The oil industry is pinning its hopes on natural gas. To hear oil executives tell it, natural gas is a veritable “bridge between a fossil fuel past and a carbon-free future,” as Bloomberg News put it recently.

It’s a story that makes sense on its face: natural gas emits about one-half of the carbon dioxide of coal and about three-quarters that of gasoline. Power plants can get more electricity per BTU of natural gas than coal, giving it a further advantage. And in an electric vehicle world, the future of gas could look bright.

But natural gas is not our climate savior. The fuel—which consists primarily of methane—is cleaner than coal and oil, but it is by no means carbon-free. For regions of the world potentially new to gas, expensive investments in pipeline or ocean transport and distribution infrastructure are required.

At best, any “bridge” that the fuel provides to a future where zero-carbon-producing power generation technologies take over is short and narrow. True, gas generation may help firm up intermittent renewables, but the goal would be to operate these as little as possible, minimizing the use of gas. And yes, gas could come back with success of carbon capture and storage (CCS), but advances in this technology have so far not panned out.

Are big investments in new gas infrastructure worth it if fully utilized for only 20 years or so? The gas bridge is getting shorter and narrower as we delay serious action on fighting climate change.

In 2015, delegates from 195 nations—including the U.S.—reached a landmark accord in Paris committing nearly every country to reducing greenhouse gas emissions. The goal of the pact is to keep global temperatures from rising more than 2 degrees Celsius. The Earth has already warmed 1 degree since the dawn of the Industrial Revolution when humans began burning fossil fuels. (Technically the U.S. withdrew from the climate pact in June, but under the rules of the deal, the earliest any country can exit is November 2020. That means the U.S. will remain a party to the agreement for the next three years and just about all of President Trump’s current term. In any event, devising an aggressive climate policy involves looking beyond any one administration.)

So what is our best hope of achieving that 2-degree target? How can we optimize that short and narrow bridge to the future?

Natural gas could have a modest role to play in the short-term. After all, the shale boom has generated lots of cheap gas in North America. In the U.S. the price of natural gas is about $3 per 1 million BTUs. Existing gas generation plants, if fully utilized, can allow a rapid shift from coal generation that could dramatically reduce US power sector emissions; a shift to gas in China could also greatly reduce its emissions, although the issue there is current lack of infrastructure and the relatively high cost of getting gas to the country.

Gas is also a flexible fuel. It has applications in residential and commercial heating, in industry, and potentially as a transportation fuel, either directly or transformed to a liquid.

The good news for the U.S. is the gas infrastructure is largely in place; the bad news—it is old and leaks methane into the atmosphere. This leakage is a nearly 35 times more powerful greenhouse gas than CO2, eroding much of its potential benefit compared with gasoline or diesel. And while the gas industry assures us that properly managed frack wells do not pose an environmental problem, induction of seismic activity from water injection and other environmental issues have occurred that have at a minimum created a concerned and wary public. So outside the power sector, especially considering leakage in the gas distributions system, a low-carbon future dictates that we phase out—rather than expand—our use of gas.

Indeed, the danger of moving ahead with investments in gas infrastructure and spreading the gas fracking boom worldwide is that once those costs are sunk, low cost gas could crowd out zero carbon options in power generation. It would also take pressure off of the drive for greater energy efficiency.

Despite the grand plans of oil company executives, it’s possible that in 20 years, gas and oil companies will be disappearing. The hope is that they will be replaced with companies focused on zero carbon energy, such as renewable wind and solar, sustainable biomass, or a next generation of inherently safe nuclear power, electrification, and energy efficiency. Research shows that renewable energy resources will supply just as much of America’s electricity demand as gas by the year 2040. This is thanks in part to production tax credits, and state level renewable energy requirements.

A serious commitment to long run climate goals requires we stay focused on planning for a zero-carbon world. A short and narrow bridge in that direction may be tempting, but we must be careful in our crossing. Otherwise our future leaders may be bemoaning our “addiction” to cheap gas, and the carbon emissions associated with it.

John Reilly is the Senior Lecturer and Co-Director of the Joint Program on the Science and Policy of Global Change at the Center for Environmental Policy Research at the MIT Sloan School of Management.