What Are Greenhouse Gases and the Greenhouse Effect

The greenhouse effect often gets a bad rap because of its association with global warming, but the truth is we couldnt live without it. What Causes the Greenhouse Effect? Life on earth depends on energy from the sun. About 30 percent of the sunlight that beams toward Earth is deflected by the outer atmosphere and scattered back into space. The rest reaches the planets surface and is reflected upward again as a type of slow-moving energy called infrared radiation. The heat caused by infrared radiation is absorbed by greenhouse gases such as water vapor, carbon dioxide, ozone, and methane, which slows its escape from the atmosphere. Although greenhouse gases make up only about 1 percent of the Earths atmosphere, they regulate our climate by trapping heat and holding it in a kind of warm-air blanket that surrounds the planet. This phenomenon is what scientists call the greenhouse effect. Without it, scientists estimate that the average temperature on Earth would be colder by approximately 30 degrees Celsius (54 degrees Fahrenheit), far too cold to sustain most of our current ecosystems. How Do Humans Contribute to the Greenhouse Effect? While the greenhouse effect is an essential environmental prerequisite for life on Earth, there really can be too much of a good thing. The problems begin when human activities distort and accelerate the natural process by creating more greenhouse gases in the atmosphere than are necessary to warm the planet to an ideal temperature. Burning natural gas, coal, and oil, including gasoline for automobile engines, raises the level of carbon dioxide in the atmosphere, upsetting a balance between the release and capture of the gas by plants and algae.Some farming practices and other land uses increase the levels of methane and nitrous oxide. Just exposing soils when plowing leads to carbon dioxide release.Many factories produce long-lasting industrial gases that do not occur naturally, yet contribute significantly to the enhanced greenhouse effect and global warming that is currently underway.Deforestation also contributes to global warming. Trees use carbon dioxide and give off oxygen in its place, which helps to create the optimal balance of gases in the atmosphere. As more forests are logged for timber or cut down to make way for farming, however, there are fewer trees to perform this critical function. At least some of the damage can be offset when young forests aggressively regrow, capturing tons of carbon.Popula tion growth is another factor in global warming because as more people use fossil fuels for heat, transportation and manufacturing the levels of greenhouse gases continues to increase. As more farming occurs to feed millions of new people, more greenhouse gases enter the atmosphere. Ultimately, more greenhouse gases mean more infrared radiation trapped and held, which gradually increases the temperature of the Earths surface, the air in the lower atmosphere, and ocean waters. The Average Global Temperature Is Increasing Quickly Today, the increase in the Earths temperature is increasing with unprecedented speed. To understand just how quickly global warming is accelerating, consider this: During the entire 20th century, the average global temperature increased by about 0.6 degrees Celsius (slightly more than 1 degree Fahrenheit).Using computer climate models, scientists estimate that by the year 2100 the average global temperature will increase by 1.4 degrees to 5.8 degrees Celsius (approximately 2.5 degrees to 10.5 degrees Fahrenheit). Scientists agree that even small increases in the global temperature lead to significant climate and weather changes, affecting cloud cover, precipitation, wind patterns, the frequency and severity of storms, and  the timing of seasons. Rising temperatures would raise  sea levels  as well, damaging infrastructure and reducing supplies of freshwater as flooding occurs along coastlines worldwide and saltwater reaches inland.Many of the world’s endangered species would become extinct as rising temperatures changed their habitat, and  affected the timing of seasonal events.Millions of people also would be affected, especially poor people who live in precarious locations or depend on the land for a subsistence living.  Food production, processing, and distribution  can be affected, as well as national security.Certain vector-borne diseases carried by animals or insects, such as malaria and  Lyme disease, would become more widespread as warmer conditions expanded their range. Carbon Dioxide Emissions  Are the Biggest Problem Currently, carbon dioxide accounts for more than 60 percent of the enhanced greenhouse effect caused by the increase of greenhouse gases, and the level of carbon dioxide in the atmosphere is increasing by more than 10 percent every 20 years. If emissions of carbon dioxide continue to grow at current rates, then the level of the gas in the atmosphere will likely double, or possibly even triple, from pre-industrial levels during the 21st century. Climate Changes Are Inevitable According to the  United Nations, some climate change is already inevitable because of emissions that have occurred since the dawn of the Industrial Age. While the Earth’s climate does not respond quickly to external changes, many scientists believe that global warming already has significant momentum due to 150 years of industrialization in many countries around the world. As a result, global warming will continue to affect life on Earth for hundreds of years, even if greenhouse gas emissions are reduced and the increase in atmospheric levels halted. What Is Being Done  to Reduce Global Warming? To lessen those long-term effects,  many nations, communities, and individuals are taking action now to reduce greenhouse gas emissions and slow global warming by reducing dependence on fossil fuels, increasing  the use of renewable energy, expanding forests, and  making lifestyle choices  that help to sustain the environment. Whether they will be able to recruit enough people to join them, and whether their combined efforts will be enough to head off the most serious effects of global warming, are open questions that can only be answered by future developments. Edited by  Frederic Beaudry.