March 31st, 2014

Dust in the wind

At least we in the US don’t have to deal with this:

When soggy, green Northern Ireland gets coated by red, Saharan dust, the locals get slightly perturbed.

The dust is being pumped northward into the United Kingdom as winds aloft flow from the south to southeast instead of the normal west-to-east direction, says senior meteorologist Jon Erdman. An expansive blocking area of high pressure is stretching from eastern Europe to southern Greenland, and that’s working in tandem with a strong southward dip in the jet stream centered just west of the Iberian Peninsula.

As a result, northern Europe has turned hazy with Saharan dust filling the air in some areas, according to a BBC report.

And of course, that made me think of this:

I tend to think of northern Europe and the Sahara as very, very far apart. But Europe is smaller than one might think, and the Sahara bigger. Actually, the Sahara and Europe are roughly equal in size. And winds can take stuff like sanddust really really far.

Speaking of climate change, the Sahara is a fairly recent phenomenon, a desert formed in an area that was once a larger desert but then became wetter before it became drier again:

A timeline of Sahara occupation:

22,000 to 10,500 years ago: The Sahara was devoid of any human occupation outside the Nile Valley and extended 250 miles further south than it does today.

10,500 to 9,000 years ago: Monsoon rains begin sweeping into the Sahara, transforming the region into a habitable area swiftly settled by Nile Valley dwellers.

9,000 to 7,300 years ago: Continued rains, vegetation growth, and animal migrations lead to well established human settlements, including the introduction of domesticated livestock such as sheep and goats.

7,300 to 5,500 years ago: Retreating monsoonal rains initiate desiccation in the Egyptian Sahara, prompting humans to move to remaining habitable niches in Sudanese Sahara. The end of the rains and return of desert conditions throughout the Sahara after 5,500 coincides with population return to the Nile Valley and the beginning of pharaonic society.

Although mankind has had some influence on the desert, it seems minimal compared to the ebb and flow of rain there, which appears to be connected to completely non-human factors, some of them unknown. Humans have been the beneficiaries or victims of the changes, but not usually the instigators of them.

Here is some speculation about what drove those changes:

About 12,000 years ago, slight changes in the Earth’s orbit around the sun brought the northern hemisphere into the limelight. Summers became warmer as more solar radiation hit the lands north of the Equator. Solar ‘insolation’ levels were up to 8 percent higher than today.

With insolation driving monsoonal climates like a huge heat engine, rainfall increased. One climate model estimated that the 8 percent increase in radiation in North Africa resulted in a 40 percent increase in precipitation….

We know what caused the greening of the Sahara: a complex interaction between solar insolation, vegetation cover, and ocean temperatures.

What is even more interesting for today’s civilizations is the speed at which these changes occurred.

Peter deMenocal, an expert at Columbia University’s Lamont-Doherty Earth Observatory, argues that it started and ended very abruptly—within a few decades to centuries—triggered largely by summer insolation crossing the threshold of 470 Watts per meter squared, 4.2 percent higher than today.

He speculates that there could be an insolation tipping point “whereby subtropical African climate flips abruptly between humid and arid”.

However, other evidence suggests a more gradual transition. Layers of sediment drilled from the bottom of Lake Yoa in northeastern Chad hint that the environment changed in phases from trees and bushes to shrubs and grasses and finally to nothing but sand.

It’s hard to imagine the Sahara as anything but sand. But could global warming prompt another greening of the desert? Not likely. Solar insolation is still too low, the monsoon is shifting southwards, and vegetation cover is decreasing.

So: the change was enormous, probably relatively sudden, and had much much more to do with changes in the earth’s orbit than anything else. And it drives home how little we know about the complex interplay of factors that cause climate change, which has been occurring as long as the earth has been here.

17 Responses to “Dust in the wind”

  1. Gringo Says:

    Speaking of long distance weather effects, in 1998 smoke from the massive forest fires in Mexico’s Yucatan reached Texas, a thousand miles away. Definitely unusual to smell smoke and realize it traveled a thousand miles to your nose.

