Earlier last year we posted a blog on whether the new natural gas boom, thanks to improved drilling technologies and hydraulic fracturing or “fracking”, was to be considered a boon or bane to Earth’s climate. The boon part comes from the fact that natural gas burns much cleaner and causes roughly a factor of two lower CO2 emissions than the burning of coal. So if the gas were exclusively used in high efficiency gas-fired power plants, or even combined heat and power (CHP) plants to replace coal combustion power plants for electricity production, CO2 emissions reduction would be maximized. The bane part is the fact that mining and use of natural gas does not happen without the inevitable gas leaks, in this case releasing a different, more powerful greenhouse gas: methane.
We concluded that knowledge on leak rates (commonly expressed as a percentage of produced gas), especially for newly developed wells and their infrastructure, was lacking. Some scientific estimates implied rates near or below 2%, while others implied 5% or more. We also pointed out that, regardless of current leak rates from booming oil&gas activities, methane leakage in general is an important issue.
The methane budget
Several recent scientific assessments put current fossil fuel related, “fugitive” methane emissions to the atmosphere at 100 million tons per year, roughly two thirds coming from the oil&gas industry, the remaining third from coal mining. It is useful in this context to realize that humans have roughly tripled the emissions of methane to the atmospheresince the beginning of the industrial revolution. Meaning, nature only provides for one third of atmospheric methane, the other two thirds are from human activities, dominated by domestic ruminants (mostly cows, i.e. the beef you eat) and fossil fuel mining and use. At the same time, nature takes care of all methane removal from the atmosphere, overwhelmingly through its slow atmospheric photo-oxidation. This oxidation is responsible for an atmospheric lifetime of methane of nine years and causes a ripple effect through atmospheric chemistry, such as via producing ozone and carbon monoxide, and via increasing the lifetime of other trace gases, including methane itself.
Inventoring human emissions
Because methane is such a strong greenhouse gas, reducing its emissions has direct benefits for climate stabilization. Methane’s comparatively short atmospheric lifetimewould make the effects of emissions reductions measurable in the atmosphere within a decade. Alas, neither the production of beef nor the mining and use of fossil fuels are on the decline. Nevertheless, much ado has been made of EPA’s 2013 US greenhouse gasinventory, in which the agency lowered its estimates of past oil&gas industry related methane emissions to below 2% of produced gas amounts. This change has been misused by “pro-fracking” advocates to again attack the initial Howarth work and argue that methane releases are much lower than presumed, while “anti-fracking” advocates have instead highlighted that methane still contitutes a large fraction of US greenhouse gas emissions.