The greenhouse effect on Earth
The greenhouse effect on Earth is essential for life on this planet, as it warms the planet to a temperature that is beneficial to life. The greenhouse gases provide a mechanism to trap heat in the atmosphere and on the planet's surface. Too much of a greenhouse effect can lead to higher temperatures which could prove to be harmful to life.
In order to understand the underlying mechanism of the greenhouse effect, we first need to discuss the electromagnetic spectrum, or EM spectrum. In general, a spectrum is a collection of related things. The electromagnetic spectrum is the collection of wavelengths of light.
The graphic above defines EM radiation in terms of the wavelength of light. Here, we use the word "radiation" to discuss radiant light, not to be confused with nuclear radiation. You can see that gamma ray radiation is the shortest wavelength, and radio waves are the longest. The shorter the wavelength, the higher the energy of the light.
Visible light makes up a very small portion of the spectrum. The light with wavelength a little longer than visible light is called infrared, or IR. "Near IR" light is adjacent to visible light, while "far IR" light has longer wavelength.
Not all wavelengths of light penetrate Earth's atmosphere equally well. The above graphic indicates atmospheric opacity as a function of wavelength. Gamma rays and x-rays do not penetrate the atmosphere much at all. For this reason, telescopes that detect these wavelengths of light are typically found in space.
Low energy light, radio waves, also penetrate the atmosphere well, until they are very long wavelength radio. Note here that by radio waves, we do not mean the sound waves that you hear from your radio. The radio waves that are broadcast from the radio transmitter are light waves. The signal is transformed into sound waves in your receiver.
Visible light penetrates the atmosphere very well. Near IR light also penetrates quite well, but far IR light is absorbed by the atmosphere. The gases responsible for the absorption of far IR light are called greenhouse gases. Notable among the greenhouse gases are carbon dioxide (CO2), water vapor and methane (CH4).
The main idea of the greenhouse mechanism is this: Near infrared light from the Sun gets through the atmosphere just fine, and reaches the surface of the Earth. When it warms the Earth, some of the energy of the light is transferred to the Earth. The light that is re-emitted by the ground and ocean has lower energy, and a somewhat longer wavelength. The re-emitted light is far IR light. It cannot pass through the atmosphere well. In the atmosphere, the far IR light is absorbed by the greenhouse gases and re-emitted. Some goes back down to the surface of the Earth. In this way, the greenhouse gases serve to trap heat.
Production of greenhouse gases
Some of mankind's activities contribute to the production of greenhouse gases, particularly carbon dioxide and methane.
About 20 pounds of CO2 are produced by burning one gallon of gas.
The US Energy Information Administration (EIA) estimates that 1.5 billion metric tons of carbon dioxide was emitted by cars and trucks in the US in 2015. This is a huge contribution to the greenhouse gases present in the atmosphere.
The move toward more energy efficient vehicles, and alternate energy vehicles like electric cars is a strong step in the direction of reducing carbon emissions. It should be noted, however, that there are other considerations that need to be taken into consideration, such as the burning of fossil fuels in the manufacture of vehicles, in the manufacture of the electricity used to charge them, and the disposal of heavy metals present in used batteries.
Some companies, like Tesla, have been in the forefront of ensuring that manufacturing plants take advantage of solar power for their operating energy source.
The black smoke in the image above comes from a coal-fired power plant in Conesville, Ohio. The white emissions are water vapor (another greenhouse gas) from the cooling towers. According to the EIA, combustion of one ton of coal results in almost three tons of carbon dioxide. The weight of the CO2 is higher because each carbon atom combines with two oxygen atoms to produce carbon dioxide. In 2011, the US emitted an estimated total of 1.7 billion tons of CO2 from coal-fired power plants (source).
Deforestation is the act of removing forests. The reduction of forests actually contributes to the greenhouse gases in the atmosphere. During the day, plants take in CO2 and emit oxygen. Reducing the number of trees means that there are less trees to remove carbon dioxide from the air. The United Nations Food and Agriculture Organization estimates that 18 million acres of forest are lost to deforestation each year.
The Amazon rain forest has been particularly hard hit by deforestation, as this photo from NASA's Terra satellite shows. Farmers clear forests for croplands, which only produce crops for a short time. The land is then used for livestock, and new land is cleared. This area in Brazil is part of over 67,000 square kilometers that were cleared by 2003 (source).
