Study: Conversion Of Forests to Cropland Cooled the Climate

Yale Study Shows How Conversion Of Forests to Cropland Affected Climate

Photo by alexmisu
The conversion of forests into cropland worldwide has triggered an atmospheric change that, while seldom considered in climate models, has had a net cooling effect on global temperatures, according to a new Yale study.

Writing in the journal Nature Climate Change, Professor Nadine Unger of the Yale School of Forestry & Environmental Studies (F&ES) reports that large-scale forest losses during the last 150 years have reduced global emissions of biogenic volatile organic compounds (BVOCs), which control the atmospheric distribution of many short-lived climate pollutants, such as tropospheric ozone, methane, and aerosol particles.

Using sophisticated climate modeling, Unger calculated that a 30-percent decline in BVOC emissions between 1850 and 2000, largely through the conversion of forests to cropland, produced a net global cooling of about 0.1 degrees Celsius. During the same period, the global climate warmed by about 0.6 degrees Celsius, mostly due to increases in fossil fuel carbon dioxide emissions.

According to her findings, the climate impact of declining BVOC emissions is on the same magnitude as two other consequences of deforestation long known to affect global temperatures, although in opposing ways: carbon storage and the albedo effect. The lost carbon storage capacity caused by forest conversion has exacerbated global warming. Meanwhile, the disappearance of dark-colored forests has also helped offset temperature increases through the so-called albedo effect. (The albedo effect refers to the amount of radiation reflected by the surface of the planet. Light-colored fields, for instance, reflect more light and heat back into space than darker forests.)

Unger says the combined effects of reduced BVOC emissions and increased albedo may have entirely offset the warming caused by the loss of forest-based carbon storage capacity.

“Land cover changes caused by humans since the industrial and agricultural revolutions have removed natural forests and grasslands and replaced them with croplands,” said Unger, an assistant professor of atmospheric chemistry at F&ES. “And croplands are not strong emitters of these BVOCs — often they don’t emit any BVOCs.”

“Without doing an earth-system model simulation that includes these factors, we can’t really know the net effect on the global climate. Because changes in these emissions affect both warming and cooling pollutants,” she noted.

Unger said the findings do not suggest that increased forest loss provides climate change benefits, but rather underscore the complexity of climate change and the importance of better assessing which parts of the world would benefit from greater forest conservation.

Since the mid-19th century, the percentage of the planet covered by cropland has more than doubled, from 14 percent to 37 percent. Since forests are far greater contributors of BVOC emissions than crops and grasslands, this shift in land use has removed about 30 percent of Earth’s BVOC sources, Unger said.

Not all of these compounds affect atmospheric chemistry in the same way. Aerosols, for instance, contribute to global “cooling” since they generally reflect solar radiation back into space. Therefore, a 50 percent reduction in forest aerosols has actually spurred greater warming since the pre-industrial era.

However, reductions in the potent greenhouse gases methane and ozone — which contribute to global warming — have helped deliver a net cooling effect.

These emissions are often ignored in climate modeling because they are perceived as a “natural” part of the earth system, explained Unger. “So they don’t get as much attention as human-generated emissions, such as fossil fuel VOCs,” she said. “But if we change how much forest cover exists, then there is a human influence on these emissions.”

These impacts have also been ignored in previous climate modeling, she said, because scientists believed that BVOC emissions had barely changed between the pre-industrial era and today. But a study published last year by Unger showed that emissions of these volatile compounds have indeed decreased. Studies by European scientists have produced similar results.

The impact of changes to ozone and organic aerosols are particularly strong in temperate zones, she said, while methane impacts are more globally distributed.

The sensitivity of the global climate system to BVOC emissions suggests the importance of establishing a global-scale long-term monitoring program for BVOC emissions, Unger noted.

0 0 votes
Article Rating
Newest Most Voted
Inline Feedbacks
View all comments
Gunga Din
September 8, 2014 4:04 pm

Man prevented the CAGW that Mann caused. Whoda thought?

September 8, 2014 4:12 pm

Considering the amount of variables that had to drive the “sophisticated climate modeling”, what do you think the error bar on that 0.1 deg C cooling is?
Not that I’m against anything that predicts cooling, but are you kidding me? 0.1? What is the precision on that value.

