• EARTH’S CLIMATE• PAST and FUTURE

• SECOND EDITION

• CHAPTER 16• Climate Changes During

• the Last 1000 Years

WILLIAM F. RUDDIMAN

© 2008 W. H. Freeman and Company

Major Concepts• Recent climate events

– Medieval warm period and the Little ice age• Sparse evidence, but don’t seem to be focused around North

Atlantic, not global events

• Ice Core records– Mountain glaciers and ice sheets

• No overall trends for last 1000 years• Significant warming of Peruvian ice sheet

• Tree Rings– Regional differences, but many show 20th Century warming

• Coral records– Seasonal records that can be used to show changes in El Nino– When put together as a combined record, show clear 20th

Century warming

Major Concepts cont.

• Hockey Stick diagram of last 1000 years– Clear limitations– Noting error envelope really important

• Forcing factors– Orbital changes– Solar variability not as important as previously thought– Volcanic emission forcing only lasts a decade at most– Greenhouse gases may have played a role in cooling

after Medieval warm period and during little ice ages

Medieval warm period ~1000 to 1300 AD; Little ice age ~1400-1900

What is missing from this diagram?

Mountain glaciers – clear annual banding

Coring Mountain glaciers – not for the faint of heart!!

Quelccaya ice cap, Peru, 1980

Do you see the Little ice age? The Medieval warm period?

One of the most significant figures from this Chapter!!!

Do you see the Little ice age? The Medieval warm period?

Tree ring records best when trees at the edge of their range or comfort zone: Why?

Tasmanian tree rings

Combined (stacked) coral record

The famous Hockey Stick Diagram!

95% confidence limit

Cooling from 1000 to 1800 AD? What do you think?

Cause of small cooling?

• Orbital changes?– Decreasing summer insolation in high

northern latitudes due to both tilt and precession cycles

• Accounts for ~0.1C, or about half of cooling

Solar Sun Spot cycle: 11 year cycle most prominent

Should this time be cooler or warmer?

Volcanic emission forcing of climate

Can these explain Little ice age or Medieval warm period?