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October 22, 1998

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.


Greenhouse gases in our backyard

Early Sunday morning shoppers at the Volcano farmers market can purchase delicious greenhouse tomatoes grown in Mountain View. In a cool mauka (inland) environment, the greenhouse provides the essential warmth that tomatoes require.

In fact, all of Earth's inhabitants rely on a naturally occurring greenhouse effect to provide the warmth necessary to sustain life. Gases in our atmosphere allow much of the incoming solar energy to reach and warm the Earth's surface. The Earth and lower atmosphere reflect some of this incoming energy back as heat energy. The gases that encircle the Earth allow some of this heat to escape into space, but absorb some and reflect another portion back to the Earth. The process is similar in Mountain View, only, the greenhouse there is made of glass instead of gas.

Without this naturally occurring greenhouse effect, the Earth's temperature would often be below freezing, rather than the global average of 15?C (59?F) that allows the existence of the familiar life-forms that we have grown to cherish (such as tomatoes) as well as those we dislike (such as mosquitoes). Our heavenly neighbors, Venus and Mars, provide an example of how the quantity of a greenhouse gas like carbon dioxide (CO2) can affect a planet. Venus's CO2-rich atmosphere creates a "runaway greenhouse effect" and an average surface temperature of 480?C (900?F). Mars, on the other hand, has a CO2 -poor atmosphere with virtually no greenhouse effect and an average temperature of -60?C (-80? F).

Increases in greenhouse gas in our atmosphere can create changes in global temperatures that, in turn, disrupt the environmental balance. Carbon dioxide (CO2) is an important component in the potent chemical cocktail of greenhouse gases. It is the gas whose concentration is most affected by human activity. The major source of human-made CO2 emissions is the burning of fossil fuels. CO2 concentrations have increased by more than 20% in the short period since industrialization and are expected to double sometime after the year 2040.

On the Big Island, we have a significant natural source of greenhouse gas. Kilauea volcano emits more than 700,000 tons of CO2 each year, less than 0.01% of the yearly global contribution by human sources. For some local perspective, this is about the same amount of CO2 as is emitted by 132,000 sport utility vehicles (there are 118,000 registered vehicles on the island).

Kilauea also emits a generous amount of sulfur dioxide gas (SO2), (over 8 million tons in the last 16 years), which reacts chemically in the atmosphere to form sulfate aerosols. These tiny solid particles and liquid droplets are familiar to us as components of vog. It is speculated that sulfate aerosols, most of which are formed by the burning of fossil fuels, actually lower, rather than raise, the Earth's temperature by reflecting away solar radiation.

The 1991 eruption of Mount Pinatubo in the Philippines ejected enough particulate matter and sulfate aerosol into the atmosphere to block some of the incoming solar radiation from reaching the Earth's surface. This effectively cooled the planet from 1992 to 1994, masking the documented warming that occurred for most of the 1980s and 1990s. Eruptions like Pinatubo have occurred several times over the last 100 years or so.

The reflection of solar radiation back to space by sulfate aerosols is estimated to have reduced the warming effect associated with increases in greenhouse gases by one-half. The next time we're tempted to grumble about the SO2 gas and vog from Kilauea, we can remember the role volcanic SO2 plays in the greenhouse effect balancing act.

Eruption and Earthquake Update

There was no change in the eruptive activity at the Pu`u `O`o vent during the past week. Lava continues to flow through a network of tubes from the vent to the seacoast where it enters the ocean in three locations near Kamokuna. Occasional breakouts from the tube system produce surface flows - mainly near the base of the pali and on the coastal flats. One of these surface flows entered the ocean about 700 m (1/2 mi) west of Kamokuna on October 19. The public is reminded that the ocean entry areas are extremely hazardous, with explosions accompanying frequent collapses of the lava delta. The steam clouds are highly acidic and laced with glass particles.

There were no earthquakes reported felt from October 9 to the late afternoon of October 22.

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Updated: 27 Oct 1998