Do Hidden Emissions Make Fracking a Bridge too Far?
August 29, 2016
Natural gas has been neck and neck with wind power for largest source of new electrical production in the US. Could this be the year renewables pull away?
Natural gas is predominately composed of methane. When methane is burned to produce electricity or heat, it releases carbon dioxide and water vapor.
But not all natural gas produced is burned. Some of it is leaked at gas wells, in compressor stations, from pipelines, or in storage. Methane is a powerful but short-lived greenhouse gas. While it is in the atmosphere, it is around 120 times more powerful than carbon dioxide per ton, but it quickly decomposes through chemical reactions and only about 20 percent of the methane emitted today will remain after 20 years.
Carbon dioxide, on the other hand, has a much longer atmospheric lifetime. About half of the carbon dioxide emitted today will be around in 100 years (and virtually none of the methane will be), and about 15 percent of today’s carbon dioxide will still be in the atmosphere in 10,000 years.
This difference in longevity makes a comparison between the two tricky. Essentially, how much methane emissions today matter for the climate depends largely on the timeframe you are considering. If you care about avoiding warming later in the century (as the United Nations does with its 2°C warming by 2100 target), there is relatively little problem with short-term methane emissions, as long as they are phased out in the next few decades. If you care about short-term changes, however, methane is a much bigger deal.
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.)
What do these leakage rates mean for the viability of natural gas as a bridge fuel? Again, it comes down to a question of time frame.
Let’s look at a simple example of a big coal power plant. One option is to leave it alone for the next 30 years, at which point it will be replaced by renewable energy.
Another option is to replace it with gas today, and replace that gas with renewables in 30 years.
The figure below shows the climate impacts over time (measured in units called radiative forcing) of existing coal (the dashed black line), new high-efficient coal plants (the solid black line), and new gas plants (the green line). The potential range of natural gas leakage is expressed by the gray envelope around the green line, with 1 percent leakage at the bottom and 6 percent leakage at the top (the green line itself shows a 3 percent leakage case).
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).
But there is much about the Earth’s climate that is still unknown, and scientists can’t categorically rule out the potential for shorter-term warming to cause unforeseen impacts.
With longer-term warming, the impacts are much more clear (and generally more dire). By the end of the century, we’d expect around 4°C warming in a world where we didn’t take any action to slow emissions. As the damages of climate change tend to increase exponentially with rising temperatures, many economists argue that the biggest impacts of climate change will occur later in the century, and that the main focus should be on reducing longer-term warming.
In the first three months of 2016, the U.S. grid added 18 megawatts of new natural gas generating capacity. It added a whopping 1,291 megawatts (MW) of new renewables.
The renewables were primarily wind (707 MW) and solar (522 MW). We also added some biomass (33 MW) and hydropower (29 MW). The Federal Energy Regulatory Commission’s (FERC) latest monthly “Energy Infrastructure Update” reports that no new capacity of coal, oil, or nuclear power were added in the first quarter of the year.
So the U.S. electric grid added more than 70 times as much renewable energy capacity as natural gas capacity from January to March.
Of course, generating capacity is often quite different from the amount of power generated, since fossil fuel plants generally are used for considerably higher percentage of the time (their “capacity factor”). That’s why renewables now make up 18 percent of total U.S. installed generating capacity — but only about 14 percent of our total power production.
On the other hand, FERC doesn’t track rooftop solar, so its estimate of solar capacity added is certainly low. Indeed, FERC’s data sources only “include plants with nameplate capacity of 1 MW or greater,” so it’s hard to know how much small-scale renewable power generation they may have missed.
It is increasingly clear that we don’t need to add significant amounts of any new grid capacity that isn’t renewable for the foreseeable future. In part that’s because demand for utility power generation has been flat for almost a decade — and should continue plateauing for quite some time — thanks to rapidly growing energy efficiency measures (and, to a much lesser extent, thanks to recent increases in rooftop solar)