Transcript Climate Change Chapter 8

CLIMATE CHANGE
SNC 2D1
Weather
• short term, local changes in factors such as:
• temperature
• precipitation
• wind speed
• cloud cover
• Relative humidity
• atmospheric pressure
• these factors fluctuate frequently sometimes on an hourly
basis
• Weather changes are caused by the movement and
interaction of air currents and ocean currents on earth, as
they carry energy that originated from the Sun
Climate
• long term changes in weather factors, usually over a
larger geographic area
• the climate in Ontario changes with the four seasons
• the climate in tropical areas like Singapore does not change as
much – only dry season and rainy season
• to determine climate patterns meteorologists collect
weather data over many years
• climate determines the types of flora and fauna that live in
an ecosystem
• White Pine trees are common in Ontario, but not in Barbados –
similarly, palm trees are not common in Ontario
Classifying Climate
• Climate zones – developed by Vladimir Köppen in the
early 1900s – he used temperature and precipitation data
along with plant communities to identify patterns within
geographic regions
Classifying Climate
• Ecoregions – based more in ecological data than the
climate zones – use information about landforms, soil
types, plants, animals and climate data
http://worldwildlife.org/science/wildfinder/
Classifying Climate
• Bioclimate Profiles – developed by Canadians – they
provide ‘climate at a glance’ in a graphical representation
of climate on a site by site basis.
• a typical bioclimate profile consists of a number of
elements which describe the temperature and moisture
conditions at the site in question
• bioclimate profiles have been developed for over 500
locations across Canada, for two climate periods of
historical data: 1961-1990 and 1971-2000.
• 1961-1990 is primarily used as the ‘baseline’ period
• 1971-2000, is the most recent 30-year ‘climate normals period’
• both can be used as a reference for predicting future
climate data
Bioclimate Profile – temperature
Bioclimate Profile – precipitation
http://www.cics.uvic.ca/scenarios/bcp/select.cgi
Factors affecting climate
• Distance from the equator (latitude)
• Proximity to large bodies of water
• Presence of ocean or air currents
• Land formations
• Height above sea level (altitude)
Sun’s Importance in Earth’s Climate
• The earth’s global climate system in powered by incoming
solar radiation – almost all energy on earth comes from
the sun
• Incoming solar energy can take three forms
• ultraviolet radiation
• visible light
increasing wavelength, decreasing energy
• infrared radiation
• When the sun’s rays hit a particle or object, they may be
• absorbed
• transmitted
• reflected
Absorption and reflection of sun’s energy
Maintaining an energy balance
• if all of the energy coming from the sun were to remain on
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the Earth, it would eventually continue to heat up to levels
that would not support life
we know this does not happen, so energy must be
released in some way
the Earth’s surface (land and oceans) emits energy to the
atmosphere
the atmosphere then emits that energy back out into
space
this energy is emitted in the form of infrared radiation
Absorption, reflection and emission
How does latitude affect climate?
• At the equator, the sun’s
rays are concentrated onto
a smaller area
• Near the poles, the same
amount of sunlight energy
is spread out over a larger
area
Components of Earth’s Climate System
• Atmosphere
• layers of mixed gases that surround the planet, reaching more than
100km above the Earth’s surface
• Layers include: troposphere, stratosphere, mesosphere,
thermosphere and exosphere
• The ozone layer in the stratosphere absorbs much of the sun’s UV
radiation, which would otherwise harm plants and animals
• The atmosphere absorbs and reflects the sun’s energy
and also transmits to the earth’s surface - transferring
energy and heat around the planet with air currents and
winds
Components of Earth’s Climate System
• Hydrosphere
• Includes all water on the earth, in solid, liquid or gaseous forms
• Liquid water (oceans, lakes, rivers) can absorb and reflect
the sun’s energy
• Water vapour (especially as clouds) reflect sun’s energy
• Ice and snow (glaciers, ice caps, permafrost) reflect a lot
of the sun’s energy
• Together all are part of the water cycle, which helps to
transfer energy and heat around the planet
Components of Earth’s Climate System
• Lithosphere
• Includes the Earth’s crust – rock, soil on land as well as under
bodies of water
• Landforms can affect the climate by changing the movement of air
