Below is a breakdown of the emissions by source.  Percentages are based on the 2018 GHG Emissions Inventory provided by the United States EPA. [1]

Carbon Dioxide (81%)

Transportation (27.3%)

Passenger Cars and Light Duty trucks (16.0%) — Are the most voluminous group, create the most emissions, and have many forms of electrical vehicles already on the market.  Even electric vehicles plugged into a fossil fuel powered grid are much more efficient than those that use gasoline (the emissions are equivalent to around 50 miles per gallon [2][3].  Electric vehicles can also stabilize the grid and take-out peaks since we can choose and incentivize when to charge them.

Large Trucks and Buses (6.7%) – Renewable solutions exist but aren’t yet on the market in large numbers.  Tesla’s published expectation to beat 2 kwh/mile only put it on par with emissions from fossil fuel trucks when plugged into a fossil fuel grid.  Efforts to improve gas mileage and get rid of gas guzzlers can be quite impactful without going electric yet in this group.

Aviation (3.8%) – There is a long way to go before a sustainable aviation alternative is proven.  If we can get through a large investment on renewables perhaps a large investment on a rail network in the lower 48 states could lead to less emissions in the future [4].

Shipping/Boating (1.2%) – Fuel uses by ships and boats.  Hydrogen or batteries are possible alternative fuels for smaller boats, while nuclear powered large vessels are possible, similar to what the military uses for submarines and aircraft carriers. [4] There is also sailing…

Electricity Generation (26.3%) – Natural gas, coal, or oil burned for electricity.  Coal is the worst offender on a per unit energy basis.  Of this number 7.3% is attributable to industry, 9.7% to commercial, and 9.2% to residential.  The scientific consensus is to convert electricity to renewables and then convert other fossil fuel uses to electricity or energy storage from electricity like batteries and hydrogen.

Industrial (12.5%) – The natural gas, oil, or coal used by industry for a variety of uses. The EPA emissions inventory lists manufacturing, construction, mining, and agriculture as the predominant activities with manufacturing being the largest.  Within manufacturing most emissions are attributable to petroleum refineries, chemicals, paper, primary metals, food, and nonmetallic mineral products.

Residential (5.1%) – The natural gas, propane, or fuel oil delivered to your home used mostly for space heating but also cooking, fire places, etc.  Electric space heating alternatives exist.

Commercial (3.7%) – The natural gas, propane, or fuel oil delivered to a commercial property used mostly for space heating but also cooking and other uses.  Electric space heating alternatives exist.

Non-Combustion (5.9%) – Carbon dioxide emissions outside of fossil fuel combustion. These emissions are mainly generated in industry such as steel production, cement production, and petroleum processes.

Methane (10%) – Methane has a relatively short lifespan in the atmosphere causing many scientists to believe it is overweighted. The global warming potential used by the EPA to get a 10% impact is 25x carbon dioxide but it has been shown that methane emitted today will only change the temperature in 100 years by about 4x that of equivalent carbon dioxide emitted [5].  (So instead of methane being a 10% GHG contributor it can be argued it is closer to 2% assuming it is properly measured).

Reducing fossil fuel consumption will also decrease the methane emitted during the mining, drilling, refining, and transport of fossil fuels.  36.1% of methane emissions were attributed to natural gas systems, coal mining, or petroleum production.  A reduction of natural gas consumption can eliminate the need for fracking practices, which are showing their fingerprints in methane levels around the world and are perhaps underestimated [6], not to mention local health concerns in the area of drilling.  Most of the remaining emissions are attributable to livestock or landfills.

Nitrous Oxide (7%) – Mainly generated in farming, small amounts are produced in combustion.

Fluorinated Gases (3%) – Mainly generated in industrial processes