- UNDERSTAND The causes of global warming
- EXPLORE major sources of greenhouse gases
- LEARN what you can do
carbon dioxide & greenhouse gas
Global warming is THE HOT environmental topic of the year. It has been blamed for everything from Hurricane Katrina to melting glaciers in the Swiss Alps, and former Vice President Al Gore made a movie about it that grossed over $20 million.
But the problem seems so huge, what can we as individuals do about it? And, even if we act together, are we already too late?
To learn more about climate change and global warming, read on. To jump directly to steps you can take to reduce climate change, click here.
causes of global warming
Over the past 400,000 years, average global temperatures have been as high as six degrees above and as low as 17 degrees below today’s average temperatures1. These changes had many different causes, including volcanic eruptions, oscillations in the Earth’s orbit around the sun and changes in greenhouse gas concentrations.
Scientists say that the earth’s average temperature could rise by between 2.5 and 10 degrees Fahrenheit by 21002. This would put global average temperatures at the highest levels in thousands of years. But it is not the level of temperature rise that makes today’s global warming dangerous: it is its speed and its causes. The temperature today is changing at a rate faster than ever, and it is caused by man-made mechanisms, not the natural ones that led to previous climate oscillations.
Today, climate change is being driven by the addition of carbon dioxide and other greenhouse gases to the earth's atmosphere at rates faster than the planet's normal mechanisms can adjust to. The result is increasing concentrations of these gases in the atmosphere, and because they trap heat, increasing temperatures. Temperature trends are best shown by the famous “hockey stick graph”, shown in the movie “An Inconvenient Truth” and repeated below.
So, why should we be worried? The reason is that changes smaller than those predicted by many climate change models could have major environmental consequences. These include:
- Rises in sea level of as much as three feet across the globe, flooding land where millions of people now live
- Reductions in rainfall across vast areas where crops are now grown
- The melting of many glaciers and a rise in snow elevations, affecting water supplies across the globe
- Storms including hurricanes of increasing intensity and frequency
- Extinction of animal and plant species as the pace of change in habitat driven by global warming outstrips their ability to adjust
Some scientists make even more dramatic predictions.
As shown in “An Inconvenient Truth”, the Greenland ice sheet is melting at a rate faster than predicted by many climate models. The melting of this sheet could shut down the circulation of warm water in the Atlantic Ocean, plunging Europe into a new ice age while the rest of the planet continues to warm. And, a catastrophic fracture of various ice sheets in the Arctic and Antarctic regions could cause sea level to rise by amounts as high as 20 feet in a very short period of time.
This all sounds grim, but there is still time for us to do something about it. Scientists estimate that stabilizing carbon emissions at the present rates for the next fifty years would avoid the most significant global warming impacts. Reductions above and beyond this would obviously help more. And, this level of reduction, although difficult, is obtainable using technologies either available today or in the near future3.
major sources of greenhouse gases
There are many different gases that contribute to climate change, but carbon dioxide is the biggest culprit, producing 60% of the human-enhanced greenhouse effect that leads to global warming4. While carbon dioxide is naturally present in the atmosphere, levels remained relatively flat until industrialization: after varying within 10% for the 10,000 years before 1800, it has increased by 30% in the 200 years since5.
About 95% of manmade carbon dioxide comes from the supply and use of fossil fuels6. These fuels provide energy because they are made up of chains of carbon and hydrogen atoms that, when broken through burning, release tremendous amounts of energy. Unfortunately, the byproduct of this burning is also tremendous amounts of carbon dioxide: burning one gallon of gas (which weighs about six pounds) produces almost 20 pounds of carbon dioxide.
Worldwide, the United States generates over 21% of the world's carbon dioxide emissions, followed by China (17%), Russia (6%), Japan (5%) and India (4%)7. Our per capita generation was nearly 22 tons per person; China, Russia, Japan and India was responsible for 3.5, 11, 11, and 1 ton, respectively8.
In the US, the government allocates emissions to four separate “sectors” for reporting purposes. These are the transportation sector, which includes all fuels consumed by any mode of transportation, the residential sector, which includes all non-transport emissions from residential settings (including electricity), commercial, which includes non-transport emissions from office, retail and other business-related activities, and industrial, which includes non-transport emissions from manufacturing and other industrial processes. The largest source of carbon dioxide is the transportation sector, followed by industrial and residential (see chart below)9.
Direct residential carbon dioxide emissions, which come from burning natural gas, fuel oil, and propane and also using electricity, represent 21% of total emissions. When you add an estimate of carbon dioxide emissions from household travel, residential consumption produces over 35% of the carbon dioxide emitted in the United States. This represents 8% of the world total. And, this STILL doesn't include the carbon dioxide produced by the factories and stores that supply us with products for our everyday lives. Taken all together, it is clear that as individuals we DO have some control over greenhouse gas emissions.
1 Petit, J.R., et al., 2001, Vostok Ice Core Data for 420,000 Years, IGBP PAGES/World Data Center for Paleoclimatology Data Contribution Series #2001-076. NOAA/NGDC Paleoclimatology Program, Boulder CO, USA
2 Intergovernmental Panel on Climate Change
3 Based on Socolow and Pacala article “Stabilization Wedges: Solving the Climate Problem for the Next 50 Years with Current Technologies,” Science Magazine, August 2004.
4 United Nations Environmental Program
5 United Nations Environmental Program
6 United Nations Environmental Program
7 US Energy Information Administration
8 United Nations, Millennium Development Goals Indicators
9 US Energy Information Administration
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