The Three Pillars of Sustainability are Environmental, Social, and Economic demands. Sustainable development is "development that meets the needs of the present without compromising the ability of future generations to meet their own needs". This requires the reconciliation of all three pillars, which are not mutually exclusive, and can be mutually reinforcing.
According to the U.S. Energy Information Administration (EIA), a division of the Department of Energy, the major Greenhouse Gases the United States emitted as a result of human activity in 2008 (and their share of total emissions) were:1
Carbon dioxide (82.8%)
Nitrous oxide (4.3%)
Hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (collectively 2.5%)
There are other greenhouse gases that are not counted in U.S. or international greenhouse gas inventories:
Water vapor is the most abundant greenhouse gas, but most scientists believe that water vapor produced directly by human activity contributes very little to the amount of water vapor in the atmosphere, and therefore EIA does not estimate emissions of water vapor. Recent research by NASA suggests a stronger impact from the indirect human effects on water vapor concentrations.
Ozone is technically a greenhouse gas because it has an effect on global temperature. However, at higher elevations in the atmosphere (stratosphere), where it occurs naturally, it is needed to block harmful UV light. At lower elevations of the atmosphere (troposphere) it is harmful to human health and is a pollutant regulated independently of its warming effects.
These gases are transparent to incoming solar (short-wave) radiation but block infrared (long-wave) radiation from leaving Earth's atmosphere. Therefore, they trap radiation from the Sun and warm the planet's surface. As concentrations of these gases increase, more warming occurs than would happen naturally.
ACarbon Footprintisa measure of the impact our activities have on the environment, and in particular climate change. It relates to the amount of greenhouse gases produced in our day-to-day lives through burning fossil fuels for electricity, heating and transportation etc.
The carbon footprint is a measurement of all greenhouse gases we individually produce and has units of tonnes (or kg) of carbon dioxide equivalent.