Study: Agricultural Irrigation Helps Shield the Tropics from Global Warming

Guest essay by Eric Worrall

According to a Swiss study, the Tropics are not warming as rapidly as expected because of large scale agricultural irrigation.

Irrigation helps beat the heat of global warming 

17 JANUARY 2020

Large-scale irrigation can help alleviate and even reverse hot extremes driven by human activity and other drivers of global warming, a new international study has found.

The research, led by ETH Zurich in Switzerland, showed that irrigation dampens and in some cases offsets the combined effects of global warming on hot days. 

The researchers compared the climate effects of irrigation with other natural and human drivers, including greenhouse gas emissions, across intensely irrigated areas in Southern Europe, North Africa, South Asia, and the United States.

Dr Annette Hirsch, from the ANU Research School of Earth Sciences, was part of the research team.

She said while not a “watershed”, the study showed that irrigation offered some hope when it came to dealing with more frequent and intense hot extremes caused by global warming. 

“There’s no doubt that as the planet warms, we will face even hotter extremes more frequently,” Dr Hirsch said. “Many studies show that under global warming, the chances of hot extremes across the planet are increasing.

“But what we found was that while global warming has increased the chances of hot extremes across the planet, in some regions expanding irrigation reduces that effect or can even reverse it.

“Our results show heat extremes are partly or completely offset by the cooling effects of irrigation.

“In this case, irrigation has the same effect for a hotter planet as pumping up the evaporative cooler in your house.”

Read more: https://www.anu.edu.au/news/all-news/irrigation-helps-beat-the-heat-of-global-warming

The abstract of the study;

Warming of hot extremes alleviated by expanding irrigation

Wim ThieryAuke J. VisserErich M. FischerMathias HauserAnnette L. HirschDavid M. LawrenceQuentin LejeuneEdouard L. Davin & Sonia I. Seneviratne 1269 Accesses93 AltmetricMetrics details

Abstract

Irrigation affects climate conditions – and especially hot extremes – in various regions across the globe. Yet how these climatic effects compare to other anthropogenic forcings is largely unknown. Here we provide observational and model evidence that expanding irrigation has dampened historical anthropogenic warming during hot days, with particularly strong effects over South Asia. We show that irrigation expansion can explain the negative correlation between global observed changes in daytime summer temperatures and present-day irrigation extent. While global warming increases the likelihood of hot extremes almost globally, irrigation can regionally cancel or even reverse the effects of all other forcings combined. Around one billion people (0.79–1.29) currently benefit from this dampened increase in hot extremes because irrigation massively expanded throughout the 20𝑡ℎthcentury. Our results therefore highlight that irrigation substantially reduced human exposure to warming of hot extremes but question whether this benefit will continue towards the future.

Read more: https://www.nature.com/articles/s41467-019-14075-4

If man made irrigation can have such a dampening impact on regional temperature, makes you wonder whether there might be an emergent form of natural irrigation which helps keep the tropics from overheating, by performing a similar temperature moderation role to agricultural irrigation.

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68 thoughts on “Study: Agricultural Irrigation Helps Shield the Tropics from Global Warming

  1. As Joe Bastardi says: “When you’re dry, you fry”.

    All this person who wrote this “paper” had to do was interview any one of a thousand meteorologists to figure out when the ground is wet, it takes longer to heat up than when it is dry. Something about evaporating water.

    • Besides drought and water shortage, it also increases humidity, rainfall and floods. It causes sea level to rise and ice to melt, except where it causes more ice.

      Plus more frequent and severe storms, plus less frequent and severe storms.

      And cooling as well as warming.

      • Great paper, it is clear Irrigation has added a lot of water vapor to the atmosphere that has warmed the planet and is the likely cause of a lot of the modern warming.

    • Global Warming is responsible for Donald Trump who is responsible for Global Warming. Dog meet tail.

      I swear that you can turn off you news channels for months and when you turn it back on the world is going to Sh!te because…breaking news about Global Warm…ahh we really meant Climate Change all along and Donald Trump.

      • I stumbled past the news on the TV the other day, you could summarize the news presented as:
        * Orange man bad!
        * Climate change! OMG we’re all going to die!

        It really doesn’t matter what day you watch the news or what news channel, it’s pretty much the same message now for a good few years.

  2. Wait, we can cool the earth simply by spreading some water out on it?
    If we stored water, and then spread it on farms, and golf courses, and even lawns,
    we’d be cooling the planet?
    Get outta here. That means that all a place like California would have to do is catch
    some of the snow melt in the spring…….

