Water evaporated from trees cools global climate

From the Carnegie Institution – maybe we should build more cooling towers.

Evapotranspiration - Image: Wikipedia

Washington, DC. — Scientists have long debated about the impact on global climate of water evaporated from vegetation. New research from Carnegie’s Global Ecology department concludes that evaporated water helps cool the earth as a whole, not just the local area of evaporation, demonstrating that evaporation of water from trees and lakes could have a cooling effect on the entire atmosphere. These findings, published September 14 in Environmental Research Letters, have major implications for land-use decision making.

Evaporative cooling is the process by which a local area is cooled by the energy used in the evaporation process, energy that would have otherwise heated the area’s surface. It is well known that the paving over of urban areas and the clearing of forests can contribute to local warming by decreasing local evaporative cooling, but it was not understood whether this decreased evaporation would also contribute to global warming.

The Earth has been getting warmer over at least the past several decades, primarily as a result of the emissions of carbon dioxide from the burning of coal, oil, and gas, as well as the clearing of forests. But because water vapor plays so many roles in the climate system, the global climate effects of changes in evaporation were not well understood.

The researchers even thought it was possible that evaporation could have a warming effect on global climate, because water vapor acts as a greenhouse gas in the atmosphere. Also, the energy taken up in evaporating water is released back into the environment when the water vapor condenses and returns to earth, mostly as rain. Globally, this cycle of evaporation and condensation moves energy around, but cannot create or destroy energy. So, evaporation cannot directly affect the global balance of energy on our planet.

The team led by George Ban-Weiss, formerly of Carnegie and currently at Lawrence Berkeley National Laboratory, included Carnegie’s Long Cao, Julia Pongratz and Ken Caldeira, as well as Govindasamy Bala of the Indian Institute of Science in Bangalore. Using a climate model, they found that increased evaporation actually had an overall cooling effect on the global climate.

Increased evaporation tends to cause clouds to form low in the atmosphere, which act to reflect the sun’s warming rays back out into space. This has a cooling influence.

“This shows us that the evaporation of water from trees and lakes in urban parks, like New York’s Central Park, not only help keep our cities cool, but also helps keep the whole planet cool,” Caldeira said. “Our research also shows that we need to improve our understanding of how our daily activities can drive changes in both local and global climate. That steam coming out of your tea-kettle may be helping to cool the Earth, but that cooling influence will be overwhelmed if that water was boiled by burning gas or coal.”

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John Marshall

These people must know about latent heat of evaporation and condensation and the heat lost/gained in this process. This is hardly ‘new’ research. I was doing experiments on this 55 years ago in physics class.
The mind boggles.

We just spent 24 hours listening to intelligent rebutals of the false theory of agw and now we are to believe the earth is getting warmer because of CO2? And of course evaperation causes cooling. Looking forward to apple harvest here in Oregon. Thank you all for the last 24 hours, it was interesting and informative.

wayne Job

So increased CO2 makes flora grow bigger and better and stronger and respires more, thus we have a negative feed back, negating any warming from CO2. Perfect natural balance, what is the problem, I see none.

Dave Springer

“Increased evaporation tends to cause clouds to form low in the atmosphere, which act to reflect the sun’s warming rays back out into space. This has a cooling influence.”

Oliver OFlynn

In all the discussion of global warming (cooling) I have never read of the contribution of the heat generated by using electrical energy. An easy sum shows that it is not negligible. Have I missed something . Oliver OFlynn

R. de Haan

How much tax money has this Carnegie Institution report cost us?

Inreased CO2, increased plant growth, more evaporation, more clouds, more reflection, cooler planet.

“The Earth has been getting warmer over at least the past several decades, primarily as a result of the emissions of carbon dioxide from the burning of coal, oil, and gas, as well as the clearing of forests.”
That’s a given, then?
Dang! Just when I’d been convinced the science was not settled.