Pat Frank
Reply to  Jake
September 8, 2014 5:34 pm

Minimal uncertainty in the simulated air temperature is about (+/-)1.5 C in the first year, and is cumulative as the root-sum-square. A modeling study like the above is pretty much physically meaningless.

Reply to  Jake
September 8, 2014 5:41 pm

If they ignore the. 1c then they will get grief from you.
If they make their best estimate they will get grief from you

Reply to  Steven Mosher
September 9, 2014 1:01 am

When anybody makes a ” model based best estimate ” which shows that something has exercised a ” cooling ” effect on current climate and then extrapolates it to 2100, we’ll naturally be sceptical as we’ve seen enough BS like this passed off at science. And the very fact that you needed to drive by and defend this raises suspicions even higher that the probability of this being BS is quite high.

Pat Frank
Reply to  Steven Mosher
September 9, 2014 9:27 am

They aren’t “estimates” Steven. They’re twaddle represented as estimates. All wrapped up in a silk bow of false precision.

Reply to  Jake
September 9, 2014 6:38 am

I believe the spec is ±5°C.
Pretty much the same as most of the GCMs specs.

September 8, 2014 4:13 pm

How do they get that I have read studies that say BVOCs are a big factor in producing clouds (which would cause cooling) also tilled agricultured land with nitrogen fertilizers, reduce the amount of carbon stored in the soil by a large amount.

NZ Willy
September 8, 2014 4:13 pm

This would surprise me, as in my countryside wanderings I’ve always found farmed fields to be warmer than the adjacent woodlands. I suppose the article’s true slant is that global warming is being concealed by agriculture, and Trenberth’s missing heat is in the cabbages. Or have I become too cynical?

Reply to  NZ Willy
September 8, 2014 5:13 pm

same here. we live in a rain forest. it is much, much cooler under the trees in daytime than compared to open areas. At night the forest may well be warmer than the fields.
Converting the forests to fields has increased the variability, but since cliamte science is all about averages they missed the forest for the trees.

Brian H
Reply to  ferdberple
September 9, 2014 1:01 am

It’s all based on comparative GHG calculations, which are inherently flawed, meaningless. Effects on the water cycle, on the other hand …

Stephen Skinner
Reply to  NZ Willy
September 9, 2014 1:13 am

Too right. A fixation on synthetic data rather than go and see what is happening. If glider pilots want to stay up in the air then crops are their friends. Albedo is irrelevant because other characteristics dominate, for example light coloured crops like wheat trap heat amongst the stalks and provide strong thermals. In addition to farm successfully requires well drained land which is of course dryer than uncultivated or forest. All this knowledge is freely available and is proven

September 8, 2014 4:15 pm

“Using sophisticated climate modeling, Unger calculated that…” evil mankind is responsible for the pause.
“Unger said the findings do not suggest that increased forest loss provides climate change benefits…”; rather it proves that no matter what mankind does, it’s wrong and the industrialised nations must pay dearly.
“The sensitivity of the global climate system to BVOC emissions suggests the importance of establishing a global-scale long-term monitoring program for BVOC emissions, Unger noted.” = control of crop production by the warmunists.

September 8, 2014 4:18 pm

Sorry, but one tenth of a degree in 150 years and a process that is not continuing at anywhere near
previous levels, is utterly insignificant, to everyone except the people conducting the study.
When she claims .6 degrees of waming in 150 years (when CO2 levels must have at least doubled)
she puts herself on the low end of sensitivity estimates, it would seem.

Reply to  Col Mosby
September 8, 2014 4:22 pm

EXACTLY!! Can you say “publish a paper or your government money gets taken away”?
0.1 degree tells me that ABSOLUTELY nothing happened. Or maybe it caused 1.0 degree cooling. Or maybe 1.0 degree warming.
What a pile of steaming cow poop.

Bob Boder
Reply to  Jake
September 8, 2014 5:36 pm

Your pile of steaming cow poop definitely has more effect on the environment.

Mike Smith
September 8, 2014 4:24 pm

Nothing to see here but more climate models. And we know how realistic they are. Move along.

Alan Robertson
September 8, 2014 4:29 pm

I suppose we could call this “Excuse for the Pause” #40.

September 8, 2014 4:30 pm

mODELS, MODELS, MoDeLs, MOdels,, etc. “Do you understand the words comin outa my mouth?????
PAY ME, NOW!!!!!

