average Central England Temperature (CET) record has gone up by just under one full degree. So we should see any thermal effect on the maximum rainfall. With that 1°C temperature rise as the backdrop, here’s the maximum central England daily rainfalls, month by month, for the last eighty years.
Figure 3. Maximum daily rainfall, 1931-2012, Central England. Data Source Photo Source
Here, we find the same thing. There is no evidence of any increase in maximum rainfall events, despite a 1° temperature rise.
Hmmm …
The part I really don’t like in all of this is that once again, all of their claims are built on computer models. But what I don’t find is any serious testing of their whiz-bang models against things like the global or the CET temperature and rainfall records. In fact, I don’t see any indication in any venue that any computer models are worth a bucket of warm spit when it comes to rainfall. Computer models are known to perform horribly at hindcasting rainfall, they do no better than chance.
So once again, we’re back in the land of Models All The Way Down. I gotta confess, this kind of thing is getting old. NOAA and NASA appear to be falling further and further behind reality, still churning out useless studies based on useless models.
Just one more waste of taxpayers money.
w.
MikeB says: April 7, 2013 at 3:17 am
“..I must agree with Nick Stokes, WernerBrozek and others here. The energy input to produce the initial 20% increase in water vapour would only be required once, not every year….”
Perpetual motion, then?
Willis,
The only NET energy absorbed by the ocean is sunlight, and the only way to change that is orbit or tilt change of Earth, albedo change, or solar intensity change. The temperature increase due to more greenhouse gases does not come from more absorbed NET energy, but is due to radiation absorption and back radiation moving the average location of radiation to space to a higher altitude, and the average lapse rate does the rest. The fact that warmer air can hold more water vapor does not matter, since once it comes out as rain, the energy to replace it with new vapor still comes from the Sun’s energy being absorbed and evaporating water, not from air temperature.
sparky says:
April 7, 2013 at 6:40 am
/////////////////////////////////////
Sparky,
As I presently see matters, we are talking about the energy required to evaporate (ie., to evaporate the extra water that will fall as rainfall). In my mind, the issue is what are we evaporating? Are we evaporating water in the liquid phase (ie., from the oceans), or are we evaporating water in the vapour phase (ie., water vapour already at height in the atmosphere).
The point you raise, is coupled with the point raised by bybobl ( April 6, 2013 at 8:18 pm). He points out:
…
“Willis, your calculation is wrong – As well as 2260 KJ per Kg you also need to cycle the water to a height sufficient to make it cold enough to condense. Lets say this is on average 3000 m
So mGh = 1 * 9.8 * 3000 = 29400 or 29.4 Kj per Kg and this effort is returned eventually not as heat but kinetic energy of the rainfall. If you calculate this for all rainfall it constitutes a negative feedback of -1.12 W/m2, which I doubt is built into climate sensitivity estimates”
…
Thus, the position is that energy is required to evaporate (whether this be water in the liquid form or in the vapour form). This energy is returned to the system when the water vapour recondenses.
On top of this, energy is required to lift the evaporated water to a height at which it recondenses. This second set of energy is returned to the system as kinetic energy and on impact with the ground (or ocean surface) that is converted to sound, heat, bouncing water droplets, more sound, more heat etc until it dissipates
Both of these different sets of energy, are in their own way returned to the system in which they inhabit, as they must if the law of concervation of energy is not to be violated.
“Doesn’t most of the energy come back when the water vapor condenses?”
—–
Yes. In the upper troposphere. The net effect of increased rainfall is increased heat transport from the surface to the upper troposphere. IOW, this is a negative feedback.
Two thoughts:
1) Assume their theory is correct; warming causes more rainfall. But Anthony has demonstrated that their has been no increase in rainfall over the past century. Doesn’t that imply there has been no warming?
