Study of the past suggests Earth's rain belts may shift farther north

June 2, 2017 by Bob Yirka, Phys.org report
“No swimming” says the sign. This should not be a problem given that this lake in the Turfan Basin of far western China has dried up completely within the past decade as the planet has warmed and precipitation has shifted away from this region. Credit: Aaron E. Putnam.

(Phys.org)—A pair of researchers with the University of Maine and Columbia University has conducted a study of the past to make predictions about rainfall patterns in coming years. In their paper published in the journal Science Advances, Aaron Putnam and Wallace Broecker outline their study and offer three ways they believe planetary warming might influence the global distribution of rainfall.

As the planet heats up due to , it is logical to assume that there will be more —warmer air holds more moisture. But where will that moisture fall, and will some areas actually see less? That is what planetary scientists are trying to figure out. In this new effort, the research pair studied a period during which the planet was warming after a cool spell to learn more about future rainfall distribution.

One of the big factors impacting rainfall distribution, the pair note, is the fact that the Northern Hemisphere has a lot more than the Southern Hemisphere—more land mass means more heat, which means the Northern Hemisphere will almost certainly see more of rainfall than the Southern Hemisphere. To learn more about how it may all play out, the researchers looked at paleoclimate data from various parts of the planet, such as closed lake basins, stalagmites and ice core samples. They also looked at materials that have been carbon dated to assemble a picture of how and where changed during a time of similar warming approximately 14,600 years ago. That led them to conclude that three scenarios are likely.

The first is that will increase while subtropical areas will get less rain. The second is that it is likely that the planet's rain belts and dry zones will shift north. The third is that it is possible that the first two scenarios will occur at the same time. This all means that tropical areas will get more rain, while the fringes and middle latitudes will likely see less rain. That might mean stronger summer monsoons, they note, and dry places like the western United States and Mongolia getting even drier.

Shoreline of Mono Lake, California in 2013. Ancient shorelines etched into the eastern flank of the Sierra Nevada indicate that this lake stood at a much higher level at times when the climate was cooler. Climate-driven reorganizations of the world’s water system during ancient periods of warming starved this lake of moisture, causing the shoreline to drop. Now we are witnessing a similar phenomenon. Today, as the increase in fossil CO2 warms the Northern Hemisphere faster than the Southern Hemisphere, the moisture that normally feeds the Sierra Nevada is being routed farther to the north. As a consequence, the level of Mono Lake has dropped. Credit: Aaron E. Putnam.

Explore further: Reduced US air pollution will boost rainfall in Africa's Sahel, says study

More information: Human-induced changes in the distribution of rainfall, Science Advances  31 May 2017: Vol. 3, no. 5, e1600871, DOI: 10.1126/sciadv.1600871

Abstract
A likely consequence of global warming will be the redistribution of Earth's rain belts, affecting water availability for many of Earth's inhabitants. We consider three ways in which planetary warming might influence the global distribution of precipitation. The first possibility is that rainfall in the tropics will increase and that the subtropics and mid-latitudes will become more arid. A second possibility is that Earth's thermal equator, around which the planet's rain belts and dry zones are organized, will migrate northward. This northward shift will be a consequence of the Northern Hemisphere, with its large continental area, warming faster than the Southern Hemisphere, with its large oceanic area. A third possibility is that both of these scenarios will play out simultaneously. We review paleoclimate evidence suggesting that (i) the middle latitudes were wetter during the last glacial maximum, (ii) a northward shift of the thermal equator attended the abrupt Bølling-Allerød climatic transition ~14.6 thousand years ago, and (iii) a southward shift occurred during the more recent Little Ice Age. We also inspect trends in seasonal surface heating between the hemispheres over the past several decades. From these clues, we predict that there will be a seasonally dependent response in rainfall patterns to global warming. During boreal summer, in which the rate of recent warming has been relatively uniform between the hemispheres, wet areas will get wetter and dry regions will become drier. During boreal winter, rain belts and drylands will expand northward in response to differential heating between the hemispheres.

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richdiggins
1 / 5 (13) Jun 02, 2017
"We consider three ways in which planetary warming might influence the global distribution of precipitation."

Ok, we've studied our favorite three scenarios. Time to publish and go on vacation.

"The first is that tropical rainfall will increase while subtropical areas will get less rain. The second is [...] The third is [...].

The fourth possibility is that their assumptions are off base and their calculations are also off as a result.