Deforestation can also occur from indirect effects of warming. This forest in British Columbia, Canada is showing drastic damage caused by an infestation of the Mountain Pine Beetle. This damaging insect has been moving north in recent years due to the milder winters. Millions of acres of trees in Canada and the northern United States are affected by this infestation. The dying forests are vulnerable to wide-scale fires.
Turning forest into rangeland has another hidden effect on greenhouse gases. Cows produce large amounts of methane, a very potent greenhouse gas. An average cow produces 70 - 120 kilograms of methane per year. With 1.5 billion cows worldwide, this has a very large impact of the greenhouse effect. Also, methane is 23 times more powerful as a greenhouse gas than CO2.
Landfill sites contribute to greenhouse gases in the atmosphere. Decomposing waste emits gas, about half CO2 and half methane. Landfill gas produces about 18% of methane emissions in the US (source). In 1994, the Environmental Protection Agency (EPA) created the Landfill Methane Outreach Program (LMOP) to offer incentive to reduce these emissions by using the methane to produce electricity. In 2012 for example, this program was responsible for reducing the amount of methane emitted, producing an energy equivalent to 240 million barrels of oil.
Another indirect effect of the warming climate is the thawing of lake beds in the arctic releasing methane that has been frozen. The methane bubbles up from the lake and is released into the atmosphere.
This video documents University of Alaska Fairbanks Professor Katey Walter Anthony as she investigates methane bubbling up under the ice of a frozen lake near Fairbanks, Alaska.
The ocean conveyor belt is a large-scale water current that loops through the ocean. Warm salty water typically rises to the surface, above cooler, less-salty water. The two mix near the polar regions when the colder surface water becomes salty due to evaporation or formation of sea ice and gets dense enough to sink. video source
With the melting of the ice caps, the northern water becomes less salty. Some climatologists think this could eventually shut down the ocean conveyor belt.
Volcanoes and tectonic plate activity play an important role in the recycling of greenhouse gases, especially carbon dioxide.
Some of the carbon dioxide in the atmosphere is absorbed by water in Earth's oceans and by the surface rock. This carbon dioxide can be eventually recycled. Earth's surface has active tectonic plates, so the surface material can be subducted beneath the surface, heated, and returned to the atmosphere in volcanic eruptions.
If all of the polar ice melted, it would raise the world's oceans an estimated 216 feet. This map shows what the coast of the United States would look like if the oceans rose this much. Florida would no longer exist as a peninsula, it would be completely underwater. The Eastern seaboard would drastically change. Huge population centers currently lie along the east coast, in the affected region. Those people would have to relocate. Elsewhere in the world, similar effects would be seen. Some island chains would be completely gone.
This graph shows the time history of CO2 measured in the atmosphere. Data for recent times was taken directly from the atmosphere. Data for ancient times was taken by analyzing ice cores. Since carbon dioxide is readily absorbed by water and ice, analysis of ice cores gives a good history of atmospheric conditions. This graph indicates a cyclic abundance of CO2 in the atmosphere over the last four hundred thousand years, with a rapid and substantial increase beginning about 1950.
A temperature anomaly indicates how far above or below a temperature is from the average. This time history of global temperatures over the time period from 1880 to the present indicates a dramatic increase in temperature that corresponds to the increase in CO2 in Earth's atmosphere. This timing also roughly corresponds with manmade carbon emissions.
There is very strong consensus among the scientific community regarding the validity of climate change data and analysis. 97 percent of actively publishing climate scientists agree that climate change is real and it is extremely likely due to human activities. A list of scientific societies supporting this statement can be found here.
Some animals species, such as polar bears, are already affected by the rise in temperatures. The early and rapid breakup of pack ice causes a dramatic decrease in food sources for them. Other ecosystems are affected in varying ways. Mangrove stands in Florida are dying because of inundation of salt water. Crops suffer from prolonged droughts. It will put a huge stress on many populations of people who live in strongly affected areas, especially coastal areas and places where desertification rapidly increases. It is likely that the added competition for resources will cause conflicts among population groups.
Without the greenhouse effect, Earth would be uninhabitable. It serves to warm the planet so that oceans are full of liquid water and life thrives. However, the rapid increase of temperature due to enhancement of greenhouse gases by human activity has important consequences that affect the planet as a whole.
How does the greenhouse effect work? How do we affect it? Please watch Earth's Greenhouse Effect and Us.