September 8, 2014 4:30 pm

I’m sort of wondering whether the “sophisticated” modelling will be made available for peer review by a couple of gimlet-eyed statisticians well known in these circles.
Methinks the odds aren’t looking too good, but hey; no harm in asking.
Ho, ho, ho

Bernie McCune
September 8, 2014 4:32 pm

They are modeling land use patterns to 2100? Is that believable? I cannot get Unger’s full paper but there does not seem to be any sort of global characterization (specific numbers) of land use change from forest to cropland. I have looked at US forest assets and though forests here were decimated from 1850 until 1930 they are coming back. And as a general rule they are something like 70% of what they were when first European contact seriously started to occur in the 1500s. Eastern forests are making dramatic inroads by taking back most of the farmland that was clearcut by early Americans.
This turnaround is not yet the case in Africa, India, or parts of South America. But even Brazil is making headway on this front and by the year 2100, I suspect whatever the soothsayers are predicting, it probably will not be near that bad since I think the rest of the world will start to follow the US, Canada, Europe and China with positive land use methods that will be noticed by 2050 or 2060. And well established by 2100.
It certainly cannot happen if we beggar these three regions in the world with energy and other restrictions that force them to cut down and burn up their forests. So I do believe that cutting down global forests as Unger suggests, is a bad thing but suggesting that it will continue is not necessarily very likely. And I would like to know how bad it is right now but am unable to determine that from this short synopsis.

Reply to  Bernie McCune
September 8, 2014 5:20 pm

So I do believe that cutting down global forests as Unger suggests, is a bad thing
Ah, the plot thickens. This report is obviously intended as support for REDD. Which is basically the UN sponsored rape of indigenous peoples through land theft by large environmental funds, with high up political support. Look for all the usual suspects, you will find them snout deep at the trough.

Reply to  ferdberple
September 9, 2014 6:48 am

Hey, you gotta grow the corn for ethanol somewhere.
Saw it all down.
The greenies need their corn gas.

Tom O
Reply to  Bernie McCune
September 9, 2014 1:59 pm

There may be “forest recovery” ongoing in the US, but the truth is “old growth” forest was mostly hardwood stands – broadleaf, and the new growth forest is probably mostly softwood stands. I don’t think the two types of forest are anything alike as far as how they affect the climate.
But the study, like any other modeling study, is going to yield whatever the modeler is attempting to show. No one, and I truly believe that, writes a modeling program that isn’t biased by their personal belief set. I Don’t think it is possible to exorcise your built in prejudices completely.

September 8, 2014 4:38 pm

The conclusions of this “sophisticated model” study simply don’t stand up to direct thermometric scrutiny. Surface temperatures are invariably cooler in forests than they are in adjacent croplands–especially when they lie fallow after harvesting.

Reply to  1sky1
September 8, 2014 7:25 pm

I also agree. At first blush, it does not make sense. I grew up on a farm in Kansas and I can you standing in the shade of trees is a lot cooler that standing in the middle of a ploughed field! Its based on findings gleaned from the output of models? Models do not produce findings/data, just possible scenarios that may or may not be right or even useful.

Reply to  1sky1
September 8, 2014 8:50 pm

Maybe higher albedo over cropland means higher air temperature. Reflected photons get 2 chances to heat the air.

Reply to  1sky1
September 9, 2014 3:14 am

But you are talking microclimate and Unger is talking gloibal climate. Not saying she is right, but it is incorrect to say she is wrong because of localized temperatures when she is talking global temperatures .

Reply to  1sky1
September 9, 2014 4:07 pm

The same physics governs the global temperature as does the local one. The authors’ notion that increased albedo of croplands leads to cooling is grossly misleading. What’s forgotten is the sharply reduced insolation acting upon the ground in forests. In the tropics, daytime temperatures in the forest canopy are several degrees above those found near the ground. And, unlike the ground, the canopy siphons off considerable W/m^2 for plant growth, instead of thermalization. It’s amazing how little desk-bound “climate scientists” are acquainted with the real-world.

September 8, 2014 4:44 pm

Save the planet! Chop down all the rain forests!

