Corn as a local climate forcing

How corn may be helping Michigan keep its cool

From the “corn is not climate” department and  David Veselenak, The Grand Rapids Press

Grand Rapids hasn’t seen the thermometer break 100 degrees since 1988. Some climatologists say the reason is corn.

In fact, since 1953, Grand Rapids has seen the thermometer hit 100 degrees only three times. Since 1894, Grand Rapids has had 30 days reach the triple figure temperature mark.

One theory: more corn has been planted the past 60 years, increasing the amount of water vapor released into the atmosphere. That decreases the amount of energy available to heat the air.

“From the 1930s to the 1950s, it looks like (the temperature) was typical. But after the 1950s, it wasn’t typical,” he said. “Clearly, something was going on in the ’30s, ’40s and ’50s, and it could have been agricultural practice.”

And the numbers support that claim. According to Iowa State University, corn production yields have jumped and so has the acreage committed to corn. In 2010, record amounts of land in the United States was being used for corn planting, with 87.87 million acres of corn, up from 86.5 million in 2009.

read the rest of the story here: How corn may be helping Michigan keep its cool

h/t to Steve Mosher via Facebook

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70 thoughts on “Corn as a local climate forcing

  1. Actually there is a correlation to corn shocks. When they got rid of them the heat went down. They must have been lightening rods for drawing heat.

  2. I remember some years back watching an agri-business TV show in the wee hours because I couldn’t sleep and there weren’t even any bad infomercials on.

    On of the guests was an exec from ADM and the discussion was corn, and ADM announced that it was shifting 10-15% of it’s crop total to corn. The reason? Subsidies for corn based ethanol made corn more profitable than other crops. I was, of course, stunned to see that ADM would stoop to such profiteering. Stunned, I tell you.

    Seriously, here’s just one more perfect example of how land use is changing climate with likely far more impact than the attendent increase in CO2, which paradoxically enhances the …. cooling effect by helping corn to grow.

  3. It is easily proven that an increase in humidity increases the heat required to take it over 100 Degrees. I have flown into Grand Rapids many times and remember it is near the lake. What is the surface temperature on lake Michigan?
    Since the AGW’s are big on demanding that CO2 causes heat increase, the corn fields are areas of low CO2 and soak up over 13,000 Kilos per acre of the stuff.

  4. But… isn’t water vapor also a powerful greenhouse gas?

    Could it be producing cooling at the surface level and still generating heat at higher levels? Someone get me a grant!

  5. The ineffable Richard Black at the Beeb has this Rice yields falling under global warming. As I read it, warmer daytime temps’ push the yields up, which they have been doing, but warmer nighttime temps’ push them down. The story seems to say that overall yields are still rising, but “at some time in the future”, they will drop. Given that even the high end of their predictions (lots of “coulds” and “mays” in this little gem) only get us into MWP territory, you have to wonder how we made it out of the Middle Ages.

    REPLY: I saw the press release earlier on it, looking into it. -Anthony

  6. Simple fix, build a large airport, move the thermometers there. And remember UHI is irrelevant.

  7. I thought this looked familiar, Chicago Tribune also covered this in the spring:

    “Amid one of the warmest springs on record in Chicago, and renewed worries about our warming planet, how is it that late summer days across the Midwest are cooling?
    The answer may be in the towering, tightly packed rows of corn that blanket Illinois at harvest and the ripple effects from industrialized farming that scientists are only beginning to understand.”

    http://articles.chicagotribune.com/2010-05-12/news/ct-met-weather-crops-20100511_1_water-vapor-climate-scientists-midwest

    …not to slight the good agronomy scientists in Michigan, mind you!

  8. This didn’t work when I was in Iowa. Corn as far as the eye could see and plenty hot, especially if you were in the corn rows detasseling.