2) If there is more rain is that a bad thing? We need rain for plants to grow. Sure if we get too much rain in one place at one time in can cause flooding. But why can’t we simply adapt to the extra rainfall by creating more reservoirs so we can store the extra water until it is needed during droughts?
cementafriend says:
Why? In modeling, everything is possible. 🙂
I’ve seen economic models projecting more than 100% employment, for example.
Mike MacCracken the decidedly busy voice of IPCC on the Yahoo group of skeptics is now proudly defending… geoengineering!
“Because of the sensitivity of rainfall in Australia to the position of the longwave trough positioned off the Western Australian coast, I have been suggesting that modifying SST in the area (e.g., via cloud brightening in the stratus decks in the region) might be a possible regional climate geoengineering option worth researching the potential for if indeed there does develop the equivalent of a semi-permanent drought as a result of climate change. Altering the main circum-SH jet stream circulation would be a huge intervention (in comparison), but it might be that in favorable years one might be able to slightly alter the SST in ways that would increase the likelihood of storms impacting the coast instead of sliding by. Only a thought, but, as you note, there are some locations where things are quite sensitive where it might make sense and not have global impacts that adversely affect other nations in the region. Thoughts?
Mike”
How about sending this clown to Meteorology 101?
richard verney says:
April 6, 2013 at 8:53 pm
I ascribe my gut instinct about numbers to exactly what you propose. Until I was out of high school I used a slide rule, the best tool ever invented to give you a feel for how big a number should be.
Thanks, Richard,
w.
Mike McMillan says:
April 6, 2013 at 11:28 pm
Ian W says: April 6, 2013 at 7:30 pm
… You can watch this heat being released in real time just go to
http://www.ssd.noaa.gov/goes/east/natl/flash-rb.html
There you will see the outgoing infrared as seen by the GOES East Satellite. Notice how the weather systems show up.
[to] Mike McMillan …
So not a net-net process as we can see energy departing from the frontal and storm systems
—-
Spiffy video.
However, it doesn’t show amount of energy departing.
If you tick the ‘IR Temp’ box at the top, it turns on the temperature scale above the rainbow legend at the bottom. Quite the opposite of what you’d expect. Red is very cold, blue is warm.
Clouds are pretty opaque to IR, so the loop is looking at cloud top temperatures, the higher the colder. Intense storms are very high, thus very cold tops, so the color is a measure of what’s going on down below, not outward radiation.
The temperature of the cloud is immaterial – atmospheric temperature is not heat – the sensor is seeing outgoing long-wave radiation from the change of state of water. In thunderstorms it is not uncommon to have 100kt updrafts carrying liquid water to higher than 30,000ft the outside air temperature of ~ –40C; and the latent heat of fusion remains just the same for water freezing as at -1C.
Werner Brozek says
April 6, 2013 at 9:32 pm
A physics teacher?
Well, then surely you must know that for your (and Nick Stokes) claim to work, there must be a physical mechanism to recover the heat and return it to the surface to evaporate more water.
So until you can propose to me how you are going to RECOVER the energy that has
a) moved aloft and
b) already been mostly converted to mechanical motion and
c) much of the remainder of which is lost to space within an hour or so of moving aloft,
… until you come up with the brilliant Brozek plan to recapture that energy, I’m gonna say you should stay schtumm about your job … because with a hole like that in your logic, in your shoes I sure wouldn’t mention the part about being a physics teacher …
w.
Nick Stokes says:
April 6, 2013 at 9:50 pm
It went aloft, bypassing the majority of the CO2 and the water vapor, and NOT warming the lower atmosphere. In fact the lower atmosphere ends up cooler from thunderstorms.
From the top of the atmosphere it is free to radiate to outer space,
As to your claim that “things can’t move that fast”, within about fifteen minutes of leaving the surface, a parcel of air leaving the surface is transported to the top of the atmosphere. So yes, they can move that fast.
No, it doesn’t “accumulate indefinitely at altitude”, but since it is quite free to radiate to outer space (very few GHGs up that high) it does so …
Regarding “where did it go”, you seem to think that the energy almost all returned to the surface, since you claim you only need to evaporate it once.