Patrick Davis

Interesting read however, its a well established fact trees have an “air conditioning” effect, not just their shade. So no surprise here for me.

Except that burning gas or coal adds water to the atmosphere. And since they don’t actually have a clue as to how much warming each molecule of CO2 causes, nor how much cooling each molecule of H2O causes, they haven’t the slightest hint of the beginning of a notion of the barest clue of an idea of what the overall effect* is.
*Haha, sorry, that funny lookin’ word there is a synonym for the common Illiterate English term “impact”

How did this paper get past the climate sensors Do I see another rebuttal paper in 18 days?
According to environmentalists … we’ve been cutting down forests. We’ve certainly been putting more land to farmland which doesn’t have vegetation when ploughed. We now have a plausable explanation for the dramatic change in “urban heating” even when population density in the US changed by a few 10s of people per km.
Like a blow from a hidden assailant out of the dark:
1. Bang goes the claims that urban heating is not affecting most temperature sensors — even in rural areas.
2. We now have another plausible explanation for any temperature rise which is not CO2 (I now count, solar activity, reduced global dimming, CO2 as other prime contenders)
3. The science is settled … is it really?
4. We now have a paper which in effects supports sunspots as it is the same basic mechanism of cloud cover.
5.And to top it all, there is now good reason to believe increasing bio-fuel output by changing farmland to crops will increase warming.
I am reminded of the scene in Jurassic Park, when the hunter is hunting the Velociraptor and with all his attention on the one before him, he fails to see the other about to hit him from the side.

Bruce Cobb

More post-normal CAGW-inspired gobbledygook. It is absurd to think that land-use decision making, which is entirely a local decision should even consider whether or not vegetation, particularly trees might have a cooling effect on the Earth. The gist of their argument seems to be to discourage development of any sort, particularly in (what else) developing countries, with the possibility of developed countries like the U.S. of paying them not to develop, “for the good of The Planet”.
Nice that they give a nod to the cooling effect of clouds, though.

roger samson

This has always been one of my pet theories. In fact folks, anthropogenic warming may slowly be occurring due to deforestation. Its possible both cosmic ray fluxuation and forest cover changes are the primary variables affecting cloud cover changes. Unfortunately there has been not enough science done on cloud formation and its impact on global climate change. Pity we rushed to cut primary forests to put up oil palm plantations when we knew so little about the science of climate change.

Frosty

There are so many land use effects on local climate, that these climate scientists seems unaware of, that it makes me wonder if there’s not an issue with basic education, or at least cross discipline basics.
Most pre 1950 land management/agricultural books will tell you to plant a copse of trees if you want to increase local rainfall, most old farmers will say the same thing in my experience.
The Holistic Management grazing techniques (increased herd numbers on smaller rotated ranges, mimicking natural herd movements) reversed desertification in Zimbabwe, during a drought!
Another example I heard about was about how prairie dogs effect local rainfall. They were seen as pests, so were eradicated in a certain area (I can’t remember where), it was found that this caused a reduction in downwind rainfall. How so? Prairie dogs build lots of tunnels, each entrance has a raised edge, like a small volcano. As the wind blows across these entrances, the higher opening creates low pressure, which exchanges air inside the tunnels, the air which is removed is loaded with +ive ions, which are attracted to the -ive ions at the cloud base, seeding clouds. Removing the prairie dogs edged the local downwind environment towards desertification. Keyline ploughing (P.A. Yeoman) mimics this tunnel system, so besides being effective in influencing run-off water to stay in the landscape (by ploughing along contour lines at the keyline), it actually increases downwind rainfall too.
Land use issues are key to local climate IMO, much more so than any possible effects of a trace gas, but then there’s not much money in it for climate scientists, or governments, so we’re stuck with the current paradigm.

MarkW

When this evaporated water condenses, it is many thousands of feet in the air, so that the heat released escapes to space much more easily. So even if that were the only affect, increased evaporation from plants would result in a net cooling. Not the balanced out that is assumed by the authors.
BTW, increased CO2 results in more plants. So CO2 results in cooling. Very interesting.

