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.
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philincalifornia says:
April 6, 2013 at 5:48 pm
“I’ll start with Duran Duran’s “Hold Back the Rain” ”
philinthebaja says:
NOAA must have received their data from Brook Benton et al who observed that “its raining all over the world”
I hadn’t read that. Sounds like this announcement should rate a excellent topic for a new thread! GK
Daveo says: April 6, 2013 at 6:41 pm
////////////////////////////////
Dave
This is a point that is explored in the Willis article on radiating the oceans and is being discussed in the recent article A Comparison Of The Earth’s Climate Sensitivity To Changes In The Nature Of The Initial Forcing Posted on April 5, 2013by Guest Blogger.
At its heart is whether the energy budget for the oceans is that they are receiving: 170 W m^-2 (solar) + 320 W m^-2 (DWLWIR), and are losing 390 W m^-2 (surface radiation) and 100 W m^-2 (sensible heat/convective/evaporative losses), thereby balancing at 490 W m^-2, or whether it is the null hypothesis (the energy flux) position that the oceans receive: 170 W m^-2 (solar), and are losing 70 W m^-2 (radiation loss) and 100 W m^-2 (sensible heat/convective/evaporative losses), thereby balancing at 170 W m^-2.
The position is more complicated because of the absorption characteristics of LWIR in water. Some 50% of this is absorbed within just 3 microns (that could, on average be, 160 W m^-2, and in the case of the tropical ocean over 250 W m^-2,).. With that order of absorption (unless the energy can be sequestered in a downward direction at a speed greater than that at which it is being absorbed) one would expect to see copious amounts of rainfall (which is not happening). This raises the issue as to whether 255K DWLWIR can perform sensible energy in the ocean environ (which is at about 288K).
Nick Stokes writes “Why every year?”
Willis did the calculation for an average of 20% increase to the average. That’s every year. If you wanted to look at individual events then they’re already much larger than the average but how does a 3.7W constant forcing save itself up over time to result in an even larger event exactly?
I can see an argument for a potential increase in the event of say 3.7 / 200 * 100 ~= 2% increase in the large event but frankly that’s going to be hardly noticed when you’re already up to your roof in water.
It sounds like this is going to be one of those “where is the heat hiding since we know the models are correct” situations. Isn’t the rainfall going to be limited by the amount of nucleation particles available anyway? As you showed, the rainfall isn’t there in the CET data but could they argue for increased humidity?
I haven’t had a chance to read this in detail but they appear to try to relate the global changes in humidity to temperature.
Global changes in a humidity index between 1931-60 and 1961-90
I assume they’re making the case that increased rainfall a “bad thing”. Given that there is a constant drumbeat that we’re running out of potable water, somehow (even if they’re models were remotely right) I can’t get too excited about a lack of drought.
Maximum one day rainfall in North America was Tropical Storm Claudette, Sept 1979 in Alvin, Texas with 42″ in 24 hours. It is hard to imagine that any change in a NON heat forcing trace gas is going to increase this record rainfall. Sadly, the GHE madness goes on, untreated.
OssQss says:
April 6, 2013 at 6:34 pm
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This is one of my bug bears.
The grumpy old man syndrome in me has argued for years that calculators should be banned in the class room until the student is about 15. To the extent that aid is required, then the student should use log/trig tables. The use of calculators hinders the student from gaining a proper appreciation of the value of numbers, mathematical functions and their inter relationships. They lose perception as to what sort of answer they would expect to see when solving a problem. Hence a lot of garbage out, because people do not appreciate that the output is probably garbage and are thereby failing to check whether they are simply inputting garbage.
All of this strikes at the point raised by Willis. What does your gut tell you? If someone is going to claim that there will in future be an increase in precipitation of some 20%, then the first question should be: how much power is required to generate this?, and the second, where is this power going to come from and how is it derived?
A disclaimer first; I do not speak on behalf of my former employer (Environment Canada). I was in the real-world-climate-data-use end of things, not in the research/theory side.