However looking at fossil records and geological records ... disagrees with the first three possibilities and hints at other scenarios.

antialias_physorg
5 / 5 (12) Jun 02, 2017
However looking at fossil records and geological records ... disagrees with the first three possibilities and hints at other scenarios.

Since they base their research on the geological records - what the hell are you babbeling about?
kochevnik
1 / 5 (12) Jun 02, 2017
As the planet heats up due to greenhouse gas emissions,
Already debunked

Entire solar system heating up. Merkel should ban autos on Mars and Venus to balance the load and make her communist constituency happy
antialias_physorg
5 / 5 (10) Jun 02, 2017
Entire solar system heating up.

Source?
Benni
1 / 5 (8) Jun 02, 2017
this lake in the Turfan Basin of far western China has dried up completely within the past decade as the planet has warmed and precipitation has shifted away from this region


Look, the PLANET is not stupid. Mother Nature is a living being & is able to see into the future.

Ma Nature saw decades ago that Donald Trump would jerk US citizens out of overpaying their share of the Paris Accord & that this would lead to lower takehome paychecks for Climatologists, this of course caused such panic with the all knowing Ma Nature that lake levels dropped.
carbon_unit
3.5 / 5 (8) Jun 02, 2017
Entire solar system heating up.

Source?

The Sun. (DUH!)

(Sorry, I could not help myself...)
SamB
1 / 5 (9) Jun 02, 2017
Entire solar system heating up.

Source?


Here it is:
http://www.space....ing.html
howhot3
5 / 5 (9) Jun 02, 2017
Pretty lame reference there @SamB. Space.news seems to be some flake rightwing BS sight. Next you will be telling us that alien microbes are taking over republicans brains and making them leftist commies. Damn... could be. It's possible... certainly could be.

zz5555
5 / 5 (9) Jun 03, 2017
Pretty lame reference there @SamB. Space.news seems to be some flake rightwing BS sight.

It's a fake story. It quotes a Dr. Mike at Lockwood Rutherford Appleton National Laboratories, but as near as I can tell, there is no such place. There is, however, a Dr. Mike Lockwood at Rutherford Appleton Laboratory who showed that the sun couldn't be causing the current warming (http://news.bbc.c...0228.stm ). It looks like they just made up Dr. Mike to fool a few gullible people.
lupus
3.4 / 5 (5) Jun 03, 2017
It must be 15 years ago that I first read how the tropics would enlarge and the mid latitude rain bands would move towards the poles. The intervening 15 years has served to verify that prediction. Mid latitude drying is seen in N.America, China, Australia and S.Africa. All Putnam and Broecker seem to have done is confirm an old prediction which is obviously true. I guess prediction of the already obvious is the safe way to go.
Anyway, nuff said, I'm going to go out on a limb and predict Brexit.
SamB
1 / 5 (9) Jun 03, 2017
Pretty lame reference there @SamB. Space.news seems to be some flake rightwing BS sight. Next you will be telling us that alien microbes are taking over republicans brains and making them leftist commies. Damn... could be. It's possible... certainly could be.


Neat.. Don't like a source, just call it 'fake' news.
Sounds like a Donald Trump tatic...
TrollBane
4.5 / 5 (8) Jun 03, 2017
"Entire solar system heating up."

"Source?"

Lower posterior seems most likely.
zz5555
5 / 5 (7) Jun 03, 2017
Neat.. Don't like a source, just call it 'fake' news.
Sounds like a Donald Trump tatic...

And SamB doubles down on the gullibility. Seriously, this was trivial to show that it's fake. Do none of the science denying people ever check their sources? (In hindsight, the answer is probably obvious - they wouldn't deny science if they ever read any actual information on it.)
antigoracle
1 / 5 (8) Jun 03, 2017
...during a time of similar warming approximately 14,600 years ago.

Imagine that Chicken Littles, the sky did not fall.
The Sahara was green though.
EmceeSquared
4.4 / 5 (7) Jun 03, 2017
SamB:
http://www.space.news

SamB:
Neat


That source story is fake news. It cites 2 sources:
theeventchronicle.com which sources its story from "UFO Sightings Hotspot"
abovetopsecret.com which is well known as a lunatic conspiracy site.

Those are not reliable sources. Except for lunacy, studded with deliberate propaganda for the gullible (and their exploiters) to distribute.

