Climate Change

[Batalov]

Originally Posted by ewmayer

...the area in which I grew up, Akron OH. ...

Ah, must have gone to high school with Jim Jarmusch? ;-)

[ewmayer]

Meanwhile, in my current home state:

Hundred Years of Dry: How California’s Drought Could Get Much, Much Worse: Scientists fear California's long-ago era of mega-droughts could be back

Californians need to be ready, because if some scientists are right, this drought could be worse than anything the state has experienced in centuries. B. Lynn Ingram, a paleoclimatologist at the University of California, Berkeley, has looked at rings of old trees in the state, which helps scientists gauge precipitation levels going back hundreds of years. (Wide tree rings indicate years of substantial growth and therefore healthy rainfall, while narrow rings indicate years of little growth and very dry weather.) She believes that California hasn’t been this dry since 1580, around the time the English privateer Sir Francis Drake first visited the state’s coast:

If you go back thousands of years, you see that droughts can go on for years if not decades, and there were some dry periods that lasted over a century, like during the Medieval period and the middle Holocene [the current geological epoch, which began about 11,000 years ago]. The 20th century was unusually mild here, in the sense that the droughts weren’t as severe as in the past. It was a wetter century, and a lot of our development has been based on that.

Ingram is referring to paleoclimatic evidence that California, and much of the American Southwest, has a history of mega-droughts that could last for decades and even centuries. Scientists like Richard Seager of Columbia University’s Lamont-Dohery Earth Observatory have used tree-ring data to show that the Plains and the Southwest experienced multi-decadal droughts between 800 A.D. and 1500 A.D.

The apparently mega-drought-induced demise of the Anasazi Chaco Canyon culture is one of the examples detailed in Jared Diamond's Collapse.

[LaurV]

Originally Posted by ewmayer

Meanwhile, in my current home state:

Hundred Years of Dry: How California’s Drought Could Get Much, Much Worse: Scientists fear California's long-ago era of mega-droughts could be back

The apparently mega-drought-induced demise of the Anasazi Chaco Canyon culture is one of the examples detailed in Jared Diamond's Collapse.

Paraphrasing Putin (the fact that global warming would be very good for Russia, because will result in better living conditions and more farming land in Siberia), I would ask if this drought would bring some prosperity to Sahara?

[fivemack]

I don't know whether the correlations are even known. The Sahara is supposedly responsible for the Amazon rain forest (because nutrient-bearing dust gets blown across the Atlantic), but the Pacific is a lot wider and the American deserts a lot smaller.

California is rich enough to use desalination to water its people, but losing the agriculture in the Central Valley would be sad. However, it looks as if there's non-trivial drought over into the Great Plains and the mid-west, and losing the agricultural surpluses from there would be significantly bad for inhabitants of the planet as a whole - the US exports twenty-seven megatons of wheat a year, enough to feed a half-billion people.

[LaurV]

The correlations are "well known" - I tried to keep myself educated in this domain, hehe, for example, since I found out that the huge part of the Asian deserts are due to the Himalayan chain (which stops the clouds on its eastern side, the clouds can't fly so high to pass over the mountain) my biggest dream is to buy a lot of very cheap desert land in the Gobi or Tibet, and then drill a tunnel through the Himalaya to bring moisture...

On the other hand, the part with US keeping the whole planet off dieing from thirst was unknown here, but it is somehow expected to be true, now, after you said it. US is still a big and sound economy (large part of my money are in US dollars right now!) despite of what other people say, or what fun I make about it, here or there.

On the other other hand, the story with the Saharan sand flying to Amazon, if true, can't explain why the water in the equatorial Atlantic is scarcer in nutrients compared with the tropical (north and south) water there (remember: the biggest fishing banks in Atlantic - the fish grow where smaller fish grow, which in turn grow where the plancton grow, etc... - are not at the equator, but at the tropical African shore, for example).

[ewmayer]

Mod. Note: I would like to move t his thread to the Science subforum where it belongs (political ramifications of GW notwithstanding) - any objections?

[kladner]

Originally Posted by ewmayer

Mod. Note: I would like to move t his thread to the Science subforum where it belongs (political ramifications of GW notwithstanding) - any objections?

None here, but I am not one of the heavy posters.

However, it looks as if there's non-trivial drought over into the Great Plains and the mid-west, and losing the agricultural surpluses from there would be significantly bad for inhabitants of the planet as a whole - the US exports twenty-seven megatons of wheat a year, enough to feed a half-billion people.

Maybe we need to cut back on the acreage devoted to animal feed. Please note that I say this from the standpoint of an omnivore. However, eating less meat would be good for me, so higher meat prices would not be a total negative.

EDIT: Obviously, though, the drought scenario would have serious repercussions for all foods, animal or vegetable.

[ewmayer]

Originally Posted by LaurV

The correlations are "well known" - I tried to keep myself educated in this domain, hehe, for example, since I found out that the huge part of the Asian deserts are due to the Himalayan chain (which stops the clouds on its eastern side, the clouds can't fly so high to pass over the mountain)

Here some links: Wikipedia indicates the Himalayas have had their predominant effect on the north-south monsoonal dynamics in central Asia:

The Himalayas have a profound effect on the climate of the Indian subcontinent and the Tibetan plateau. They prevent frigid, dry Arctic winds blowing south into the subcontinent, which keeps South Asia much warmer than corresponding temperate regions in the other continents. It also forms a barrier for the monsoon winds, keeping them from traveling northwards, and causing heavy rainfall in the Terai region. The Himalayas are also believed to play an important part in the formation of Central Asian deserts, such as the Taklamakan and Gobi.[22]

With respect to the Sahara, Wikipedia indicates the 41-kyr earth-tilt variation cycle as the major culprit, at least in the more recent (order of 1 Myr, compared to 10s of Myrs for the Himalayan uplift) period marked by quasiperiodic waxing and waning of ice ages. This says the monsoons in that region were actually locally induced by large air masses heated over N Africa:

The climate of the Sahara has undergone enormous variations between wet and dry over the last few hundred thousand years.[15] This is due to a 41000 year cycle in which the tilt of the earth changes between 22° and 24.5°.[16] At present (2000 AD), we are in a dry period, but it is expected that the Sahara will become green again in 15000 years (17000 AD).

During the last glacial period, the Sahara was even bigger than it is today, extending south beyond its current boundaries.[17] The end of the glacial period brought more rain to the Sahara, from about 8000 BC to 6000 BC, perhaps because of low pressure areas over the collapsing ice sheets to the north.[18]

Once the ice sheets were gone, the northern Sahara dried out. In the southern Sahara though, the drying trend was soon counteracted by the monsoon, which brought rain further north than it does today. In this period, there was still a monsoon climate in the Sahara. Monsoons form by heating of air over the land during summer. The hot air rises and pulls in cool, wet air from the ocean, which causes rain. Thus, though it seems counterintuitive, the Sahara was wetter when it received more insolation in the summer. This was caused by a stronger tilt in Earth's axis of orbit than today (24.5 degree tilt vs the 23.4° tilt today[16]), and perihelion occurred at the end of July around 7000 BC.[19]

By around 4200 BC, the monsoon retreated south to approximately where it is today,[9] leading to the gradual desertification of the Sahara.[20] The Sahara is now as dry as it was about 13,000 years ago.[15] These conditions are responsible for what has been called the Sahara pump theory.

[cheesehead]

"Global Warming Science Is Not Overheated"
http://www.thestreet.com/story/12438...verheated.html

[chappy]

Moderately NSFW (It's not TV it's HBO)

[Xyzzy]

http://www.miamiherald.com/2014/06/0...ism-could.html