DiannaDark wrote:scientists don't really know a lot, every 50 years or so they have to throw the books out with all their genius ideas of everything out and write new ones
That's not technically true.
It depends how good the science is. Yes, they keep discovering new things and changing and refining theories, but a lot of what they knew before is still true. Gravity and acceleration, for example. As we come up with new ways to observe, collect data, and test hypotheses, of course we're going to discover new things. That's good. If my grandfather had lived about three more years, he would have gone from living in the time of horses and carriages as the primary family form of travel to seeing us put men on the moon. That's a LOT of science discovered in just under seventy years. Saying they "don't know a lot" may be somewhat dismissive. There IS a lot we don't know, but we're learning a lot all the time.
One of the things that does concern me is that a lot of Americans (and I'm limiting this to Americans only because that's the culture I'm most familiar with. It's quite possibly true of others.) don't really understand what the scientific process is. They accept pseudo-science and bad science.
Anyways... To wander back to global warming, there's quite a bit we can prove. The greenhouse effect is pretty well understood. Essentially certain gasses in the Earth's atmosphere trap infrared radiation, making the planet warmer. It's called the greenhouse effect because you can see the same effect occur in a greenhouse-that's why they're so warm.
The most important of those gasses are water vapor, carbon dioxide, and methane. When there's more of those gasses in the air, the air holds more heat. This is something that can and has been observed and measured repeatedly in scientific experiments. More of those gasses = more heat trapped.
Without the greenhouse gas effect, scientists estimate that the Earth's average temperature would be around -18 or -19 degrees Celsius (0 or 1 degrees Fahrenheit). Because of the greenhouse effect, the Earth's actual average temperature is 14 degrees Celsius (57 degrees Fahrenheit).
However, the greenhouse effect is becoming stronger. This is something that has been distinctly measurable over the past 150 years. Many scientists believe it is because we are burning fossil fuels, which is adding CO2 to the atmosphere. Going back to the greenhouse effect, we know if we add carbon dioxide, it's going to increase the effect and make things warmer.
And the thing is, they can measure how much CO2 has been added. It's a LOT. A lot more than can be explained by nature or by the planet's natural warming or cooling cycles. I'm too lazy to look it up right now, but I will if you want.
One last thing before I go and feed my cat. I found this brief explanation and kind of liked it:
By Kevin Trenberth, head of the Climate Analysis Section, National Center for Atmospheric Research, Boulder, US:
The Earth is habitable because of a natural greenhouse effect brought about mainly by water vapor (60%) and carbon dioxide (26%). Otherwise its average temperature would be below zero Fahrenheit. Humans are altering the composition of the atmosphere, mainly by burning fossil fuels. As a result carbon dioxide has gone up over 35% since pre-industrial times and over half of that is since 1970. This changes the greenhouse effect and traps radiation that would otherwise escape to space, producing warming. The warming is manifested in many ways, not just increasing surface temperatures, but also melting ice, and changing the hydrological cycle and thus rainfall. Since 1970 the effects are large enough to be outside the bounds of natural variability for global mean temperatures, but global warming does not mean inexorable increases in temperature year after year owing to natural variability.
source:
http://simpleclimate.wordpress.com/2010/11/24/pick-the-best-simple-climate-change-explanation/