11.1 Natural Climate Change Science 10 p.464-481.

11.1 Natural Climate 11.1 Natural Climate ChangeChangeScience 10Science 10

p.464-481p.464-481

ClimateClimate describes the average conditions of a region.describes the average conditions of a region.

is usually measured over 30 years or more.is usually measured over 30 years or more. Climate = clouds, precipitation, average temperature, Climate = clouds, precipitation, average temperature,

humidity, atmospheric pressure, solar radiation, and wind.humidity, atmospheric pressure, solar radiation, and wind.

BC’s climate zones

• Climate and geography combine to allow specific organisms to grow.– Biogeoclimatic zones have

distinct plants, soil, geography, and climate.

– British Columbia has 14 distinct biogeoclimatic zones.

Paleoclimatologists study long-term patternsPaleoclimatologists study long-term patterns• environment (using fossils)environment (using fossils)• growing seasons (using tree rings)growing seasons (using tree rings)• types of rainfall (using river sediments)types of rainfall (using river sediments)• air condition and composition (using glacier ice cores)air condition and composition (using glacier ice cores)

Gases trapped in the ice, specifically COGases trapped in the ice, specifically CO22,,

reveal long-term atmospheric levels.reveal long-term atmospheric levels.

Fossils and sediment evidence show Earth’s Fossils and sediment evidence show Earth’s climate has changed often and drasticallyclimate has changed often and drastically• 21 000 years ago, much of Canada and northern Europe 21 000 years ago, much of Canada and northern Europe

was under glaciers.was under glaciers.

Ice core data reveal COIce core data reveal CO22 levels for the past levels for the past

650 000 years.650 000 years. Scientists have tested the atmospheric COScientists have tested the atmospheric CO22 for for

the past 50 years the past 50 years

Factors That Influence Climate:Factors That Influence Climate:1) Composition of Earth’s Atmosphere1) Composition of Earth’s Atmosphere

Earth’s atmosphere is a boundary, so very little energy Earth’s atmosphere is a boundary, so very little energy (except radiant energy) enters or leaves(except radiant energy) enters or leaves

The Earth’s “natural greenhouse effect” allows a The Earth’s “natural greenhouse effect” allows a narrow range of temperatures.narrow range of temperatures. Solar radiation comes in, is Solar radiation comes in, is absorbed, and is then emitted andabsorbed, and is then emitted and trapped before being able to escape.trapped before being able to escape. Greenhouse gases in the Greenhouse gases in the atmosphere absorb thermal energy.atmosphere absorb thermal energy.

• This keeps Earth an average of 34ºC This keeps Earth an average of 34ºC warmer than it would be otherwise.warmer than it would be otherwise.

• More greenhouse gases could make it too warm.More greenhouse gases could make it too warm.

2) Earth’s Tilt, Rotation and Orbit2) Earth’s Tilt, Rotation and Orbit Earth’s tilt is responsible for the seasonsEarth’s tilt is responsible for the seasons

In summer, we are tilted toward the SunIn summer, we are tilted toward the Sun In winter when we are tilted away from the SunIn winter when we are tilted away from the Sun

• Earth’s tilt varies slightly (currently 23.5º)– When tilt is largest, climate experiences the largest

extremes

Earth “wobbles” as it rotates on Earth “wobbles” as it rotates on its axis.its axis. the axis changes so the angle of the axis changes so the angle of

incidence of solar radiation also incidence of solar radiation also changeschanges

• Earth’s revolution around the Sun is elliptical and changes shape.– On a 100 000 year cycle, Earth’s elliptical orbit

becomes more circular.– When the orbit is most elliptical, Earth can be farther away from the Sun.

3) The Water Cycle3) The Water Cycle describes the circulation of water on, above, and describes the circulation of water on, above, and

below Earth’s surface.below Earth’s surface. water vapour = 70% of the greenhouse gasses in the water vapour = 70% of the greenhouse gasses in the

atmosphereatmosphere When temperature increases, more water evaporates When temperature increases, more water evaporates

and causesand causes1) More solar energy absorbed1) More solar energy absorbed

by this greenhouse gas.by this greenhouse gas.

