According to some of the most complete calculations available, when we use natural gas to generate electricity in an average power plant, it results in 40 percent less warming than if we generate the same electricity with coal. If we fully utilized the natural gas-fired power plants that already exist in this country, we could significantly reduce the amount of coal we’re burning practically overnight. What’s more, primarily because of access to new natural gas reserves, proved reserves of natural gas recently shot up to 284 trillion cubic feet – more than we’ve had on hand at any time since 1971.

It’s for these reasons, among others, that many experts and policymakers have proposed switching to natural gas as a “bridge fuel” to immediately reduce greenhouse gas emissions while we undertake the much larger and long-term project of ramping up the percentage of our energy generated from renewables, which is currently about 7 percent. (Most of the that renewable energy is hydroelectric and biomass, to boot.)

Still, there’s another side to the story: recent research on the lifecycle of natural gas, from the moment we remove it from the ground to the moment it’s burned, has challenged assumptions about its climate-friendliness. At base, economic and policy assumptions about whether we can use natural gas to reduce emissions in the short-term depend on what we know about the effects of its extraction and use on the atmosphere.

A controversial paper

Methane, the primary constituent of natural gas, is up to 100 times more powerful a greenhouse gas than carbon dioxide over a 20 year time horizon (though other studies have found it is 72 times more powerful). As many climate scientists have pointed out, it’s precisely these near-term warming effects that we want to avoid if we wish to avoid pushing the climate toward disaster.

This discussion was heightened last month when Robert Howarth, a professor of ecology and environmental biology at Cornell University, published a controversial paper arguing that natural gas from fracking has a greater net warming effect on the climate than burning coal.

Howarth and his co-authors argue that one of the main problems with methane is that, as a gas, it tends to leak into the atmosphere both when it’s drilled and when it’s transported. Hydraulic fracturing, or fracking, is the process by which wells are drilled into shale rock, then water and a mix of chemicals are injected at high pressure, to crack or “frack” the deposit, allowing natural gas to escape.

“If you look at the inventory of emissions of human-controlled methane from the U.S., 25-50 percent of it is from [the use of] natural gas,” says Howarth.

Capturing “fugitive” gas

Industry has a monetary incentive to eliminate these losses, at least during the drilling and initial distribution stages, but thus far it has been slow to do so. Granted, there are barriers to eliminating leaks. For example, when a new well is being drilled, gas storage infrastructure must also be built in advance in order to capture the gas that leaks during the drilling phase. The EPA has studied Reduced Emission Completions technologies, and concluded that on the average well, these technologies mean a higher up-front investment, but they pay for themselves after 3-5 months by capturing gas that would otherwise be lost. Still, at present they are rarely built.

Howarth came to the conclusion that when we use frack-produced natural gas to generate electricity, the net effect on the climate is worse than coal when looked at from the perspective of the next 20 years. (When looked at over the course of the next 100 years, natural gas comes out ahead of coal, because methane is removed from the atmosphere more quickly than carbon dioxide.) This distinction is crucial: as conventional natural gas wells in the U.S. decline as a proportion of our gas production, more and more of our gas will come from fracked wells.

Conclusions questioned

Howarth’s conclusions have come under fire from both scientists and industry.

Science is an iterative process, and Howarth himself admits that the data he used to determine the natural gas lost during the drilling process were sparse. Unfortunately, they’re the only data available.

The conclusion of scientists like Bill Chameides, Dean of Duke’s Nicholas School of the Environment, is that we simply don’t yet have enough information to determine the climatic effect of natural gas from fracking. That won’t change until academics and industry obtain better measurements of losses of methane during drilling.

Natural gas key to more renewables

What’s more, because natural gas power plants can be fired up so quickly, they play a unique role in the world’s electricity production system — they are activated when supply, as from renewables, is outstripped by demand.

“I would say that without natural gas, the grid will not be able to manage the variability and intermittency in power output from wind and solar plants,” says Paulina Jaramillo, a professor of engineering at Carnegie Mellon.

As executive director or the RenewElec project, which aims to increase the proportion of intermittent sources of renewable energy in the world grid, Jaramillo specializes in thinking about the transition off fossil fuels. She doesn’t believe we’ll be able to get more solar and wind on the grid without natural gas, precisely because the only alternative — storage mechanisms like batteries and demand-side management — aren’t far enough along.

Howarth believes that in the future, the major drivers of these human emissions of methane will prove to be use of natural gas, especially if we come to rely on it for an ever larger portion of our energy.

The good news is that it seems the effects of methane gas can be limited through action by industry. But the economics of drilling, mediated by the actions of regulators, will determine just how “clean” natural gas ultimately proves to be.

Christopher Mims is a contributor to Good, Technology Review and The Huffington Post, and is a former editor at Scientific American and Grist.org. He tweets @mims.