By Zeke Hausfather
23 August 2016
(Yale Climate Connections) – For the past century, coal has been king, providing the majority of U.S. energy for electricity generation.
But a combination of new federal and state environmental policies and a glut of cheap natural gas (mostly from hydraulic fracturing, or fracking) have led to a dramatic shift during the past decade, with coal dropping from 50 percent to 32 percent of our electricity generation and gas increasing from 18 percent to 33 percent.
Just under a third of existing coal-based power generation in the United States has been shut down, and the Obama administration has aggressively embraced the replacement of coal with gas as a key part of meeting its 2030 climate targets. We are quickly traveling down a gas bridge away from coal. But will this shift actually be a good thing for the climate? […]
How much methane leaks from the natural gas system is very much an open question. For a long time official Environmental Protection Agency numbers suggested the emissions were small and falling fast, only amounting to around 1.5 percent of total production.
But dozens of independent academics doing research using aircraft, satellite data, and other instruments have consistently found higher emissions than officially reported.
Adam Brandt at Stanford University published a high-profile paper in the journal Science in 2014 summarizing all the research to date. He found that overall emissions were likely between 25 and 75 percent higher than reported by EPA, suggesting that actual natural gas leakage rates are probably somewhere between 2 and 4 percent of gas production. (Some researchers have found leakage as high as 10 percent for individual fields, but there isn’t evidence that those findings are characteristic of the sector as a whole.) […]
If leakage is higher than 3 percent, there are some periods in the next 30 years when gas will result in more climate impact than new coal plants. If leakage is higher than 4 percent, there are some periods when gas will be worse for the climate than existing coal plants.
But no matter what the leakage rate is, gas will still cut the climate impact by 50 percent in 2100 compared to new coal and 66 percent compared to existing coal. So whether switching from coal to gas is beneficial in this simple example depends on how you value near-term or longer-term warming.
The importance of near-term warming is tough to assess. Climate models, by and large, don’t predict any irreversible changes in periods as short as 30 years, and potential tipping points in the climate generally depend more on the peak warming that occurs (which in nearly all foreseeable cases would occur after 2050). […]
Renewables are getting cheaper, and although it might not be practical to replace all coal plants with renewables immediately, it’s definitely possible to do so in the next decade if renewables continue to fall in price. If we replace coal with gas today, we’ve sunk costs into new gas infrastructure that we might be loath to replace a few years later with renewables. In this way, a gas bridge could delay the widespread adoption of renewables. [more]