  9. Dear Henry and DJ Meredith…

    I think any increase in water vapor density is a good explanation over increases of local temperature. I have made some calculations (very accurate) on the available microstates in water vapor (4% of the mixture of gases in the atmosphere) and carbon dioxide (0.038% of the mixture of gases in the atmosphere) and found the water vapor is the main interferer of photons, as from the solar photon stream as from the surface photon stream. Carbon dioxide doesn’t make a big difference:

    http://climaterealists.com/index.php?id=6111&linkbox=true&position=7

    Please, read the comments below the article because some gremlins of grammar and distraction crept into the text when I was writing the paper. :)

    Dear Anthony, sorry for promoting my article; I think those calculations are the key on this issue. Many thanks! :)

  10. Having spent most of my weather forecasting days in Grand Rapids, I believe it is more than just corn crops that have prevented our highs from reaching 100 degrees. Since 1964, the high has only hit 100 twice. But take a look at this week in 1936:

    7/8 101 in 1936
    7/9 101 in 1936
    7/10 102 in 1936
    7/11 99 in 1936
    7/12 106 in 1936
    7/13 108 in 1936
    7/14 102 in 1936

    Look at this period in 1934:

    7/20 99 in 1934
    7/21 104 in 1934
    7/22 97 in 1934
    7/23 101 in 1934
    7/24 103 in 1934
    7/25 100 in 1934

    Truly amazing. What is also interesting is that Grand Rapids has only failed to drop below 80 degrees for a minimum temperature twice in the entire record since 1892. Once in 1995 and then way back in 1902.

    If the lack of heat recently has been that dramatic due to higher dew points from the corn (an acre of corn during peak growing season can give off around 4,000 gallons of water to the air EACH DAY), then why haven’t the higher dew points kept temperatures at night warmer? I think this is MUCH too simple an explanation and likely only plays a very small role.

  11. Ahh, but corn is also a fertilizer hog, especially nitrogen. Which means the field must be regularly replenished with N. Which, in commercial quantities, is made from natural gas/oil/coal ( to obtain the required hydrogen ) via the Haber–Bosch process. The Haber process is important because ammonia is difficult to produce on an industrial scale, and the fertilizer generated from the ammonia is responsible for sustaining one-third of the Earth’s population.

    So in order to use increased corn production to reduce or control temperature would require an equivalent increase in Haber process fertilizer production and distribution thereof. You just can’t do it with only cow patties and crop rotation.

    Drill baby, dig baby. TANSTAFL rules.

  12. I believe that the increased yields of corn in the US Midwest has increased the amount of water vapor in our atmosphere, which lowers the daytime high temperatures and raises the night temperatures. Overall, the amount of water transpired to the atmosphere in the US Midwest is greater today than it was a half century ago just based on changes in agricultural practices and corn production: the more plants and greater yields per acre imply an increased need for and use of water by corn. All plants transpire, that is, release water vapor into the atmosphere through their leaves. Corn is unique in that it belongs to a family of plants that transpire, or sweat, both day and night. Stand in any large cornfield and you can feel the increased humidity. The average corn yields in Illinois have increased from about 50 bushels per acre in 1950 to more than 130 bushels per acre in 2000. Planting densities climbed dramatically as well, from about 18,000 seeds per acre to nearly 30,000 seeds per acre during the 1970s, when farmers started planting crop rows closer together. The higher the dew-point value the more difficult it is for the human body to cool itself through evaporation from the skin.

    http://www.niu.edu/pubaffairs/RELEASES/2002/aug/corn.shtml

  13. Not to too my own horn, but I had a very similar post in the notes and tip section that appears to be gone?

    What’s up with that???

  14. I’m more inclined to believe this is a function of cold Lake Michigan and prevailing westerly flow. I live about 3 miles west of the lake. An east wind can easily drop the temperature 20-30F, depending on time of year. With Grand Rapids being east of the lake (albeit 30-or-so miles), a prevailing west wind will certainly have a moderating effect.

  15. It seems to me that the real question is the difference between growing corn and growing anything else. Corn might account for a certain amount of water vapor, but to make any historical reference, it needs to be compared to what was growing before corn, even if that was just prairie grass.

    That said, here in Kansas, the daytime temps are nowhere near records, heat wave or not. Our records were still mostly set in the 1930s.

  16. Correlation isn’t causation. If more water vapor is being released as a result of more corn being grown, then I would hesitate to suggest growing corn decreases temperature.

    We all know water vapor is the dominant greenhouse gas.

    I would suspect off-hand that perhaps there has been a change is wind patterns in the area before I considered corn growing as the cause of less/no 100 degree days.

    Obviously air circulation doesn’t at all depend on the moisture generated from growing corn locally, winds blow from many miles away. I suspect that perhaps more wind has been blowing down from the North for whatever reason.