Before panicing, let’s ask how relevant this claim is to the real world? First of all, what is PMP? According to the WMO manual at…
http://library.wmo.int/pmb_ged/wmo_332.pdf
top paragraph on page 23 of the document…
> Probable maximum precipitation (PMP) is defined
> as the greatest depth of precipitation for a
> given duration meteorologically possible for a
> given size storm area at a particular location
> at a particular time of year, *WITH NO ALLOWANCE
> MADE FOR LONG TERM CLIMATIC TRENDS.*
(emphasis mine)
Basically, it’s a worst-case theoretical scenario, that could possibly ever happen, assuming a fully saturated atmosphere at the location. This goes well beyond a real life “perfect-storm”, and into model territory. Surprised? Water vapour pressure, and
therefore the atmosphere’s ability to hold water, goes up *EXPONENTIALLY* with temperature. See
http://en.wikipedia.org/wiki/Vapour_pressure_of_water
So it’s not surprising that the output of the PMP equation shoots way up with a minor rise in temperature.
While the PMP equation output looks impressive, it’s not used that much. In real-life the 10 to 100 year return period of an event is used in designing stuff. E.g…
5 minute to 1 hour precipitation events are of extreme interest to engineers designing sewers, to be able to handle storm runoff.
1 to 30 day events are of interest to conservation districts, flood-control agencies, hydro authorities, mines with tailings ponds etc.
To summarize… if the study shows a 20 or 30 percent magnitude increase in the values of 10-to-100-year return-period events, and assuming the models are accurate, then there would be reason for alarm. If not, then any media hype of this article would be at best irrelavant, and at worst, misleading.
atarsinc says:
April 6, 2013 at 8:34 pm
“…I did some study since I asked about initial temp conditions….”
Most people would do the study before spouting off. That is why I question your sincerity. I suspect that you have no interest in learning, only in trying to push your agenda.
Nevertheless, I will try to answer your confusion about “every year”. The heat is transferred to the upper atmosphere where it eventually ends up getting radiated into space. The heat then must be made up for by “new” heat captured from the Sun. Willis is making the rather simple point that more rain requires more energy. Some on this thread are so obsessed with promoting CAGW that they refuse to seek truth. Neither the science nor the temp history supports AGW.
(That’s it for tonight.)
Dear Mr. Parsons,
I think I’ll try and answer your criticisms.
My last physics class was over forty years ago and I spent my working life as a musician, operating engineer, and a couple of other things best not mentioned so I’m no expert. Even so most of the answers seem obvious to me.
Since 4.52e+8 joules is the additional energy needed to evaporate the amount of water required to yield a 20% increase in precipitation for one year, each year that continues needs that amount of additional energy from somewhere.
To be conservative, Willis used the evaporation energy for 100 deg. C. i. e. boiling point water. Cooler takes more, see the rubber handbook.
I hope this part is just sloppy reading of the post, not an attempted cheap shot. Willis first referred to global figures for both precipitation and temperature. Then after that, he used Central England as a check. He did not refer to his location at all.
An analysis of Nick Stokes’ point with any rigor would take much more time and calculating than I feel up to at the moment so I’ll content myself with quick and dirty and save the hard figures for later. The energy of evaporation would come through the atmosphere as (mostly) visible light, strike the water, and be converted to heat, evaporating the water. Convection currents carry the water vapor to a high altitude where it condenses. The latent heat from condensation is released as infra red radiation. The altitudes where this happens are above the lion’s share of atmospheric CO2. Therefore, the majority would be radiated to space and little would penetrate back to the surface and be available to re-evaporate water.
That last is basically the “Tropical Thunderstorm Thermostat” effect Willis described a few months ago. The full story should be quite a bit more complicated than that. I’ll get to work on it and report the results unless someone with a sharper pencil than I have beats me to it.