Bill Illis
September 8, 2014 4:55 pm

Converting forest to cropland did increase the Earth’s Albedo but it is small and it was mostly over by about 1940 and hasn’t changed much since. Roger Pielke Sr. has been making this point for decades and every single climate model will have already fully accounted for the impact. So, the point trying to be made in this study is way, way off in fake excuse/propaganda land.

September 8, 2014 5:06 pm

Wait…wouldn’t these be the same BVOCs that Reagan said cause more pollution than automobiles?
The ones that he was accused of being monumentally stupid for saying such?
So…they could cause warming and according to the EPA, gasses that cause warming are pollutants, right?
So this paper is saying trees DO cause pollution and Reagan was right.
Or do we get to recycle and throw the claims of monumental stupidity back at the enviro crowd?

September 8, 2014 5:15 pm

I don’t buy it, and this is an obvious attempt at trying to attribute more warming to CO2 (see, we would have seen more warming if we didn’t have all this farmland.)
Don’t be a sucker.

Reply to  MattN
September 9, 2014 4:12 am

My thoughts exactly.

Bob Boder
September 8, 2014 5:33 pm

Does this mean the lost heat is in my bread or the lumber in my deck? I am confused.

September 8, 2014 5:51 pm

For the last 100 years, the US has been converting cropland back into forests.

Reply to  MarkW
September 8, 2014 8:52 pm

But China, India, Brazil etc. have been doing the reverse.

Reply to  phlogiston
September 9, 2014 7:04 am

Send the EPA, greenpiece and wwf to China, India, Brazil etc.
Let them fix the problem at the source.
Ms Unger should grab Ms Oreskes and they should be out there in those filthy countries coordinating saving the planet with her favorite the dictators in the world, including China. They have the right idea.
Too bad they won’t go protest where the problem is.
We are suffering because of environmentalists failure to stop pollution.
Let’s get with the program you two.

September 8, 2014 5:58 pm

Lotta people don’t seem to believe this – but it’s true. This is nothing but a rerun of a NASA study from 2003(?). That study was buried deep because it failed to support the “consensus” AGW theory at the time. Somehow I’ve seen a number of older research findings show up over the last few years. Since I retired 8 years ago, I can afford to find them amusing, if not hilarious.

Leonard Weinstein
September 8, 2014 6:05 pm

Measurements have shown an increase in methane that was quite large over time (from ice bubbles in the past to direct measurements at present), and always increased. Here it is claimed methane was somehow reduced due to cutting forests.The only claim of the study that makes sense is that things are more complicated than previously thought, but this does not clarify any issue.

September 8, 2014 7:11 pm

Assuming the calculated result of 0.1 degree is reasonable, shouldn’t the conclusion have been that conversion of forest to farm land has had a negligible effect on the climate? Doesn’t sound quite so exciting, but if solid it would be a meaningful contribution nonetheless.
I wonder what Roger Pielke Sr. thinks of this — if I understand him correctly, he considers land use a major factor in local climate change. Maybe he would be willing to provide some comment?

September 8, 2014 7:24 pm

“We believe that humanity has reached Peak Farmland, and that a large net global restoration of land to nature is ready to begin,” said Jesse Ausubel, director of the Program for the Human Environment at the Rockefeller University in New York.
The report projected that ~370 million acres could be restored to natural conditions such as forest by 2060. That is 1.5x the area of Egypt or 10x the size of Iowa.
The entire state of Main has gone from mostly farmland to mostly forest.
Forbes Economics writer, Tim Worstall, thinks the prediction may be conservative as:
Crops could soon be grown in greenhouses the size of skyscrapers in city centers. Birds Eye and other food producers are investigating building them. And another development: hydroponics using seawater as both the growing medium and the cooling necessary in a desert.
From another source: Nanotechnology guys have developed an experimental RO filter capable of reducing the cost of potable water to 1/100th of current cost which could provide all the H20 the world would need.

September 8, 2014 7:25 pm

That study must been conducted under double secret probation by big oil. Anything cooling goes against the narrative and is therefore suspect.

Reply to  LogosWrench
September 8, 2014 7:53 pm

Unless of course, it’s a warm cooling.

Reply to  LogosWrench
September 8, 2014 9:53 pm

I believe you are missing the point. This study tries to imply that the anthropogenic forcing from CO2 has been somewhat hidden by land conversion (in this case). Hence, it is just singing along with the AGW choir.