  17. This reduces the longwave radiation available for GHGs to absorb because the plants use it for photosynthesis.

  18. @ starzmom:

    Same in OH. There are July records as high as 110 from back in the 19th century. But I would bet my bottom dollar that there is more corn here now.

  19. One theory: more corn has been planted the past 60 years, increasing the amount of water vapor released into the atmosphere. That decreases the amount of energy available to heat the air.

    That theory goes against all I’ve read about water vapor being the dominate GHG.

  20. Anyone got any figures as to how much transpiration in litres per hour an acre of corn puts into the atmosphere as opposed to the equivalent acreage of trees or any other crop?

  21. John Egan says: August 9, 2010 at 4:56 pm
    Sounds pretty corny to me.

    <sniff>Too predictable.</sniff>

    Curiousgeorge says: August 9, 2010 at 5:50 pm
    . . . So in order to use increased corn production to reduce or control temperature would require an equivalent increase in Haber process fertilizer production and distribution thereof. You just can’t do it with only cow patties and crop rotation.

    No, you do it with CO2. An opportunity to recycle my CO2/corn chart :

  22. Ah, thank you, Deekaman.
    I think your explanation is better than corn for the milder temperatures. I also think that each of the states of Indiana, Illinois, and Iowa plants more corn than Michigan plants.

  23. Welllll, I don’t know for sure, but it is interesting. IIRC, before the corn there were trees on that all that land –aspen, birch, maple, red pine, white pine, I think. Does corn release more energy through evapotransporation than those trees?

  24. Prof Freeman Dyson writes:

    The fundamental reason why carbon dioxide in the atmosphere is critically important to biology is that there is so little of it. A field of corn growing in full sunlight in the middle of the day uses up all the carbon dioxide within a meter of the ground in about five minutes. If the air were not constantly stirred by convection currents and winds, the corn would stop growing.

    CO2 is essential to all life on Earth. More is better.

  25. Sounds to me that vegetation forms a negative heat island effect that needs to be corrected for. All that corn is hiding just how hot the planet really is.

  26. I agree with C James. There’s more at work than H20. It’s the weather pattern. The record highs listed were from the withering peak of the Dust Bowl years. There were no upper air maps, but if these maps could somehow be reconstructed, we would see huge upper ridges with closed 500mb heights near 600dm. A pattern like that occurred in the hot summer of 1988. A number of stations in southern Wisconsin repeated reached 100 degrees UPWIND from the water-vapor releasing corn belt.

  27. kramer says:
    August 9, 2010 at 7:01 pm

    That theory goes against all I’ve read about water vapor being the dominate GHG.
    ============================================================
    Actually, it’s totally consistent. They are using a bit of a misnomer (or even outright misdirection) when they talk about ‘heating’ the air. The air gets ‘heated’ but doesn’t have as dramatic a rise in temperature because it contains a lot of water. CO2, water, and ‘air’ all absorb heat energy, but it takes more energy to raise a given mass of water vapor 1 degree than it does to raise dry ‘air’. I place air in quotes because it’s really a mixture of gases, each having it’s own specific heat.

    For this reason talking about global warming in terms of atmospheric temperature is highly suspect, IMO. Temperature is heavily dependent on the mixture of gases (as well as any other state changes that may absorb or reject heat energy, like thunderstorms).

  28. Why is this idea being limited to corn? Historically, this area and much of Eastern N. Amer. was forest. That was cut. Where farming declined a forest has grown back. In other regions irrigated agriculture has grown with inputs of water vapor to the local atmosphere that was not there before. And whether it is corn or something else, the basic principle is the same.

    As to the story about rice @ timbrom — 5:26 pm

    Different plants have different “preferred” temperatures and in the daytime their growth can slow or stop when their “preferred Temp” is exceeded. In hot climates grape growers will mist the vines so as to not exceed the desired temperature. Hot temperature at night is also a problem because the vines will use their reserves to provide “cooling respiration” and this can effect quantity and quality. For example, grapes that might otherwise be deep blue or black can lose color, and thus value.

