Chapter 3 illustrated how the Earth's energy drives plate tectonics, affecting CO2 levels and interactions with air masses in the atmosphere. Related to this, the energy of volcanoes can also affect climate because volcanoes emit both aerosols and CO2 into the atmosphere. When a volcano erupts, it can send ash and sulfate gases to great heights in the atmosphere. If the sulfate combines with water, it produces tiny droplets of sulfuric acid, called aerosols. Aerosols are very small solid particles or liquid droplets dispersed in a gas—usually air.
When aerosols enter the atmosphere, they tend to block the Sun's incoming energy. If sunlight cannot reach the Earth's surface, this causes a cooling effect. Fortunately, aerosols do not stay in the atmosphere for extremely long periods of time like certain greenhouse gases do. Some particulates such as ash are big enough that they settle out of the atmosphere quickly. The finer the particulates, the longer their potential time in the atmosphere. Aerosols are not responsible for long-term climate change. Over a period of time, precipitation removes them.
Major volcanic eruptions can have a noticeable short-term effect on climate. For instance, in 1815, the Tambora volcano in Indonesia erupted. A major eruption, its particulates were carried high into the atmosphere and carried around the Earth. Effects were noticed as far away as New England in the United States, which had a "year without a summer." Climatologists calculated that the Tambora eruption alone was responsible for lowering global temperatures by as much as 5°F (3°C). A massive volcanic eruption can cool the Earth's climate for one to two years.
Volcanoes do emit CO2 and, because this is a greenhouse gas, if enough is released, it can contribute toward global warming. According
Mount St. Helens erupted on May 18, 1980. The eruption sent volcanic ash, steam, water, and debris to a height of 60,000 feet (18,288 m). The volcano lost 1,300 feet (396 m) of altitude and about two-thirds of a cubic mile of material. (Austin Post, USGS)
to scientists at the USGS Volcano Hazards Program, there is evidence that the majority of the past 400 million years has seen an elevation in global temperatures because of volcanic eruptions. This ties in with the plate tectonic theory presented in chapter 3.
Just as short-wave radiation comes from the Sun, long-wave radiation comes from the Earth. Like the Sun, the Earth also gives off radiation; but unlike the Sun, the wavelengths given off are very long. It gives off longer wavelengths because it is a much cooler body than the Sun (the hotter the body, the shorter the wavelength). Sometimes it is possible to indirectly see heat radiation. On a hot day, the shimmering effect seen just above a hot road surface is the heat being radiated from the road. The amount of energy given off by the Earth is equal to the amount it receives from the Sun. Otherwise, the Earth would just continue to heat up. Fortunately for life on Earth, the Earth is able to maintain an energy balance, which will be discussed later in this chapter.
Outgoing energy from the Earth comes from several sources: plants, animals, volcanoes, rocks, buildings, and roads, to name a few. All of the outgoing energy added together is the same amount as the amount of radiation the Earth absorbs. This is why the Earth maintains a fairly constant temperature. If the input/output were not equal, then if outgoing radiation was higher than what was absorbed, the Earth would cool down. If outgoing was less, the Earth would heat up.
The ability of an item to give off energy is called emissivity. Each object on Earth has its unique emissivity. For comparisons, scientists assign a black object an emissivity of 1.0. They compare all other objects to this base. For example, a rock has an emissivity of 0.8, which means it emits only 80 percent of the absorbed energy compared to what a black object would. The concept of emissivity is important when dealing with global warming because when objects begin to retain—or absorb— heat, instead of emit—or release—it, it heats up the atmosphere. An example of this is CO2 absorbing infrared energy, which in turn heats the atmosphere.
The general emissivity in areas can also be changed and upset in other ways, sometimes creating a negative result toward increasing global warming. Changing the use of the land's surface can have a significant impact. For example, deforestation of the Earth's rain forests changes the energy balance and the amount of energy leaving the Earth, which can then have long-term effects on the climate.
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