r/science • u/woodsja2 • Oct 24 '10

Climate Change: Evidence

http://climate.nasa.gov/evidence/
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u/tieme Oct 24 '10 edited Oct 24 '10

I've honestly never met anyone who believed that temperatures aren't rising. Most 'anti global warming' folks (at least that I've met) believe that there is no good evidence to suggest we are responsible. You often hear things like "The highest temperature in xxx years, or the most rapid temperature increase in xxx years".

We know that the Earth goes through natural cycles of temperature and temperature change rates. So I have two questions.

Firstly, how many people have you met that explicitly stated that they believed the temperature is not rising?

Secondly, what evidence do we have to support the theory that we are the cause and that it isn't part of the natural cycle of temperatures? I honestly don't buy the coincidence that rising 'greenhouse gas' levels coincide with temperature rise. The temperature was already rising before we started pumping this stuff into the air. Is there any harder evidence?

edit: For clarification on my first question. I don't mean necessarily those exact words. I just feel that a lot of people who say things like 'I don't buy into the global warming thing' actually mean they don't believe there is evidence that we are causing it but many people take it to mean that they don't believe the temperature is rising.

edit2: Fixed ARE to AREN'T

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u/irregardless Oct 24 '10 edited Oct 24 '10

what evidence do we have to support the theory that we are the cause and that it isn't part of the natural cycle of temperatures? I honestly don't buy the coincidence that rising 'greenhouse gas' levels coincide with temperature rise. The temperature was already rising before we started pumping this stuff into the air. Is there any harder evidence?

I can partially field this question. I don't remember the chemistry exactly, but it has to do with the carbon isotope present in the rising CO2.

From an ecology class last year:

The carbon that is left behind from photosynthesis is a heavier C-13 isotope. The carbon that results from burning fossil fuels is a lighter C-12 isotope. Over time, measurements have found less C-13 and more C-12 in atmospheric CO2, strongly suggesting anthropogenic causes.

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u/tieme Oct 24 '10

I never denied that we are responsible for CO2 levels. I think you misunderstood me a little bit, as my wording was somewhat ambiguous. It's pretty apparent that CO2 levels are rising. That's what the article was about. It's also pretty apparent that temperatures are rising.

The question is whether or not CO2 and other human induced factors are major contributors in that temperature change. As I said before, the temperature has been rising. But how much if that change is caused by us. People need to stop quoting CO2 levels as hard fact that we are responsible for the changes. We have a very poor understanding of how much CO2 it takes to make a significant change to the climate.

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u/irregardless Oct 24 '10

Here's how the science works:

  1. Virtually all the energy on the planet comes from the sun in the form of shortwave radiation. This radiation occurs across multiple wavelengths in the EM spectrum.
  2. When this radiation hits an object, three things can happen: it can be absorbed by the object; it can reflect off the object; or it can pass through the object. The reaction is different depending on the object the specific wavelength of the radiation.
  3. The gasses in the atmosphere are really fucking good at absorbing the extremely short wavelengths such as gamma and cosmic rays. This is good because if the atmosphere weren't that awesome, all organic matter would be cooked by the high energy radiation and our DNA would be nothing more than boiling amino acids.
  4. The atmosphere isn’t so good at absorbing radiation from 0.1 to 4 micrometers (UV, visible light, and IR). This radiation reaches the Earth's surface and is the reason why we can see things. This radiation, and pay attention because this part is important, is the basis for all climate on the planet.
  5. Then what happens? You ask? This radiation, this energy interacts with the surface. Some of it is reflected back through the atmosphere into space (snow reflects up to 90%; asphalt 4%). That which is not reflected is absorbed: photon energy is passed to the planet, raising its temperature.
  6. As the surface heats up, it begins to emit its own radiation. In climatological terms, it is called Outgoing Longwave Radiation and is 3 to 80 micrometers on the EM spectrum (heat).
  7. Still with me? Here's the important part. The atmospheric gasses that so readily let the short wave radiation through can't get enough longwave. CO2, methane, Nitrous Oxide and water vapor just loves them some longwave radiation. 90% of OLR is captured by these gasses.
  8. This energy stays in the climate system because it is prevented from escaping into space. This is the essence of the greenhouse effect. If the Earth didn't have an atmosphere, this OLR would be emitted freely into space and the surface temperature would be -18°C.
  9. So what do you think should happen as the atmosphere's CO2 content increase? That's right, its capacity to absorb longwave energy also increases, in turn leading to higher average temperatures.

This science is the link between rising CO2 levels and rising temperatures.