What Are They?
Greenhouse gases (GHG)
These are gases that contribute to the greenhouse effect on Earth by trapping gases into the atmosphere.
By order of abundance in the atmosphere, GHG are:
Water vapour (H2O)
Carbon dioxide (CO2)
Nitrous oxide (N2O)
Hydrofluorocarbons (includes HCFCs and HFCs)
Most of these gases are naturally present in the atmosphere. They are not directly harmful to humans or animals’ health (except ozone (O3) above concentrations of about 0.1 ppm). However, human activity has increased their concentration, creating a warming effect with rippled effects on the environment and society.
Others are pure products of human activity (CFCs, HCFCs & HFCs).
According to the EPA, the impact of these gases on climate change depends on three key factors:
How much is in the atmosphere?
Concentration is the quantity of a particular gas in the air - increased emissions of GHG emissions result in higher concentrations in the atmosphere.
When measuring GHG emissions, two measures are commonly used:
1. “CO2 equivalent” units of CO2 (CO2e)
2. Another measure is the atomic weight, typically “carbon.”
However, converting GHGs to kg of carbon is not helpful as it does not compare different GHGs.
Please use CO2e. Make sure that the metrics are actually comparable to GHG emissions (such as by looking at CO2e and not CO2). CO2 emissions make up 76% of the CO2e.
Companies in their reports mention their data in CO2e, while some sites that give per capita emissions use CO2 metrics. Therefore, please convert CO2 to CO2e (equivalents) for an accurate comparison.
How long do they remain in the atmosphere?
These gases can stay in the atmosphere for different amounts of time, ranging from a few years to thousands of years. However, these gases remain in the atmosphere long enough to become well mixed, so the amount measured in the atmosphere is equivalent worldwide, regardless of the emissions’ location.
How strongly do they impact the atmosphere?
Some gases are more effective than others at warming the planet. For each greenhouse gas, a Global Warming Potential (GWP) has been calculated to reflect how long it stays in the atmosphere on average and how strongly it absorbs energy. Gases with a higher GWP absorb more energy, per unit of mass, than gases with a lower GWP, thus contributing more to warming Earth.
The IPCC considers 6 GHGs to be relevant for human-caused climate change:
Global Warming Potential
Carbon dioxide (CO2)
Nitrous oxide (N20)
124 - 14,800
7,390 - 12,200
Sulfur hexafluoride (SF6)
Nitrogen trifluoride (NF3)
- “CO2e” (e standing for “equivalent”) takes into account the various greenhouse effects of these gases in terms of warming and lasting. This is a simple unit that agglomerates ALL GHG.
- Even if the individual warming effect can be mentioned in an analysis, it can be misleading to state that, for example, methane (CH4) has 25 times more GH effect than CO2, as this is already accounted for in the CO2e reporting.
Scientists define energy as the ability to do work. We have learned to change energy from one form to another, to use it to do work.
Different forms of energy exist, including:
There is also a multitude of sources of energy, which can be split into two basic categories:
Renewable energy sources, which can be easily replenished (biomass, hydropower, geothermal, wind, solar, nuclear energy*)
Nonrenewable energy sources, which cannot be easily replenished (petroleum, hydrocarbon gas liquids, natural gas, coal)
*Nuclear energy can sometimes be considered by companies as renewable, so use your critical judgment when reporting their figures.
Companies consume energy, often electricity, throughout their operations, products, and services. All forms of electricity generation and consumption have an environmental impact on air, water, and land, but it varies depending on the type of energy and quantity.
Energy vs Electricity
As you look through a company’s report, they will often state their electricity consumption, especially renewable electricity consumption. Keep in mind that electricity is only one part of their energy consumption. For example, the company may report that they use 50% renewable electricity, but you may find that only 15% of their total energy consumption is renewable.
Energy vs Power
Energy is the “quantitative property that must be transferred to an object in order to perform work on, or to heat, the object”. In other words, it describes the quantity of work needed to perform a particular task.
Power is an “amount of energy transferred or converted per unit time”. In other words, it describes how fast a task can be done.
For example, a typical windmill delivers 3 megaWatt (MW) = 106 W. During one hour at full power, it will have produced 3 MW x 1 hour = 3 MWh (Energy = Power x Time)
Thus, energy units: GJ, Watt Hour (Wh, kWh, MWh, and further multiples)
Power units: Watt (W, kW, MW, and further multiples)