It's widely documented that Russia has been creating fake news sites and armies of trolls that promote them to destabilize the West, undermine its communications, politics and decisionmaking. This is widely known.

SamB, either defend your use of these garbage sources or admit you're just a troll.
EmceeSquared
4.5 / 5 (8) Jun 03, 2017
antigoracle:
Imagine


Here we see the troll lazily blurting the favorite troll fallacy, a strawman. Nobody said the sky is falling, except the troll.

However, 14,600 years ago the Earth didn't feature a global civilization of over 6 billion people, many of whom are within one drought of starving or one meter elevation of drowning, and many of whom have nuclear weapons to use in a last desperate act.

Also , while 14,600 years ago is the closest era scientists can use as a model for ours in any detail, the rate we're changing the climate is far quicker than in that previous era. We're already extincting species at a far faster rate, and what we're doing to rainfall is even more extreme.

So the consequences are dire. The trolls don't care, so they post easily debunked garbage. Because their only objective is Fear, Uncertainty and Doubt.
KBK
1 / 5 (6) Jun 04, 2017
Entire solar system heating up.

Source?


Multiple.

Go look for it. Prove him wrong.

Good luck with that.
ka_
3 / 5 (2) Jun 04, 2017
Quote from article:
"One of the big factors impacting rainfall distribution, the pair note, is the fact that the Northern Hemisphere has a lot more land mass than the Southern Hemisphere—more land mass means more heat, which means the Northern Hemisphere will almost certainly see more of rainfall than the Southern Hemisphere."

This does sound somewhat odd. I do indeed understand it will be more rainfall closer to the north pole which would be cooler than the tropics, but is it anything preventing the hot air from staying in atmosphere until it gets to the cooler southern hemisphere?
ka_
3 / 5 (2) Jun 04, 2017
I might have realized my mistake myself:

Density of air... The air will probably get denser in the south and less dense in the north creating a new balance where most of the hot moist air remain in the northern hemisphere.

Am I on the right track?
ka_
3 / 5 (2) Jun 04, 2017
A question:
Does increased temperature in the at atmosphere result in less rain at daytime and more at nighttime in general? Or will we squarely assume more and thicker clouds which will cool down the temperature enough to make it rain despite the average temperature being higher?
Shootist
1 / 5 (6) Jun 04, 2017
The planet has been both warmer and colder than it is today and that within historic times.

The climate always changes.
Shootist
2 / 5 (4) Jun 04, 2017
I might have realized my mistake myself:

Density of air... The air will probably get denser in the south and less dense in the north creating a new balance where most of the hot moist air remain in the northern hemisphere.

Am I on the right track?


No, you're quacking at the wrong occluded front.
Captain Stumpy
5 / 5 (6) Jun 05, 2017
@shooty the illiterate idiot
The planet has been both warmer and colder than it is today and that within historic times
so, using your own logic and example, lets see how that works in reality:

people have always died
and no one lives forever,

therefore homicide is a good thing because the cops, scientists and all those "judgemental" people out there just don't understand about how reality and nature works
zz5555
5 / 5 (3) Jun 05, 2017
This does sound somewhat odd. I do indeed understand it will be more rainfall closer to the north pole which would be cooler than the tropics, but is it anything preventing the hot air from staying in atmosphere until it gets to the cooler southern hemisphere?

Sorry for the late reply but, yes, there is something preventing that. The atmosphere is made up of bands around the earth. When they talk about the rain belts moving north, they're talking about the hadley cell moving poleward (https://en.wikipe...ley_cell ). The hadley cell generates rain near the equator. The dry air then rises and moves poleward - that's why the arid regions are there. Between the north and south hemispheres, is the intertropical convergence zone, which makes it difficult for air to move between the hemispheres (though there is some exchange).
zz5555
5 / 5 (3) Jun 05, 2017
A question:
Does increased temperature in the at atmosphere result in less rain at daytime and more at nighttime in general? Or will we squarely assume more and thicker clouds which will cool down the temperature enough to make it rain despite the average temperature being higher?

I'm not aware of any change in the timing of rainfall, but I'm not an expert. As for the clouds, more clouds don't necessarily mean cooler temperatures. Clouds can cool or warm depending on where and when they occur. There was something called the Iris hypothesis that proposed that increasing clouds in the tropics would cool the earth and mitigate the current global warming. However, there's been enough data to show that's wrong. The cloud changes will either contribute to the warming or have a cooling effect that's too small to make any difference.

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