11.1 natural climate change looking forward by studying ... · 1 (c) mcgraw hill ryerson 2007 11.1...

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(c) McGraw Hill Ryerson 2007

11.1 Natural Climate Change

• “Climate” describes the average conditions of a region.Climate is usually measured over a minimum of 30 years or more.Climate = clouds, precipitation, average temperature, humidity, atmospheric pressure, solar radiation, and wind.The size of the region can range from an island to the entire planet.

See pages 464 - 465

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.


Looking Forward by Studying the Past

• Paleoclimatologists study long-term patterns in various regions.

Fossils may show what kind of environment was present.Tree rings show evidence of growing seasons.River sediments can reveal types of rainfall.Glacier ice cores show air condition andcomposition for thousands of years.• Gases trapped in the ice, specifically CO2,

reveal long-term atmospheric levels.Fossils and sediment evidence show Earth’s climate has drasticallychanged often in the past.

21 000 years ago, much of Canada and northern Europe was under glaciers.

See pages 466 - 467


Looking Forward by Studying the Past(continued)

• Ice core data reveal CO2 levels for the past 650 000 years.Scientists have also tested the atmospheric air for CO2 for the past 50 years

See pages 466 - 467


Factors That Influence Climate:Composition of Earth’s Atmosphere

• Earth is a closed system.A system is a group of parts that all function together as a whole.Very little energy (except radiant energy) enters or leaves the system.

Earth’s atmosphere is the outer boundary.• A greenhouse is a closed system that absorbs thermal energy .

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

This keeps Earth an average of 34ºCwarmer than it would be otherwise.More greenhouse gases could make it too warm.

See page 468


Factors That Influence Climate:Earth’s Tilt, Rotation and Orbit

• Earth’s tilt is responsible for seasons in northern hemisphere.In summer, we are tilted toward the Sun, decreasing the angle of incidence.In winter when we are tilted away from the Sun, solar radiation has a large angle of incidence.

Earth’s tilt varies between 22.3º and 24.5º(currently 23.5º) in 41 000 year cycles.When tilt is largest, climate shouldexperience the largest extremes.

• Earth also “wobbles” as it rotates on its axis.Because the axis changes on a 23 000 year cycle,the angle of incidence of solar radiation also changes.

• Earth’s revolution around the Sun is elliptical, not circular.On a 100 000 year cycle, Earth’s elliptical orbit becomes more circular.When the orbit is most elliptical, Earth is farther away fromthe Sun. See pages 468 - 470


Factors That Influence Climate:The Water Cycle

• The water cycle describe the circulation of water on,above, and below Earth’s surface.

70 percent of all greenhouse gases in the atmosphere is water vapour.When temperature increases, more water evaporates.More water vapour in the atmosphere may have two effects.

More solar energy may be absorbed by this greenhouse gas.More solar energy may be reflected back out to space and never reach Earth.

See page 471

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

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Factors That Influence Climate:Ocean Currents

• Convection currents in the oceans move large amounts of thermal energy all around Earth.

Deep ocean currents (200 m and deeper) flow based on density differences.They behave like massive convection currents, with warm water rising in the tropics and cold water from the higher latitudes replacing it.

See pages 471 - 473

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


Factors That Influence Climate:Ocean Currents (continued)

• Salinity of water also changes density.Cold water (found at the poles) is more dense than warm water. Salty water (found at the poles) is more dense than fresh water.Large changes in ocean water density can reverse current direction.

• Surface currents (0 - 200 m) are warmed by from solar radiation.The thermocline is the region separating surface and deep ocean currents.Upwelling occurs when cold, deep water rises into surface currents.

La Niña is an example of upwelling.• When this occurs, cool water at the surface of the Pacific Ocean causes

warm winters in southeastern North America, and cool winters in the northwest.

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

See pages 471 - 473


Factors That Influence Climate:The Carbon Cycle

• Carbon dioxide is a very important greenhouse gas.Even though each molecule absorbs only a small amount of thermal energy, there are more CO2 molecules than any greenhouse gas other than H2O.

Without CO2 to trap infrared radiation from Earth’s surface, the average temperature of Earth would be below freezing.

The carbon cycle maintains a balance of CO2 in the atmosphere.Deep oceans are carbon sinks, as are forested areas.• CO2 in the ocean is converted to carbonates (CO3

2-), in shells.• Phytoplankton use CO2 for photosynthesis at the ocean’s surface.

Weathering of rocks releases carbon.• Carbonic acid is formed when water reacts with CO2 in the

atmosphere.Forests take in CO2 while growing but release CO2 when burned or when decaying.

See pages 473 - 474


Factors That Influence Climate:The Movement of Tectonic Plates, andCatastrophic Events

• Large=scale disasters can quickly change atmospheric conditions.Erupting volcanoes can release ash and molten rock that absorb radiation.

Water vapour and sulfur dioxide (changed into sulfuric acid) can reflect solar radiation back into space.

Meteorites and comets are thought to have caused dramatic changes.These large masses strike Earth and the result is large quantities of dust, debris and gases in the atmosphere.Solar radiation is affected so much that it is thought that these events are responsible for some of Earth’s largest extinction events.

See pages 475Take the Section 11.1 Quiz

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


11.2 Human Activity and Climate Change

• Climate change is the change in long-term weather patternsin certain regions.

