Opposing Lectures on How to Mitigate Global Warming

Dr. Alex LaGatta (Environmental & Earth Science) offers a brief summary of the two talks given during Jan Term by Dan Kammen and Rich Muller.

Dan Kammen promotes embracing renewables wholeheartedly, while Rich Muller proposes using natural gas as a bridge to renewables. He emphasizes the huge role China plays in global warming, and argues that any strategy aimed at curbing emissions is pointless if it doesn't make it affordable to China and the developing world. Energy consumption, mostly in the developing world, is expected to grow 40% by 2035. China is already the world's largest emitter of GHG and getting them to convert their coal-fired plants to natural gas will be more cost effective than encouraging them to convert to renewables. Having China embrace electric cars would actually make things worse, if China is producing its electricity from coal.

As a reminder, natural gas (CH4) is a much more potent greenhouse gas (GHG) than carbon dioxide (CO2), but it has a significantly shorter atmospheric lifetime than CO2. Combustion of natural gas is also far cleaner (half the CO2 of coal), and more efficient than any other fossil fuel. For these reasons, some believe it has the potential to be a bridge fuel on the road to lower emission technologies (solar/wind/nuclear/conservation). 

I have read several papers in the last couple of weeks and will attempt to summarize the ideas percolating in the scientific community.

One of the big issues with using natural gas as a bridge fuel is that it may subvert and delay the adoption of near-zero carbon technologies (NZCT).

Another issue with natural gas is the leakage (fugitive methane) into the atmosphere. Leakage occurs during production, transmission, storage, processing and distribution. In California alone, PG&E manages 40,000 miles of gas transmission lines. Estimates of leakage in the literature vary widely from about 1% to about 4% nationwide, with point sources (wells) emitting up to 17% (NOAA). The EPA estimated methane leakage to be 1.5%, however most believe this is inaccurate. Because it is a gas and distribution is extensive, it is difficult to assess how much is escaping. Many studies converge on estimates between 2-4%.

Richard Muller and others argue that because of the short half life for CH4 in the atmosphere (8.6 years), and assumed lower leakage rates, there are significant advantages to using natural gas over coal in the short term (40-50 years). They suggest that fugitive rates at or below 3% support natural gas as an effective bridge fuel. Others (NCAR and Prof. Kammen) calculate that leakage rates > 2% will negate any advantage over coal. An Op-Ed in the New York Times argues that natural gas is not a bridge but instead a gangplank to more warming and away from clean energy.  

Fugitive methane has greater climate impact in the short term (~20 years) as the CH4 has little time to oxidize and remains a more potent GHG. Natural gas has a compelling place in addressing long term climate impacts (100 year horizon), if the leakage rates are minimized. If short term climate impacts (20 year horizon) are prioritized, and leakage rates are on the high end (3-6%), then natural gas will do more harm than good. And if embracing natural gas delays the adoption of NZCT, the same holds true.

Natural gas is not a good bridge fuel if we are expecting to transition to near zero carbon technologies (NZCT) soon. For example if we are expecting to transition to NZCT in the next 5 years, then opening a natural gas plant with a life expectancy of 30-35 years will not help. However if natural gas is eschewed as a bridge and zero carbon technologies are not deployed quickly, this would be a very bad situation with a lot of long-lived CO2 in our atmosphere.

Deploying near-zero carbon technologies (wind/solar/nuclear/conservation) rapidly can achieve substantial benefits in the second half of the century. The first half of this century we will continue to see warming for various reasons. One, emissions will continue to rise until zero carbon technologies are deployed worldwide, and even if there were universal consensus today, this transition will take significant time and energy. These emissions of CO2 will be long lived. And lastly, the thermal inertia of the oceans produces a climate lag. Water has a high heat capacity, thus it takes a long time to heat up and an equally long time to cool down. Even if we shut off all CO2 emissions today, the atmosphere would continue to warm over the next 40-50 years.

 Aggressive scenarios for mitigation of global warming suggest a minimum of 20 years for the full adoption of NZCT, and many models predict the concurrent deployment of NZCT and natural gas systems to handle issues of intermittency. China may need to embrace natural gas to improve its air quality, particularly in the residential sector where many homes use coal briquettes for heating and cooking.

It seems paramount that we monitor methane emissions and employ best practices at well sites. Small changes in percentage have large implications for climate. A very recent paper (accepted but not yet published) reveals that US methane emissions have increased 30% from 2002 - 2014. While they cannot pinpoint the exact source (oil and gas systems versus livestock) due to spatial overlap, the huge increase in fracking over the same time period suggests a link.

If gas was a perfect system (no leakage), then transitioning to natural gas would be a no-brainer. If we had 100 years to sort this out, natural gas would again be an excellent choice. But we don't have 100 years. And leakage is widespread. And, at least for now, estimates of fugitive methane are growing.

To remain below the 2°C target, the world needs to reduce GHG emissions immediately. Since China has committed to peaking CO2 by 2030, it seems all but guaranteed the 2°C will be breached.

Regardless of whether you believe that natural gas can serve as an effective bridge, it seems that everyone agrees that wholehearted commitment to near zero carbon technologies is imperative. As Myhrvold and Caldeira (2012) put it: this underscores the urgency in developing realistic plans for the rapid deployment of the lowest GHG-emission electricity generation technologies. Technologies that offer only modest reductions in emissions such as natural gas and carbon capture storage, cannot yield substantial temperature reductions this century.

Given this big picture agreement, the "debate" between Professors Kammen and Muller is not really a matter of science. It instead lies in the realm of policy and economics. Those who advocate for the immediate, widespread adoption of NZCT tend to also favor the aggressive implementation of a carbon tax (or cap-and-trade policy) so that the long term environmental costs of fossil fuel use are included in the mix. Those who advocate for increased use of CH4 as a bridge fuel are generally less supportive of an aggressive carbon tax, and less optimistic that NZCT can be widely-deployed over the next few decades. So while there is widespread agreement that we need a zero carbon energy infrastructure ASAP, there is debate regarding the best way to reach this goal.

Finally, of all the near-zero carbon technologies, conservation will yield the largest immediate benefits.