Since human carbon dioxide (CO2) emissions from burning fossil fuels have been estimated to cause approximately 50% of global warming over the past 30 years (the other 50% being mainly due to other greenhouse gas emissions such as methane, and a small amount due to solar effects), a good way to evaluate your personal global warming impact is to calculate your carbon "footprint". A carbon footprint tells you how much CO2 is released due to your various activities, such as travel, energy consumption, food consumption, etc.
The more information entered into a carbon footprint calculation, the more accurate it will be. For example, if you use a carbon calculator which only asks in which country you reside, it will give you a less accurate carbon footprint estimate than a calculator which asks in which state you reside (if you live in the USA), because power generation sources vary greatly from region to region.
Carbonfootprint.com provides a very detailed (and thus accurate) carbon footprint calculation. It also gives you helpful options, for example entering your yearly home energy consumption in US dollars, kilawatt-hours, or British pounds. Or if you prefer you can checkout the carbon footprint calculator at www.livclean.ca. ClimatePath also provides a streamlined calculator that lets you quickly estimate your footprint based on your home size, location, automobile/driving details, and air travel, and allows you to offset based on the footprint you calculate. It is important to note that whatever the level of detail, carbon footprinting is never an exact science, even for the largest of companies.
If you would prefer to calculate your own carbon footprint without the aid of a calculator, here are some tips:
Try to find the precise CO2 emissions of your car (or motorcycle, or whatever mode of transportation you use). The simplest way to do this is to enter '[car make and model] CO2 emissions g/km' into a search engine. Car emissions are generally measured in grams of pollutant per kilometer, hence the 'g/km'. For example, the Toyota Prius emits 104 g/km of CO2.
Once you find your average transportation emissions, estimate the mileage you travel per year. In order to convert from kilometers to miles (or vice-versa), 1 mile = 1.61 km. Multiply your vehicle's average emissions and yearly mileage to get total transportation emissions. For example, if you drive a Prius 10,000 miles per year:
CO2 emissions = 104 g/km * 10,000 mi/yr * 1.6 km/mi = 1,674,400 grams of CO2 per year.
In the end you'll either want to know your emissions in pounds (lbs) or tons of CO2. 1 lb = 453.6 grams, and 1 metric ton = 2204.6 lbs.
In the Prius example, 1,674,400 grams * 1 lb/453.6 grams = 3,691.4 lbs of CO2, or
3,691.4 lbs * 1 ton/2204.6 lbs = 1.67 tons of CO2 per year from driving a Prius 10,000 miles per year.
If this is too much math, a good quick estimate is 20 lbs of carbon per gallon of gas used.
If you have some old energy bills, you can calculate your carbon footprint due to energy consumption. In the USA, the EPA has a very useful tool which allows you to input your zip code and find out how clean the electricity you use is. Using this calculator will give you a good ballpark of the CO2 emissions from your local electricity consumption pounds per megawatt-hour (lbs/MWh). Another way to determine this value even more accurately is to try and find the number directly from your electric utility provider. For example, Pacific Gas & Electric has its own carbon calculator.
Once you know your home electricity use and the associated CO2 emissions, it's another case of multiplication. For example, if you use 8,000 kilowatt-hours per year, there are 2 people in your home, and your utility provider produces 1300 lbs of CO2 per megawatt-hour (and a megawatt is 1,000 kilowatts):
CO2 emissions per person = 8,000 kWh/year * 1300 lbs CO2/MWh * 1 MWh/1000 kWh / 2 people = 5,200 lbs of CO2 per person.
The simplest way to calculate your carbon emissions from air travel is to estimate the distance you fly each year. According to the Sightline Institute, based on Boeing 747 emissions and the average occupancy of USA flights, every 2,062 miles traveled accounts for 1 ton (2204 lbs) of CO2 emissions per person. So for example if you travel 1,000 miles per year on airplanes:
CO2 emissions per person = 1,000 miles * 1 ton CO2/2062 miles = 0.485 tons of CO2 per person.
This figure is an estimate and will vary depending on factors such as airplane type, headwinds, and how full the airplane is.
See How Your Footprint Stacks Up:
The average annual carbon footprint is:
Californians: 23,000 lbs. = 10.4 tons of CO2 per year
Americans: 44,000 lbs. = 20 tons of CO2 per year
Industrial Nations: 24,000 lbs. = 11 tons of CO2 per year
Worldwide: 8,750 lbs. = 4 tons of CO2 per year