The 'strawman' albedo effect

From ETH Zurich , something that actually makes sense.

Straw albedo mitigates extreme heat

Wheat fields are often tilled immediately after the crop is harvested, removing the light-coloured stubble and crop residues from the soil surface and bringing dark bare earth to the top. Post-harvest tilling is a widely practised and common management technique in Europe. However, ploughed fields can have a negative effect on the local climate during a heat wave. This effect was addressed in a recent study conducted by researchers at ETH Zurich led by Edouard Davin, senior lecturer at the Institute for Atmospheric and Climate Science, and Sonia Seneviratne, professor of land-climate dynamics, which has now been published in the scientific journal PNAS.

Unploughed stubble is lighter in colour and reflects more solar radiation than tilled surfaces. Measurements taken show that approximately 30% of sunlight is reflected back due to the albedo effect – the albedo is a measure of the reflectance capacity of reflective surfaces. Ploughed fields reflect only 20% of incoming solar radiation. Model simulations have shown that this difference results in a 50% higher level of reflection in unploughed fields and that this in turn has a significant effect in extreme heat. In the event of a heat wave, such as the one in Europe in 2003, unploughed farm fields could reduce the local temperature by as much as 2 °C.

Regional effect

The hotter it becomes, the greater the albedo effect and the resulting temperature reduction. “Cropland albedo management has more effect during heat waves because there is almost no clouds during these events and more radiation can be reflected back into space”, says first author Edouard Davin. However, this effect is only short term and local — perhaps at the most regional, but never trans-regional. “In other words, if all French farmers were to stop ploughing up their fields in summer, the impact on temperatures in Germany would be negligible,” says Seneviratne. Leaving fields untilled would also have no noticeable effect over the long term on global warming trends and more frequent heat waves. Nevertheless, as Seneviratne points out, the local impact is important and could help break peak temperatures on extremely hot days.

Overall, says Seneviratne, no-till farming makes more sense in regions where summers are regularly very hot due to high levels of sun exposure e.g. in areas around the Mediterranean. Nonetheless, on heat days, the effect is also relevant in Central and Northern Europe. As part of the study, which was carried out jointly by the ETH researchers and French scientists, Davin analysed solar radiation measurements on farmland near the southern French city of Avignon. The researchers also conducted model simulations for Europe that incorporated the projected effect of unploughed cropland.

The scientists also report that the cooling effect of an unploughed field cannot be attributed solely to changes in albedo values. Crop residue acts as an insulating layer that holds back moisture from deeper soil strata and releases it only slowly — this long process of evaporation also helps reduce the air temperature during a heat wave. In a ploughed field, on the other hand, moisture evaporates more rapidly and almost completely in extreme heat. Thus, there is an additional cooling effect of no-till farming through slow evaporation.

No-till farming common in the Americas

The researchers believe no-till farming is a useful option in order to mitigate the local effects of climate change — for example, on extremely hot days in summer. “It is important that cropland albedo management can dampen heat waves because these events, although rare by definition, have a large impact on humans and ecosystems,” Seneviratne explains. Even though the rise in average global temperatures has stagnated in recent years, there has been an increase in extreme heat events over land areas.

Europe in particular has sufficient potential to use no-till farming as a tool to lower temperatures on hot days. Until now, European farmers have left only an extremely small portion of their fields unploughed after a harvest and globally the region accounts for only 2% of all unploughed cropland. The situation is very different in the US and South America, which account for 85% of the world’s unploughed farmland.



Davin EL, Seneviratne SI, Ciais P, Olioso A and Wang T. Preferential cooling of hot extremes from cropland albedo management. PNAS Early Edition, published online 23 June 2014. DOI: 10.1073/pnas.1317323111

39 thoughts on “The 'strawman' albedo effect

  1. “Nonetheless, on heat days, the effect is also relevant in Central and Northern Europe.”
    In northern Europe by the time the harvest is in too much heat is never a problem. And if you don’t plow the field pretty immediately you’re not likely to get a second opportunity.
    By the way it’s 8 degrees centigrade (45 fahrenheit) outside here in southern Sweden just now. How’s that for a heat-wave?

  2. No till is possible in North America because we plant GMO crops (Roundup Ready corn and soy). GMO crops are forbidden in Europe. Absent glyphosate herbicide, the weed problem would be unmanageable without tilling. Same reason wheat fields ARE tilled in North America–no round up ready wheat.
    Interesting observations, but the authors know nothing about farming.