currents and precipitation (rain shadow effect)
• Living things
• Plants, animals, fungi, bacteria – all are part of the climate system
since they interact with water and air
• Plants take in CO2, while animals and other organisms release it
into the atmosphere
• Some organisms also produce other waste gases, such as
methane, which along with CO2 also affect the absorption of the
sun’s energy by the atmosphere
The Greenhouse Effect
• Without the climate system, the Earth’s average global
temperature would be about -18°C, but because of the
greenhouse effect, it is actually 15°C
• Much of the sun’s high energy radiation passes through
the gases of the atmosphere where it is absorbed by the
Earth’s surface
• Here it is converted into infrared radiation (thermal energy
and emitted back to the atmosphere
• Some gases absorb this IR radiation well, and then reemit it in all directions – about half of it back to the earth’s
surface
The Greenhouse Effect
http://phet.colorado.edu/en/simulation/greenhouse
Greenhouse Gases
• Most of the atmosphere is N2 and O2 which do not absorb
infrared radiation
• The gases in small proportion are responsible for the
greenhouse effect, including:
Greenhouse Gas
Concentration in atmosphere
Carbon dioxide
385 ppm
Water vapour
0–4%
Methane
1.785 ppm
Nitrous oxide
321 ppb
• The contribution to the greenhouse effect depends on the
concentration of the gas in the atmosphere, as well as how
much thermal energy each molecule of gas can absorb
Carbon Dioxide
• CO2 is estimated to contribute to 25% of the greenhouse
effect on Earth
• pre-industrial (before 1750) levels were around 280 ppm
• natural sources include:
• Cellular respiration of plants and animals
• Volcanic eruptions
• Burning and decay of organic matter
• the carbon cycle has long maintained a balance in the
CO2 levels
• carbon sinks remove CO2 from the atmosphere and
convert it into organic molecules like sugars
• terrestrial plants and algae in the oceans and lakes are
important carbon sinks
Water Vapour
• The amount of water vapour in the atmosphere depends
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on the temperature
As temperature increases, more water evaporates
Warmer air can also hold more water vapour
With more water vapour in the air, the greenhouse effect
is intensified, further increasing the temperature
This is called a positive feedback loop, where the effect
enhances the original cause
In negative feedback loops, the effect decreases the
original cause
Positive Feedback Loop
Higher
temperatures
leads to
more water
vapour
More water
vapour leads
to higher
temperatures
Methane and Nitrous Oxide
Methane
• one molecule can absorb about 23 times more thermal
energy than a molecule of CO2
• Natural sources include plant decomposition in swamps,
and animal digestion
• Pre-industrial levels were 0.700 ppm
Nitrous Oxide
• Can absorb about 300 times more thermal energy than
CO2
• Natural sources include bacterial activity in soils and
water
• Pre-industrial levels were 270 ppb
Energy Transfer
• Energy and heat can be transferred in three ways:
• Conduction – through collision of particles
• Convection – through movement of fluids (liquids or gases)
• Radiation – infrared (thermal) energy through space
Energy Transfer in the Atmosphere
• The sun’s rays near the equator cause air to rise
• Once it reaches the troposphere, it cools and descends
• This movement of air creates a circular current called a
convection current
• This pattern is repeated near the poles
• The rotation of the Earth from east to west causes these
winds to twist (this is called the coriolis effect)
• These twisting winds are known as the prevailing winds these tend to move warm air from the equator up towards
the poles – if they did not exist, there would be a much
greater difference in temperature between the equator
and the poles
Prevailing Winds
Energy Transfer in Oceans
• Water moving toward the poles gets cooler
• As some of it freezes into ice, the remaining water becomes
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saltier, making it more dense
The higher density, cooler, saltier water sinks
Warmer water from the equator flows toward the poles to
replace it
This creates the thermohaline circulation, and acts like a global
conveyor belt, distributing heat through ocean currents
Warm and cold ocean currents have a significant effect on
climate
• Newfoundland’s climate is affected by the cold Labrador current
• Northwestern Europe has a warmer, damper climate than would be
expected based on the latitude due to the warm Gulf Stream
Thermohaline Circulation
Think you understand heat transfer?
• Try the Heat Game !
