April 09, 2015

Human Alteration of Climate: What the Media Rarely Talks About

Have humans already changed the climate of our planet?

The answer is emphatically yes.   

The media talks about this issue all the time, but they almost entirely talk about the impacts of greenhouse gases such as CO2.   

But there is far more human-induced climate change than that, and these changes are ones that folks from all political leanings can agree upon.   And the magnitude of such changes may surprise you.

Cooling Due to Irrigation

Large areas of the earth's surface are being irrigated for agriculture.   Such irrigation inevitably causes substantial surface cooling, particularly in summer, due to evaporation from the wet ground and from plants.  During the day, a substantial proportion of the sun's rays reaching the surface are used to evaporate water.

Want some examples?  Consider the HUGE irrigated region of the Central Valley of California (a semi-arid region), which is obvious from the green coloring in this satellite image.

Of the large irrigated areas of eastern Washington.

But why stop there?   There are huge swaths of land around the world that are being irrigated (see map)

Irrigation can cool the land surface down several degrees centigrade (2-5F) during the day.   We have even tried turning eastern Washington back to desert in our local weather simulations and the result was substantial warming for the irrigated regions (3-5F).  There have been a number of studies of the effects of irrigation on surface temperature, with several of them noting the the irrigation cooling counterbalanced greenhouse warming in places like the Central Valley of CA (e.g., reference).

Heat Island Effects in Urban Areas

There has been substantial warming in our urban areas, particularly at night.  This is often called the urban heat island effect.   First, urban areas are not as moist, thus  there is less evaporation during the day.   Concrete, stone, and asphalt absorb, store, and release solar warmth.   Combustion for heating and transportation release lots of heat.  The result?  Urban areas can be 2-10F warmer than nearby rural regions.

Here is documentation of the heat island for the minimum temperatures around London for mid-May of one year.  5C or 9F warmer in the central city.    Seattle also has a heat island, with the warmest temperatures often around Boeing Field.  One time I drove around central Puget Sound with thermometers (helped by lots of students)....it was 15F cooler in Woodinville than downtown Seattle.

The climates of major cities throughout the world have been substantially warmed by such urbanization at the surface;  this effect is as large as that produced by human greenhouse gas emission and in the same direction....warming.

Changes in Clouds

The cloud distributions on our planet have been substantially modified by our species.   For example, over the Pacific (and other locations with low stratus/stratocumulus clouds) one frequently sees strange cloud lines, often called ship tracks.  Here is an example:

These ship tracks are caused by combustion products from ship acting as cloud condensation nuclei, increasing the number of cloud droplets, and thus producing whiter clouds.

And then there are contrails, the lines of high clouds behind high flying aircraft.   There are a LOT of contrails and they have substantially changed the climatology of upper level cloudiness around our planet.  Here is an example from the surface:

And another from space.

These are only a few examples of high mankind is changing the climate of our planet, and I am not even breaking a sweat---there are many more.   Greenhouse gas emissions are important, but we are doing a lot more to the climate of the planet that rarely gets on the media radar screen.


  1. So I guess my childhood notion that air planes made clouds (contrails) was not far wrong.

    Hee hee a thinker ahead of her time.

  2. I know some folks that claim there is no natural weather anymore. It is all controlled by "them". Now I see where they get it from but of course their is no grand conspiracy.

  3. How does the total area compare to warming that could come from diking and flood control. Extensive flood plains used to serve as evaporative cooling basins, but are now drained. The central valley of CA is a good example. At some times of the year, it would have been quite wet naturally, but how would that compare to total area irrigated? A pulse of large scale evaporative cooling through natural spring flood cycles, vs. having the "drip" on all summer through irrigation

  4. Let's not omit, "Deforestation". It has had a regional climatic impact. Especially in Pakistan, the Middle East and North Africa where once forested lands are now desert (too much CCN)

    Two hundred and fifty million years ago, primitive plant life from the carboniferous period altered our atmosphere (O2 and CO2) giving rise to land animals and sequestering carbon as coal, gas, oil and limestone.

    Anthropomorphic CO2 like the tree mosses of the carboniferous period has the ability to alter climate on a global scale.

  5. Just curious:
    You mentioned the Central Valley of CA. That area I believe was opened up from damming the rivers that feed into what would naturally be a gigantic lake.
    What would be the difference between the now heavily irrigated terrain and the body of water the proceeded it as far as how it effects the climate?

    1. The area was prone to flooding before the dams. But, was not recently a large lake. The LA basin was also prone to flooding during El Nino events with cut-off lows before the concrete river drainages were out in. But, neither of these basins was recently a lake.

  6. When I lived in Wisconsin we blamed the corn transpiring in Iowa for increasing the humidity in the summer. I live in Georgia now and the humidity up north on those really hot summer days was worse than anything I've experienced down south, even though I had air conditioning both places. So the crops we plant are also making a difference.

  7. And some people want to put sulfuric acid in the stratosphere.

    I love azure-blue sky and clear air. These can still be seen in the mountains at times. But I want to say again- we should NOT put sulfates (or anything else) in the stratosphere. There's too much meddling already.

    1. Sulfur dioxide, not sulfuric acid. In theory, it would not cause acid rain if injected at high altitude. Definitely a last resort, I would hope.

  8. I agree that irrigation can cause cooling, but I wonder if there is a full accounting. Central California was considered marshland in the late 1800s. Over 50% of the wetlands have been lost. Lake Winnemucca in Nevada or Owens Lake have been drained.

    Does added water from irrigation outweigh the loss of wetlands? Also the cooling of irrigation is seasonal versus the annual cooling natural wetlands.

  9. I sent an email to your environmental reporter
    this morning about her using the slur
    " Climate Denier " about you yesterday on air.
    I don't even know all your views on this as
    I am a new listener having recently moved to
    WA..but the slur was uncalled for. There are
    no ' settled ' arguments on the climate as
    you even illustrate here. Miss Pailthorp owes
    you an apology.

  10. Hi Jake and Scooter,
    I studied meteorology in the mid-1970s in Greeley, Colorado. The farmlands around Greeley converted from potatoes to irrigated corn fields to support the Monfort feed lots. The normal annual rainfall (30 year average)increased from 11.5 to 12.5. My meteorology professor believed the increased rainfall was due to widespread irrigation fueling summer thunderstorms. I don't recall any temperature change. Caveat: the 30 year average for the 1970's excludes the dust bowl years of the 1930's.


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