Thursday, August 18, 2011

Pondering Climate and the Greenhouse Effect

While most of the world has moved on to other more pressing issue, the climate change debate still rages among the devoted. Joseph Postma is a smart guy with degrees and everything that believes that CO2 has no significant impact on climate at all. Postma has a published paper, The Model Atmospheric Greenhouse Effect,where he attempts to set the scientific world straight. I can't really comment on the paper because the error in calculating the average solar power at the Earth's surface is so obvious, I won't waste my time. A year or so ago when I first heard of this my bullshit detector went off and I did the rough calculations myself and they happen to agree with NASA and the rest of the mathematically literate world, not Mr. Postma.

Most view Postma arguments comical or worse, but he some sway in the radical skeptic community. One defense he uses for his calculations is that there would be no liquid water on the planet if NASA's numbers are right. He is wrong, but the liquid water thing is something I have never written about.

Water is a remarkable substance. While all life needs to consume water to survive, water is much more important to our survival. On our world which has a surface covered with 70% water, things are a lot different than if there was less or if it were not located where it is. For example if the water was only at the poles and all the land mass was at the equatorial region, there would be no life as we know it. If there was 50% water and 50% land the same thing. Climate is somewhat stable because of the amount, location and properties of water. Our climate is extremely sensitive to water in all its phases.

First, think about the reflectivity of the Earth or its albedo. Snow is highly reflective, the tops of clouds highly reflective and liquid water high absorptive of solar radiation. Snow and ice reflect between 90 and 95 percent of the sun's rays. Water absorbs about 93% of the sun's rays. Same molecule, radically different properties. Water also has one of the highest thermal capacities of any element as a liquid, solid or vapor. It is remarkable.

The average albedo of the Earth right now is about .7 meaning we absorb about 70% of the solar radiation. The vast majority of that albedo is due to water which covers most of the Earth's surface and a good portion of the atmosphere. While the climate change debate is mainly about CO2 which may cause a percent or so change in the outgoing radiation that cools the Earth, water can make a 10% change in the outgoing and the absorbed incoming with just a little push.

With climate, water's importance is best viewed by the conditions during the glacial periods. Some trigger, an asteroid impact, slight change in orbit, passing through a comet's tail can reduce the absorbed solar radiation enough that more ice and longer lasting snow cover persists for a while. This decreases the Earth's albedo which decreases the heat absorbed, decreasing the heat stored in the oceans. The Earth moves toward what has been called a snowball Earth. Unlike too much global warming, too much global cooling has happened pretty regularly. Luckily, Snowball Earth is not really a complete snowball. Glaciers move further towards the equator and move closer to the surface, but never completely cover the entire planet. If they did, Earth would not recover without another catastrophic event. All indications I have seen indicate that the Earth recovers naturally until the albedo increases to a magic number that cues a new interglacial period like the one we enjoy now.

It is not really magic, but the combination of the right albedo, the right solar cycle series and the right amount of volcanic activity cue the change. There is not a lot of solar change, nor a lot of volcanic change, but a little of each change albedo which feeds back on itself to cause the big change. Just like the right decrease in albedo triggered and amplified the cooling, the right increase in albedo triggers the warming. The Earth has two temperature set points controlled primarily by albedo which is controlled by water.

Mr. Postma seems to think that the calculated average solar energy input is not enough to sustain liquid water. In my opinion this is the most glaring error of his paper. Even in the glacial periods which have much lower solar energy absorbed there is still liquid water near the equator. Since there is much more water along the equator than there is land, even a snowball Earth can sustain life.

Water is also the largest unknown in the global warming debate. A warmer world means the atmosphere can hold more water vapor which can either add to the warming or tend to reduce the warming. The room for warming to increase albedo is not as large as the room to reduce albedo. There will always be ice and snow at the poles in winter which will persists into the summer. The normal weather patterns with more water vapor in the air means the chance of larger snow storms and rain storms increase, both reduce albedo. The warming can cause longer and more severe droughts, but droughts are over land and most of the droughts will be in the temperate latitudes. Droughts in the temperate zones have less impact on albedo, tend to increase atmospheric dust which can promote cooling and increase radiative cooling locally because of less water vapor.

Increased water vapor also tends to block a portion of the CO2 radiative impact at the surface. The reason most impact of increased CO2 should be at the poles and upper troposphere is because there is less competition with water vapor.

So while there is no guarantee that warming will not be enough to worried about, thanks to water the likelihood of catastrophic warming is reduced.

Note: The average albedo is more like 30% meaning the absorbed is 70%. So the references to albedo are reversed, but the idea remains the same.

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