2) More solar energy reflected2) More solar energy reflected

back out to space and neverback out to space and never

reachs Earth.reachs Earth.

The water cycle stores and transfers large amounts of thermal energy.

4) Ocean Currents4) Ocean Currents Convection currents in the oceans move large Convection currents in the oceans move large

amounts of thermal energy all around Earth.amounts of thermal energy all around Earth. Deep ocean currents flow based on density differences.Deep ocean currents flow based on density differences.

• They behave like massive convection currents, with They behave like massive convection currents, with warm water rising in the tropics and cold water from the warm water rising in the tropics and cold water from the higher latitudes replacing it.higher latitudes replacing it.

Deep-ocean currents move cold, salty water below the surface and warm, less-salty water near the surface.

Salinity and temperature change water densitySalinity and temperature change water density Cold water and salty water (found at the poles) are more Cold water and salty water (found at the poles) are more

dense than warm water and fresh water.dense than warm water and fresh water.

Surface currents (0 - 200 m) are warmed by solar Surface currents (0 - 200 m) are warmed by solar radiation.radiation. The The thermoclinethermocline is the is the

region separating surfaceregion separating surface

and deep ocean currents.and deep ocean currents. UpwellingUpwelling occurs when occurs when

cold, deep water rises cold, deep water rises

through the thermocline through the thermocline

into surface currents.into surface currents.

La NiñaLa Niña is an example of upwelling. is an example of upwelling.

When this occurs, cool water at the surface of the When this occurs, cool water at the surface of the Pacific Ocean causes warm winters in southeastern Pacific Ocean causes warm winters in southeastern North America, and cool winters in the northwest.North America, and cool winters in the northwest.

El NiñoEl Niño is the reverse: warmer water on the surface of is the reverse: warmer water on the surface of the Pacific Ocean results in warm winters in the the Pacific Ocean results in warm winters in the Pacific Northwest and in eastern Canada.Pacific Northwest and in eastern Canada.

5) The Carbon Cycle5) The Carbon Cycle(remember this from chapter 2!)(remember this from chapter 2!)

Carbon dioxide is an important greenhouse gasCarbon dioxide is an important greenhouse gas 22ndnd most prevalent greenhouse gas most prevalent greenhouse gas

• Without COWithout CO22 to trap infrared radiation from Earth’s to trap infrared radiation from Earth’s

surface, the average temperature of Earth would be surface, the average temperature of Earth would be below freezing.below freezing.

The carbon cycle maintains a balance of COThe carbon cycle maintains a balance of CO22 in the in the

atmosphere.atmosphere.• Deep oceans are carbon sinks.Deep oceans are carbon sinks.

COCO22 in the ocean is converted to carbonates (CO in the ocean is converted to carbonates (CO332-2-), in shells.), in shells.

Phytoplankton use COPhytoplankton use CO22 for photosynthesis at the ocean’s surface. for photosynthesis at the ocean’s surface.

• Weathering of rocks releases carbon.Weathering of rocks releases carbon.

• Carbonic acid is formed when water reacts with COCarbonic acid is formed when water reacts with CO22 in the in the

atmosphere.atmosphere.• Forests are carbon sinksForests are carbon sinks

take in COtake in CO22 while growing but while growing but

release COrelease CO22 when burned or when burned or

when decaying.when decaying.

Meteorites and comets are thought to have Meteorites and comets are thought to have caused dramatic changes. caused dramatic changes. cause large amounts of dust, debris and gases in cause large amounts of dust, debris and gases in

the atmosphere.the atmosphere. Solar radiation is affected so much that it is thought Solar radiation is affected so much that it is thought

that these events are responsible for some of that these events are responsible for some of Earth’s largest extinction events. (dinosaurs!)Earth’s largest extinction events. (dinosaurs!)

Take the Section 11.1 Quiz

Large comet and meteor collisions with Earth can cause debris to block solar radiation and cause changes all over the Earth.