A wonderful video from NASA, called “Dynamic Earth”, exploring the sun’s impact on our planet and how it powers the climate:
Just under 5 minutes, worth watching.
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Watching the Deniers 
Nicely done video, but it did leave me with a question: the narrator indicates that there were two main forces “protecting” the earth from the fate of Venus: the Earth’s magnetic field and the clouds/ice reflecting energy.
1) Doesn’t Venus have a magnetic field? They might not… it might have to do with an iron-based core or something… anyone know?
2) The second “protection” seems to be putting the cart before the horse: the video seems to claim the solar wind stripped the Venusian atmosphere of water vapor. Wouldn’t it have done the same to early Earth?
My guess on both the above without further research is that distance may be the more important factor. By the time the sphere of solar winds has reached earth its impact per square surface area is probably a very small fraction of what it is at Venusian distances.
Anyone out there a bit more buffed up on astro-geological theory than I am?
– MJM
Venus may have had global ocean, which may have feed what is known as a runaway “moist” greenhouse effect early in its history. I’m not expert, but re Venus see these:
Skeptical Science: http://www.skepticalscience.com/Venus-runaway-greenhouse-effect.htm
And this: http://en.wikipedia.org/wiki/Runaway_greenhouse_effect#Venus
NASA for similar observations on Earth at a very localized level: http://www.nasa.gov/centers/ames/news/releases/2002/02_60AR.html
I’m no expert, but…
Venus indeed doesn’t have an internal magnetic field, even though it probably has a partially molten core like the Earth. Maybe something to do with the apparent absense of plate tectonics and convection. There might have been one in Venus’ youth.
It’s certainly possible that Venus had oceans and relatively mild temperature in the past for hundreds of millions of years, maybe even longer. I’d guess the loss of water from the top of atmosphere mostly happened after the runaway greenhouse vaporized it all. In any case, it should be a slow process – Mars still has some atmosphere left, even though it’s much lighter (easier to bump molecules off the top of the atmosphere – escape velocity is one part of the equation) and haven’t had a magnetic field for a long time.
Interesting stuff, but what I’m really waiting for are the little green fellers to come out and wave to the cameras for us up on Mars.
:>
MJM
The depressing thing about the video is that it points up the need for a whole concatenation of conditions being “just right” for a nice water-based life-friendly planet to develop. Take away the magnetic fields, move it a bit in or out, reduce the density so the atmosphere flies away… plus of course you always have inconvenient things like massive asteroid impacts, huge solar flares, erectile dysfunction… all sorts of things can go wrong.
– MJM
Depressing, and yet wonderful mate. And the Earth we live on is precious. Which is the very reason for my advocacy…
When you stop, and think about what an incredible and complex array of systems that makes our civilization possible, and for us to live, work, marry, yeah and smoke…
Why put it at risk? If there was even a 1% chance of AGW being true, why risk this complex pattern of biology, climate, hydrological cycles, energy balance budgets etc. through selective denial and non-action?
People may think I’m this angry blogger throwing bricks at deniers.
Actually I live a perpetual state of wonder and curiosity.
Embrace the knowledge dude.
Why put it at risk? Because there are downsides to the GW argument as well. While solar and wind power are obviously less polluting and may be cheaper than our current dependence on things like oil and nuclear, it’s not as clear in the short term — and short term increases in cost have real consequences. On a personal level I’d like to see $1/gallon tax added on to gasoline every year for the next five to ten years: it’d be good for the environment, good for people’s health, it would save a lot of children and pets from being run over, and it would make life much more pleasant for me as a bicyclist. I spent years working towards goals such as that. … But I no longer feel I have the right to make those decisions in such extreme ways for others.
– MJM