The shale gas boom led to vigorous debate whether there is place for inexpensive gas as a “bridge fuel” toward a low-carbon future. While zero-emitting technologies exist and have been implemented with some success, they remain relatively expensive. Natural gas is far cleaner than the coal in electric power and gasoline in automobiles. Switching to natural gas will not ultimately lead to a zero-carbon future, but it can reduce emissions with less economic impact - buying time before renewables reach a price point where they can reasonable scale.
Researchers from prominent universities, like Cornell University's Robert Howarth and Stanford University's Mark Jacobson, are adamant that cheap natural gas is a distraction. While there is broad consensus that they are probably right in terms of passenger vehicles, debate rages on electric power. Howarth argues that fugitive methane emissions from shale gas recovery and expanding gas infrastructure may counteract any climate gains we might incur in the electricity sector. Jacobson argues that we are capable of a zero-carbon future with existing technology, and we should pursue this immediately.
Other well-regarded researchers indicate that fugitive emissions are likely much lower than Howarth's estimates and total emissions will still fall from fuel-switching in electric power, and that Mark Jacobsen's argument, while attractive to green advocates, has serious technical and economic limitations (just Google "Mark Jacobson criticisms"). This opposing perspective tends to view natural gas as a great substitute for coal power in providing baseload power. They also argue that gas power is a flexible technology that can even help intermittent renewables increase their market share. That is, gas power, unlike many other technologies, can ramp up and down quickly when it becomes cloudy or the wind stops blowing temporarily to make sure electricity supply meets demand. From this perspective, natural gas can be an effective bridge fuel.
Regardless of your personal view on natural gas as a bridge fuel, the debate is largely moot; natural gas is already being used as a bridge fuel in the US electricity sector. The figure below shows that gas power is replacing coal power and total CO2 emissions are declining as a result -- even without drastic policy measures.
In the current, and foreseeable, electric power system, renewables, like wind and solar, will not be able to comprise a large share of electricity due to their intermittency. When the sun doesn't shine, the wind is not blowing, and demand exceeds the supply of other renewables like hydroelectric, the electric system NEEDS something to cover the gap in supply and demand. Otherwise, your lights will go out and you face the cascading problems that accompany power outages. The recent Delta flight cancellations are a timely reminder of how this issue is anything but innocuous. Right now, the gap can be bridged with natural gas.
The key technology that can replace combustion in peak demand is energy storage. Store the sun's rays and winds when we don't demand the power and unleash it when we demand more than we can supply- either with large utility scale batteries or many small batteries installed in commercial real estate and households.
Energy storage is also a game changer for emissions in transportation, which just surpassed electricity production as the largest source of US CO2 emissions. The carbon-friendly winner in the transportation sector is the plug-in electric vehicle. Larger and cheaper batteries will increase their penetration of, shifting the sector's primary fuel source from high-emitting gasoline to less-emitting electricity - where a zero-emitting electricity sector also relies on energy storage technology.
Fortunately, technological development is driving down costs and the end of the natural gas bridge is almost in sight. However, electric utilities need an injection of innovation (many still operate as state-regulated monopolies) and the right rate structures (e.g. time-of-use pricing) need to be implemented in order for new innovations in energy storage to compete in the market place.
While other alternative may surface, at this point, it seems that the natural gas bridge to a low-carbon future is leading to solid ground built on energy storage.