Monday, March 1, 2010

Global Warming: Caused by Humans

I spent a long time poring over articles and trying to compile a list of relevant scientific data that shows the overwhelming evidence that man-made global warming is happening, and I wanted to represent it in such a way that non-science geeks like myself could understand. But as it turns out I’m not the first to try and do this—big surprise! After finding the below video about global warming science, via MyDD, I decided to forgo researching anymore and decided maybe I should go into the science a little bit. This video has it all, please enjoy:

I would like to clarify one point in greater detail that the video just didn’t have time to go into, and that is the idea that greenhouse gasses released into the atmosphere are derived from human use of fossil fuel. In the video they mention that the isotopes of carbon that are detected in the air indicate that the large increase of CO2 in our atmosphere over the last hundred years or so originate from fossil fuel rather than from volcanic eruptions or any other natural process: "the CO2 released by burning fossil fuels like oil, coal, and gas, has a different chemical signature than living animals and plants". I would like to go into some more detail here and turn the conversation a bit more towards the science behind how we know where the carbon comes from.

There are three main types of carbon, carbon-12, carbon-13, and carbon-14 that are all present naturally in our atmosphere and we breathe them in with every single breath. Carbon-14 is very important for figuring out the age of materials that are up to about 70,000 years old but since fossil fuels come from the dinosaur ages, starting about 65 million years ago, we will forget about carbon-14 for now. Carbon-12 is by far the most abundant (98%) type of carbon in the atmosphere (and universe) and this is because it is the most stable form of carbon. There is much less carbon-13 in the atmosphere but there is enough to be easily detectable. The only difference between carbon-12 and carbon-13 is that carbon-13 has one more neutron in it’s nucleus (12 + 1, amazing!) which makes it slightly heavier than carbon-12 and why they can be distinguished using a technique called mass spectrometry. The mass difference between the two types of carbon is very import for understanding where the CO2 in the atmosphere comes from.

During photosynthesis a plant takes in carbon dioxide (CO2) from the air and with the help of sunlight converts it into sugar that it can use for energy. Most of the CO2 molecules contain carbon-12, because it is the most abundant, but a small percentage contains carbon-13. Well, it turns out that, through very complex physics, that plants tend to prefer the lighter, more abundant carbon-12 than they do the slightly heavier carbon-13. So if you take a plant and analyze the ratio of carbon-12 to carbon-13 you will find that there is a higher ratio of carbon-12 in the plant than there is in the air. As we know, fossil fuels are simply plants that died many millions of years ago and their rotting remains slowly turned into what we know as oil. Oil has the same ratio of carbon-12 to carbon-13 that plants do. If we then take a look back through history by measuring the amount of carbon-13 found in tree rings and ice core samples we find that the ratio of carbon-12 to carbon-13 has been about the same for nearly 10,000 years. However, within the last 100 years there has been a very significant increase in carbon-12. This increase indicates that the fossil fuels are being burned and released into the atmosphere thus increasing the carbon-12 content without affecting the carbon-13 content, thus changing the ratio that has stayed constant for so many thousands of years. There is no other explanation than fossil fuel burning for the increase in carbon-12 in the atmosphere in the last 100 years because, as far as we know, there is no other significant source of CO2 that contains a higher ratio of carbon-12 to -13 than that from plant or fossil fuel burning.

This still leaves the question as to how much CO2 can actually increase the temperature of the planet. At this point however it is unequivocal that humans are the main cause of the increase in CO2 to the atmosphere through fossil fuel burning.

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