  29. Karl says: “from the withering peak of the Dust Bowl years”
    August 9, 2010 at 7:57 pm

    This might be of interest:

    NASA Explains ‘Dust Bowl’ Drought (NASA/Goddard Space Flight Center (2004, March 19).) [http://www.sciencedaily.com/releases/2004/03/040319072053.htm]: “cooler than normal tropical Pacific Ocean temperatures and warmer than normal tropical Atlantic Ocean temperatures contributed to a weakened low-level jet stream and changed its course. The jet stream, a ribbon of fast moving air near the Earth’s surface, normally flows westward over the Gulf of Mexico and then turns northward pulling up moisture and dumping rain onto the Great Plains. As the low level jet stream weakened, it traveled farther south than normal. The Great Plains dried up and dust storms formed. Analysis of other major U.S. droughts of the 1900s suggests a cool tropical Pacific was a common factor.”

    I copied the above from http://www.appinsys.com/GlobalWarming/PDO.htm

  30. So, the answer to “Global Warming” is for the IPCC decree that maize should be the only acceptable food crop? After all, it cools the Earth.

    Instead of this cooling effect being due to increased transpiration, I would posit that this rapidly growing plant converts more light energy into chemical energy than most others. As there is less light energy remaining to heat the ground, the ground cannot get as hot. The cooler ground therefore cannot heat the air to the same degree as before, thus the measured air temperatures are lower.

    As to why it appears to be hotter inside a maize field than outside of it, all plants transpire and generate very high local humidities. Because the maize plants are so tall (7-8′) there is little if any air circulation inside the crop and the dense humid air stays in place. Warm humid air feels hotter than hot dry air.

    As an aside, the GHG hypothesis is that certain gasses absorb IR radiation from the ground. Theoretically this is so as can be seen from absorption spectra. The question I would like to ask is “How much of the heat from the ground is directly radiated as IR compared to quantity of heat removed by the conduction of heat by the moving air? This is anomalous to the cooling of a heat engine by air, radiation is a very minor component in the cooling process, until the temperature of the coolant and of the heat source approach the same temperature at which time catastrophic failure will rapidly occur. If ground level air temperatures are predominantly due to the heating of air (as opposed to the heating of CO2) then surely the CO2 effect is exaggerated.

    I hope I have not been too rambling in this post but I was trying to keep my thoughts in order and kept on running into side tracks in my mind.

  31. Thanks for providing this link,

    http://www.appinsys.com/globalwarming/RS_Illinois.htm

    It contains this information:

    Energy Secretary, Stephen Chu: “in the Midwest, the temperature will increase 5 to 10 degrees Fahrenheit on average. With hotter summers, that means that during the growing season, the soil moisture will decrease by 20 to 30 percent. Now, if you take that at face value, then the great agricultural machinery of the U.S. is at risk, with huge economic consequences.”
    [http://berkeley.edu/news/media/releases/2005/10/03_chu.shtml]

    Bah!! Univ of Ill. ag faculty have determined that Illinois will be a net winner due to longer growing season, increased yields from higher carbon dioxide levels, and increased precipitation IF the Hockey Team models hold together!

    Stephen Chu’s job is going to be at risk in the not-so-distant future….

  32. Could it be that humiity there helps keep it cooler?

    I notice that all of the areas alongside freeways etc that don’t get irrigated stay green all summer. Presumably because of thunderstorms and high water table in the area.

    So how does tha play into the temp?

  33. Here in the Pacific Northwest I remember many triple digit temperatures during the summers in the lower valleys of southeastern Washington State during the 1950s and 1960s. However after the appearance of more dams along the Snake River and the Columbia River there is much more irrigation that has essentially greened the Columbia Basin in the central part of the state – and since 2000 we have had fewer triple digit days during the summer. It would be interesting to see if plots of humidity correlate with the number of acres irrigated.

  34. Has anyone here traveled to the Midwest corn belt? I’ve been in Iowa when the temperature was 95 degrees with 99% humidity. In much of the corn belt there is no irrigation other than rain so the moisture being transpired into the atmosphere came from the atmosphere in the form of rain. Before the assumption is made that transpiration from corn is causing cooling the calculation must be made for what would happen to that same rain falling on grass or forest land and being put back into the atmosphere via evaporation or evapotranspiration.

    The argument being made would be better tested in the Central Valley of California. Prior to the advent of dams and irrigation, the predominant crop was wheat or other grain crops. Now, with about 75 million irrigated acres in the valley, we should be able to compare the temperatures from the late 1800’s and early 1900’s to current temperatures.

