1. The “Desert Maker” - Climate Changes in History Phil Gersmehl Michigan Geographic Alliance pgersmehl@gmail.com

2. To understand how climate could play an important role in history, students should be aware of three things: 1. the system that makes tropical deserts, 2. the system that causes natural climate cycles, 3. the difference between weather and climate.

3. 1. What makes deserts? Typical textbook maps have a lot of info. Fun to look at, almost impossible to remember.

4. Let’s remove the clutter and focus. “Describe the pattern of dry climates.”

5. The cause of tropical deserts is rain near the equator. Sun-heated air rises and makes rain over the equator... AND it has to come down somewhere.

6. With the earth’s size, rotation speed, distance from sun, etc. “down” is about 25 degrees of latitude from where it went up.

7. And where the air comes down, it makes a desert. With the earth’s size, rotation speed, distance from sun, etc. “down” is about 25 degrees of latitude from where it went up. How would you describe the geographic pattern of deserts? “Start 1000 miles west of each continent on the Tropic line. Fan out to about 20 latitude degrees by the time you hit land.”

8. How does this relate to history?

9. This is a simple version of the temperature graph. Agriculture starts Irrigation needed South Asia flourishes Anatolia is rainy Greece is rainy Rome expands into Europe Barbarians invade Rome, Han dynasty collapses Vikings, Mongols Ming dynasty collapses Hunters thrive Upland farmers do well

10. To help us remember these facts, let’s put them on a world map of deserts. Remember, the great Tropical deserts form where air that rose up at the equator is pushed back down toward the surface This downward air movement (called the Subsidence) will be farther from the equator if warmer ground pushes air more strongly upward near the Equator.

11. When the global average temperature is HIGH, the “desert-maker” shifts toward the poles. Which places are likely to be hurt ?

12. When the global average temperature is HIGH, the “desert-maker” shifts toward the poles. Which places are likely to be helped ? ? ?

13. When the global average temperature is HIGH, the “desert-maker” shifts toward the poles. Which places are likely to be helped ? Plus some large cold areas that might get warm enough for farming.

14. When the global average temperature is LOW, the “desert-maker” shifts toward the equator. Which places are likely to be helped ?

15. When the global average temperature is LOW, the “desert-maker” shifts toward the equator. Which places are likely to be hurt ?

16. 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.

17. Agriculture starts Irrigation needed South Asia flourishes Anatolia is rainy Greece is rainy Rome expands into Europe Barbarians invade Rome, Han dynasty collapses Vikings, Mongols Ming dynasty collapses Hunters thrive Upland farmers do well You’ll hear this again: Climate changes had a big impact on history. Global warming is bad for some countries and good for others.

19. 6000 to 4500 3900 to 3200 2800 to 2300

21. What about today?

22. The name is covered, because this is about ideas, not personalities

23. 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 at three graphs together, to see how they compare.

24. One conclusion is beyond doubt: temperatures have been higher in the past than they are today.

25. Temperatures were much higher in the distant past and a little higher quite recently. PRESENT AVERAGE

26. BUT, there is a big problem with this graph. the most recent measurements do not fit on the scale.

27. When we adjust the vertical scale so the numbers all can fit, you can see that carbon dioxide today is WAY above its “normal” range.

28. In just a few hundred years, humans have “pushed” the climate system far out of line with “normal” cycles. In 2014, 397

29. In 2013. the Pacific Ocean had very high temperatures in Autumn. One result was one of the strongest hurricanes ever measured near the Philippines.

30. Weeks later, this hurricane carried enormous amounts of energy northward.

31. Excessive heat moving toward the pole can push cold air toward the equator can push cold air toward the equator Excessive heat moving toward the pole

32. This map shows world temperature two months later. When you cite 2014 as an unusually cold winter in Michigan, you must consider 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”

33. And if you look at the total for the entire year, the imbalance becomes even more obvious. 5 small areas “cooler than average” 0 areas “record coldest” 14 large areas “much warmer than average” 16 areas “record warmest”

34. As one Blogger asked: Can global warming be real if it is unusually cold in the United States?

35. As one Blogger asked: Can global warming be real if it is unusually cold in the United States?

36. Agriculture starts Irrigation needed South Asia flourishes Anatolia is rainy Greece is rainy Rome expands into Europe Barbarians invade Rome, Han dynasty collapses Vikings, Mongols Ming dynasty collapses Hunters thrive Upland farmers do well You’ll hear this again: Climate changes had a big impact on history. Global warming is bad for some countries and good for others.

37. Copyright 2015, Phil Gersmehl Teachers who saw this presentation at a workshop or downloaded it from our internet site have permission to make a copy on their own computers for these purposes: 1. to help them review the workshop, 2. to show the presentation in their own classrooms, at sessions they present at teacher conferences, or to administrators in their own school or district, 3. to use individual frames (with attribution) in their own class or conference presentations. For permission for any other use, including posting frames on a personal blog or uploading to any network or website that can be accessed from outside your school, contact pgersmehl@gmail.com