  3. “However, ploughed fields can have a negative effect on the local climate during a heat wave.”
    “During a heat wave” is weather, not climate.

  4. I find it interesting how the cooler air respects country boundaries.
    The air that is cooled (actually not heated as much) by these techniques in France, stays in France and knows not to migrate to Germany, where presumably, it isn’t wanted.

  5. Rud Istvan says:
    June 23, 2014 at 1:39 pm
    Never the less, no-till cultivation is catching on here in the rolling hills of the Columbia Plateau & Palouse Country dryland wheat region. We need to summer fallow to build up enough moisture to make a crop every other year, so if no-till can make it here, it can make it anywhere, with or without RR wheat. (My neighbors are the ranchers with surprise volunteer RR wheat in their fields, about whom you might have read.)

  6. Rud Istvan says:
    June 23, 2014 at 1:39 pm
    Actually I knew organic no till farmers before the conventional guys were doing it.

  7. Rud Istvan says:
    June 23, 2014 at 1:39 pm “No till is possible in North America because we plant GMO crops (Roundup Ready corn and soy). GMO crops are forbidden in Europe. Absent glyphosate herbicide, the weed problem would be unmanageable without tilling. Same reason wheat fields ARE tilled in North America–no round up ready wheat.
    Interesting observations, but the authors know nothing about farming.”

    Organic farming by definition cannot use any herbicides. They must till in order to remove weeds to plant the seed. During the growing season, weeds must be removed by tilling between the rows. The weeds which grow in the crop rows must be removed by hand. That means that hundreds of hours of labor must go into a single acre of farmland for weeding by tractor and by hand. There is also increased erosion and moisture loss from so many tills during the season for organic farmers.
    The labor required to weed by hand is back breaking. This was outlawed in California at one time because it was so painful for the workers’ backs. Organic farmers now have waivers from these laws protecting workers from bending over to pull weeds.

  8. My guess is that farming practices are those which are best for farms and for farmers. So, whatever the localized effect is of tillage on temperatures matters not one whit. The implication of these sorts of studies is always that government somehow needs to meddle.

  9. “However, this effect is only short term and local — perhaps at the most regional, but never trans-regional. “In other words, if all French farmers were to stop ploughing up their fields in summer, the impact on temperatures in Germany would be negligible,” says Seneviratne. Leaving fields untilled would also have no noticeable effect over the long term on global warming trends and more frequent heat waves.”
    The heat is not the pivotal issue in farming; farmers are well aware they have to plant at the right time in order to control the weeds springing up from the first till, and to have the crops established before the dog days of summer.
    The danger for growers is the combination of moisture and heat. The most dangerous time of year for growers is after a heavy rain when it is warm. This is when fungi attack the foliage and fruits. Thousands of varieties of crop destroying rusts, blights, and fungi are waiting in the wing to attack the beloved French grapes and hops, the tomatoes, and the sugar beets in Germany – and every other crop cultivated in Europe. The use of fungicides is the only thing that makes these crops productive and fit for sale. Heat + moisture = rot fungus blight rust mildew smut etc etc Requires Fungicides. Heat is normal. Banning fungicides is not sustainable.

  10. Have any of these people ever talked with a glider pilot? My understanding is that the dark ploughed fields warm more quickly and generate thermals under the hot sun. Also, all one has to do is take a drive through farmland with the windows open to notice the effect discussed. Oh wait…’climate models’ need computers, not field observation. (yes, a smarmy comment; no offense intended to those who actually get outdoors; you have my respect!).

  11. Theyouk says:
    June 23, 2014 at 2:34 pm
    Not just gliders. You can get a bumpy ride in a prop job crossing from ploughed to growing fields.
    No till has been around for a long time in North America as stated, even with hay.

  12. I read the other day that northern farmers will till the warmer surface soil under in order to put more warmth down too seed depth.And this allows earlier planting.

  13. Zeke says:
    June 23, 2014 at 2:28 pm
    Is there a trade-off? If you use RR crops and no till methods do you wind up with more problems from insects?

  14. No till farming requires herbicides; the reason you cultivate several times is to kill the weeds.
    I’ve done enough cultivating after harvest and while the land lies fallow: there is a “seed bank” of weeds of more than 10 years in the soil. Weeds are highly effective in survival. If whatever defines “weediness” could be gene-transferred into food crops, we’d have food for 20 billion.

