AOSC 200Lesson 23

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• HISTORICAL DOCUMENTS• TREE RINGS• POLLEN RECORDS• GLACIAL ICE – AIR BUBBLES AND DUST• SEA-FLOOR, MATINE SEDIMENTS.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

CLIMATE CLUES

Fig. 14-14, p. 422

Cave drawing from the Sahara Desert

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

TREE RINGS

Fig. 14-16, p. 423

Plot of annual precipitation in Iowa

derived from the analysis of tree rings

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

POLLEN RECORDS

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

Fig. 14-18, p. 426

Concentration of Carbon Dioxide and Methane determined from air

bubbles in ice cores.

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

Fig. 14-20, p. 428

Variation in average temperature determined from O18/O16 ratio in fossil shells

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

Fig. 14-21, p. 430

Annual acidity of layers of an ice core in Greenland

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

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)

SUNSPOT NUMBERS 1600-2000

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 (1400-1850)

Fig. 14-26, p. 436

Continental Drift

Fig. 14.27