From the HockeySchtick: A paper published last week in Climate Dynamics finds man-made agricultural irrigation “causes significant cooling of global average surface air temperatures over land and dampens regional warming trends” by increasing cloud cover and precipitation.
According to the authors, “irrigation, however, is typically not included in standard” climate models, and thus, “irrigation should therefore be considered as another important anthropogenic climate forcing in the next generation of historical climate simulations and multi-model assessments.”
The negative feedbacks from evaporation & convection of water vapor, clouds, and precipitation illustrate how the climate is self-regulating, independent of CO2.
The paper:
Irrigation as an historical climate forcingBenjamin I. Cook, Sonali P. Shukla, Michael J. Puma, Larissa S. NazarenkoAbstract:
Irrigation is the single largest anthropogenic water use, a modification of the land surface that significantly affects surface energy budgets, the water cycle, and climate. Irrigation, however, is typically not included in standard historical general circulation model (GCM) simulations along with other anthropogenic and natural forcings. To investigate the importance of irrigation as an anthropogenic climate forcing, we conduct two 5-member ensemble GCM experiments.
Both are setup identical to the historical forced (anthropogenic plus natural) scenario used in version 5 of the Coupled Model Intercomparison Project, but in one experiment we also add water to the land surface using a dataset of historically estimated irrigation rates. Irrigation has a negligible effect on the global average radiative balance at the top of the atmosphere, but causes significant cooling of global average surface air temperatures over land and dampens regional warming trends.
This cooling is regionally focused and is especially strong in Western North America, the Mediterranean, the Middle East, and Asia. Irrigation enhances cloud cover and precipitation in these same regions, except for summer in parts of Monsoon Asia, where irrigation causes a reduction in monsoon season precipitation. Irrigation cools the surface, reducing upward fluxes of longwave radiation (increasing net longwave), and increases cloud cover, enhancing shortwave reflection (reducing net shortwave).
The relative magnitude of these two processes causes regional increases (northern India) or decreases (Central Asia, China) in energy availability at the surface and top of the atmosphere. Despite these changes in net radiation, however, climate responses are due primarily to larger magnitude shifts in the Bowen ratio from sensible to latent heating. Irrigation impacts on temperature, precipitation, and other climate variables are regionally significant, even while other anthropogenic forcings (anthropogenic aerosols, greenhouse gases, etc.) dominate the long term climate evolution in the [climate model] simulations.
To better constrain the magnitude and uncertainties of irrigation-forced climate anomalies, irrigation should therefore be considered as another important anthropogenic climate forcing in the next generation of historical climate simulations and multi-model assessments.
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John Christy did a study on this YEARS ago, and the study was addressed on this blog.
http://wattsupwiththat.com/2007/02/13/irrigation-most-likely-to-blame-for-central-california-warming/
http://wattsupwiththat.com/2010/09/12/christy-on-irrigation-and-regional-temperature-effects/
Thanks to transpiration, DAYTIME temperatures were lower than on non irrigated land, but
NIGHTTIME temperatures were higher, with overall slight warming , and a moderation in temperature extremes.
wow…they discovered that ground water is cooler than air temperature
…next thing you know, they will discover that asphalt, air conditioners, and heaters make it warmer
Now the climate nazis want to ban irrigation? Do they comprehend where their food comes from? What are they going to eat, each other?
[your statement is both wrong and misguided – mod]
My guess it that overall it causes warming, but cooling during the growing season. Albedo probably decreases during the off seasons (darker soil and darker/greener vegetation all around and downsteam from fertilization (probably in some in the ocean as well)).
Lets see, cities don’t add heat to the environment and thus don’t raise recorded temperatures —
but farmland irrigation cools the environment and lowers recorded temperature (And don’t forget suburbanites watering their lawns!).
Now we see why rural station temperatures must be adjusted up to match the higher temperatures found in cites.
Oh, God! It is too early in the morning for stuff like this!
Eugene WR Gallun
I should clarify some. Globally, I think it will cool/be neutral due to water cycle, transpiration, etc. At the surface level, I think it will warm spring and fall and cool in the summer. I think expanding farm land (increasing irrigation) will warm the upper troposphere because of high aerosol concentration mean more latent heat release. Transient warming, during expansion/growth and neutral/cooling long-term/steady state.