  15. Hm, as a Canadian, I find it odd that farmers are plowing fields in mid summer, just don’t see that here in Ontario. They’ll hay 3 or sometimes 4 times a season; but no plowing ’til fall, after final harvest.
    (I’m assuming an earlier start allows for 2 crops per season in France?) Just find it odd, in a: wow we sure don’t do that here having to wait until almost June to plant.
    Wonder how the red soil compares to plowed or non-plowed soils like the province of New Brunswick has. Red soil, red potatoes, very tasty too.

  16. James Strom says, “Is there a trade-off? If you use RR crops and no till methods do you wind up with more problems from insects?”
    I do not know if no-till farming increases the need for insecticides. In other words, by practicing no-till, does the farmer provide a more commodious place for insects to overwinter? That is a great question, and it would indeed be a trade-off between soil erosion, which no farmer wants, and insects.
    I do know that nitrogen-fixing cover crops have been used in the US for over a century, and these do increase the harmful insect population for farmers.
    I also can provide an example of the field margins (which are sometimes required by law between fields to “promote biodiversity”) which become habitats for pests:

  17. Don’t ask, don’t till….
    (sorry, couldn’t resist….)….
    The watermelon, libbie, probably-think-milk-comes-from-factories greens don’t realize, as usual, that farmers’ jobs are farming, and producing food that said watermelons actually deign to eat…
    I’m more inclined to trust the methods of farmers, who have been working the land for THOUSANDS of years, as opposed to models, probably created by programmers who rarely see the light of day (hey, I resemble that remark…)(programmer, NOT greenie…)…
    I grew up in a town in California where they would pick the cauliflower and let the stems/roots/etc. rot and become compost for the next generation of cauliflower…unfortunately, we’d get rain around the same time….you could smell the, er, effects for miles….kind of stunk like CAGW does now….

  18. Tillage is used to prepare seed beds for planting and to control weeds that might otherwise compete with the emerging crop seedlings for light, water, and nutrients. The advent of herbicides does make no-till (also known as direct-seeding) an option, but the technology involved is in no way limited to Round-up Ready (glyphosate resistant) crops as one poster has erroneously suggested. Other herbicides and crops are commonly employed in direct-seeding or no-till establishment of crops.
    The fact that soil temperatures are lower without tillage has been well-known for many decades and it is the lower temperatures in the seed bed that is one of the limitations to crop performance with no-till systems in some crops and in some regions. As one poster mentioned, storage of water by summer fallow is important in rain-limited areas in the semi-arid regions of the Pacific Northwest USA. This factor can limit the performance of crops in no-till systems because tillage breaks up the continuity of the soil, thereby reducing the vapor loss of water from the soil surface. This is done by shallow tillage in summer creating a “soil mulch” which separates the stored water deeper in the soil profile from potential loss to the atmosphere.
    Even with the limitations, the extent of direct-seeded crop establishment is growing each year because of the fuel cost savings and increased protection of the soil resource from erosion losses.

  19. There is no doubt that climate science is one of the most versatile sciences that have ever existed. [ sarc/ ]
    It now seems that climate science is sticking it’s unwanted, noxious, notoriously stinking nose into telling farmers how they are supposed farm so as to “save the planet” all over again.
    As an example of the petty, piffling, utterly irrelevant levels of use to society that climate science has now sunk to, this so called research on straw retention has to be another prime example.
    Or maybe it is all just another of the usual climate science smoke and mirrors with nothing of substance to support it, to ensure that those same climate scientists have their next grant application once again munificently funded at the usual tax payer’s expense.
    It seems that once again climate science with this latest offering is just grasping at straws!

  20. No till farming has been utilized in the United States for at least 40 years. I can’t speak very much, if at all, about modern farming practices since those wretched days are decades behind me. (You can tell I liked it, huh?) But I doubt these university types could tell you as much as I about it, or even as much as my pet Neon Tetras in my tropical fish tank could tell you, but I’ll bet you they’re going to try – and no, I don’t mean it’s the Neon Tetras who are going to try; they have more respect than that. Anyway, farmers; long before Mother Nature planted these researchers in some woman’s womb; discovered it was easier, less work, less time consuming, and less expensive to skip plowing a field after it had been harvested and just disc the damn thing because they’d always have to disc it anyway after they’d plowed it. And, no, they didn’t need Obama, or taxpayer grant recipients to tell them this. Not plowing the fields reduced soil moisture loss, and most importantly it reduced topsoil loss. Plus, it gave them more time to get in the planting in the Spring. (It also gave the farmers more time to cavort and conspire with Mother Nature to plant more future researchers in women’s wombs so I guess one would have to determine a cost benefit ratio to no longer plowing fields.)

