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Today’s objectives:
-we will be able to define key terms in Gateway 2-we will be able to explain the various causes of climate change
Temperature Anomaly
It is a departure from a reference value
or a long term average.
A positive anomaly indicates that the
observed temperature was warmer than the
reference value, while a negative anomaly indicates that the observed
temperature was cooler than the reference value.
How has global climate changed?
Source: http://climate.nasa.gov/news/index.cfm?NewsID=249
Global Climate Change
Variation in global climate in the long term
Increase
Decrease
Certain years higher
increase in temperature
Global Climate Change
Increase in global temperatures over a long period of time GLOBAL
WARMING
Decrease in global temperatures over
a long period of time GLOBAL
COOLING
Climate change in the past 150 years
Significant but irregular temperature rise of 0.3 to 0.6 since 1881
Global cooling recorded after WWII for several decades because of industrial pollution and volcanic activity Amount of sunlight that reaches earth’s surface is
reduced because of large amount of particles in the atmosphere low temperature
Also known as global dimming
Global warming over last century: world warming on an average of 0.74 especially since 1970s
Watch the video below to find out more about climate change
https://www.youtube.com/watch?v=8YQIaOldDU8
WHY?
Climate change
Natural causes
Variation in solar output
Volcanic eruptions
Human causes
Burning fossil fuels
Deforestation
Changing land use
Watch the video below to find out about the causes of climate change
You have to fill in the handout based on what you watched. You can also use the following slides below to help you with your handout.
You can also look at your textbook 103-108 for the answers. (But it might be more boring for you)’
https://www.youtube.com/watch?v=RHrFBOUl6-8
Natural causes (1) Volcanic Activity
Produces large volumes of carbon dioxide, water vapour, ash and dust
Sulphur dioxide + water sulphur-based particles in atmosphere that reflect solar energy back into space
Results in a reduction in amount of sunlight that reaches earth’s surface: also known as global dimming
E.g. When Mount Pinatubo in Philippines erupted in 1991, 17 million tonnes of sulphur dioxide was released into atmosphere. The sulphur-based particles reflected solar energy back into space & lowered temperature in northern hemisphere by 0.6
Natural causes (1) Volcanic Activity
Usually have few long-term effects on climate
Because temporary global cooling effect will cease once the volcanic dust & ash settle
E.g. Global climate returned to original state 2 years after Mount Pinatubo eruption. The large volume of carbon dioxide released by volcanoes was still 100 times lesser than those by human activities.
Natural causes (2) Variations in solar output
Sun emits solar radiation at different rates due to changes in magnetic field An increase in magnetic activity increase in
solar radiation. Magnetic activity of the sun has a cycle that
lasts about 11 years. Through the study of sunspots, the solar
activity cycle was discovered Many sunspots indicates high solar activity
& higher temperature
Greenhouse Effect
Incoming shortwave radiation from the sun passes through the greenhouse gases found in atmosphere
Some shortwave radiation is reflected back to space
Most shortwave radiation is absorbed by the earth’s surface which then heats up as a result
The warmed surface of earth emits longwave radiation to the atmosphere
Greenhouse gases absorb longwave radiation, warming the atmosphere
ENHANCED Greenhouse Effect Increase in the concentration of greenhouse
gases in atmosphere rise in global temperatures
Happens when human activity causes greenhouse gases to be released at a far greater rate than natural emission of greenhouse gases
Increase in concentration of carbon dioxide usually the greatest amongst the greenhouse gases
Human (1) Burning fossil fuels Fossil fuels: coal, oil, natural gas
Large amount of fossil fuel burnt for industries, transportation, electricity etc. gives out large amount of greenhouse gases, esp. carbon dioxide
Greater amount of greenhouse gases traps more heat temperature increase
Human (2) Deforestation
Forests cleared for development, agricultural and commercial activities like cattle ranching, commercial logging etc.
Forests absorb billions of tonnes of carbon dioxide each year via photosynthesis, absorbing a significant amount of global greenhouse gas emission. With deforestation lesser trees to absorb
carbon dioxide larger concentration of CO2 in atmosphere
Human (2) Deforestation
Soil: very large source of carbon because carbon is accumulated through decay of organic matter like dead leave and animals Exposes soil to sunlight Increases soil temperature and rate of
carbon oxidation Causes carbon dioxide to be released from
soil into atmosphere
Human (3) Changing land useAgriculture Population increases need for more
food More land used for agriculture (practice
of cultivating land, producing crops & raising livestock)
But such activities release a lot of greenhouse gases into atmosphere!
Human (3) Changing land use
Cattle Ranching Rice Cultivation
Cattle release methane as waste gas
Requires the use of tractors which run on fossil fuel and it releases carbon dioxide
Methane is a greenhouse gas
Use of fertilisers increases nitrous oxide in soil and is eventually released when rain flows through soil
Dead leaves and manure (organic matter) releases methane when they decompose.
Human (3) Changing land useIndustrialisation A lot of carbon dioxide is produced when
fossil fuels are burnt for manufacturing industries
E.g. manufacturing a mobile phone releases 60kg of carbon dioxide.
Countries like China and India are contributing more to global carbon dioxide emissions in recent years due to rapid industrialisation
Human (3) Changing land useUrbanisation Process by which an increasing number
of people live in urban areas such as cities/towns. Large amount of fossil fuels burnt to
provide energy for household activities like cooking, lighting
High concentration of cars, buses increase amount of greenhouse gases