1 The Greenhouse Effect Natural and Anthropogenic.

1

The Greenhouse EffectNatural and Anthropogenic

The Natural Greenhouse Effect• Greenhouse gases prevent thermal energy from

getting to Space.• Radiation from the Sun passes through the

Earth’s atmosphere and is absorbed by the Earth’s surface

• Becomes thermal energy and Earth warms up• Earth’s warm surface emits lower-energy IR

radiation• Gases in the atmosphere trap this radiation• GHGs in atmosphere absorb radiation and

some is sent back to Earth’s surfaceThis is called the Natural Greenhouse Effect

Greenhouse Gases

A greenhouse gas (GHG) is any gas in the atmosphere that absorbs lower-energy infrared radiation

Greenhouse Gases:Water vapourCarbon dioxideMethaneOzoneNitrous oxides

Water Vapour• Most significant contributor to the

natural greenhouse effect• Responsible for 65 – 85% of

greenhouse effect• Added by evaporation, human activity

has little impact.

Relationship to temperature:• Water evaporates more readily when it is warmer• Warmer air can hold more water vapour• Therefore, as Earth’s temperature rises, more liquid

water becomes water vapour• The more water vapour there is, the warmer the

earth becomes.•This is called a positive feedback loop

• Living things and the oceans are carbon sinks they absorb carbon dioxide from the atmosphere and store it in another form

• Main natural source is animal respiration and main human source is burning fossil fuels. Plants can clean this carbon dioxide from the air as part of the carbon cycle (photosynthesis), but the more deforestation and urbanization that occurs, the less plants there are to carry out this task.

Carbon Dioxide

• The effects of water and carbon dioxide amplify each other. If CO2 causes a temperature increase, there is more evaporation which then also causes more of a temperature increase. The same positive feedback loop applies to cooling.

Methane

Much less methane in atmosphere than CO2 in the atmosphereBUT… a methane molecule can absorb more

thermal energy than that of CO2

Bacteria that break down waste produce methane and these bacteria mainly exists in bogs and swamps. Human sources include landfills and oil processing sites.

Ozone (O3)

In the stratosphere, ozone acts to absorb UV radiation, protecting the Earth

In the troposphere, ozone acts as a greenhouse gas

Ozone in the Stratosphere• Ozone protects us from ultraviolet radiation

and the atmospheric ozone layer in the stratosphere is declining.

• Chlorine destroys ozone and humans have released a lot of chlorine into the atmosphere from the use of chlorofluorocarbon (CFC) and Freon in many refrigerants and air conditioners, amongst other applications.

• These halocarbons stay in the atmosphere for a long time. Even though many nations banned their use in the late 80’s they are still present.

Ozone in the Troposphere• Ground level ozone is a significant personal

health issue. • Hydrocarbons and nitrous oxides create

ground level ozone forming smog in major urban centres, like Toronto.

• The combination of ground level ozone and warm temperatures means health warnings are required because it is too hard to breath outside.

Nitrous Oxides

Smaller concentration in atmosphere, but more effective as a greenhouse gas

Naturally produced by reactions between bacteria and the soil and water

Natural sources include tropical soil and oceans (recall the nitrogen cycle). Human sources include fertilizer, sewage treatment and car exhaust.

Other factors effecting the Greenhouse effectHuman activities!!

Summary

Certain gasses naturally trap heat Greenhouse Effect

Natural Greenhouse Gasses include:Water vapourCarbon dioxideMethaneOzoneNitrous oxidesOthers

The Anthropogenic Greenhouse EffectAnthropogenic means originating in human activity.

Global Warming• Scientists measure the amount of one substance that is mixed

with another using concentration. • For about the past 50 years scientists have been measuring the

concentration of CO2 in the atmosphere. • When we talk about the concentration of gases, we usually talk

about parts per million (ppm).• Example: CO2 levels in 1960 were 315 ppm. This means that

there were 315 mg of CO2 for every kg of air. Another way of saying this is that for every million units of atmosphere there are 315 units of CO2. According to co2now.org, in December 2010 the concentration of CO2 was 389.69 ppm.

Anthropogenic Greenhouse Gases• The anthropogenic greenhouse effect is the increased capacity

of the atmosphere to absorb and trap thermal energy because of the increase in greenhouse gases caused by human activity.

• Processes that add greenhouse gases to the atmosphere are called sources. Processes that absorb greenhouse gases are called sinks. Figure 1 shows the human sources of carbon emissions and the sinks that carbon goes into.

Humans and CO2

Humans and Methane• METHANE:• <20% of anthropogenic greenhouse effect• Comes from:• Agricultural activities such as rice farming and cattle ranching• Decay of organic material in landfills and sewage treatment plants• Coal mining and natural gas extraction release trapped methane• Deforestation

Humans and Other Gases• NITROUS OXIDE:• <10% • From livestock feed, waste management and fertilizers

• CFCs• Refrigeration agents (in fridges and air conditioners)

So What Can We Do?• There are several ways for humans to reduce our greenhouse

gas emissions. These include, but are not limited to:• Conserving electricity: lights off and unplug those chargers!• Improving home-heating efficiency: new furnaces, digital

thermostats and sealing up windows• REDUCE, reuse and recycle: this applies to so many things! For

starters – stop wasting paper! Print double sided and use narrow margins on your page. Print only once.

Homework• Take this energy quiz now and test your knowledge of energy

use leading to greenhouse gas emissions. [Application]• Come up with 3 simple things you can do in your own home to

reduce the impact of your greenhouse gas emissions. These can include both decreasing sources and adding sinks. All three should be inexpensive and easy to implement. [Application]