Legislation introduced in the Senate and already passed in the House calls for reducing US greenhouse gas emissions by 83 percent by 2050, relative to 2005 levels. Leading climate scientists and most world leaders believe that level of reduction is needed in the US and other industrialized countries to prevent the global average temperature from rising more than 2C above preindustrial levels.
Since more than 80 percent of US energy comes from fossil fuels today, and burning fossil fuels accounts for most US greenhouse gas emissions, cutting emissions by 83 percent will mean big changes. This animation illustrates this for the electricity-generating sector, which contributes about 40 percent of US CO2 emissions. Coal generates about half of our electricity today, but due to its high carbon content, it accounts for more than 80 percent of all CO2 emissions from electricity.
Fast-forwarding to 2050, we show four ways that the electricity system could have 83 percent lower CO2 emissions while also supplying about 50 percent more electricity than today. We constructed each of these scenarios to rely heavily, but not exclusively, on one low-CO2 source: nuclear, renewables like wind and solar, coal with CO2 capture and storage, and improved efficiency (which isn’t actually an energy source, of course, but it’s a legitimate way to reduce emissions). In each case, the low-carbon power sources would need to be constructed at rates that are aggressive by historical standards, but not implausible.
The final image in the microanimation shows a fifth scenario for an 83 percent emissions reduction. With comparable contributions from nuclear, fossil fuels, renewables, and efficiency, this scenario might be easier to achieve than the ones that rely heavily on a single low-CO2 source.
In summary, there are different ways to reach a low-carbon electricity system by 2050, but the job of getting there is formidable, and no single source will be able to achieve all of the reductions by itself. In all cases, improving efficiency is critical, and fossil fuels would have to be severely restricted or used only with carbon capture and sequestration.