Geoengineering - Possible Ways to Counteract Global Warming

To All:
    In this month's (Nov. 2008) issue of Scientific American, there is an article on proposed ways to cool the Earth. Some excerpts follow:
============================================================http://www.sciam.com/article.cfm?id=geoengineering-how-to-cool-earth
#1.    Particles in the Stratosphere:
    The geoengineering scheme Crutzen and Wigley both defend is the cheapest and most certain to work; The idea is to inject several million tons a year of sulfur dioxide (SO2) into the stratosphere. There it would react with oxygen, water and other molecules to form minute sulfate droplets made up of water, sulfuric acid (H2SO4) and whatever dust, salt or other particles onto which the acid and water condense. Clouds of sulfate droplets would scatter sunlight, making sunsets redder, the sky paler and the earth’s surface, on average, cooler—everyone agrees on all that. In 1991 the volcanic eruption of Mount Pinatubo in the Philippines put 20 million tons of SO2 into the stratosphere, and it had all those effects: it cooled the earth by nearly one degree Fahrenheit for about a year. “So we basically know it works,”
#2.    Sea Mist in the Troposphere:
    John Latham’s idea for cooling the planet is essentially to whiten existing marine clouds by lacing them with lots of ship tracks—but made in a cleaner way. Latham, a retired English cloud physicist, thinks spraying microscopic drops of seawater into the sky from a fleet of unmanned sailing vessels could do the trick.     In principle, adding particles to the atmosphere makes for more but smaller drops, hence whiter and more reflective clouds.
#3.     A Sunshade in Space:
    This proposal calls for placing a sunshade at L1, the inner Lagrangian point, a million miles from the earth in the direction of the sun. (At a Lagrangian point the sun exerts the same pull of gravity as the earth does.) From L1 a sunshade would cast an even shadow over the planet without polluting the atmosphere. ===========================================================    Now as the article says, these ideas are not without possible unknown risks, and even if they work they are short term stopgap measures. But at least some people are doing more than just complaining about the problem and are generating & offering possible solutions - if only temporary.
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Acid rain?
JC
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John R. Carroll wrote:

John:
    Yes, that's one of the possible downsides.
====================================================================    Whether or not there is less of it, the rain is likely to become more acidic if we put millions of tons of sulfuric acid into the stratosphere. Globally, the acid increase will probably be small—because we are already putting so much SO2 into the lower atmosphere... ====================================================================
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BottleBob wrote:

Uh... Isn't sulfuric acid in the atmosphere a big part of what's wrong with Venus? And isn't water the "worst" of the so-called greenhouse gasses, in terms of its ability to let sunlight into the atmosphere, and then trap heat before it can escape into space?
KG
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Kirk Gordon wrote:

Kirk:
    Yes, Venus has sulfur dioxide clouds. But I think Venus' runaway greenhouse effect is mainly due to it's atmosphere being predominately CO2 AND being thick, to the extent of ~ 1,300 PSI at the surface.
================================================================Atmosphere of Venus:
    Venus has an extremely dense atmosphere, which consists mainly of carbon dioxide and a small amount of nitrogen. The atmospheric mass is 93 times that of Earth's atmosphere while the pressure at the planet's surface is about 92 times that at Earth's surface—a pressure equivalent to that at a depth of nearly 1 kilometer under Earth's oceans. The density at the surface is 65 kg/mł (6.5% that of water). The enormously CO2-rich atmosphere, along with thick clouds of sulfur dioxide, generates the strongest greenhouse effect in the solar system, ===============================================================

    If the Earth didn't have ANY water vapor in the form of clouds, it's albedo (reflecting ability) would drop and more radiation would reach the surface, BUT...
==================================================================http://en.wikipedia.org/wiki/Albedo
Clouds
    Clouds are another source of albedo that play into the global warming equation. Different types of clouds have different albedo values, theoretically ranging from a minimum of near 0% to a maximum in the high 70s. "On any given day, about half of Earth is covered by clouds, which reflect more sunlight than land and water. Clouds keep Earth cool by reflecting sunlight, but they can also serve as blankets to trap warmth."[ =================================================================    Now what confuses the issue is that water vapor and sulfur dioxide clouds can have the dual effect of cooling AND warming, that are diametrically opposed.
    Perhaps the space based filtering ideas might be a more clear cut option.
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========================================> Atmosphere of Venus:

========================================>
==========================================>
Bob, I believe there is something about the size of the droplets, that affects the albedo. This is IIRC the concern of current "Global Dimming" studies, where the fine particulates of jet aircraft help to create smaller more reflective droplets, and affect "global dimming"
Interesting, apparently on 9/12 the temperature of the earth dropped from grounding the airfleet. So the study goes.
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Half-nutz wrote:

HN:
    The original Sci-Am article mentioned that:
=============================================================http://www.sciam.com/article.cfm?id=geoengineering-how-to-cool-earth&page=4
    The basic mechanism of the aerosol indirect effect is simple enough. The amount of sunlight reflected by a cloud depends on the surface area of the water drops that make up the cloud. “If instead of having a few big drops, you have a lot of little drops, then for the same amount of water [condensing from the vapor phase into droplets], there’s more surface area,” Latham explains. In principle, adding particles to the atmosphere makes for more but smaller drops, hence whiter and more reflective clouds. ============================================================> Interesting, apparently on 9/12 the temperature of the earth dropped

    I think you meant to say the temp. increased, not dropped.
==============================================================http://archives.cnn.com/2002/TECH/science/08/07/contrails.climate/index.html
    During the three-day commercial flight hiatus, when the artificial clouds known as contrails all but disappeared, the variations in high and low temperatures increased by 1.1 degrees Celsius (2 degrees Fahrenheit) each day, said meteorological researchers.     While the temperature range is significant, whether the jet clouds have a net effect on global warming remains unknown. ==============================================================
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=====================================>
======================================>
Bob, Right again.
Seems counterintuitive that H2O is the primary greenhouse gas, and ALSO a possible reflector. it is an amazing world we live in isn't it?
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