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 Thiery, Auke J. Visser, Erich M. Fischer, Mathias Hauser, Annette L. Hirsch, David M. Lawrence, Quentin Lejeune, Edouard 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.
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.
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.
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.
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!
“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.
“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.
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.
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.
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!
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.