    A February 2007 posting, http://wattsupwiththat.com/2007/02/13/irrigation-most-likely-to-blame-for-central-california-warming/, argues that irrigation is the likely cause of warming in California’s central valley. Marlyn Shelton, in a 1987 study published in Landscape Ecology, however, makes the case for no appreciable difference in evapotranspiration from the historic native plant communities and the irrigated agriculture that has replaced them.

    Corn cooling off Grand Rapids makes a good headline, but seems to be short on substance.

  35. So is this the discovery of a CCI (Corn Cooling Island)? After all UHI is a well established fact.

  36. Farmers in Iowa figure they need about an inch of rain per week during the height of the growing season. But that does not capture the whole water balance, because over the growing season corn (or soybeans or grass) pulls water that went into the soil when the snow melted in spring.

    Farmers in Iowa keep a careful check on surface and subsurface soil moisture in the weeks before planting, because the amount carried over will affect the growth of the crop.

    Whoever wrote that report never was a farmer in the Midwest.

  37. Oh for Pete’s sake! Hell, the population in that state is getting older too and correlates well with the rise in CO2, the cooling, the corn, and increased use of old geezer toiletries. Is there no test to get into college these days?????? If you can spell your name are you now qualified to get a grant and do research???????????????? Have research labs turned into romper rooms??????????????????????? Do you get to publish papers the day after you stop pooping in diapers????????????????????????????????

  38. So we have Urban Heat Islands to take the climate up, and Rural Heat Sinks to take the weather down. Simple? I could get a grant for this.

  39. Sigh, so did they do a differential between the lack of 100 degree days in other corn producing areas and then compare that to other areas that don’t plant much corn? I think the lack of 100 degree days in Grand Rapids is because, oh, I don’t know, maybe their latitude!!!….just guessing, but it seems to me, the further north one goes, one sees less and less 100 degree days. But maybe I’m wrong. Maybe all the dumb bastages at the equator had to do was plant corn and they wouldn’t be so darn hot all the time. sheesh.

  40. One gram of living matter requires the transpiration of 100-1000g of water, which is released into the atmosphere

  41. “From the 1930s to the 1950s, it looks like (the temperature) was typical. But after the 1950s, it wasn’t typical,” he said. “Clearly, something was going on in the ’30s, ’40s and ’50s, and it could have been agricultural practice.”

    What was going on is that the official temperature record for Grand Rapids switched from the city station to the airport station in 1956, and that is why temperatures appear to have “dropped”. In actuality, they have not.

  42. Eh?

    “increasing the amount of water vapor released into the atmosphere. That decreases the amount of energy available to heat the air.” hang on, I thought water vapour caused the deadly Co2 feedback, but here is causes cooling??? Which is it???

  43. They have found the opposite of UHI and may soon adjust temperatures upwards to account for the temperature ‘bias’. :o)

    If the biosphere is greening then would the effect be observed in those areas? The edge of the Sahara etc. There maybe lack of thermometers in cooling areas as many are stuck near airport runways and restaurant car parks.

    http://www.co2science.org/subject/other/co2amp.php

  44. http://www.mlive.com/news/grand-rapids/index.ssf/2010/08/how_corn_may_be_helping_michig.html

    “From the 1930s to the 1950s, it looks like (the temperature) was typical. But after the 1950s, it wasn’t typical,” he said. “Clearly, something was going on in the ’30s, ’40s and ’50s, and it could have been agricultural practice.”

    Surely this is all down to low precipitation, in July particularly, if the land is parched, then peak daily temperatures will climb much higher.

    “With more water being released by the plant through evapotranspiration, sun rays heat the vapor first, then the air. With less sun energy, air temperatures can see a decrease.”

    Really! reminds me of Bush.

    87.87 million acres! that is

  45. timbrom says:
    August 9, 2010 at 5:26 pm
    The ineffable Richard Black at the Beeb has this Rice yields falling under global warming.

    REPLY: I saw the press release earlier on it, looking into it. -Anthony
    —————
    “An important factor accounting for the slowdown in yield growth is the reduced public investment in agricultural research and development (R&D). In particular, international donors have not provided sufficient support for agricultural R&D that is directly related to increasing crop productivity. ”

    http://beta.irri.org/solutions/index.php?option=com_content&task=view&id=15&Itemid=54&limit=1&limitstart=1

    World production

  46. Please do this study in IA and IL where the states are giant cornfields, I think you will find this grossly simplistic argument fails, but who knows…

  47. The US has strong intellectual property protection for germplasm, better genetics, and the rest of the world does not. Thus the only areas with increasing productivity are the US and places in the world where are stolen genetics work, such as Europe and China. The world needs to reward private investment, and then they will get private investment. Public breeders worldwide pretty much suck compared to Pioneer and Monsanto.