    You folks must be the embodiment of evil to suggest such a thing.

  3. What expectation is there that there will be more papers published explaining why warming is less than predicted around the world?

  4. As the earth warms or cools, equatorial locations remain at 23C throughout the millennia, while the gradient decreases in a warmer world. We need to give the government even more money to warm the Earth. The warmer the ice caps get, the better.

  5. Ha. A bloke called Bradfield came up with similar idea for Australia years ago. Divert the eastern coastal rivers inland, irrigate vast areas of desert and modify the climate. Of course his plan was dismissed then. Every so often someone brings it up again and it dismissed by experts again. Now we have some scientific backing for his ideas

  6. The cooling of the planet will be attributed to the success of the ‘Paris Agreement’. Then we can all relax.

  7. in reality, such a small percentage of the land area is irrigated, and for only a short time per growing season, that their hypothesis is only plausible sounding supposition.

    • It isn’t the actual water that does the cooling. It is the plant growth the irrigation allows that does the cooling. Look up the term “evapotranspiration”.

      It’s like Freeman Dyson said – you have to study the earth as a holistic entity. If you make your models dependent only on CO2 levels and leave out the cooling provided by the increased plant growth that the CO2 stimulates then you can never get the physics of the models correct.

  8. Well gee wiz. Climate Nazi discovered at long last the evaporative cooling properties of water vapor. Then the simpleton tries to coopt the effect for her own nefarious purposes.

    But wait a tick. What about the evaporative properties of CO2? Why are these not displayed, “discovered”, explored, or examined?

    Reality doesn’t support their agenda.

  9. “Donald Trump rejects environmental ‘prophets of doom’ in Davos address”

    https://www.sbs.com.au/news/donald-trump-rejects-environmental-prophets-of-doom-in-davos-address?fbclid=IwAR0gJI1IxiyOYuQpdgNxRws3ZvTPuguqCE3a4s8SZbEX4CddinzffAdcT8k

    “”We must reject the perennial prophets of doom and their predictions of the apocalypse,” Mr Trump said, hours after Ms Thunberg told the World Economic Forum that governments had done “basically nothing” to reverse climate change.”

    • Thanks for that link, Mark.

      We need to get a transcript of that speech. Trump said a lot of things of interest to WUWT. He used the term “alarmists” to describe people who have made dire predictions in the past about such things as overpopulation and how their predictions had failed.

  10. Once again it seems that water is much more ubiquitous in its’ ability to influence the environment than CO2 .
    Carbon Dioxide keeps getting burdened with blame by those who are bent on only seeing “hell-on-earth” scenarios in earths future while insisting that only people can be the sole cause behind the claimed “inevitability” that all are headed to a future climate furnace.

    How fortunate WUWT is to have free thinkers combing through and contributing to it such as Willis Eschenbach . It is clear to me that I much prefer the built-in wonder and curiosity that he often provides, (along with many others). The reported new research in the above article seems to be synergistic with Willis’ report, posted about two weeks back. Thanks again Willis. (Here’s the link to it for your convenience: https://wattsupwiththat.com/2020/01/07/drying-the-sky/ )

    Water is truly a wonder to behold.

    • Carbon dioxide influences the climate indirectly, just as water does, for without enough of it plants don’t grow, just the same as with water. The difference you’re mostly pointing out seems to be the direct influence, which is obviously high for water vapour but, as you realise, quite low for CO2.

  11. Here are the rules for policy-based science. Decide how all the others (not yourself) should live virtuous lives. Decide on the policy changes that will coerce those others into making those changes no matter how badly they erode the quality of life. Find scientists with a bare minimum of skills and no ethics who will produce “scientific findings” and especially catastrophic predictions that make the case for those desired policy changes. When the predictions all fail, instruct the “scientists” to make the case for how they were right all along by casting about for excuses. They need not consult the real world but simply build models. Fly off to some sunny location first class to receive humanitarian awards and to chat a how great you are for helping people live shorter more modest lives.

  12. Doesn’t more evaporation of water mean more Water Vapor – the Big Dog (95%) of green house gases? And isn’t the latent heat of evaporation still in the atmosphere until lost to space by complex means?

    • According to Climate Science, any water that evaporates as a result of Global Warming is lost forever. That settles it.

      • But the sea level is rising at a rate of about 1 Km per year, so that replaces the lost water. Doesn’t it?