  21. Each farming area and region in each country around the world has it’s own specific means of dealing with the everyday problems of climate differences, weather patterns, soils types, seasonal changes, crop types and varieties, rainfall or lack of, pests and weeds, fertilizer requirements, stubble retention or disposal / incorporation, commodity prices and their ever ongoing rapid changes, Government regulations and controls, government taxes, government subsidies if applicable and etc and etc.
    Farmers will switch and change, ie adapt rapidly to changes in all those and many more factors as circumstances dictate.
    If they don’t they go broke and out of business and very rapidly at that when the narrow economic margins in farming are considered along with the constant high economic, weather and disease and pest risks to crops that farming has always entailed.
    Any farmer’s concerns as to the atmospheric temperature differences created by retaining or disposing or incorporating stubble residues ie straw [ soil temperature effects from the various stubble strategies are well researched ] would lay somewhere way below a farmer’s end of the day decision as to whether he has a beer or not.
    Climate science once again demonstrates it’s total irrelevancy for any practical and useful purposes.
    Could somebody somewhere please point out one single example where climate science as currently practiced has been of ANY perceivable or useful benefit to our national and global societies and industries ?
    Accurate and trustworthy SEASONAL predictions of which none so far exist, would be of huge benefit to a numerous range of industries.
    Predictions for a future climate going forward of 2 or so more years, if ever achieved in the next 3 or 4 decades, are basically useless as so many other factors both natural and man made also change in that 2 + year long time slot which would negate any so called climate predictions.

  22. The other really big issue here is:
    – no-till farmland and pasture-land sinks 0.3 tons per acre per year of Carbon on average; 1 ton of CO2 equivalent;
    – tilled land sinks Zero.
    How many acres of no-till farmland is there? How many acres of grassland or pasture is there? 0.3 tons Carbon and 1 ton of CO2 times billions of acres equals a huge number. If you do the math here you would get into the 25% range of human emissions being sunk in grassland and zero-till farmland being removed from the atmosphere each year.
    25% used to be worth a lot of Carbon-sequestration offset dollars for farmers awhile ago. Not anymore as the market has collapsed, but the sequestration numbers continue to increase as the no-till practise has continued increasing. It is a significant fraction of our emissions which is not recognized by the enviros.

  23. Michael Palmer wrote, “I truly find this baffling. Before the advent of farm machines, tilling used to be hard work – why was it invented if it is superfluous?”

    Agricultural mechanization continued through the early 1900s with the development of many tools that helped farmers cultivate the earth ever more intensively, including tractors that could pull multiple plows at once. Tillage practices were about to undergo profound scrutiny, however. The Dust Bowl era between 1931 and 1939 exposed the vulnerability of plow-based agriculture, as wind blew away precious topsoil from the drought-ravaged southern plains of the U.S., leaving behind failed crops and farms. Thus, the soil conservation movement was born, and agriculturalists began to explore reduced tillage methods that preserve crop residues as a protective ground cover. Spurring the movement was the controversial publication in 1943 of Plowman’s Folly, by agronomist Edward Faulkner, who challenged the necessity of the plow. Faulkner’s radical proposition became more tenable with the development of herbicides—such as 2,4-D, atrazine and paraquat—after World War II, and research on modern methods of no-till agriculture began in earnest during the 1960s.
    There is something magical and satisfying about a freshly plowed, disked and seeded field that isn’t present when seed is drilled into last years stubble.

  24. One would think that these people had never heard of the “dirty thirties” and the steps taken by the agriculture industry to avoid its re occurrence.

  25. I have to apologize for subjecting your readers to another of my comments but the following is just flat out wrong:
    ‘Unploughed stubble is lighter in colour and reflects more solar radiation than tilled surfaces.’
    Now, the last time I shaved my dear niece said to me, “Uncle Tom, you look like a chipmunk.” So, for understandable reasons I haven’t shaved again for decades. But, I can assure you, the stubble that was on my face back then could not possibly have reflected more solar radiation than the rather lengthy (I use a rubber band on it sometimes), and far lighter coloured surface that replaced that stubble. To prove this point may I point out that young girls have tugged at their mother’s sleeves, pointed slyly in my direction and whispered, “Mommy, it’s Santa Claus.”
    That has happened more than once. Honest. And, due to the fact that I weigh a svelte 128 lbs., I know it’s the beard.

