Today’s level of carbon dioxide (CO2)concentration is around 375 parts per million. This is considered to be the highest level in 420,000 years. Since pre-industrial times, CO2 concentration in the atmosphere has increased by about 31 per cent, methane concentration by about 150 per cent and nitrous oxide concentration by about 16 per cent.
When we drive our car, heat our homes, make hot water, watch TV, use other electrical devices, we inject CO2 into the atmosphere. Visit the Personal CO2 Calculation, fill in the required details in the form and the calculator will tell you your yearly direct personal CO2 emissions. In leading industrial countries, individual energy use and carbon emissions have actually increased in recent years. See table Carbon Dioxide Emissions From Energy Consumption by Sector for amount of carbon emissions by sector.
 Maximum Emissions
Developed countries, led by the US, are responsible for maximum emissions. Though, owing to industrial development over the last 20 years, Asian countries have seen increased emissions, they still emit much lower amounts than developed countries. See The Top 20 Carbon Dioxide Emitters for comparisons in emissions.
- 25 per cent man-made carbon emission from deforestation: According to the Food and Agriculture Organization (FAO) of the United Nations, deforestation accounts for around 25 per cent of man-made emissions of CO2. About two billion tonnes of carbon are released per year on account of deforestation. This carbon release mostly happens due to felling of tropical forests in Asia, South America and Africa. According to the FAO, 283 gigatonnes (Gt) of carbon are stored in the biomass of the forests. There is also a combined one trillion tonnes of carbon altogether in forest biomass, deadwood, litter and soil. This works out to 50 per cent more than the amount of carbon found in the atmosphere.
- More greenhouse emissions from livestock than cars: Another report of the FAO states that livestock generates more greenhouse gas emissions than transport. This is because of increased consumption of meat; global meat production is expected to rise to 465 million tonnes in 2050 against 229 million tonnes in 1999-2001.
- Better road conditions reduce CO2 emissions: Better infrastructure in terms of improved roads and traffic management leads to reduction of CO2 emissions. This was experimented successfully in Japan when the "Oji Section" of the Tokyo Metropolitan Expressway opened in December 2002. It was found that because of the new road and better flow of traffic, annual CO2 emissions reduced by between 22,000 and 31,000 tonnes.
 Greenhouse Gas Emissions
Greenhouse gas emissions come from four main sources:
- The burning of fossil fuels to make electricity.
- Industrial, commercial and residential burning of fossil fuels for heat and the use of other emission-producing processes.
- The burning of fossil fuels to power transportation.
- The emissions produced through agriculture and miscellaneous activities.
Apart from CO2, the primary emissions and their sources are as follows:
- Methane emissions: Methane emissions are caused by both man-made and natural sources. It is estimated that human-related activities, such as fossil fuel production, animal husbandry (enteric fermentation in livestock and manure management), rice cultivation, biomass burning and waste management, release 60 per cent of global methane emissions in the atmosphere. Natural sources of methane emissions include wetlands, gas hydrates, permafrost, termites, oceans, freshwater bodies, non-wetland soils and other sources such as wildfires.
- Nitrous oxide: Nitrous oxide (N2O) is also produced by both natural and human-related sources. Primary human-related sources of N2O include agricultural soil management, animal manure management, sewage treatment, mobile and stationary combustion of fossil fuel, adipic acid production and nitric acid production. Nitrous oxide is also produced naturally from a wide variety of biological sources in soil and water, particularly microbial action in wet tropical forests. For more information on international emissions of N2O from human-related sources, visit International Analyses
 Air Quality Emissions
The primary air quality emissions and their sources are as follows:
- Ozone: Chemical reactions between human-produced and other atmospheric emissions cause ozone emissions. When in the upper atmosphere, ozone protects the earth from the sun's radiation and is beneficial. But in the lower atmosphere, the smog it creates causes respiratory problems and damage to plant and animal life.
- Carbon monoxide: Fossil fuels used in transportation are the main cause of carbon monoxide emissions. To some extent, these emissions also result from electricity production and natural events such as forest fires. Once released in the air, carbon monoxide aggravates heart disease and damages the human nervous system.
- Nitrogen oxide: Nitrogen oxide emissions are caused from the burning of fossil fuels for transportation, electricity, and building and industrial use. It also creates acid rain and ozone in the lower atmosphere, and its emissions cause direct respiratory problems.
- Sulfur dioxide: Burning of fossil fuels with trace amounts of sulfur, like coal and oil, creates sulfur dioxide. The major source of sulphur dioxide, however, is the use of fossil fuels in electricity production. Lesser sources are industrial metal processing, energy production and transportation. Sulfur dioxide creates acid rain and contributes to respiratory problems.
- Particulates: Many different chemicals, including dust, dirt, soot, smoke and other miniscule solids released into the air are called particulates. Major causes are construction activities like road building.
 Volatile Organic Compounds
Many consumer products such as paints, solvents, adhesives, carpeting, deodorants, and cleaning fluids contain volatile organic compounds (VOCs). When released into the air, VOCs react with other chemicals to create ozone in the lower atmosphere.
 Measuring Emissions from Satellite
The US is planning to launch two greenhouse gas observation satellites — GOSAT and OCO — in 2008 for measuring CO2. These are being launched to reduce uncertainty about human impact on climate. The data provided by the satellites will have the potential to revolutionise our quantitative understanding of the land-component of the carbon cycle.
 Preventing Emissions
Nearly 82 per cent of emissions take place because of the burning of fossil fuels to generate electricity and power our cars. The remaining emissions are from methane from waste in our landfills, raising livestock, natural gas pipelines and coal, as well as from industrial chemicals and other sources.
There are three areas where we as individuals can make the most impact in reducing carbon emissions:
- The electricity we use in our homes.
- The waste we produce.
- The transportation we use.
Below are tips on how to reduce carbon emissions and help prevent climate change:
- Change a light. Replace a regular light bulb with a compact fluorescent bulb.
- Drive less. Reduce gas consumption by biking or walking.
- Recycle more and buy recycled. Recycling and buying products with recycled content helps save energy, resources and landfill space.
- Check your tires. Keep tires properly inflated.
- Use less hot water. By saving energy that goes into heating water, you not only reduce your energy bills, but also CO2 emissions.
- Avoid products with a lot of packaging. Purchase products with the least amount of packaging.
- Adjust your home's thermostat. Keep your thermostat at 68°F in winter and 78°F in summer.
- Plant a tree. Trees not only absorb CO2, their shades also keep surroundings cool.
- Turn off electronic devices when not in use. Keeping your TV, VCR, computer and other electronic devices turned off can save each household thousand of pounds of CO2 each year.
 Eye Openers
- If every household in the US replaced a burned-out bulb with an energy-efficient, compact fluorescent bulb, the cumulative effect would prevent greenhouse gas emissions equivalent to that from nearly 800,000 cars. It would also save enough energy to light 2.5 million homes for a year.
- On average, a passenger car emits 5.17 tonnes of CO2 each year, while a home emits 4.08 tonnes of CO2 per person each year in the US.
 References and Useful Links