  13. Irrigation cools the area locally but adds water vapor ( the 800 # Gorilla of Greenhouse Gases) to the atmosphere.
    I have not seen a study of how much water vapor man is adding and has that had an impact to the Global Temperature.

    • Given that the combustion of hydrocarbons ideally produces CO2 and H2O, then quite a lot of H2O would be added by burning hydrocarbons. Less so for coal as it is (ideally) pretty much all carbon, so would not produce any H2O. However, coal fired power plants (and any other steam based power plants that use cooling towers) would release a fair bit of water vapor through the cooling towers. Not sure of the actual numbers on that though.

      All of that water vapor would release energy as it cools and through the latent heat of condensation when it changes state. Effectively, the H2O would be transporting energy upwards to be released from the clouds. From there, it could go in any direction, some up and out, some down and some sideways.

      As noted by others D Boss’ link is an interesting read on this.

    • There is a complex dance that goes on with H20 in the atmosphere. Some processes do add water vapor to the atmosphere. How much of that becomes precipitation is dependent on a lot of things. The fact that precipitation occurs moves some of that H2O out of the atmosphere.Then there is the issue of how much does that increased water vapor cause more clouds? Increased water vapor doesn’t always result in increased cloudiness but still impacts energy flows.

      The vagaries of that complex dance are not handled very well by the current climate models if at all.

  14. anybody ever been to the Bellagio in Las Vegas

    a sprinkler system cools the outside near the swimming pool

    (at least it did when I was there a few years ago)

    • I experienced the same thing at an outdoor restaurant in Arizona. A very energy-efficient way of staying cool, compared with air conditioners – no need for a compressor to re-condense, no need for a radiator to dispose of the latent heat from re-condensation, no latent heat to increase the local UHI effect.

      Those who want us to reduce energy use should recommend water evaporation for those who live in hot, dry places. Not much use in Florida, where the humidity in summer is about 250%.

      IIRC the spray is so fine that the water droplets have completely evaporated before they fall on customers, but the cooled air sinks by gravity.

  15. From Willis’ article last week, whenever sea surface temperatures exceed about 26 C, evaporating sea water causes thunderstorms to form, which brings cooler air and water from above down to the surface. As long as most of the tropics are covered by water (as they are now), they have a built-in thermostat that keeps them from heating up very much. The Sahara Desert is an example of what can happen to a large land mass in the tropics far from any ocean.

    Man-made irrigation has been going on for over two millenia, from the Roman aqueducts transferring water from the Alps and Appenine mountains to the fertile but dry plains near the Mediterranean, and continuing wherever there is a natural hot, dry season and a wet season. It is not clear whether irrigation affected climate change, because there was the Roman Warm Period between about 100 BC and AD 400, and the climate cooled shortly after the fall of the Roman Empire, when their aqueducts fell into disuse. The climate re-warmed around AD 900 (Medieval Warm Period), but it is not clear whether irrigation increased at that time.

    Man-made irrigation can also change the vegetation in a localized area, which may affect the climate. A good example of this is the valley between the Great Salt Lake to the north and the freshwater Utah Lake to the south, squeezed between the Wasatch Mountains to the east and the Oquirrh Mountains to the west. Fresh water from Utah Lake naturally drains northward via the Jordan River into the Great Salt Lake, which has no outlet. When the Mormon settlers arrived in 1847, they found a dry and barren valley, with only grass and sagebrush growing, and the summers were extremely dry (they still are).

    The settlers built many canals leading from Utah Lake northeastward and northwestward across the valley, which tended to slow down the spring runoff from the mountains, and used the water for summer irrigation, which also tended to lower the water level in the Great Salt Lake, since evaporated water (which tended to accumulate as snow on mountains to the east) was not replenished. Many of the farms in the Salt Lake Valley have been replaced with suburbs over the past 30 years, but the developed land has many mature trees, which probably could not survive without irrigation, as well as green lawns which could not grow without being sprinkled in summer (any lawn where the sprinkler system is off quickly turns brown about mid-July).

    Growing trees and grass naturally transpire water vapor to the atmosphere. Is it possible that using spring runoff from the mountains to irrigate vegetation in the valley in the summer has increased summer humidity in the valley, and possibly increased summer rainfall?

  16. Well everyone knows – You sweat to keep cool. So does the Earth; but the scientists think otherwise and are desperately trying to convince us that they are right.
    You only have to ask: – If CO2 heats up the Earth, what is it that cools it? There must be something for there to be a balance. But nobody seems to be interested in answering that question.

