Although many agree that the climate is warming – the evidence has become too overwhelming – there remains debate over the role of humans. The strong carbon dioxide patterns that seem to line-up with the industrial revolution of course does not demonstrate a true cause-and-effect relationship. (Good point to discuss with students and remind them that correlation doesn’t mean causation.). Nonetheless, there does exist some very strong evidence that fossil fuel combustion is contributing to global warming and global climate change.
**To continue with this graph it will be worthwhile to recall what an isotope is with your students (i.e. variation in the number of neutrons in an atom’s nucleus which changes the atomic mass).**
This graph comes form Ghosh and Brand (2003) and was published in the journal, International Journal of Mass Spectroscopy. What is important for the students to understand is that the ratio of 13C/12C is different between the atmosphere and plants. Specifically, the ratio of 13C/12C is lower in plants than the atmosphere. If rising CO2 is coming from a plant-source such as fossil fuels than the atmospheric ratio of 13C/12C should be declining. This is indeed what is occurring . The above graph needs to be read carefully as the y-axis has been flipped from the traditional way student’s are accustomed. Notice that it is more negative as you move up the y-axis although the point is still the same. Over time (x-axis) the amount of 13C in the atmosphere is declining. Although forest fires for example would contribute to this isotopic change, the combustion of fossil fuels undoubtedly contribute and they do at a significantly greater level. (Have students review Carbon From Anthropogenic Sources) It would also be worthwhile to note that many contemporary forest fires are also the result for a warmer-drier climate and human activity.
1.Ask students how the trend in Forest Fires (e.g. throughout the American West) would contribute to this graph?
2.Consider a potential guest speaker (e.g. USFS official) to discuss forest fires, forest management, and climate change.