September 8, 2014 7:51 pm

The percentage of the planets surface covered by crop land is 37%?

Reply to  DocRock117
September 8, 2014 8:14 pm

@ docrock: It seems that the 37% that could maybe, perhaps if all things go right it could maybe, be perhaps in the correct circumferences be just be perhaps be the correct thing if it all falls into the right, you know, the correct place where ever that could just be in all instances be or might be just what we might be looking for,
Hey. Would I be a politician Doc? or a good bureaucrat? (or did I forget something here possibly? oh right I forgot that word)

Michael D
September 8, 2014 7:55 pm

Sorry, don’t buy it. We were told long ago that the “science is settled.” /sarc

Dr. S. Jeevananda Reddy
September 8, 2014 8:32 pm

I termed this cooling effect as “rural-cold-island effect” similar to “urban-heat-island effect”. Here the important point is: met network is dense in urban areas but it is sparse in rural areas. Thus the urban-heat-island effect is over emphasized in the global temperature averaging and under emphasized the rural-cool island effect. In fact satellite measurements takes this in to account. Because of this the satellite data based temperature pattern is far lower than the ground based observations. There is a need to look in to this angle and derive the correct picture of global average temperature trend — rhythmic part is already there.
Dr. S. Jeevananda Reddy

September 8, 2014 10:36 pm

Since the mid-19th century, the percentage of the planet covered by cropland has more than doubled, from 14 percent to 37 percent.
Say what? Do you mean 37% of land area? Even that sounds like way too much.

Dave Wendt
Reply to  Juice
September 8, 2014 11:59 pm

Since the mid-19th century, the percentage of the planet covered by cropland has more than doubled, from 14 percent to 37 percent.
This is complete nonsense!
World arable land: 10.43%
permanent crops: 1.15%
other: 88.42% (2011)
This entry contains the percentage shares of total land area for three different types of land use: arable land – land cultivated for crops like wheat, maize, and rice that are replanted after each harvest; permanent crops – land cultivated for crops like citrus, coffee, and rubber that are not replanted after each harvest; includes land under flowering shrubs, fruit trees, nut trees, and vines, but excludes land under trees grown for wood or timber; other – any land not arable or under permanent crops; includes permanent meadows and pastures, forests and woodlands, built-on areas, roads, barren land, etc.

September 8, 2014 10:40 pm

All around the world, crop yields have rapidly increased since 1980 according to World Bank’s crop yield data:
USA’s crop yields alone have increased 70% since the early 80’s (from 3,984kg/hectar to 6,744/hectar– last 4-yr avg) and this is true for almost all countries around the globe.
Farmers are growing much more on less land; not exactly in agreement to the narrative portrayed by CAGW warmunists and to the assumptions of this paper.
Ironically, this incredible increase in crop yields is partially due to increased CO2 levels/CO2 fertilization and also to: cheap gas, cheap petrochemical fertilizers/insecticides and GMO advances; all of which are anathema to the CAGW warmunists/enviro-wackos.
I swear the warmunists are out to destroy mankind, not save it….

September 8, 2014 11:43 pm

I would like to see figures comparing effects on atmospheric water vapour of farmland vs forest. For years now I have felt that this farmland-forest is probably by far the biggest anthropogenic input and have been disappointed that up to now have never read anything about it in the climate wars. The carbon business is a scientific sideshow albeit it gets nearly all the screaming headline ink.

September 8, 2014 11:47 pm

PS. I am thinking about the forest-to-farmland change in the past few thousand years. I don’t think since the industrial revolution is the huge shift. In China, India and Europe the big changes were from around 1000 to 1500 AD. Europe used to be one huge forest, for example. Now there aren’t hardly any. Same in England. I suspect similar story in Africa albeit probably they deforested more like 1000 BC. Probably no way of calculating the effect climate-wise but still I wonder if there isn’t quite a significant one.

September 9, 2014 12:52 am

I wonder if the Black Death (with the resultant reafforestation) resulted in a warming of the climate?

Bob Boder
Reply to  flydlbee
September 9, 2014 9:37 am

Off course not, it caused the little ice age because since there were less people there must be less global warming, since we all know it is only man that can cause global warming!