    • EUREKA! That must be it! All the bedwetters sweating over “Global Warming” have actually cooled the planet! For god’s sake don’t tell Greta, we need to keep her followers in a high state of panic or we really will start to warm up!

      Now, where did I leave that /sarc tag?

  17. Here’s where I am curious.
    Increasing CO2 leads to better water use efficiency in plants. This should lead to more plants growing in arid and semi-arid regions. Plant growth also improves soil fixation and water retention in soil. The plants then transpire at a relatively fixed rate thereby releasing water back into the local environment where it can (in theory at least) precipitate and be used again. This happens in the Amazon. It seems that the current initiatives in Africa should allow a smaller amount of irrigation to fix soil and improve productivity over a pretty broad region of the Sahel, even in drier weather. However, the mere presence of the plants should improve rainfall allowing the Sahel to grow northward slowly turning the Sahara back into plains.
    Does anyone know of studies that examine the possibility and the possible timeframe?

  18. Well, after much massaging of data, lets quickly review the “Settled Science”.
    Since the end of the Little Ice Age, we have warmed 1.1°C.
    Half of that from Hydrofluorocarbons.
    Half from Irrigation
    Half from volcanoes
    Half from aerosols.
    All of it from Donald Trump
    And from Evil Capitalism
    And from Brexit.
    And mostly from racist White Men, especially old ones.
    All settled science.
    97% of all Scientists agree.
    “How Dare Y’all?”

    Not sure what is left for a trace gas essential to all life on Earth…

  19. It seems the climate charlatans are realizing that we are entering a cooling period and since they can’t back off with the CO2 fraud, they invent new fairy tails to circumvent the inconvenient truth that CO2 has rather nothing to do with climate.

    I expect more and more sharticles explaining that through magical actions, like the fake fight against the ozone depletion, or in this case, the irrigation cooling effect on the tropics, and so on, we reversed the climate trend despite the evil CO2 growing emissions.

    One thing is certain, the climate clown show is not about to stop.

  20. ♦ Water vapour warms the earth by the greenhouse effect.
    ♦ Water cools the surface by evaporation.
    ♦ Water vapour cools the earth by condensing to form clouds that reflect incoming solar radiation.
    ♦ Condensation of water vapour transfers heat it removed from the surface, back into the atmosphere at various levels, where more of it radiates to space than would have at surface.
    ♦ Water’s very high latent heat of evaporation compared with other liquids makes this heat transfer mechanism much more efficient.
    ♦ Ocean currents move heat from the tropics towards the Arctic.
    ♦ Other ocean currents prevent heat from the tropics from being transferred to the Antarctic.
    ♦ Ice floats on water – if it was denser than water, the Arctic Ocean would be frozen to the seabed and there would be no habitat for fish, seals and polar bears. No other liquid has this property,

    It’s all about water. Water and adiabatic expansion. CO2 has a greenhouse effect, but it’s a drop in the bucket (so to speak)

  21. “In this case, irrigation has the same effect for a hotter planet as pumping up the evaporative cooler in your house.”

    Evaporative coolers work very poorly in high humidity regions.
    Which tropics lack high humidity?

    Just how do they reach this absurd conclusion?

    “Here we provide observational and model evidence that expanding irrigation”

    Simple, they programmed it into their models.
    It’s called confirmation bias.

  22. What a strange article.

    I would expect that irrigation at large scale in warmer climates (where they need to irrigate) would cause HIGHER temperatures not lower. Is directly related to population growth, because all people need to eat annd hence argicultural production has risen a lot over the last 70 years or so.

    They say that CO2 has a longer residence time (stays longer in the atmosphere), but really all that matters is production vs consumption.

    Irrigation causes additional water vapour in the air. See Kansas or India for example. In Russia, they irrigated so much that an entire sea ran dry. In other places, mighty rivers became small streams, unless it happened to rain out again in the same area (as in India: it rains out on their side of the Himalayas).
    And yes the humidity does and can increase without any help from (say) CO2.
    Water vapour is a much more powerful GHG than CO2.

    Of course, this is ‘merely’ during growing seasons (2x per year I think in Kansas, hence a large part of the year), and the effect is ‘regional’, although the same happens over very large stretches of land in a lot of places (not always on such a massive scale as (say) in Kansas, Russia, India, China or Indonesia).
    And the effect is not small. Check out some estimates from studies in Kansas (close to 10% higher humidity or similar) or the effect to the regional climate in (say) India.