Best wishes,
Kat
My home is Martha Stewart free. My computer is Microsoft free.
richard verney says:
April 6, 2013 at 8:53 pm
John Parsons AKA atarsinc
Richard, intelligent post as usual. “… where is this power going to come from and how is it derived?” That’s the point. If you accept the AGW hypothesis, the power (I think you meant energy) comes from rerediated LWIR. JP
Maybe they misread a cry for help from Flim Flannery. Guys, It was drought he was spruiking, not rainfall.
Or maybe it’s a new one, not yet tried? After the hockey sticks and all the other alarms that aren’t, you would think they would be more careful. “High confidence”? “We are delighted with our new computer game.”
Good catch Willlis
Another reality check would be to examine whether the statistics realistically follow Hurst Kolmogorov dynamics, or if they are modeled as white noise or Markovian processes. e.g. see:
HURST-KOLMOGOROV DYNAMICS AND UNCERTAINTY Demetris Koutsoyiannis JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION
Vol. 47, No. 3 June 2011 481-495
PS Note improvements over the Clausius-Clapeyron equation for accurate modeling. At ~50C, Koutsoyiannis reduces the difference from IAPWS data from 6.8% down to 0.07%.
Koutsoyiannis, D., Clausius-Clapeyron equation and saturation vapour pressure: simple theory reconciled with practice, European Journal of Physics, 33 (2), 295–305, 2012.
Nick Stokes says:
April 6, 2013 at 6:03 pm
We need it every year because we are evaporating that much additional water per year, and by and large the energy needed to do that is not being recycled. In fact, quite the opposite—what moves back down to the surface is not energy but cold wind and rain.
No, we need the heat each and every year, to evaporate the additional 200 mm of water. But wait … it’s worse than that.
The assumption is being made that this is all driven by some mythical increase in temperature, that is in turn driven by an increase in downwelling radiation.
So not all of the increase in downwelling radiation can be going to evaporation. Some must be going to do the actual heating. That means it will take an increase of more than the 14 W/m2 calculated above, in order to provide 14 W/m2 to do the evaporation AND provide energy for the heating.
As to the energy being released as latent heat on condensation and used to re-evaporate, that sounds good in theory. But at that point where it condenses it is inside the thunderstorm. From there, the sensible heat released by condensation drives the vertical movement inside the cumulonimbus tower, and thus is converted into mechanical motion. A large percentage of this happens near the equator at the ITCZ, and that sensible heat released by condensation is what powers the entire global circulation of the Hadley cells.
And as a result, that energy is generally lost to the surface and not available to evaporate further water. It has done its work and left town, we need new energy to evaporate more water. That sensible heat from condensation has gone aloft and been turned into mechanical energy.
Many thanks,
w.
atarsinc says:
April 6, 2013 at 8:34 pm
Nick Stokes’ (and others’) question about energy “per year” is still out there. Want to take a stab at that? JP
As a physics teacher, I agree with Nick Stokes on the point that IF the energy is provided once, it need not be provided again. Let me illustrate with an example. Now I know we cannot ignore friction, however let us for the moment assume we have a roller coaster with no friction. And let us assume that 10 people are raised to a height of 20 m and then they can go round and round for years, going down 20 m and then up 20 m again. However if we somehow give them the energy to go up 40 m, then they can go up and down 40 m for years without any new input of energy again assuming no friction. The problem is where this energy would come from in our weather system in the first place. For example, could a few hydrogen bombs evaporate enough water to give the climate this boost if that is desired?
Nick Stokes says: “I don’t get this arithmetic at all.”
We’ve known that for a long time.
Damn! Dere’s more smoke cummin’ out da (CAGW) machine.
Forrest M. Mims III says:
April 6, 2013 at 6:37 pm
You old-fashioned scientists always want to mess things up with actual measurements … that’s a clear career-stopper in 2013.
Indeed, however, the relative stability of the climate system is a recurring surprise to me. It doesn’t react the way anyone expects it to.
I see it as that occurring because the earth’s climate is running flat out all of the time, and so it will take a whole lot to disturb that a little. It’s going as fast as it can given the circumstances, it’s running as always just past the onset of turbulence.
w.
bobl says:
April 6, 2013 at 8:18 pm
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
————————————————
I’m curious about this interesting comment bobl. What happens to the kinetic energy when the raindrop either splatters on the ground, or enters water (a puddle, a river a lake or the ocean)? It must translate into heat, surely ?