    It is my understanding that air pollution from China is crossing the Pacific.

  2. Sam L. Says:

    I wonder how our orbit could have changed. A change in our axial tilt does happen, and that’s more likely, as they say ” brought the northern hemisphere into the limelight. Summers became warmer as more solar radiation hit the lands north of the Equator.” This would also happen south of the Equator.

  3. John Says:

    Sam, the earth axis goes through a process called precession. It is like a spinning top that has a slow wobble to it. This cycle takes roughly 26,000 years to complete one wobble.

    The seasons on earth are not related to our distance from the sun, but rather the angle at which sunlight strikes the surface. The more indirect the angle the colder it is (winter) while the more direct angle leads to warmer weather (summer).

    Currently in our orbit, the earth is at its closest point to the sun (perigee) during the northern hemisphere winter, while we are at our farthest from the sun (apogee) during northern hemisphere winter.

    Due to precession, 13,000 years ago this was reversed. During that time frame the northern hemisphere was tilted towards the sun which leads to the increase in insolation.

    Our current precession, and orbital position is now heading back towards the cold side of things. The long term danger for humans is not warming, but cooling (on scales of several thousand years).

  4. John Says:


  5. John Says:

    Errr, edit above, Northern Hemisphere summer occurs at apogee.

  6. Geoffrey Britain Says:

    Ah Kansas, the antithesis of optimism or even forlorn hope. As for the song title, “Dust in the Wind” I guess the publicity department nixed the more accurate, “Life Sucks and Then, You Die”…

  7. parker Says:

    Short term weather patterns are a complex affair and although 10 day forecasts are more accurate today than just 10 years ago, it remains difficult to accurately predict weather patterns over a 3 month period. The predicting climate of the planet 50 or 100 years hence is far more complex than predicting weather patterns. This is why AGW computer models are largely garbage in garbage out. The known knowns are far out weighted by the unknown unknowns.

  8. J.J. Says:

    The climate history of the Sahara should serve as a cautionary tale to all AGW believers. Climate has changed in cycles throughout most of Earth’s history. Humans were no factor then, so why are humans a factor now?

    Use of fossil fuels with release of CO2 is a straw-man argument for which the evidence is thin to non-existent. Variations in axial tilt, continental drift, solar flare activity, volcanic eruptions, and (possibly) meteorite collisions with Earth have had far greater impact on climate than humankind’s puny effects. But those are things over which government has no control. However, prohibiting CO2 emissions is a dandy way for governments to control their citizens. They just can’t resist that urge to power.

  9. Mchenry bob Says:

    On a shorter time scale there was the Roman Warm Period, the Medieval Warm Period,and the Little Ice Age. A couple of historians have posited the reason the breadbasket of the Roman Empire (North Africa)is now a desert was the bad agricultural practices of Arabs and Islam. To what extent can forests perpetuate their own climate as opposed to goathherds? Then there’s Greenland.

  10. kcom Says:

    I used to live in West Africa below the Sahara and it was a yearly occurrence for the Harmattan winds to bring Saharan dust to our area. That was during the dry season. The rainy season, not so much.

    Recently in that area they’ve had an outbreak of Ebola. I guess it’s a good thing that Ebola can’t travel on dust particles.

  11. blert Says:

    The weight of the evidence points to the Earth being struck by a meteor.

    It hit in the high latitudes and shattered the North American glacial field.

    It was, in the manner of Shoemaker-Levy, a series of impacts, all into the ice, leaving us with a major shift in the Earth’s angular momentum — as these things go.

    Whence, the Great Lakes suddenly started draining to the east — whereas they’d been flowing south down to the Gulf.

    It caused the mega fauna to perish — poof.

    It caused the Solutreans to re-position down and away from Delaware and Maryland — really quickly.

    It caused a massive tsunami that took out Doggerland and split England from Northwest Europe — poof. The tsunami’s debris field is still to be seen all over the northern latitudes. (Shetland)

    The planet didn’t decide to just go off its axis because it had an itch.

