dtb said:

>You and I had quite a lot of agreement on some earlier
>threads, but this time I have to disagree -- not a good
>argument at all."

I was actually fishing for a response from Mark, who I agree with on almost everything except global warming and exobiology (It's a refreshing change to argue against him about something). However dtb is another person whose intelligence and knowledge I greatly respect.

>The issue isn't whether our total power output compares to
>solar input, but whether something we are doing is changing
>the value of one the feedback terms in the climate equation.

The feedback mechanism is obviously of extreme importance. However the relative magnitude of human activity compared to the power of nature is also of importance and typically brushed aside in the global warming debate. How many times have you seen the 127 million gigawatts solar power rating cited? Probably almost never and yet it's a trivial calculation to make.

>The global warming argument is that what we are doing has
>a lot of leverage.

I remain skeptical. I would argue that the other feedback mechanism of cloud cover and water vapor acting as a green house gas would compensate for greater carbon dioxide and methane concentration.

>Take a silly example -- if we put our minds to it, I'm sure that in
>the next fifty or so years we could place in orbit huge sheets of
>mylar that would reflect almost all incoming solar radiation.
>That'd be a big project, but trivial in energy use compared to
>incoming solar energy. Even so, it would turn the planet into a
>giant Sno-Cone.

Let's examine the silly example. Assume an altitude of 200 km that covers the earth. Assume the mylar is 0.1 mm thick. Assume the mylar has a density of 1.4 g/cm^3. The mass of the mylar is:

4 pi (6369.0e3 + 200.0e3)^2 * 1.0e-4 * 1.4e3 = 7.59e13 kg

I don't think the human race has enough money to cover the cost of launching 76 billion metric tons into low Earth orbit.

The point here is that planets are big. We human beings like to think we're significant but compared to an entire planet, we aren't.

Gary