Willis Eschenbach says: April 6, 2013 at 9:32 pm
“It has done its work and left town,”
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.
Forrest M. Mims III says:
April 6, 2013 at 6:37 pm
Beyond Willis’ assessment, which is on target, where is the increased water vapor? It’s certainly not in my Texas measurements, where total column water vapor (PW) has declined -1.1 mm/decade since February 1990. Nor is there any obvious up or down global trend in PW in the latest NVAP-M study (see http://wattsupwiththat.com/2012/12/14/another-ipcc-ar5-reviewer-speaks-out-no-trend-in-global-water-vapor/). The missing increase in water vapor ………………
—————————————————–
The missing water vapor has just gone in hiding with the missing heat.
Oh noes!
Now what will we do?
cn
atarsinc says:
April 6, 2013 at 6:46 pm
Because the annual rainfall is supposed to increase, so we need extra energy every year to evaporate the extra water.
That’s the value if you start at 100°C, boiling temperature. At 0°C it’s higher, about 2,500 joules per gram. So at ambient temperatures the latent heat of vaporization is slightly larger than the value I used, but that only reinforces the conclusions.
Oh, please. Do note that on the map in Figure 1, it shows these increases will happen everywhere. I’d already investigated the global question in Figure 2 and the associated discussion, showing no increase in either mean or maximum rainfall despite global warming. So I went on to investigate the local question, picking England because the records are good, and again saw no increase in local rainfall despite about a degree in local warming.
So what on earth is wrong with investigating the question at both the local and the global levels?
Next, I’d be damn careful about claiming that I am consciously doing something that “I know doesn’t fly.” I don’t do that, JP, and I don’t appreciate the accusation. If I know it doesn’t fly I don’t put it out there. I think that investigating this question on both the global and local levels is perfectly appropriate. I find your high-handed assumption, that you can see into my head and tell whether I think something will fly, to be ridiculous. It turns from ridiculous to insulting, however, when you assume that a) you are right in your ridiculous claims of mindreading and that b) as a result you assume I am acting in bad faith, knowing something won’t fly but putting it out there anyway.
Like I said … I don’t do that, for ethical reasons. But heck, I wouldn’t do it for purely practical reasons. I can’t afford to put anything out there that won’t fly, the Argus-eyed Intarwebs see right through that kind of nonsense.
Can’t say I found you all that respectful, my friend, and I fear you haven’t understood my logic. I’ve addressed Nick’s point above. Let me know if you still have questions, but please leave the speculation about motives at home.
w.
PMP itself is a funny concept. We can say that at a point we can predict the probable maximum precipitation? Probable itself connotes probabilities and thus if the PMP at a site is x mm of precipitation then what is the probability of x +/- delta x? Doesn’t make sense to me. And to say that an artificial construct is going to increase my 20-30% decades out even makes less sense to me.
But measurements show no increase of water vapour in the atmosphere… Oh and the little increase in mid latitude is explained by renewed advections of moist tropical air in response to colder polar air masses descending further south.
Looks like another case of statistical mishap? Perhaps these author should watch Briggs presentation at http://bishophill.squarespace.com/blog/2013/4/6/briggs-on-statistics.html
So, even though a 3-degree C warmer atmosphere can hold 20% more water, Willis suggests this can’t fall out as 20% more rain. If the thunderstorms of the future aren’t as high, maybe, but I don’t see that in the reasoning. Instead it is suggested that evaporation won’t be able to keep up when the surface and atmosphere are warmer. This doesn’t make sense because a warmer atmosphere holds more water vapor and so makes evaporation easier. The energy is provided by the sun which has plenty to spare in its several hundred W/m2. The idea that GHGs are providing the energy for evaporation is wrong, so that comparison is bogus. They provide the energy for the surface warming and the evaporation increases as a response to changing surface temperatures.