Otter (ClimateOtter on Twitter)
September 9, 2014 1:31 am

Did not the skeptic science kidz write an article claiming that a) The Black Plague killed off a lot of people, and therefore b) a lot of farmland went back to forests, thereby C) soaking up CO2, and D) causing the LIA?
Isn’t this the exact opposite?

September 9, 2014 3:05 am

“The conversion of forests into cropland worldwide has triggered an atmospheric change that, while seldom considered in climate models,”
Wait a moment, doesn’t that mean that the iterative climate models accumulate a small error with each time step, always in the same direction… meaning that after a week or two of simulated time they’re completely off the tracks…
…and that the climate scientists would then introduce an arbitrary unphysical fudge factor counteracting that error; call it a parameter and NEVER TALK ABOUT IT…
…and that therefore climate modeling is advanced fudgeology…
Hey that sounds like easy money count me in!

September 9, 2014 4:33 am

Is it possible that Nadine Unger could be so short sighted as to not take into account that forest vegetation stays put but farm vegetation (crops) goes someplace ~else~; I.E. that it MOVES to another location?
Am I supposed to focus on the rotting leaves that fall to the forest floor but ignore the methane generated by cattle eating harvested feed stock? Are we supposed to now also ignore the CO2 emitted from burning bio-fuel to claim it is “saving the planet”?
Being that his paper is pay-walled I have no way to check … but if he is not accounting for the subsequent release of GHG’s from the harvested crops in all the places where that happens, including GHG’s gases emitted from sewerage treatment facilities which came from farms for example – then this “study” is a complete crock.

Mark H UK.
September 9, 2014 5:19 am

Surely albedo in the Arctic and Antarctic where the suns radiated heat reflects back off ice and snow leaving the air temperature below zero (cold) is different to a field full of crops where the radiated heat is absorbed first by the field,crops etc and the resulting warm air rises as thermals (hot) and gives glider pilots and soaring birds of prey the fun they have come to know and love.Do modelmakers ever go outside,or am I just being to simplistic here.

September 9, 2014 5:24 am

The great American white pine forests were chopped down en masse 100-150 years ago so it follows this must have introduced a step-cooling effect, rather than a “spread out” cooling effect from 1850 to 2000, right? I recall recent articles that pine forests emit lots and lots of volatile organic compounds. The while pine logging occurred on an industrial scale and removed multiple state-sized swaths of pine trees in a small amount of time, making the Tunguska event, which knocked down 830 square miles of Siberian forest in 1908, not even worth mentioning (sorry, I just did). This particular step-cooling effect happened right about when the warmists like to start their Great Century of Warming charts. Maybe the number adjusters should consider adjusting the long ago temperature charts upwards rather than the usual downwards?

September 9, 2014 5:29 am

“Meanwhile, the disappearance of dark-colored forests has also helped offset temperature increases through the so-called albedo effect.”
That’s a cart of equine fecal matter by the simple fact that the steady state for forests is COOLER than grasslands and farm fields. On Unger’s planet the darker looking suburbs with all the trees are always warmer than the city.
Forests are almost always COOLER! And cooler not just because of transpiration – because of photosynthesis, forests convert more UV into chemical energy.
(Riitters et al., 2002; Wickham et al., 2008b).
Based on our results, reforestation in the continental United States can add promotion of cooler surface temperatures to the numerous other ecological benefits that forests provide.

Peta in Cumbria
September 9, 2014 5:55 am

There is, just up the road from me, a place called Kershope Forest. It butts up against a much larger stand of trees going by the name of Kielder Forest. Sometimes I go there.
Even well before you can even see any trees and in a car, you can feel ‘something’, a chill in the air. Get closer still and you see what looks like and actually is, low fog. Still can’t see any trees at this point.
When you do see the trees, you do indeed see a low cloud hanging over the forest on what would be an otherwise bright day. Those tress have a MAJOR effect on their local environment.
Then work out what’s going on water-wise. Does a mature tree get through 100 gallons of water per day?
If so, lets use UK gallons= 454 litres. To evaporate that much water needs about 1,000,000,000 joules of energy, or, over the course of one day, a power of over 11KW.
Spread that over the area covered by the tree, say 100 metres square and the cooling power is????
Is someone remind me what the warming power, watts per square metre of our CO2 emissions are supposed to be…….