Maybe “irrigating” city people was why temperatures starting falling in the 50’s?
http://pix.avaxnews.com/avaxnews/47/30/00003047_big.jpeg
I can only guess that people back then were thankful to have coal fired electricity to pump water to cool things off…
http://avaxnews.net/touching/Summer_Heat_3.html
Yes yes, water moderates temperature extremes, but in AGW theory water increases temperature. No doubt there is an elaborated theory to “prove” why this is so. This theory will be supported by more theory and the whole of the inverted pyramid of theory will rest on the absorbency spectrum of … yes, you guessed it: CO2.
Did they mean irrigation or imagination?
I thought it caused warming in arid climates (e.g. the Central Valley).
Does that make irrigation a non-insane way to engineer the climate to be cooler?
Yeah, all that evaporation not normally there.
Will vary with efficiency of irrigation, though efficiency may expand areas irrigated thus evaporation roughly constant.
What about less water elsewhere due diversion to irrigated areas?
Local irrigation causes GLOBAL cooling, wow now that is what you call powerful stuff, we no longer need to control CO2 just put in a bit of irrigation.
Well, things are not completely understood about irrigation and cooling, but here’s what we do know. . .
1. Whatever it is that is going on, we are near a point of no-return.
2. To get a better understanding of the situation, there is an urgent need for a massive increase in grants given to proper thinking academics. . . .
3. To ensure that the future is kept safe for the children, the government in general and the EPA and the IRS in particular must be given massive powers to do whatever it is they would like to do. . . .its for the children, people!!!
4. And oh yeah. . .the science is settled, and if you don’t agree with it, then you are a disreputable and despicable denialist. . . .
5. The Koch brothers also have something to do with it, and they are on the wrong side of history. . .
So, is this article saying that clouds are a negative feedback?
Walmart: Cooling mist devices. Come on! Walmart for crise sake!!!!!
Head. Wall.
If visitors to Las Vegas, say in two weeks, walk around some of the newer outside shopping areas they can watch this miraculous new ‘research’ in action.
Las Vegas outside venues have frequently installed misting systems to regularly ‘mist’ and cool the air. Shoppers can be surprised when they’re suddenly enveloped in mid-day spraying.
A) Misting does lower the temperature of the immediate environs.
B) Not all native Nevadan’s appreciate the frequent abuse of water as it drives up their home water costs and it raises the humidity levels around Las Vegas.
Across the West, when one crosses a water course, if people got out of their cars and walked the area (without trespassing) they would notice that streams make the immediate area much cooler.
Duh! One would wonder why these alarming folks don’t suddenly decide to add the irrigated area’s historical temperatures into the global average. That’ll take some forcing though, instead they’ll use fanciful model estimates plugged into their models to cool near term temperatures while preserving alarmist’s favorite predictions of gloom, doom and damnation.
Jesus wept!
The latent heat required to evaporate a few millimeters of water at the surface is equal to that required to heat the entire column of atmosphere above it 1 degree C..
Size of Kansas => 81,823 mi² = 52,366,720 ac
Area under irrigation = Irrigated Area 3,123,271 acres
Water Pumped 3,430,047 acre-feet
1998 data
So putting 12″ of water over 6 percent of the land causes ‘cat-astro’ effects on temperatures??
DD More, A foot of water is the equivalent of cooling the entire atmospheric column 1 C over 6 % of Kansas about 75 times, but if only the bottom 1000 feet is cooled, then it is equivalent to cooling that 1000 feet about 2000 times, or cooling the bottom 1000 feet of the entire state about 120 times, so that surface thermometers would be skewed 1 C. cooler for 4 months of summer per year. I know that is making lots of assumptions, but gives you an idea of the cooling effect of water evaporation.
Hmm and yet Phoenix is still hot. If anything the extra irrigation there made it hotter and more unpleasant.
I don’t get it at all.
The orders of magnitude are such that this is a meaningless discussion.
Total Earth Area km2 510’072’000 (1km2 = 100 Ha = 247.1 acre)
and according to FAO, in 2011:
Land area 130’034’198 25.5%
Agricultural area 49’116’227 9.6%
Arable land and Permanent crops 15’529’766 3.0%
Arable land 13’962’795 2.7%
Total area equipped for irrigation 3’182’902 0.6%
Anthropogenic cooling/warming with watering (or not) 0.6% the globe surface!
Who is kidding?
Irrigation has a minimal impact on the global surface temperature, however it can have a major impact locally. If you want to experience an example of Anthropogenic Local Warming (ALW) try visiting Palm Springs or Tucson. These desert communities, which used to enjoy cool evenings and mornings, are surrounded by a plethora of golf courses, which noticeably increases the humidity and reduces radiation cooling. I doubt the same could be said for increased levels of CO2 around urban areas.