So the burning down of the rain forests in S America and SE Asia over the last 30 years or so could well have been responsible for the recent warming and now that there’s none left the rise has levelled off?
NB I was in Singapore during the great Indonesian burn off in ’96

old construction worker

Who would have “thunk” evaporation of water would have a cooling effect? Do we live in a big “swamp cooler” or what?

Stephen Wilde

Hmmm.
More CO2 soon leads to more and bigger plants in more locations. Perhaps the additional evaporative cooling amounts to more than the projected CO2 warming?
At the very least it would reduce sensitivity to more CO2 in the air.
So that is another negative system response to add to the negative system response from clouds and a faster water cycle.
“Also, the energy taken up in evaporating water is released back into the environment when the water vapor condenses and returns to earth, mostly as rain. ”
Crikey, that is just daft. Rain is colder than the air around it because the energy released by condensation higher up gets radiated out to space faster than it would have been if the energy had been retained at the surface.
Evaporation DOES affect the global energy balance by transporting energy upwards for a quicker loss to space thereby offsetting the slower loss to space that would otherwise arise from the thermal characteristics of GHG.
This article concedes more evaporation but then denies the well known thermal effects of more evaporation in order to preserve the faulty CO2 paradigm.

Bloke down the pub

The evapotranspiration cycle may be energy neutral, but if it helps to transport energy to higher altitudes it is likely to increase the heat lost to space.

Mike Davis

Some folks have been saying this for years! Although the last sentence is still based on pathological science!

“The Earth has been getting warmer over at least the past several decades, primarily as a result of the emissions of carbon dioxide from the burning of coal, oil, and gas, as well as the clearing of forests.”
And ~96% of total global CO2 emissions come from other sources other than anthropological sources, i.e. natural sources. In a few years time, we may be more concerned with global cooling than global warming. Oh, and we haven’t seen any global warming since about 1998 (unless you use James Hansen’s tainted surface temperature products).

Also related is Anna Makarieva’s hypothesis about the generation of winds covered here a while back.
http://wattsupwiththat.com/2011/01/21/an-appeal-to-the-climate-science-blogosphere/#more-32135

Ralph

>>>But because water vapor plays so many roles in the climate
>>>system, the global climate effects of changes in evaporation
>>>were not well understood.
But the science was, nevertheless, settled.
.

Gary

Globally, this cycle of evaporation and condensation moves energy around, but cannot create or destroy energy. So, evaporation cannot directly affect the global balance of energy on our planet.

Willis is not going to like this statement. Dr. Spenser, neither.

I’m amazed people don’t see the importance of this paper. Think it from the point of view of the “treehugger”. We need a way to explain to them that there are other things that effect climate. They want to believe that chopping down trees is bad, they also want to believe warming is bad.
So, now we can encourage them to say: chopping down trees causes global warming
Which is the same as saying:
Chopping down trees caused global warming
This is the equivalent of throwing a bitch in heat into the foxhounds. How can they resist making the connection? They can’t … it ticks all boxes. But as soon as they start saying: “chopping down the amazon causes global warming”, they are also saying that: “CO2 isn’t causing that global warming”, and more importantly: “we also don’t think the science is settled … not when it suits us”.

Viv Evans

I hope I got this right: increased evaporation has a cooling effect, but evaporation cannot affect the global energy balance? IAW, there must be warming somewhere to offset this cooling, right?
Hm.
One thing’s for sure: this is again our fault, for chopping down trees. I bet the CO2 police will now enforce a massive tree planting policy, aimed at us.

John B (UK)

“Using a climate model”…………………..
?????
sigh……

Alan D McIntire

John Christy put out a paper on this effect years ago.
http://ams.confex.com/ams/84Annual/techprogram/paper_68739.htm
Due to irrigation of the central valley in California, daytime temperatures went down and
nighttime temperatures went up. By introducing water and irrigation to a desert region, the net effect overall was a slight warming. I suspect that much of the measured slight warming worldwide is due to this irrigation effect.