    One of the (presumed) fragments is in a New Jersey museum — having been excavated in the 19th Century at great expense. They blew the dating. Radio isotopes were totally unknown. They took a stab at it via ice layers.

    Some compounded effects occurred: Norway sluffed off a massive hunk into the North Sea. That debris is still there — as is the blast debris kicked loose from New York and the Long Island moraine. (It used to run all the way through to New Jersey.)

    This super EOTWAWKI is the basis for the Biblical legacy of Noah. The planet was getting super flooded all over — in this case with tsunami effects far beyond the scale of Fukushima.

    The debris also includes micro blast fragments that blew up back and out — reaching all the way to New Mexico and Arizona.

    What started out as a total bummer — ended up being the beginning of a new age for Man. The high latitude hit triggered more extreme Summers and Winters — by just a tad.

    It as these longer Summers that suddenly really opened up the Bering land bridge. One needed the entire transit to occur at practical temperatures — and sufficiently long days. The Bering bridge didn’t really stay open as long as many think. The very events that made it really practical — caused the ocean to rise. This explains why the DNA for Asiatic Americans (the Red Man) is so tight — and why it connects by DNA drift back to the Old World so surprisingly recently.
    (more toward 9,000 ybp not 11,500 ybp.)

    The Bering bridge worked best in the generations just before it was flooded out. Until pretty late in the game, the total hazard of the transit was tremendous. Domesticated dogs made it — no horses, no camels, no cattle. The fact that horses did not reflux back into North America tells us that the transit was still a brutally cold one. Only cold adapted mammals made the trek. Everything points to a pretty tight corridor — that only seems wide from our far remove.

    (It was not enough that the ice and snow gave way, the underlying rocks had to be suitable for transit. Permafrost would ‘ve been a serious factor — no doubt. Consequently, one must expect that a fair amount of the transit occurred in canoes / rafts and other lash-ups. The dog could travel with us. No horse, camel or cow could endure the deep cold to get across a great lake of glacial melt.

    Some evidence of what they looked like can be observed in the Yukon and Klondike even today. Yeah, it’s brutal.

    From the Baltic to the Persian Gulf to the Black Sea, human habitations went under the waves. They are still awaiting science.

  12. Don Carlos Says:

    “Argues, speculates, suggests”….anything but facts.

  13. Philip Ngai Says:

    The important lesson here is that we don’t know what the future will bring. If we are a society with plenty of energy, we can tolerate a lot more disruption from events beyond our control than a society living on the edge. For example, California is currently suffering a drought. If we had plentiful nuclear power, we could make as much fresh water as we needed.

  14. J.J. Says:

    Philip Ngai: “If we are a society with plenty of energy, we can tolerate a lot more disruption from events beyond our control than a society living on the edge.”

    Yep, adaptation rather than mitigation is the way to go. And nuclear is one of the ways forward. Using nuclear for desalinization would be a benefit for California and other drought struck areas.

    Victor Davis Hanson has a great post up about
    the way California has caused much of their present problem by refusing to build more reservoirs that were once planned. That, and the decision to favor the Delta Smelt over the farmers of the Central Valley.

  15. Surellin Says:

    Hmmm, warmer temps and the Sahara becomes green. I almost wish AGW were true.

  16. Sgt. Mom Says:

    When I was stationed in Athens, Greece, in the early 1980s, it was common to have a slight rain shower bring down a good pasting of very fine Sahara dust with it – they called it a ‘mud rain’ – and it would leave a nasty splatter on cars, and an even nastier slick on the roads. It happened all the time. The very car-proud Greeks with a late-model auto would run out and wash/polish it off their cars at once. Street parking, of course.

  17. SteveH Says:

    The earth’s climate has always been in flux and will forever be. The only thing that makes this fact of nature suddenly alarming are modern narcissistic progressives, who are certain that human being’s and their lifestyle habits play a major role on such a grand scale.

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