Our Changing Earth

Physical geographers are the men and women who study these changes to Earth’s landscapes...

Physical geographers study patterns of climates, land forms, vegetation, soils, and water. They forecast the weather, manage land and water resources, and analyze and plan for forests, rangelands, and wetlands.

Geographic Inquiry Process ASKING GEOGRAPHIC QUESTIONS-What are we observing? ACQUIRING GEOGRAPHIC INFORMATION What information do we need and where do we get it? What do we thing the information will tell us? ORGANIZING GEOGRAPHIC INFORMATION How can the information be organized for analysis and display? ANALYZING GEOGRAPHIC INFORMATION Does the data support or challenge the initial hypothesis. Are there patterns or connections? ANSWERING GEOGRAPHIC QUESTIONS What are my conclusions? What are my next steps?

The story of one geographer...

Megadrought – a drought lasting many years or decades. Medieval Warm Period: The period from about 900 AD to 1400 AD in which global temperatures are thought to have been a few degrees warmer than those of the before and after periods. Words to know:

Scientific Study What evidence is there a medieval warm period existed? What process is used to prove existence of past climate changes? To learn how Dr. Stine’s research provided answers to the following questions? Let’s start at the beginning...

What do you see? What questions do you have?

Observation In the 1980’s Dr. Stine began his research at Mono Lake in California and observed stumps of long dead trees below the lakes natural elevation. Some were near the shoreline and some were under water.

Hypothesis For the presence of stumps the lake must have been lower. Two possible generations of trees How did he go about testing this hypothesis?

Dr. Stine used radiocarbon dating to date the wood from the trees in both areas. The “death rate” from one generation of trees was AD 1000 The “death rate” from the other group of trees was AD 1350.

Conclusions That decades prior to death of trees, climate must have been drier. There was not a single drought, but two droughts.

Further Inquiry How long did these Medieval droughts last? Was drought only in the area of Mono Lake?

Tenaya Lake (Yosemite, California)

Hypothesis “If these trunks were actually rooted on the lake floor, they must have grown when the shoreline stood at least 70 feet below its modern elevation” The lake had remained the same height and location since the last glacial ice move over 14,000 years ago, so the stand of trees must have been able to grow during a time of drought.

Tenaya Lake Again he followed the Geographic and Scientific Inquiry Models. Used a tape measure to measure the water depth and collected wood sliver from outermost wood for radiocarbon dating Virtual Tour of Tenaya Lake a/Mariposa/Yosemite/TenayaLake/Tour?w=4 8E a/Mariposa/Yosemite/TenayaLake/Tour?w=4 8E

Data Showed two generations of Tenaya Lake tree trunks. First group killed around 1100 AD. Second group killed approximately 1350 AD. Tree ring dating (dendrochronology) shows first group lasted about 140 years and the second at least 100 years.

Tree Ring Dating Tree Ring dating can show how long a tree lived. Also, ring widths are indicators of climate during different periods of time.

And more... West Walker River stumps dated to two the same drought periods. More stumps... Fallen Leaf Lake, California – Lake Tahoe Basin study by John A. Kleppe. Other evidence points to regional droughts in the Medieval period.

“ Most people don’t think beyond a few generations back in time. But we need to.” Dr. Scott Stine, August 2005

The Next Big Question... Were there also droughts in other parts of the West during this time?