GaryP

Will there also be increased organics released into the air from all this water evaporating from trees? These will tend to increase nucleation sites for water droplets and increase cloud cover.

Cementafriend

I am amazed that this paper was accepted by the reviewers. Does no one search the internet or look at Russian literature. Look at this web site http://www.bioticregulation.ru/pubs/pubs2.php

Ron Cram

Wait. Are you saying sophisticated IPCC climate models don’t take this into account? Really?

patrioticduo

They obviously needed a few hundred thousand in grants to conclude on something that bleeding obvious, previously known, and well established.

Nuke Nemesis

Roger Carr says:
September 16, 2011 at 4:16 am
“The Earth has been getting warmer over at least the past several decades, primarily as a result of the emissions of carbon dioxide from the burning of coal, oil, and gas, as well as the clearing of forests.”
That’s a given, then?
Dang! Just when I’d been convinced the science was not settled.

There is not one shred of evidence given to support that statement, is there? Yet this will be added to a catalog listing it as a scientific paper supporting the “consensus.”

Robertvdl

“evaporation of water from trees and lakes could have a cooling effect on the entire atmosphere.”
And evaporation of Ocean water ?

arthur clapham

It is very presumtious to state the world has been getting warmer over several decades,
I have lived through several decades and can see no difference since my boyhood.
Iwould like the truth and some proof of this statement please!!

Ron Cram

I am having a hard time reconciling these two statements:
New research from Carnegie’s Global Ecology department concludes that evaporated water helps cool the earth as a whole, not just the local area of evaporation, demonstrating that evaporation of water from trees and lakes could have a cooling effect on the entire atmosphere.
and
Globally, this cycle of evaporation and condensation moves energy around, but cannot create or destroy energy. So, evaporation cannot directly affect the global balance of energy on our planet.
These statement appear to contradict each other. If the first is true, the AOGCMs need to account of evapotranspiration. If the second is true, they do not. Which is it?

chris y

As the Daily Bayonet says- “Wait, What?”
It appears that this climate model study has stomped on CACC.
The authors state- “The researchers even thought it was possible that evaporation could have a warming effect on global climate, because water vapor acts as a greenhouse gas in the atmosphere.”
“was” possible?!?
The settled science says that surface warming from any forcing causes increased humidity due to evaporation of water. The increased water vapor concentrations then cause a greater greenhouse effect, further warming the surface. This positive feedback is claimed to double or triple the temperature increase from CO2 alone.
“But because water vapor plays so many roles in the climate system, the global climate effects of changes in evaporation were not well understood.”
This is a direct challenge to the water vapor positive feedback being settled science. This is heresy, a direct challenge nailed to the front door of the CACC cathedral.
But now we have this paper’s stunning claim.
“Using a climate model, they found that increased evaporation actually had an overall cooling effect on the global climate.”
This is another Trenberth travesty. Say goodbye to the water vapor based positive feedback multiplying factor for CO2 warming. The AR5 lead authors will have to find a way to exclude this paper from the next report, even if they have to redefine what peer reviewed literature is…

Pamela Gray

Just one more reason treehuggers will use to stop timber sales. Before loggers came along, our forests burned naturally, cleaning up the floor and continually replacing fully mature adult trees with meadows and thinned younger trees. We replaced that with something similar: timber sale harvest/slash burning. For some reason, tree huggers want to replace all of that with some kind of no touch no burn forest system that will only lead to one thing: catastrophic burns from fuel heavy forests. And this is good how?

“The Earth has been getting warmer over at least the past several decades, primarily as a result of the EMISSIONS OF CARBON DIOXIDE from the burning of coal, oil, and gas” (caps added)
Immediate deduction of 30 IQ points and a major downgrade of the value of the presentation and content.
Is this now simply another attack on human activities and an argument for de-industrializing and planting more trees?
Forget mowing the lawn ever again—I have a great excuse! There oughta be a law.