  48. DJ Meredith says:
    August 9, 2010 at 4:57 pm

    “the attendent increase in CO2, which paradoxically enhances the …. cooling effect by helping corn to grow”

    Not necessarily. As CO2 level rises transpiration declines. Stomata, pores in the plant, iris open and closed to exchange gases (oxygen and CO2). Water vapor is lost while the stomata are open. As CO2 level increases the stomata are opened less because the gas exchange goes faster. Good stuff. Adequate water is often a limiting factor in crop yields so anything that lowers water requirements is a good thing.

  49. Surface cooling due to land use changes

    http://climateresearchnews.com/2008/10/surface-temperature-cooling-due-to-land-use-change/

    Researchers ran simulations with the Regional Atmospheric Modeling System developed by Pielke and others at Colorado State. The RAMS model suggested average July temperatures for the Fort Collins area might decrease by one degree Fahrenheit as a result of increased cooling.

    http://www.sciencedaily.com/releases/1998/07/980723070425.htm

  50. Ref – NoMoreGore says:
    August 9, 2010 at 5:27 pm
    “So, it’s settled then. We plant. And Earth is saved.”
    ____________________________

    No! No! NO! REMEMBER … AGW is counterintuitive!

    H2o and co2 are the BIG Kahuna’s in this worldwide problem! AND AND AND – If corn is helping Michigan keep its cool it is causing inestimible problems elsewhere in Asia and Africia and Australia and Austria and Alabama! When are we going to finally admit that WE CAN DO NOTHING TO SAVE OURSELVES? We are Doomed! All Is Lost!

    PS: Please Help Us Save The World for Our Little Fur & Feathered Friends. Please Send a Last Will Bequest To atAlbert.Org as fast as you can. Remember, No One Lives Forever;-)

    (sarq off)

  51. Could this be a prelude to Hansen justifying homogenizing cooler rural temps to the far more accurate airport temps?

  52. IMHO: The hydrated version

    In the USA, slightly higher temps (~.4 F) in the latter part of the 20th century have caused increased precipitation. (This is what GISS data indicates.) Increased precipation leads to increased humidity (intuitive, humidity data not available or I haven’t found any). Increased humidity leads to increased occurrences of dew, and heavier amounts, as well as rain. Dew and rain evaporates taking energy and water into the air. In a well mixed atsmosphere (IPCC), increased humidity reflects sunlight AND takes energy to the top of the troposhpere into space. Trees and untilled perennial grass store more energy/unit area than corn stover on an annualized basis, so I don’t believe cooler temps have anything to do with corn acres. As George Smith says, it’s the water’s negative feedback stupid. (non-IPCC) .

  53. so H2O, a much more powerful GHG than CO2, causes cooling, while minute amounts of CO2 cause catastrophic warming.

    yeah right.

    i bet the nearby airports use by giss show warming, and plenty of 1oo degree highs.

  54. I went on a fishing trip in the U.P. in June 1995. On the second day temps soared to 104 deg! The fish stopped biting and I got a bad sunburn.

  55. One thing I’ve noticed over decades in rural areas is that there is a definite high-temperature “limit” during summer heat-waves, depending on the amount of moisture in the landscape (cities are different due to a lack of local transpiration). Where I’m at now in western MD, 90-92F (33C) is the limit when moisture levels are high. As drought increases, the temp limit does too. I have moderate drought now, and the highest highs have been 95-97F (36C). Nearby urban areas have easily been 100F+.

    This shouldn’t be surprising because plants (especially forests) are finely-tuned evaporation “machines” that regulate their evaporation rates by stomatal opening & closing, trying to keep their leaf-surfaces around the optimal 70F (21C). As available moisture decreases tho, the plants have to increasingly close their stoma to conserve water.

    Think of the amount of area presented by the leaf canopies — huge areas regulated to remain at near 70F by evaporating water. That’s got to be quite a modification on the local weather, and regional weather where forests are extensive. Increasing drought, tho, decreases the cooling effect.

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