Alan McIntire
September 9, 2014 6:14 am

“Study: Conversion Of Forests to Cropland Cooled the Climate”.
Sounds plausible to me.
It may be warmer in a field than in a forest in the DAYTIME, but remember there is also nighttime. I see that overall, fields would be cooler than forests. Compare the Sahara Desert with Florida. Although the Sahara Desert gets much hotter in daytime, it gets much colder at night, so overall Florida is warmer than the Sahara Desert at a similar latitude. I suspect that the same effect works for forest versus field, but to a lesser extent.
Note that in addition to chopping down trees, there are also plenty of drainage ditches built to keep fields from becoming too soggy. That would also have an effect on the water cycle and water vapor in the air. Perhaps it was the settling of North America that helped bring about the little ice age.

Mark H UK.
Reply to  Alan McIntire
September 9, 2014 6:27 am

Is’nt the Sahara cooler at night due to lack of cloud cover and amount of inland desert area.

Robert of Ottawa
September 9, 2014 6:53 am

Using sophisticated climate modeling ha!

September 9, 2014 7:04 am

“During the same period, the global climate warmed by about 0.6 degrees Celsius, mostly due to increases in fossil fuel carbon dioxide emissions.”
The state of climate “science” today: one insight that may advance the science is more than destroyed by coupling them with facts that remain to be proved especially in light of contrary theories such as that advanced by Murry Salby:

Reply to  buckwheaton
September 9, 2014 7:06 am

Better link: (but the audio is poor)

Stephen Skinner
September 9, 2014 7:09 am

“The conversion of forests into cropland worldwide has triggered an atmospheric change that, while seldom considered in climate models, has had a net cooling effect on global temperatures, according to a new Yale study.”
This is said with absolute certainty, which is staggering because this ‘conclusion’ (net cooling) is based on assumptions and a crude application of the Albedo ‘effect’ without even checking that this is what happens. It is not what happens. It is more than likely that any warming since the end of the Mini Ice Age has been driven by land clearance, including draining and urbanisation, otherwise its natural.

September 9, 2014 7:25 am

This is an interesting twist that I knew nothing about, but to acknowledge the complexity of the system and then assert that this tidbit is the final piece to the puzzle is just plain stupid. Transpiration from grasslands can be almost an order of magnitude higher than woodlands, cycling water (the real greenhouse gas) much faster, thereby maintaining more water molecules in the atmosphere.

September 9, 2014 7:32 am

But all the above contradicts BOTH the “usual assumption” (by the CAGW religion) that the snows and glaciers on Mt Kilimanjaro were melting “because of global warming” AND it’s usual counter-argument (that the snow and ice was lost on Mt Kilimanjaro “because the forest down low were being rapidly cut down for farmland and as firewood” to feed the local peoples…..

September 9, 2014 7:35 am

One thing that needs consideration is winter. Albedo on cropland, especially covered w/snow, is high. Forests, especially w/evergreens, not so high. And conifers spreading into treeless, usually snow-covered sub-Arctic tundra would presumably warm the area alittle in winter/spring.
So it’s complicated & may be quite dependent on location, precip, latitude, forest-type, etc.

September 9, 2014 8:06 am

“…..Conversion Of Forests to Cropland Cooled the Climate……”
Really ??
Pray tell, what caused the ice ages???
Did some aliens from a far away solar system denude the earth’s forests which then resulted in an ice age. And these aliens did this several times !!! Wow.
More BS from the climate frauds. They cannot explain the historical climate changes; ice age to warming to ice ages to warming to……. you get the picture. Yet, they presume to isolate one factor that MAY affect climate (take your pick; forests , crops, CO2, cow farts, etc.), and claim this one factor will increase/decrease global temperatures, and these “scientists” have NO IDEA how the many myriad factors that can affect climate interact !!!
They can’t even predict the weather two months hence….oops, sorry, weather is not climate, unless of course the weather “affirms” the AGW thesis.
Has anyone noticed that the AGW folks are all anti-capitalists or socialists?

