In 2013, the Intergovernmental Panel on Climate Change (IPCC) released its fifth report, attributing 95% of "all" climate warming--from the 1950s through today--to humans. Not only did the report--like previous IPCC reports dating back to 1990--accredit global warming to anthropogenic carbon dioxide emissions, but over time the vast majority of scientists have endorsed this view of human-caused climate change. Still, many students question whether climate change is real, whether it is part of a natural cycle, and whether other sources besides humans may be responsible. To compare the role of natural Earth processes in CO[subscript 2] emissions with humans' role, the authors designed a student research investigation described in this article. Students graph volcanic and human components in CO[subscript 2] emissions, analyze their results, and then can compare their results with those in peer-reviewed scientists' reports.