Sunday, February 21, 2010

AGW the Theory

With Climate Change in the news almost constantly, we are seeing one scandal after another regarding the proponents of the theory of Anthropogenic Global Warming (AGW). Anthropogenic means man made and the theory of AGW says that the global warming we have experienced in the past 100 years is due to mankind and specifically our use of fossil fuels as our main energy source.

We will be looking at this over the next few days. Today I want to look at the theory and science behind AGW.

There has been climate change happening since the beginning of time on the earth. If you ask scientist about the melting ice in the arctic, they will tell you the usual part of this is that there is any ice at the two poles. For most of the geological history of the planet, the world was ice free.

At the same time there was a period when the earth was entirely covered by ice. This was known as the Cryogenian period and occurred between 850 and 630 million years ago. In recent history (the last 500,000 years) we’ve experience 4 ice ages each lasting approximately 100,000 years followed by 15,000 year interglacial periods when the planet warmed.

So back in the 1970s when we had experienced 30 years of cooling temperatures, there were some scientists who worried that we were entering another ice age, but then the temperatures started getting warmer.

In 1988 Dr. James Hansen, the head of GISS, testified before congress that the greenhouse gases mankind was emitting into the atmosphere through the use of fossil fuels was causing a warming of the planet. He warned of dire results from this warming.

Here is what he was talking about. By burning fossil fuels mankind puts carbon into the atmosphere in the form of CO2. CO2 is a greenhouse gas whose molecules will capture certain wavelengths of radiation converting them into energy that warms the molecule which in turn warms the planet.

The radiation from the sun is short wavelength radiation. It will pass easily through the atmosphere, but can be reflected back into space by cloud albedo. Low, thick clouds (such as stratocumulus) primarily reflect incoming solar radiation, causing it to have a high albedo, whereas high, thin clouds (such as Cirrus) tend to transmit it to the surface but then trap outgoing infrared radiation, causing it to have low albedo. It contributes to the greenhouse effect. Snow at the poles also has an albedo effect.

Radiation from the sun is absorb by the ground and then reradiated as long wave radiation. The long wave radiation can be absorbed by greenhouse gases. The energy in this radiation warms the greenhouse molecules which will release the radiation in all directions including back to earth thereby warming the surface again.

Greenhouse gases are important for life on earth. They raise the temperature of the planet. Without greenhouse gases the average temperature would be -18 degrees C versus the 14 degree C we actually experience. The main greenhouse gas is water vapor. We know that CO2 is also a greenhouse gas and one molecule will raise the temperature by X while the next molecule of CO2 will raise the temperature by X-a.

We know that CO2 as a greenhouse gas will increase the temperature by 1.2 degrees Centigrade every time you double the amount of CO2 in the atmosphere (it isn’t linear). This is agreed to by all and is the science that is “settled.” This is the first leg of the AGW theory.

The AGW theory says once the temperature starts to rise due to CO2, more water vapor will be put into the atmosphere as feedback. They see this addition water vapor actually breaking up the low level clouds and forming high level Cirrus clouds that will trap more heat. This in turn will raise the temperature even more and eventually (although the AGW supporters see this as happening soon) you will hit tipping points where permafrost starts to melt, bogs start to warm and all of these give up more and more greenhouse gases causing a runaway greenhouse effect which will raise the temperature even more, melt the ice at the poles and raise the ocean levels by 20 to 30 feet. It is from this that we find the disaster scenarios we keep hearing about in the press. This feedback is the second leg of the AGW theory.

Now to make the above scenario of runaway warming more real, we have to look back on the past and see if the warming we’ve experienced is unique (the Holocene period—approximately the last 10,000 years). Up until the late 1990s we had a temperature record (based on writing at the time and proxies) that said although we are experiencing warming mankind had experienced warming before in the Medieval Warm Period (MWP 800 AD to 1300 AD) the Roman Warm Period (200 AD to 500 AD), and Middle Holocene Period (5000 BC to 3000 BC).

Michael Mann and a number of scientists from the CRU at East Anglia University were all involved in Paleoclimatology focusing on the past 1000 years. Mann came out with his famous hockey stick graph which eliminated the MWP. He declared that any vestige of MWP was purely a localize weather event in Europe and the warming we’ve seen in the past 100 years is without precedent in the past 1000 years. This was the final leg of the AGW theory.

The last 10 to 15 years have not shown any real warming which is a problem for AGW supporters. But they counter this observation by saying the past decade was the warmest ever recorded (in the past 130 years). At the same time, they claimed global warming was happening even faster than they thought and used the melting of Ice in the Arctic to illustrate that point. Finally they said, the general consensus of climate scientists supports the AGW theory and anyone who disagrees is a “denialist.”

Next—The skeptics view of the theory of AGW

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