Answer: There are many gases in nature that have a greenhouse effect, such as water vapor, which is the most important one. However, the main cause of global climate change is the increase in the concentration of some greenhouse gases in the atmosphere due to human activities. The Kyoto Protocol specifies six types of greenhouse gases, namely carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). Because carbon dioxide is particularly dominant among these six gases, and in actual monitoring and calculation, it is often converted into carbon dioxide equivalent (CO2e) for comparison and research based on the different greenhouse effect capabilities of various gases. Therefore, we are accustomed to using "carbon" to refer to greenhouse gases. For example, we refer to "greenhouse gas reduction" as "carbon reduction".