Recalculation of Leaking Methane Impacts May Affect Natural Gas Market

Environmental advocates are trying to change how policymakers consider the climate impacts of methane, a potent greenhouse gas.

The change, if implemented, could make natural gas a less attractive option for generating electricity in power plants.

At issue is the global warming potential (GWP), a number that allows experts to compare methane with its better-known cousin, carbon dioxide.  While CO2 persists in the atmosphere for centuries, or even millennia, methane warms the planet on steroids for a decade or two before decaying to CO2.

In those short decades, methane warms the planet by 86 times as much as CO2, according to the Intergovernmental Panel on Climate Change.

But policymakers typically ignore methane's warming potential over 20 years (GWP20) when assembling a nation's emissions inventory.  Instead, they stretch out methane's warming impacts over a century, which makes the gas appear more benign than it is, experts said.  The 100-year warming potential (GWP100) of methane is 34, according to the IPCC.

There is no scientific reason to prefer a 100-year time horizon over a 20-year time horizon; the choice of GWP100 is simply a matter of convention.

The 100-year GWP value underestimates the gas's negative impacts by almost five times, said Ilissa Ocko, a climate scientist at the nonprofit Environmental Defense Fund.  The quick warming in the short run catalyzed by methane can affect environmental processes, such as the flowering of plants, she said at the American Geophysical Union meeting last week.

"The short-lived climate pollutants [like methane] that we emit from human activities are basically controlling how fast the warming occurs," she said.  "This is because they are very powerful at absorbing radiation."

EDF and some scientists are calling on the United Nations and policymakers to stop relying on GWP100.  They would instead like experts to use GWP20 and GWP100 as a slashed pair.

A push for quicker reductions
... The effort has gained urgency since the United States has become a large natural-gas-producing nation.  Its emissions of methane between 1990 and 2013 have fallen by 15 percent, according to U.S. EPA, though some studies have suggested that methane inventories may be faulty.

If the proposed nomenclature change is adopted by the United Nations, which collects greenhouse gas inventories from nations every year, it could change the optics of the climate change reductions nations are implementing, said Bryce Payne, director of science and technology at Gas Safety Inc., a company that measures methane emissions.

At present, nations report methane emissions in terms of CO2 equivalents, using GWP100 as the conversion factor.  This allows nations, such as the United States, that use natural gas to generate electricity to present a cleaner façade to the world than they have in reality, he said.

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