Chapter 4 Sections 3 and 4 Long Term Changes in Climate Global Changes in the Atmosphere.

Chapter 4Sections 3 and 4

Long Term Changes in Climate

Global Changes in the Atmosphere

4.3 Long Term Changes in Climate

1. Studying Climate Change Climate changes occur, in small areas and

throughout the world.

Climate changes generally happen slowly but have great consequences.

ex: - Ancestral pueblos of Southwest US - Greenland – 780 million years ago has fossil evidence of a warm, moist climate.

How do scientists study ancient climates?

Follow an important principal:

If plants and animals today need certain conditions to survive, then those similar plants and animals of the past also required those conditions

Sources of Information Pollen

Pollen is specific to a particular type of plant. Lake bottoms covered in thick layers of mud,

plant material and pollen that has settled there over thousands of years.

Scientists can drill down through these layers and study the cores

This helps scientists determine the plant life that existed in an area long ago.

Tree Rings Every growing season a tree grows a new layer

of wood under its bark forming rings.

In cool climates The amount of

growth (the thickness of the ring) depends on the length of the warm growing season.

In dry climates The thickness of

the ring depends on the amount of rainfall

2. Ice Ages

Throughout history climates have changed.

Over millions of years – warm periods have alternated with cold periods

Cold periods are known as ice ages (glacial episodes)

Huge sheets of ice covered large parts of the Earth’s surface.

Glaciers transform landscapes by carving giant grooves into solid rock and depositing large amounts of sediment.

Evidence suggests that in the past 2 million years, there have been many ice ages, some lasting as long as 100,000 yrs.

Long warm periods exist between ice ages

Scientist believe we are in a warm period between ice ages.

Glacier Grooves National Park, OH

Last ice age ended about 10,500 years ago. Ice covered much of N. Europe and N.

North America

Ice was as much as 3 km thick

When ice sheets melted, coastal areas flooded, inland the Great Lakes were formed.

3. Causes of climate change Earth’s position relative to the sun

The shape of Earth’s rotation around the sun changes slightly over long periods of time.

Solar Energy Changes in climate linked to changes in the

number of sun spots. Sunspot – dark, cooler regions of the Suns surface Increase and decrease in numbers cycle every 11

years. More sunspots = increase in temperatures.

sunspots

Volcanic Activity (major eruptions) release huge quantities of ash and gas into the

upper atmosphere It can stay there for many years May filter out some of the incoming solar

radiation.

Movement of Continents Pangea existed 225 million years ago Fossil evidence suggests that Polar continents

were once located in the equatorial region. Movements of continents changed positions of

land and seas, affecting global wind patterns and ocean currents

As continents continue to move, climates will continue to change.

4.4 Global Changes in Climate

1. Global Warming Over past 120 years, average temperature

of the troposphere has risen 0.5 degrees Celsius

Scientist question the cause of this increase: Human activities? Natural variations?

A. Greenhouse Effect Natural process where gases in Earth’s

atmosphere trap and hold in the solar energy from the sun

Water vapor, carbon dioxide and methane are examples of green house gases.

Burning wood, coal, oil and natural gas add CO2 to the atmosphere This could be causing an increase in temperature.

B. Natural Variations Increase in temperature could be due to

natural causes. Changes in solar energy can increase or

decrease temperature.

C. Possible Effects Advantages:

Farmers in cool areas could plant more crops Cold areas could become farmland

Disadvantages Water evaporations increases, leaving soil dry

and creating “dustbowls” Ocean water temperatures could increase

therefore increasing hurricane development Melting of polar ice caps and glaciers. Sea levels

could rise – low lying areas could flood.

2. Ozone Depletion Hole in layer has increased in size. Chemicals produced by humans have been

damaging the ozone layer Chlorofluorocarbons (CFC’s) Once used in refrigerants and aerosol cans

UV radiation breaks down CFC’s into atoms, including chlorine (Cl)

Cl reacts with ozone (O3)and turns it into oxygen atoms.

Less ozone = more UV radiation = cancer