If President Obama’s Clean Power Plan is going to work, lots of things will have to fall into place. Perhaps the most important is the reduction in greenhouse gases that is expected from increased use of natural gas to generate electricity.

Under the plan, which aims to reduce electricity sector emissions by 30 percent by 2030, the EPA projects that coal-fired power will drop more than a quarter from its current 40 percent share of U.S. electricity generation. Most scenarios project that natural gas will pick up the majority of that gap.

The generally accepted climate benefit of natural gas is that it emits about half as much CO2 as coal per kilowatt-hour generated. But this measure of climate impact applies only to combustion, it does not include methane leaks, which can dramatically alter the equation. Methane is a potent greenhouse gas that forces about 80 times more global warming than carbon dioxide in its first 20 years in the atmosphere. Methane’s warming power declines to roughly 30 times CO2 after about 100 years.

No one has any idea how much methane is leaking from our sprawling and growing natural gas system. This is a major problem, because without a precise understanding of the leak rate natural gas could actually make climate change worse, but we would never know.



Our analysis shows that very modest leak rates can severely undermine the climate benefits of natural gas. Three factors drive any assessment of the impacts of leaks in the natural gas system, and by extension, our ability to achieve the goals set out in the proposed EPA rule: the estimated methane leak rate from drilling through end use; methane’s initial potent warming potential that then decreases over time; and the rate at which we switch from coal to gas.

When leak rates, methane potency, and the speed of transition are considered, the sensitivity of the climate benefits of natural gas power come into focus. Our analysis looked at various leak rate scenarios, but each one assumed a conversion rate of about 1.8 percent of all coal–fired generation to natural gas per year, the rate needed to achieve a 25 percent reduction in coal use by 2030. That rate is equivalent to reducing coal electricity for 15 years at about half the annual rate of the 2008 to 2013 period, one of the fastest conversion periods ever.

Based on this rate of transition:

With a 2 percent leak rate, which is roughly the EPA’s current estimate, by 2030 greenhouse gas emissions from the electricity sector would be about 10 percent lower than today. By 2060, we would reach a 24 percent reduction, still well short of the 30 percent target.



With a 4 percent leak rate, by 2030 greenhouse gas emissions from electricity generation would be just 2 percent lower than today. If the shift to gas continues until 2060 at the same pace, we would see a 10 percent reduction in impact, or just one-third of the way to EPA’s 2030 reduction target of 30 percent. Notably, under this scenario, by 2060 half the coal power in the country would have to be replaced with natural gas to achieve a mere 10 percent reduction in emissions.



Even if we assume there are no leaks anywhere in the entire natural gas system, it would take 30 years, until 2045, to achieve a 30 percent reduction in electricity sector greenhouse gas emissions.



Climate Central’s interactive tool lets you assess the impact of other leak rates and coal-to-gas transitions. The fact is that even with modest leak rates and a fairly aggressive transition, we could still end up with little or no climate benefits by 2030 after an enormous financial and political investment in natural gas.

But what about the long-term, after 2030? Will investments in natural gas made to comply with Obama’s climate plan help or undermine efforts to achieve the larger reductions needed to achieve even more important mid-century goals? Does natural gas really work as a so-called bridge fuel to a cleaner energy future?

It is difficult to answer that question, but one thing is clear: there is no short, 10- or 15-year natural gas bridge to a renewable energy future. Billion dollar investments made in natural gas today will be with us for the next 40 to 50 years. This fact only reinforces the urgent need to truly understand the extent and magnitude of methane leaks throughout the entire system. Without objective, real-time, statistically valid measurements of methane leaks, we can’t even begin to make an intelligent assessment of the climate impacts of any future energy mix that contains natural gas.

See our 2013 report on methane leaks in the natural gas system, which does not include the updated global warming potential for methane.

This article is reproduced with permission from Climate Central. The article was first published on August 5, 2014.