Here's a figure showing gross emissions of greenhouse gases in the US. Emissions that are not carbon dioxide have been converted to its "equivalent."
Given the predominance of carbon dioxide emissions, let's dig into those a little deeper. Most of the carbon dioxide emissions come from burning fossil fuels. This table shows the breakdown into a few main sectors.
Moreover, methane emissions landfill, leakages in natural gas systems, and the digestive tracts of livestock make up the equivalent of 449 million metric tons of carbon dioxide emissions in 2017. Agricultural soil management released nitrogen oxides that are the equivalent of 266 million metric tons of carbon dioxide in 2017, roughly equivalent to fossil fuel-related carbon emissions from the residential or the commercial sector. Hydrofluorocarbons that are being used to to replace ozone-depleting substances account for another 152 million metric tons of CO2-equivalent emissions.
This EPA report is a tabulation of greenhouse gas emissions. It isn't about questions of how emissions of greenhouse gases might affect climate, or estimating economics costs from changes in climate, or about what methods of addressing greenhouse gas emissions are likely to be more or less cost-effective. For discussions of these points, I recommend a three-paper "Symposium on Climate Change" in the Fall 2018 issue of the Journal of Economic Perspectives. (Full disclosure: My actual paid job, as opposed to my blogging avocation, is Managing Editor of the JEP.) The papers are:
- "An Economist's Guide to Climate Change Science," by Solomon Hsiang and Robert E.Kopp
- "Quantifying Economic Damages from Climate Change." by Maximilian Auffhammer
- "The Cost of Reducing Greenhouse Gas Emissions," by Kenneth Gillingham and James H.Stock