Our Carbon Footprint

What is a carbon footprint?

According to Wikipedia:

A carbon footprint is "the total set of greenhouse gases (GHG) emissions caused by an organization, event or product" ^[1]. For simplicity of reporting, it is often expressed in terms of the amount of carbon dioxide, or its equivalent of other GHGs, emitted.

The concept name of the carbon footprint originates from ecological footprint discussion.^[2] The carbon footprint is a subset of the ecological footprint and of the more comprehensive Life Cycle Assessment (LCA).

An individual, nation, or organization's carbon footprint can be measured by undertaking a GHG emissions assessment. Once the size of a carbon footprint is known, a strategy can be devised to reduce it, e.g. by technological developments, better process and product management, changed Green Public or Private Procurement (GPP), Carbon capture, consumption strategies, and others.

The mitigation of carbon footprints through the development of alternative projects, such as solar or wind energy or reforestation, represents one way of reducing a carbon footprint and is often known as Carbon offsetting.

 What is your carbon footprint?

 Find out by clicking on the icon::

Assignment:  Write a paragraph reaction to the results of your carbon footprint.  Is it what you expected?  Do you make more or less of an impact than you expected?  What changes could you make that would make a difference? (Experiment with different answers to see how that affects the calculation of your footprint). 

If there is a problem with the carbon footprint calculator, try one of the following sites instead:

Natural Greenhouse Effect vs. Anthropogenic Greenhouse Effect

The Natural Greenhouse Effect

The sun's radiation, much of it in the visible region of the spectrum,

warms our planet. On average, earth must radiate back to space the

same amount of energy which it gets from the sun. Being cooler than the

sun, earth radiates in the infrared. (An object, when getting warmer,

radiates more energy and at shorter wavelengths. On cooling, it emits

less and at longer wavelenghts. Lava or heated iron are examples.)

The wavelengths at which the sun and the earth emit are, for energetic

purposes, almost completely distinct. Often, solar radiation is called

shortwave, whereas terrestrial infrared is called longwave radiation.

Greenhouse gases in earth's atmosphere, while largely transparent to

incoming solar radiation, absorb most of the infrared emitted by earth's

surface. The air is cooler than the surface, emission declines with

temperature, so the air or, rather, its greenhouse gases emit less

infrared upwards than the surface. Moreover, while the surface emits

upwards only, the air's greenhouse gases radiate both up- and downwards,

so some infrared comes back down. Clouds also absorb infrared well.

Again, cloud tops are usually cooler and emit less infrared upwards

than the surface, while cloud bottoms radiate some infrared back down.

All in all, part of the infrared emitted by the surface gets trapped.

Satellites, viewing earth from space, tell us that the amount of

infrared going out to space corresponds to an `effective radiating

temperature' of about -18 o C. At -18 o C, about 240 watts per square

metre (W/m**2) of infrared are emitted. This is just enough to balance

the absorbed solar radiation. Yet earth's surface currently has a mean

temperature near 15 o C and sends an average of roughly 390 W/m**2 of

infrared upwards. After the absorption and emission processes just

outlined, 240 W/m**2 eventually escape to space; the rest is captured

by greenhouse gases and clouds. The `natural greenhouse effect' can

be defined as the 150 or so W/m**2 of outgoing terrestrial infrared

trapped by earth's preindustrial atmosphere. It warms earth's surface

by about 33 o C.

As an aside, note that garden glasshouses retain heat mainly by lack

of convection and advection [Jones]. The atmospheric `greenhouse'

effect, being caused by absorption and re-emission of infrared

radiation, is a misnomer. We won't get rid of it, though ;-)

Under clear sky, roughly 60-70 % of the natural greenhouse effect is

due to water vapor, which is the dominant greenhouse gas in earth's

atmosphere. Next important is carbon dioxide, followed by methane,

ozone, and nitrous oxide [IPCC 90, p 47-48].

Clouds are another big player in the game. Beginners please don't

confuse clouds with water vapor: clouds consist of water droplets or

ice particles or both. Under cloudy sky the greenhouse effect is

stronger than under clear sky. At the same time, cloud tops in the

sunshine look brilliantly white: they reflect sunlight. Globally and

seasonally averaged, clouds currently exert the following effects:

Outgoing terrestrial infrared trapped (warming) about 30 W/m**2

Solar radiation reflected back to space (cooling) nearly 50 W/m**2

Net cloud effect (cooling) roughly 20 W/m**2

Earth's present reflectivity or albedo (whiteness) is near 0.3. This

means that about 30 % or slightly over 100 W/m**2 of the sun's incoming

radiation is reflected back to space, while roughly 240 W/m**2 or about

70 % is absorbed. Almost half of earth's current albedo and perhaps

20 % of the natural greenhouse effect is caused by clouds. Quantities

involving clouds are hard to measure and may vary by a few W/m**2,

depending on whom you listen to.

Globally averaged, the surface constantly gains radiative energy,

whereas the atmosphere scores a loss. Sending up about 390 W/m**2,

the surface absorbs roughly 170 W/m**2 solar radiation and over 300

W/m**2 infrared back radiation from greenhouse gases and clouds.

The atmosphere, clouds included, radiates both up- and downwards,

altogether over 500 W/m**2. It absorbs roughly 70 W/m**2 solar

radiation and 350 W/m**2 terrestrial infrared.

The surface's radiative heating and the atmosphere's radiative

cooling are balanced by convection and by evaporation followed by

condensation. When evaporating, water takes up latent heat; when

water vapor condenses, as happens in cloud formation, latent heat is

released to the atmosphere. Information in this section comes from

[Berger] and [Hartmann, chapters 2-4], unless indicated otherwise.

(source: http://stason.org/TULARC/science-engineering/climate-change/3-The-natural-greenhouse-effect.html)

The Human Greenhouse Effect

The part of the greenhouse effect caused by human activity is called he anthropogenic greenhouse effect. It is also sometimes referred to as the enhanced greenhouse effect. 

Here are examples of how humans contribute to the Greenhouse Effect:

Go to Part Five: Science Research Assignment

SNC2P1 Unit 4