• If not, review the Earth as a
System video
Long-term cycles in climate
• The earth is 4.6 billion years old, and has undergone
many changes in its history
• Many of these changes affected climate in dramatic ways
• Any change that affects Earth’s energy balance will cause
a change in climate
• These could be due to geologic changes in the Earth’s
crust, or variations in the Earth’s orbit, or in the amount of
energy put out by the sun
Long-term changes: Continental drift
• The earth’s land masses have moved over the surface of
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the globe, and continue to move today
This is due to shifting plates on the crust, explained by the
theory or plate tectonics
When continents move, ocean currents are affected,
which affects heat transfer
Today, most of the Earth’s land mass is in the northern
hemisphere – because there are fewer large bodies of
water, this results in cooler winters and warmer summers
Uplifting of new mountain ranges can also affect local
climates by influencing the movement of air masses
Continental Drift
Long-term changes: Milankovitch cycles
• The last 800,000 years have seen the Earth’s climate
cycling between freezing ice ages and warmer interglacial
periods
• Currently the Earth is in an interglacial period which has
existed for the last 10,000 years
• There are several factors which cause these alternating
ice ages and interglacial periods – collectively they are
known as the Milankovitch cycles, after engineer and
amateur astronomer Milutin Milankovitch
• Each of these factors changes the amount of solar
radiation affecting Earth
Milankovitch cycles - eccentricity
• The shape of Earth’s orbit varies over time, changing from
circular to an oval shape & back again every 100, 000
years, affecting length and intensity of seasons.
• Orbit closer to sun (more solar radiation)
• Orbit farther from sun (less solar radiation)
Milankovitch cycles – Tilt
• The angle of the earth’s axis changes in a 41,000 year
cycle
• Currently the tilt is 23.5°, slowly decreases to a minimum
angle of 22.1° and then back to a maximum of 24.5°
Milankovitch cycles – Precession
• The direction of the tilt of the earth’s axis changes in a
26,000 year cycle
• Similar to a spinning top as it slowly changes the direction
in which it points
• The Earth’s axis currently points toward the star Polaris,
but in 1000 years, it will point toward the star Airai
Milankovitch cycles – Overall effects
Milankovitch cycles – Overall effects
• Together these Milankovitch cycles act as the main trigger
for the 100,000 year cycles in glaciation
• With small changes in the amount of energy the Earth
receives, positive feedback then enhances these changes
thousands of years
Short term variations in climate
Volcanic Eruptions
• Volcanoes release enormous amounts of rocks, dust and
gases high into the atmosphere
• These emissions can travel with air currents over large
areas, shading the earth and reflecting solar energy
• In particular, sulfur dioxide reflects a lot of solar radiation,
cooling the earth temporarily
• These effects can last for weeks, months or years
depending on the size of the volcanic eruption
Short term variation in climate
• Mount Pinatubo
• Erupted in July 1990, emitting between 15-30 million tons of sulfur
dioxide high into the atmosphere – most of the gases were released
in a 9-hour period on July 15
• This increase in atmospheric SO2 has been linked to the average
global cooling of between 0.4°C – 0.5°C in 1992-1993
Short term variation in climate
Air and Ocean Currents
• can have sometimes abrupt
changes in climate
• about 12,800 -11,500 years ago,
after the last glacial period, an
unexpected cooling occurred for the
next 1300 years (± 70 years).
• one hypothesis to explain this is that
large amount of ice was melting,
releasing large volumes of fresh
water into oceans – it is thought that
this disrupted the thermohaline
circulation, causing the abrupt
cooling of the planet for a while
• this period is referred to as the
Younger Dryas, or “the Big Freeze”
Short term variation in climate
El Niño
• a recurring disruption in the Pacific trade winds and ocean
currents that brings warm moist air to the west coast of
South America, which is usually cool and arid
• Normally, the Pacific trade winds blow from east to west,
dragging the warm surface waters westward, where they
accumulate into a large, deep pool just east of Indonesia,
and northeast of Australia.