These changes can affect the flow of thermal energy over the entire Earth.Several ice ages have occurred in the past million years.Global warming refers to a global increase in average temperature.

Both the causes and effects of global warming are unknown and controversial.

See pages 482 - 483


The Enhanced Greenhouse Effect

• The enhanced greenhouse effect increases thermal energy absorbed.More greenhouse gases in the atmosphere = increase of natural greenhouse effectGreenhouse gases include water vapour, CO2, methane, nitrous oxide, and CFCs.

Global warming potential (GWP) refers to the ability to trap thermal energy.• CO2 is given a GWP of 1; CFCs are 4750-5310.

See page 484

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The Enhanced Greenhouse Effect:Carbon Dioxide and Methane

• CO2 levels have increased greatly in the past 200 years.Since the Industrial Revolution, humans have greatly increased their overall use of fossil fuels, which release CO2 when burned.Deforestation has changed carbon sinks, such as forests, into carbon sources.Many people are attempting to reduce CO2 emissions by using alternative energy sources or by reducing their energy use.Carbon offsets, such as wind farms, can be purchasedto offset CO2 emissions.

• Methane is very efficient at trapping thermal energy.25X more efficient than CO2Methane is produced by bacteria breaking down wastes inoxygen-free environments, animals digesting plant matter, rice paddies (and other natural wetlands),and the burning of fossil fuels.

See page 485

Livestock produce 18 percent of the total methane in the atmosphere.


The Enhanced Greenhouse Effect:Nitrous Oxide, Ozone, and Halocarbons

• Nitrous oxide, N2O, is the third largest contributor to the enhanced greenhouse effect.

Even though there are only small amounts, it has 300X more GWP than CO2.N2O comes from bacteria, fertilizers, and improper disposal of human and animal waste.

• Ozone is an important UV radiation blocker in the stratosphere.At lower altitudes, however, it is a very powerful greenhouse gas.

This ozone comes from solar radiation reacting with pollution from the burning of fossil fuels, and is released from photocopiers and certain air conditioners.

• Halocarbons, used as refrigerants, are strong greenhouse gases.Chlorofluorocarbons (CFCs) are the best-known halocarbons.Halocarbons are also the main reason for ozone layer depletion.

See page 486


Albedo and Climate,Making Predictions About Climate Change

• The albedo at Earth’s surface affects the amount of solar radiation that region receives.

Changes in a region’s albedo - for example, snow cover melting earlier in the season than it did previously - Could result in climate change.Forests have a low albedo. Deforestation increases albedo.

Forests also emit large amounts of water vapour, which reflects solar radiation back into space.Deforestation’s effects on climate change are unknown.

See page 487

Albedo for different surfaces


The Role of Science in Understanding Climate Change

• Scientists use computers to model what Earth’s climate might be like.Although models differ, most indicate that a decrease in the production of greenhouse gases is necessary to stop the apparent global warming trend.

• Global warming models use data from multiple locations over long periods of time.General circulation models (GCMs) are computer models used to study climate.

GCMs take into account changes in greenhousegases, albedo, ocean currents, winds andsurface temperatures.GCMs are also used for weather forecasting,climate analysis, and climate change predictions.Scientists are always trying to improve GCMs.GCMs predict the future and reveal the past.

See page 488

Projected global temperatures.


The Role of International Cooperation inClimate Change

• It is believed human-induced climate change is a recent occurrence.The United Nations and the World Meteorological Organization created the Intergovernmental Panel on Climate Change (IPCC) to address global concerns about climate change and global warming.

The IPCC, formed in 1988, hasmembers from 130 countries.The IPCC examines possibleclimate change, highlights thecauses, and suggests solutions.

The United Nations Framework Convention on Climate Change created a voluntary treaty toencourage governments to reduce greenhousegas emissions.

Per capita emissions of greenhouse gases for various countries.

See page 489


Global Impacts of Climate Change

See pages 489 - 490

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Impacts of Climate Change on Canada

• Being in the northern hemisphere, Canada could be strongly affected by global warming.

Parts of Canada have had average temperature increases of 0.5ºC to 1.5ºC.Southern and western parts of the country have been most affected.The Arctic regions are losing permafrost and Arctic Ocean ice cover.Growing seasons are getting longer and more precipitation is falling.• There could be heavier spring rains and severe droughts in the future.• Fisheries could be very negatively affected.• Pollution concerns could lead to health issues.

Most regions of British Columbia will probably be warmer, sea levels will rise, and fresh drinking water may be harder to find as glaciers disappear.

See pages 490 - 492


Impacts of Climate Change on Canada

See pages 490 - 492


Impacts of Climate Change on BC

See pages 490 - 492


Uncertainty and Decision,An Action Plan for the Global Community

See pages 493 - 496

• Although climate change is a controversial issue, our actions now are important.

Improving our environmental approach will help, no matter how dramatic climate change actually is.Not acting could result in huge problems.The United Nations suggests the precautionary principle, “better safe than sorry.”

• Relatively small changes could have large positive impact on the climate in Canada.

Reduce vehicle greenhouse gas emissions.Reduce industrial greenhouse gas emissions.Increase use of energy-efficient products.Improve indoor air quality.

Take the Section 11.2 Quiz

11.1 natural climate change looking forward by studying ... · 1 (c) mcgraw hill ryerson 2007 11.1...

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