Ex-Wx Forecaster

Wait a minute…I thought evaporation resulted in cloud formation, which reflected heat back to Earth and warmed the planet. At least, that’s what the IPCC has been saying for the past couple decades. I mean, it’s in their models, it can’t be wrong.

Re: the Amazon
The rainforest is resilient and grows back very quickly. Recent estimates have it growing back much faster than it is being cleared. As farmland the soil is poor and only produces a few crops and then the people move on. The forest takes the land back. There is more rainforest now than there was 40 years ago. City expansion is really not a big factor.
The Greenies always talk about the damage without ever talking about the healing. Bleached coral reefs recolor back to health rather quickly. Greenies NEVER go back later to check on bleached corals as they really do not want to know that they have recovered quite nicely, thank you. They want the crisis to be human and resolution not be natural.

trbixler

So the lake in Central Park helps cool and the Atlantic ocean is not mentioned. Of course the Atlantic is but one of the oceans and maybe they might evaporate a little as well.

TomL

Isn’t this a rather involved way of saying that water vapor acts as a negative feedback on temperature?
When does the editor resign?

Greg Holmes

The big engine is in the sky, its big and hot, sometimes very hot sometimes not so hot, but how can we tax it folks?

“Water evaporated from trees cools global climate”
[church lady]Well, isn’t that inconveeenient?[/church lady]

Stephen Skinner

So when I sweat and it evaporates taking heat from me into the surrounding air, that heat radiates back and makes me hotter?

Shouldn’t apologies and resignations be forthcoming? Clouds sure seem to be doing a lot of things while not playing a significant role in our climate.

Crispin in Waterloo

roger samson says:
September 16, 2011 at 4:34 am
…In fact folks, anthropogenic warming may slowly be occurring due to deforestation.
++++++++
Good to hear from you, Roger. For folks who don’t know, Roger is probably the single greatest motivator for switchgrass as a native, local biofuel. Practically created the concept. I have several products to test courtesy of him.
Yeah, but Roger, what do you have as info on the (natural) reforrestation of the NE USA as people left the farms? Is total forest cover in, say, the USA increasing? Virginia, NY (etc) are getting massive regrowth. Then, is there an increase in Arctic vegetation with increasing temps? I read once it’s about 6 C in the past 150 years. That should bring a very large increase in mass, a draw-down of CO2 and an increase in transpiration.
I am not arguing against your point, I want to look at the global forest cover. One of Harold Annegarn’s remote sensing students is trying to use satellite radar to estimate the total biomass using average tree height. Resolution is tricky but it is already working for very tall and short trees.
We see reports now and then about total tree cover but they are always alarmist and never talk about areas with increasing vegetation, as if that is ‘off message’. That means it is not a ‘report’ but a ‘message’. What can you report? Is there any correlation (even anti-) with tree cover or total biomass and temps?
I would not be at all surprised to find a long-lasting influence. It is abnormal for watered soil to have nothing growing on it.

Robertvdl

The cooling effect of trees is that the energy coming from our star does not heat the surface of the earth but the leaves of the tree.
These leaves evaporate water to cool themself.
Both the ground under the trees and the leaves don’t accumulate heat so the moment the sun is gone there is no heat radiation. Our buildings and roads do accumulate heat. That’s why a big city is a bad place to sleep when it’s warm and moisty.

Warren in Minnesota

The Carnegie Institution says:
“The Earth has been getting warmer over at least the past several decades, primarily as a result of the emissions of carbon dioxide from the burning of coal, oil, and gas, as well as the clearing of forests.”
The Earth has not been warmer this last decade and the emission of carbon dioxide has continued. The premise and the conclusion, primarily as a result, is illogical and unfounded.