1. AOSC 200 Lesson 23

3. DETECTING CLIMATE CHANGE
DIFFICULT TO DETECT CLIMATE CHANGE EXCEPT OVER LONG PERIODS OF TIME.
INSTRUMENTAL RECORDS GO BACK ONLY A COUPLE OF CENTURIES. THE FURTHER BACK, THE LESS RELIABLE ARE THE DATA.
SCIENTISTS MUST DECIPHER CHANGES FROM INDIRECT EVIDENCE
HISTORICAL DOCUMENTS
TREE RINGS
POLLEN RECORDS
GLACIAL ICE – AIR BUBBLES AND DUST
SEA-FLOOR, MATINE SEDIMENTS. OXYGEN ISOTOPE RATIOS IN FOSSIL SHELLS
FOSSIL RECORDS

4. CLIMATE CLUES

5. Cave drawing from the Sahara Desert
Fig , p. 422

6. TREE RINGS
In regions with distinct growing seasons, trees growth appears as distinct rings. Typically one ring per year.
Dendrochronology
Width of the ring is a function of available water, temperature, and solar radiation.
Tree species have different responses to these three factors – hence the factors can be separated by looking at different species

7. TREE RINGS

8. Plot of annual precipitation in Iowa derived from the analysis of tree rings
Fig , p. 423

9. POLLEN RECORDS
Pollen degrades slowly and each species can b a identified by the shape of its pollen
Radioactive carbon dating
As the climate changes, different types of species become dominant
Hence the pollen record can be used to identify the type of climate that existed

10. POLLEN RECORDS

11. ICE SHEETS
Bubbles of air trapped in ice can be analyzed to determine atmospheric composition.
Glaciers that exist today can hold bubbles that are tens or hundreds of thousand of years old.
Dust in ice sheers can be caused by climate-changing volcanoes, or dry windy conditions that lead to soil erosion.
Find that the colder periods of the Earth history (20000, 60,000 and 100,000 years ago) are usually much dustier

12. Concentration of Carbon Dioxide and Methane determined from air bubbles in ice cores.
Fig , p. 426

13. MARINE SEDIMENTS/FOSSIL RECORDS
Foraminifera are micro-organisms that live in the sea and have a calcium carbonate shell. CaCO3
Oxygen has two isotopes which have an atomic mass of 16 and 18
The ratio of these two isotopes in the foraminifera is a function of the sea temperature
Fossils reveal ancient animal and plant life that can be used to infer climate characteristics of the past

14. Variation in average temperature determined from O18/O16 ratio in fossil shells
Fig , p. 428

15. NATURAL CAUSES OF CLIMATE CHANGE
UNRELATED TO HUMAN ACTIVITY.
VOLCANIC ACTIVITY
ASTEROID IMPACTS
SOLAR VARIABILITY
VARIATIONS IN THE EARTH'S ORBIT
PLATE TECTONICS
CHANGES IN THE OCEAN CIRCULATION PATTERNS

16. Annual acidity of layers of an ice core in Greenland
Fig , p. 430

17. VOLCANIC ACTIVITY
MOST VOLCANOES EJECT DUST ETC. INTO THE TROPOPSHERE WHERE IT IS QUICKLY RAINED OUT.
HOWEVER LARGE VOLCANOES CAN EJECT GASES, ESPECIALLY SULFUR DIOXIDE, INTO THE STRATOSPHERE.
IN THE STRATOSPHERE THE SULFUR DIOXIDE TRANSFORMS INTO AEROSOLS, WHICH REMAIN IN THE STRATOSPHERE FOR ONE TO TWO YEARS.
THIS WILL TEND TO COOL THE TROPOSPHERE - SCATTERS SOLAR RADIATION BACK TO SPACE.
ERUPTION OF MOUNT TAMBORA IN INDONESIA LED TO 'YEAR WITHOUT A SUMMER'
MOUNT PINATUBO, 1991, LOWERED TEMPERATURE BY 0.5 C

21. Variations in the Earth’s orbit
Over long time periods the shape of the earth’s orbit around the sun, and the tilt of its axis are not constant. We can identify three ways in which these factors change
Precession – the Earth wobbles on its axis similar to a spinning top. (27,000 years)
Obliquity – its inclination to the solar plane changes (41,000 years)
Eccentricity – the elliptical shape of the orbit changes (100,000 years)

22. SUNSPOT NUMBERS

23. SUNSPOT NUMBERS
The output of energy from the Sun has an eleven year cycle – which also follows the number of dark spots on the Sun – sunspots.
People have been observing sunspots since the invention of the telescope, 1600
In the period 1645 and 1715 the number of sunspots was dramatically lower – Maunder minimum.
Coincided with the little ice age ( )

24. Continental Drift
Fig , p. 436

25. Fig