The Moveable “Desert Maker”

Phil GersmehlMichigan Geographic Alliance

pgersmehl@gmail.com

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

Teachers who saw this presentation at a workshopor downloaded it from our internet site have permission

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For permission for any other use, including posting frames on a personal blog

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contact pgersmehl@gmail.com