  26. Michael Palmer: When a field has used up nutrients close to the ground, plowing was the only answer. Plowing digs pretty deep and brings that deeper soil with its nutrients (like worm castings) to the surface. Then you had to slice through the rather large clods with disks to change the plowed ground into a finer layer of top soil for drilling (the final process that plants the seed in the ground). It was a pain to plow every year, so even back in the old days, it did not happen every year unless absolutely necessary. And some crops were never plowed until they needed to be completely reseeded because the crop was a perennial.

  27. The albedo from no-till won’t help global warming. Deforestation, concrete, and blacktop doesn’t contribute to global warming. Nope, it’s just that bad CO2 caused by those mean old energy companies.

  28. There are many conflicting positions and policies regarding tilling in Europe and – it seems to me – this is just some ag scientists trying to get a ‘climate change” link into theirt research – good on ’em!
    Tilling is about weed control and when you have a selective herbicide (one that kills weeds and not your crop plant) people have been using no-till because it is much much more effective. The problem was the lack of and expense of selective herbicides and so plant breeders have been selecting for tolerance cheap broad spectrum herbicides for many many years. Mutation breeding has been very successful for one class of herbicides (sulfonyl-ureas), but when companies developed engineered lines tolerant to glyphosate and glufosinate (both very cheap and environmentally nice as they break down quickly in the soil) farmers leaped on them wherever they were allowed to.
    However, leaving stubble in a field is not the same as no-till. No till is about how you prepare before planting, not what you do after harvest, unless you are talking about winter sown crops (which is something relatively rare in North America, which has snow cover at much lower latitudes). Stubble retention is often about soil structure and can be both a good and a bad thing depending on what soil you happen to be working with. There is also an issue with an increase in a group of fungal diseases referred to as necrotrophic – that is, they live on dead plant material as opposed to living plants. Burning stubble was employed as a pretty effective control mechanism for these necrotrophs, but that had other environmental issues and is pretty much banned now.
    The other issue with European agriculture which has recently (10-20 years) come up is the consideration of nitrate run-off from agricultural fields left bare over the winter. When crops are growing in spring and summer there is almost no leaching of nitrate from the top soil into the water table. However, over the winter when the soil is bare, microbial action breaks down organic nitrogen in plant matter to nitrates, which leach during winter rainfall. In order to prevent this, countries have put in place requirements for planting of a catch crop over the winter – often referred to as “anti-brown field” policies. Stubble is not a living plant and so to plant a nitrogen catch crop often involved getting rid of the stubble before you can get your seeders in there.
    Thus we have a complicated mixture of agronomic and policy issues to consider here. As I said at the top, kudos to this group fotr getting a climate change angle in there – this should ensure their funding for a few more years.

  29. Unploughed stubble is lighter in colour and reflects more solar radiation than tilled surfaces.

    There is a noticeable darkening of wheat stubble with time in sunny inland Australia due to oxidation. It is not a constant light colour.

  30. Zeke says:
    June 23, 2014 at 2:28 pm

    We used to burn fields to reduce fungus. Natural and sustainable practice. But people don’t like all the smoke. Boo hoo. Ok, so then you can be slowly poisoned by RoundUp residues. Why don’t we just ban farming? All food comes from Safeway anyway.

  31. From what I see in the US mid-Atlantic states, no-till farming is the norm now for some yrs.

  32. Theyouk says:
    June 23, 2014 at 2:34 pm
    “Have any of these people ever talked with a glider pilot? My understanding is that the dark ploughed fields warm more quickly and generate thermals under the hot sun”
    Many years ago I learned to fly a microlight (generally known as ultralights elsewhere) from a site in the middle of the East Anglian Fens in the UK. The soil there is not just dark, but black (it’s dried out peat, and the most productive soil in the country). I can confirm that ploughed fields generate VERY powerful thermals on a sunny, summer day!

  33. Interesting, there could be a ploughed field heat island effect. Wheat from Texas to Canada is harvested from June to July respectively, just as summer heat waves arrive.
    I wonder if this shows up in the temperature record via night time temperatures increasing more near cropland that is harvested early summer, i.e. wheat, versus rangeland and cropland that is harvested late summer, i.e. corn.

  34. Here in SE Missouri there is an interesting local phenomena associated with post-harvested wheat fields: It’s called the “Oopsy! grass fire!”. It’s simply amazing how many farm machines, tossed cigarettes, and lens-shaped pieces of broken glass “accidentally” light off the stubble, reduce it to carbon, and make it easier to plow under and return to the soil.
    I chuckle every time I see one. Like last week.

  35. Is the next step a campaign to ‘preserve the albedo’ by letting the stubble lay in the fields to nourish the weeds, and then to till only after first snowfall?

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