    • I’m not sure why you think the relative humidity in Kansas is high. The average daily humidity for the year runs between the low 60%’s and the high 60%’s. That’s actually pretty temperate when compared to places like Florida!

      Irrigation results in more greening of the land. Plant evapotranspiration is a big contributor to cooling the local atmosphere.

      This is all stuff that the climate models don’t consider. It’s probably why average maximum temperatures across the central plains of the US are actually going down, not up as global warming predicts.

      The environment of this earth is far more complicated than the climate models allow for. It’s why I don’t trust them.

  23. If it cools the tropics, then it cools the polar regions because that’s where their heat comes from!!! Come on Swiss guys, your better 5han this.

  24. The Warmistas are desperate to explain away every part of the mountain of evidence that the CO2 Global Warming story is false. Here, in this case, irrigation is their chosen shield. All the ‘climate models’ fail to deal with clouds and other violent motions in the atmosphere. Irrigation is just another of the thousand factors that the models ignore. Willis drew attention to the many emergent forms of natural climate control that keep the World’s weather remarkably stable. Clouds keep the tropics from overheating, As Willis has said, it is remarkable that the Earth’s climate is so stable not that it is so changeable.

  25. Water vapor is a greenhouse gas, greenhouse gases cause global warming.
    Global warming is not”hotter” days. Global warming is an increase in global average temperature. Global warming is NOT more hot days, instead it’s the increase of yearly average daytime and night time temperatures.

    The global average temperature is about 15 C. The average temperature of the tropics is about 26 C. The tropics has the majority of water vapor of the world.
    Global warming is largely about increasing the average temperature nearer the polar regions.
    Canada has average yearly average temperature of about -4 C if Canada average temperature increase to 0 C, that would indicate a large increase in global temperatures. Canada has increased it average temperature from around -6 to -5 C over the last 100 years, and that indicates global warming. If Canada average temperature were to become -7 C or colder, that indicate we might be entering a glacial period, or that is global cooling.

    The hottest days are in deserts {not much water vapor] and the hottest day ever recorded was “on 10 July 1913 in Furnace Creek (Greenland Ranch), California, United States” which is a desert, and it was 56.7 °C (134.1 °F).
    Or we have not had hotter daytime temperature in last 100 years. Which also expected, if one has global warming. Global warming is not hotter days, but it is warmer nights {and warmer winters}

    Or increased CO2 levels are suppose to increase global water vapor, if CO2 don’t do this, then there will very little increase in global temperature from any higher CO2 levels. This also the case with any other greenhouse gas {such as methane}.

    • “Global warming is not hotter days, but it is warmer nights {and warmer winters}”

      So we will use less fuel to keep us warm, and thus produce less CO2, which will stop Global Warming.
      The problem is self-correcting!

  26. “might be an emergent form of natural irrigation which helps keep the tropics from overheating, by performing a similar temperature moderation role” I contend that nature has its own means of balancing these things out to avoid extremes.

  27. “makes you wonder whether there might be an emergent form of natural irrigation which helps keep the tropics from overheating”

    I will take what is a thunderstorm for $500.

  28. In the tropics more humidity jacks up the ‘feels-like’ temperature, so there’s no effective reduction in heat-stress due to increased moisture levels at lower surface temperatures. What does cool things down is liquid rain evaporating plus transpiration, but increased humidity in the air alone is much more unpleasant than drier air at significantly higher temperature. What higher humidity means to me in the tropics is the weather is more unpleasant more often, except for the times where it rains, and for the day after that, but beyond that it’s unpleasantness and heat-stress effects are being enhanced once again, because the temperature is actually scarcely any lower, when UHI is part of the mix.

  29. This study does not tell even layman meteorologists anything they did not already know.

    The tropics cannot heat up much unless you remove the water vapour from the tropical atmosphere, which acts as a huge temperature regulator.

    Not that people living in, or visiting, don’t think the tropics are incredibly hot when the humidity is 95% on a 34 deg C day.

  30. Check out fig.2 in the original Swiss publication: on those world maps India has the biggest “man made” cooling due to agricultural irrigation.
    Cool!

  31. Without carbon dioxide in the atmosphere, the Earth’s climate would change markedly, because plant growth stops. Given our relative drought of atmospheric carbon dioxide, I see no reason why we should not champion the work that CO2 does on the climate front.

    The real work, that is, rather than the imagined destruction that comes from fossil fuel use.

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