Best support for influence of human activities on climate change
Every time I think this political debate has been put to rest, I hear it resurrected. Are humans contributing to climate change? Yes. Is it because of carbon dioxide emissions? Yes. Period.
This is one of the most compelling figures that summarizes this phenomenon. Climate scientists used climate models to try and predict observed climate over the past century (1900-2000). The black line shows exactly what the climate did during that time frame. Climate in this case is temperature. The blue shows a climate model that included only natural factors. The pink shows a model that includes natural factors plus human factors (e.g. carbon emissions). As you can see, the pink and the black line overlap exactly, while the blue fails to match what actually happened. Conclusion: humans have influenced the climate over the past century. Period.
Perhaps the most interesting part of this is that the blue and black line actually do overlap for the beginning of the century, but then begin to diverge in the second part of the century. This is consistent with increases in CO2 emissions.
Source: Climate Change 2007: The Physical Science Basis: Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, FAQ 9.2, figure 1, page 121