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1. What makes deserts? A typical climate map has a lot of info. It’s almost impossible to remember.
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The Moveable “Desert Maker”
Phil GersmehlMichigan Geographic Alliance
Climate Changein
History
To understand the role of climate change in history, students should be aware of three things:
1. the system that makes tropical deserts,
2. the systems that cause natural climate cycles,
3. the difference between weather and climate.
1. What makes deserts?A typical climate map has a lot of info.It’s almost impossible to remember.
Let’s “declutter” and focus.“Describe the pattern of dry climates.”
Q. What causes tropical deserts?
A. Rain near the equator.
This globe is turnedso the equator is up.
Sun-heated air rises and makes rainover the equator . . .
AND
it has to come down
somewhere.
Given the earth’s size, 24-hour rotation, distance from sun, etc.“down” is 20-25 degrees of latitude from where it went up.
And where the air comes down, it makes a desert.
Given the earth’s size, 24-hour rotation, distance from sun, etc.“down” is 20-25 degrees of latitude from where it went up.
And where the air comes down, it makes a desert.
Given the earth’s size, 24-hour rotation, distance from sun, etc.“down” is 20-25 degrees of latitude from where it went up.
How would you describe the geographic pattern of deserts?How would you describe the geographic pattern of deserts?“Start 1000 miles west of each continent on the Tropic line.
Spread to about 20 latitude degrees; stop at the mountains.”
“Rainshadow” desertseast of the mountains
in the westerly wind area
How does this relate to history(and our GLCEs)?
This is a simple graph of temperature thru time.
Agriculturestarts
Irrigationstarts
South Asiaflourishes
Anatolia(Turkey) is rainy Greece
is rainy
Rome expandsinto Europe
Barbariansinvade Rome, Han dynasty
collapses
Vikings, Mongols
Mingdynastycollapses
Hunters thrive
To remember these facts,put them on a world map of deserts.
Remember, Tropical deserts formwhere air that rose up at the equator
is pushed back down.
This downward air movement(called the Subsidence)
will be farther from the equatorif warmer air makes
stronger storms near the Equator.
This downward air movement(called the Subsidence)
will be farther from the equatorif warmer air makes
stronger storms near the Equator.
The science is not“easily accessible”
to ordinary citizens.
It does, however, makesome specific predictions.
When the global average temperature is HIGH,the “desert-maker” is pushed away from the equator.
Which places are likely to be helped?
? ????
When the global average temperature is HIGH,the “desert-maker” is pushed away from the equator.
Which places are likely to be helped?
Plus some large northern areas that might get warm enough for farming.
When the global average temperature is HIGH,the “desert-maker” is pushed away from the equator.
Which places are likely to be hurt?
When the global average temperature is LOW,the “desert-maker” shifts toward the equator.
Which places are likely to be helped?
When the global average temperature is LOW,the “desert-maker” shifts toward the equator.
Which places are likely to be hurt?
When the global average temperature is LOW,the “desert-maker” shifts toward the equator.
Which places are likely to be hurt?
Plus some large areas that still have plenty of rain but are colder.
Agriculturestarts
Irrigationneeded
South Asiaflourishes
Anatoliais rainy Greece
is rainy
Rome expandsinto Europe
Barbariansinvade Rome, Han dynasty
collapses
Vikings, Mongols
Mingdynastycollapses
Hunters thrive That’s the science
behind a simple fact:
Climate changes hada big impact on history.
Global warming is bad for some places and good for others.
Whatabout
today?
The name is covered, becausethis is about ideas, not personalities
Here’s why there are “natural” cycles of climate:Earth’s orbit is not a perfect circle.It’s a wobbly tilt on a wobbly oval.
You can find the details on a lot of web sites:
www.ncdc.noaa.gov/paleo/ctl/clisci100ka.html
almost 6 peaks in 500,000 years =1 cycle in roughly
90,000 years.
Wobble #1. From a circle (r = 93 million miles)to an ellipse (r = 90 to 95Mmi, in different seasons)
about 13 peaks in 500,000 years =1 cycle in roughly
41,000 years.
Wobble #2. From a tilt of about 22.3 degrees to a tilt of nearly 24.5 degrees.
about 23 peaks in 500,000 years =1 cycle in roughly
21,000 years.
Wobble #3. From the sun being closer in July to being closer in January.
A high pointin solar radiation
comes roughly once every 100,000 years.
Put this all together – sun intensity varies a lot.
We also have450,000 years oftemperature data
from ice coresin Antarctica.
A high pointin temperature
roughly once every100,000 years.
The record ofcarbon dioxideshow the same
five peaks.
S U N S H I N E
C A R B O N D I O X I D E
T E M P E R A T U R E
Let’s look atthree graphs
together,to see how
they compare.
Solar energy,temperature, and
carbon dioxide are obviously related(but it’s complicated).
Temperature and carbon dioxideare related, andone conclusion
is beyond doubt:
temperatureshave been higher
in the pastthan they are
today.
Temperatures were much higherin the distant past
and a little higherquite recently.
PRESENTAVERAGE
BUT, there is a
big problemwith these graphs.
The most recentmeasurements
do not fiton the scale.
When we adjustthe vertical scaleso the numbers
all can fit,
you can see thatcarbon dioxide is
WAY above its “normal” range.
In justa few hundred years,
humans have “pushed”the climate system
way out of linewith “normal” cycles.
In 2015, 402
In October 2013,
the Pacific Ocean hadvery high temperatures. One result was
one of the strongesthurricanes ever measured
near the Philippines.
Weeks later,this hurricane carriedenormous amounts
of energy northward.
Excessive heatmoving toward the pole
can push cold airtoward the equator
Excessive heatmoving toward the pole
This map shows world temperature two months later.Winter 2014 was unusually cold in Michigan,
BUT look at the average for the globe as a whole.
5 areas “much cooler than average” 0 areas “record coldest”
19 areas “much warmer than average” 9 areas “record warmest”
And if you look at the total for the entire year,the imbalance becomes even more obvious.
15 7422 196
As one Blogger asked:
Can global warmingbe real
if it is unusually cold in the United States?
As one Blogger asked:
Can global warmingbe real
if it is unusually cold in the United States?
Eh
Si
Ja
NdiyoHaa’n
Oui
Na’am
Hai
OoSim
Da
Evet
Tak
Aye
Ya
Ee
HanAapHwa’a
‘Ae
To
Shi
AeChaiTamo
Yin
A
EniE
IaDiSi
Ngee Yao
Interesting fact: these researcherscome from universities and government labs in Australia, Argentina, Canada, China, England, Germany, Israel, Italy, Korea, and South Africa,
as well as NCAR, NOAA, and 3 U.S. universities.
Copyright 2015, Phil Gersmehl
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