September 9, 2014 10:34 am

Well, Fukuoka’s method of bringing rain to desert areas was to plant trees near deep aquifers to bring up the water. Trees attracted rain somehow and he could change microclimates that way in previously dried-out areas. Shortly put: trees attract rain = create more cloud cover = cooling. Therefore, to my mind, it is quite possible that widespread deforestation has a general warming effect. Of course, there could be other effects which go into Earth’s complex system which obviate such cooling. The point is, where is the hard core analysis on this in climate science? You would think this topic would have been researched and argued about to death in the past two decades (if not earlier), but I don’t recall ever reading anything substantive about it. I always assumes the global warming thesis was reasonable until a few skeptics stimulated me to look into it a little and the more I looked the more amazed I was at just how haphazard the so-called ‘scientific method’ is, moreover how brazenly they come to sweeping conclusions based on tiny amounts of data points. It’s the same in so many science-related fields. At this point, I trust engineers to use physical sciences to come up with nifty technological advances, but the more theoretical approaches including evolution, climate etc.) I regard as little better the religulous masturbation. The debates go on forever because the scientific method is not designed to deal with such issues and shouldn’t be used that way. In any case, unless and until they include things like deforestion / reforestation in their models, they will remain worthless as they have thus far proven.

September 9, 2014 11:53 am

I wonder what the net effect would be, then, if we could somehow pull a massive stunt off such as completely “regreening” the Sahara Desert with grasslands (as it once was, as is my understanding) OR (less likely, but intriguing idea) turn it into something as lush as the Amazon rainforest. Of course there are many variables present here. The biggies that come to mind right away: On the one hand, a lot more carbon uptake than the current sand and rock, naturally, but no doubt counteracting any slight cooling effect due to removal of CO2 from the atmosphere would be the fact that the Sahara from space looks rather bright. So there’s the loss of reflectivity, or its albedo effect, right? Yes, either project would require massive infusions of fresh water and a pricey distribution system, and would be an engineering marvel for all time to behold. So also add to the mix massive redistribution of water from one point to another, even if such volumes could be easily found nearby. I’m sure the list goes on and on…
Still, it would be interesting to see what would happen. Imagine for example the possible food production factor alone. In any case, are we to assume then, based on the study above, that a massive grassland or cropland would cool the planet slightly more than an Amazonian type vegetative zone?

Robert Clark
September 9, 2014 10:45 pm

Does this count as another explanation of the hiatus?

September 10, 2014 4:11 am

The paper by Unger is primarily about the effects of deforestation on BVOC emissions. However in her introduction she mentions that “…the disappearance of dark-colored forests has also helped offset temperature increases through the so-called albedo effect.” In other words deforestation is thought to have a local cooling effect on account of the increased reflectance of visible light by seasonally bare earth as compared with perennially vegetated areas. However visible light is not the only part of the electromagnetic spectrum that has to be taken into account when assessing the effect of forest vegetation on climate. About 50% of near-infrared radiation between 0.7 and 1.3 μ (microns) will be reflected by leaves, the other 50% being transmitted. Without the leaves, 100% of that part of the spectrum is transmitted, and, if it strikes bare earth, will be absorbed, thus warming the earth’s surface (as compared with a forested area) and counteracting part of any albedo cooling effect from deforestation.
Ref: Knipling (1970): Physical and Physiological Basis for the Reflectance of Visible and Near-Infrared Radiation from Vegetation. Remote Sensing of Environment, 1, 155-159.
This paper is accessible at
I get the impression that that the role of near-infrared radiation in surface climate has been neglected by climatologists in recent decades. Might it be inconvenient for supporters of the CO2-driven global warming paradigm to have to take into account other anthropogenic factors than CO2 emissions which may have contributed to surface warming in the 20th century?

September 10, 2014 6:12 am

Every science reporter should have to read John Ioannidis’ paper, or the Atlantic article about him. Then they would realize that the vast majority of academic papers that are publised aren’t “truth” so much as flotsam generated to support grants and academic careers.

Tom G(ologist)
September 10, 2014 9:16 am

” large-scale forest losses during the last 150 years have reduced global emissions of biogenic volatile organic compounds (BVOCs), which control the atmospheric distribution of many short-lived climate pollutants,”
And these are the SAME arboreal pollutants about which Ronald Regan was scorned for mentioning.

Tom G(ologist)
September 10, 2014 9:23 am

On another note, I can’t even BEGIN to enumerate the myopically induced inadequacies of this little piece of ‘research’.

%d bloggers like this:
Verified by MonsterInsights