But since the only thing returning to the surface around a thunderstorm is cold wind and cold rail, along with dry descending air between the storm towers, what is the MECHANISM by which you claim the energy returns to the surface? Bear in mind in your answer that much of the energy has been turned into mechanical motion and much of the energy has left the earth via radiation … so how does that lost energy return to the surface in your theory?
w.
Jim D says:
April 6, 2013 at 10:40 pm
Jim, if you quote my words before you start, you might avoid making such an fool of yourself in public.
I said no such thing. I said that the additional energy to evaporate that additional water wasn’t available. Learn to read, my friend, it will help you in the future.
w.
Martin Lewitt says:
April 7, 2013 at 12:31 am
Run the damn numbers, Martin. Yes that might make a bit of a difference, a few percent … so what? We’re talking orders of magnitude, and you want to point out a few percent?
Second, the part that many people forget about the “positive feedback” from thunderstorm generated water vapor is that the majority of it is inside the storm, where it doesn’t make a damn bit of difference as a GHG.
Finally, it is not necessary for the humidity to rise in order to get more rain. All that needs to happen is that the wheel turns faster, with more and larger and more active thunderstorms in a given area. In fact, contrary to what you might expect, a thunderstorm LOWERS the local relative humidity, due to the dry descending air between the thunderstorms … which REDUCES and even REVERSES the water vapor feedback effect.
w.
Stephen Richards says:
April 7, 2013 at 1:36 am
Thanks, Steven. You must have missed the first part of the sentence where I said:
So your volume is one square meter of water 200 mm deep, or 200 litres, or 200 kg.
w.
richard verney says:
April 7, 2013 at 5:58 am: “…Is it not likely that a large percentage of the additional rainfall will come from water vapour already in the atmosphere (possibly already reasonably high up in the atmosphere) such that less energy is required than you are proposing?…” Why would that happen. Apparently their model has the air temperature increasing, thus the capacity to hold water in vapor form increases. Unless additional moisture is added to the air, it seems to me that there would be less rainfall until there is some trigger that causes sudden condensation. And once that moisture is condensed and rained out, that warmer future air has to restock itself – to a greater capacity than today’s cooler air.
Willis, since you had not argued about the Clausius-Clapeyron part, it seemed you accepted it. Now it seems you are saying you do not accept that a 3 C warmer world can have 20% more moisture in the atmosphere. That is the part of your argument you forgot to justify. Or maybe you said there can be 20% more moisture but not 20% more rain as a result (which is what I suggested, but you denied), so which is it? Arguments that are not joined together get these kinds of questions. It is a form of skepticism.
Figure 3. Maximum daily rainfall, 1931-2012, Central England. Data Source Photo Source
Here, we find the same thing. There is no evidence of any increase in maximum rainfall events, despite a 1° temperature rise.
If there was no increase in rainfall with a 1 degree warming was there actually a 1 degree warming in the first place.
For tthose doubting Willis Eschenbach’s figures, see Trenberth figures here. He’s one of the CAGW crowd.
http://stephenschneider.stanford.edu/Climate/Climate_Science/EarthsEnergyBalance
Note from Trenberth’s figures we get about 490 watts radiation at the surface, 168 watts direct from the sun, 324 watts in back radiation from the atmosphere. We lose 24 watts to convection, 78 in evaporation, so SENSIBLE heat is only about 388 watts- giving us 14C.
If rainfall increases 20%, that 78 watts would have to increase by 20%, , or by 15.6 watts.
Yes, we can have more water vapor in the atmosphere without additional evaporation,, but we don’t get more RAINFALL without increasing that 78 watts going into evaporation.