Ocean temperatures are
shown in the image at
right, illustrating a
‘normal’ condition
El Niño
• this warm pool of water helps to maintains the convection
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currents and trade winds in the atmosphere
meanwhile, the deeper, colder waters in the eastern Pacific are
allowed to rise to the surface, creating an east-west
temperature gradient along the equator known as the
thermocline tilt.
in the spring, the trade winds diminish and are usually
replenished to maintain normal conditions.
however, during an El Niño year, the trade winds are not
replenished, and so the ocean currents are not pushed
westward - this allows warm water to move eastward
below the surface, the thermocline flattens out, preventing
upwelling of cold water in the eastern Pacific
the eastern Pacific warms and water levels rise
the western Pacific cools and water levels drop
El Nino
Above: Red is 30 °C and blue is 8 °C.
Feedback Loops and Climate
• A process whereby an initial change in the atmospheric
process will tend to either:
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Reinforce the process – positive feedback
Weaken the process – negative feedback
recall: the water vapour feedback loop
Higher
temperatures
leads to more
water vapour
More water
vapour leads
to higher
temperatures
• This becomes much more complex if clouds and ice are
considered
Cloud altitude and feedback loops
trap thermal
energy near
Earth’s
surface
clouds
form at low
altitude
even warmer
temperatures
warmer
temperatures
Cooler
temperatures
Reflect
Sun’s
radiation
back to
space
Clouds form
at high
altitudes
more low
clouds
Albedo
• albedo is a measure of the
proportion of radiation
reflected by a surface
• ice and snow have high
albedos, while green plants
and soil have lower albedos
• A planet’s average albedo
takes into account the
proportion of different
surfaces
• The Earth’s albedo is 0.30 –
0.40
Albedo Effect
• This is the positive feedback loop between the amount of
ice on the Earth and it’s average temperature
Ice melts
Less of
Sun’s
radiation
reflected by
ice
Earth’s
temperature
increases
More ice
forms
More of
Sun’s
radiation
reflected by
ice
Earth’s
temperature
decreases
Studying Clues to Past Climates
• Weather data has been reliably recorded for at least the last
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200 years
This provides a good record of the Earth’s climate for this
period – but what about earlier in the past?
Some informal records can be relied upon – journals, paintings,
farming records and oral histories
Paleoclimatologists study past (sometimes ancient) climate
They use records in nature, called proxy records, including:
• Ice cores
• Tree rings
• Coral reefs
• Rocks
• Ocean sediments
• Caves
Ice Cores
• Ice sheets found in Antarctica,
Greenland, and Canada’ arctic
can be kilometres deep, formed
from hundreds of thousands of
years of snowfall, compacted
into layers
• Air bubbles trapped in these
layers contain trace amounts of
gases that tell us what the
atmosphere was like in the past
• Ions and isotopes can also be
detected which give clues to
past global events (sulphate
ions from volcanos) and past
global temperatures (oxygen
isotopes)
Tree Rings
• Trees grow quickly in the spring, and
more slowly for the rest of the season –
this produces the annual growth rings
• Warm wet years produce thicker annual
rings, and during drier cooler years, the
rings are thinner
• We can use trees from different sources
(living trees, dead trees, timbers found in
ancient buildings) to build a climate profile
for a geographic area by matching up
similar growth patterns in the tree rings
• By matching tree ring widths, we can
develop a chronology that extends quite
far into the past, especially knowing that
some trees can live for 1500 years or
more!
Tree Rings
Dendrochronology
Coral Reefs
• Coral reefs also grow in a
yearly pattern, called
laminations
• Small samples of coral can
be analyzed for oxygen
isotopes to indicate the
temperature of the oceans
when the layers were
formed
• The laminations are only
visible under UV lamps, not
under visible light
Rocks, Ocean Sediment and Caves
• Earth’s lithosphere was formed by
slowly building up layer upon layer –
often trapping clues to climate in these
layers
• Plant materials, such as pollen can be
used to identify the species of trees that
existed in the past which can give clues
about the temperature and climate
• Ocean sediment cores can be drilled
and analyzed for fossils of marine plants
and animals – oldest layer is at the
bottom of the core, so we can get a
picture of how life has changed on the
planet for thousands of years
What Do You Think Now?
• About half of the energy on Earth comes from the Sun.
• The greenhouse effect is a natural phenomenon.
• Carbon dioxide is an important part of Earth’s climate system.
• Earth’s climate has remained very stable for thousands of years.
• Volcanic eruptions cause the climate to change.
• Weather and climate are the same thing.