Willis Eschenbach says:
April 7, 2013 at 10:28 am
until you come up with the brilliant Brozek plan to recapture that energy,
We saw a recapturing of energy with the change in December to January anomalies between the SST and UAH. From December to January, the SST on Hadsst2 went down from 0.340 to 0.283. At the same time, UAH went up from 0.202 to 0.504. So the loss by the sea was recaptured by the lower troposphere. And in February, the Hadsst2 rose from 0.283 to 0.314 while the UAH dropped from 0.504 to 0.175. Is it not logical to assume that some of the energy that the sea surface gained in February was what it recaptured from the troposphere? Energy cannot be created or destroyed although I would agree that some will be lost to space, but not all of it.
And by the way, this is not a “brilliant Brozek plan” that I am talking about. It is from Dr. Spencer who said the following about the January anomaly:
http://www.drroyspencer.com/2013/02/apparent-reason-for-january-2013-tropospheric-warmth/
The final paragraph says:
“I have other plots (cloud water, surface wind speed), but the above two plots tell the crux of the story: Above-average moist convective heat transport from the ocean surface to the atmosphere appears to have led to sea surface cooling, and tropospheric warming, in January 2013.”
Demetris Koutsoyiannis says:
April 7, 2013 at 1:49 am
You’re welcome, Demetris. I actually linked to your work (although not by name) in the head post when I said:
And I should have known that if I ventured into the realm of water, I’d find your footprints there before me.
For those not familiar with the name, Demetris is one of my heroes in the climate world for his clear mathematical understanding and researches into the Hurst-Kolmogorov phenomenon. Plus which, he writes about it clearly and understandably. He’s Greek, so he’s probably personally responsible for the whole Euro crisis deal, but he’s a good, insightful, clear-spoken scientist anyway …
I couldn’t agree more. That in part is why I titled the post “Improbable” maximum precipitation.
Thanks for the links, Demetris.I often skip over links in comments to my posts … but not the ones you put up.
w.
Alan D McIntire says: April 7, 2013 at 1:12 pm
“If rainfall increases 20%, that 78 watts would have to increase by 20%, or by 15.6 watts.”
No dispute there. But OLR can’t increase by 15.6 watts, unless the air becomes extraordinarily hot. There’s no other heat sink up there. That heat has to come back down.
Leonard Weinstein says:
April 7, 2013 at 8:18 am
Sorry, not true. See my post “Radiating the Ocean” for lots of discussion of the question. Short answer is that longwave radiation is absorbed by the ocean as well, not just shortwave. And since we are talking about the surface evaporation and not just the planet as a whole, we have to look at that as well.
w,
Frank Kotler says:
April 6, 2013 at 6:01 pm
Back when global warming was actually happening, it didn’t cause increased rainfall, but now that it’s not happening it could cause almost anything!
You know how much energy it takes to evaporate all those cats and dogs? 🙂
Right on the point, you summarise well.
And now having forecasted that it will bring more droughts, more rain, more snow, less snow, it can be everything, there is always a peer review study to have said it.
Nick Stokes says:
April 6, 2013 at 9:50 pm
Where did it go? And how? You can’t just go on turning it into kinetic energy. Things can’t move that fast. And it can’t accumulate indefinitely at altitude. There’s a conservation issue there.
The only way it can leave the planet is as OLR. But that requires a warmer atmosphere.
Willis answered your question above.
http://wattsupwiththat.com/2013/04/06/improbable-maximum-precipitation/#comment-1267901
Bear in mind that the water cycle is net energy transfer from the surface to the higher atmosphere. the net energy transfer through radiation inside the atmosphere is much lower, a think that warmista keep on ignoring.
Thanks again, Willis, your words about me are very kind. I am glad you agree and for the explanation about “Improbable” (I had suspected it).
In terms of the euro crisis, I pride myself saying that I have (and I claim) 1/11,000,000 of the responsibility (the denominator is the population of Greece),
richard verney says:
April 7, 2013 at 8:28 am
You’ve said this twice, Richard, and I fear I haven’t understood it either time. How can you evaporate water in the vapor phase? It’s already evaporated.
I think what you mean is the evaporation of liquid water at altitude, but it’s not clear.
w.