Actually they are quite correct – let’s see why:
Last time I calculated this 2007 was the latest full year figure available for US coal-fired electrical generation and it’ll do fine for our purposes. Rationale for the figures used at end of item.
Total atmospheric persistent carbon dioxide emitted from all U.S. coal-fired generation (in full year 2007) = 0.968 / 7.81 = 0.12 ppmv.
Cutting that in say, half, via transition to natural gas means you can theoretically “save” annual accumulation of 0.06 ppmv CO2, right?
How much difference will that make? Very little.
Call it 90 years to end of century, so 90*0.06 = 5.4 ppmv “saved”.
And how much warming avoided is that? It’s doubtful we can measure it but assuming the developing nations only push atmospheric levels to 500 ppmv the “saving” works like this 5.35LN(505.4/500) = 0.06W/m2.
Hansen claims we’ve added two little Christmas Tree Lights (2W) per meter squared over the planet and over 150 years this has resulted in perhaps 0.7 °C warming. The coal to gas conversion above is equal to about 1/40th of that, less than 0.02 °C over the best part of a century.
The corollary of course is that since cutting about 4 billion metric tons of annual CO2 emissions for 90 years results in such trivial “cooling” then continuing to add it to the atmosphere makes no appreciable difference either.
Bottom line is that yes, natural gas is a “weak weapon against warming” but so what? CO2 is a pathetically weak “threat” to begin with.
Here’s NatGeo’s pitch:
Although natural gas burns more cleanly than coal, a new study argues that replacing all the world’s coal power plants with natural gas would do little to slow global warming this century.
“There are lots of reasons to like natural gas, but climate change isn’t one of them,” said physicist Nathan Myhrvold, lead author of the new study. “It’s worthless for [fighting] climate change, as far as we can tell.”
According to the U.S. EPA, the average emission rates in the United States from coal-fired generation is 2,249 lbs/MWh of carbon dioxide. We convert 2,249 lbs to 1.02 metric tons for the purposes of calculation.
Using 2007 (the last full year available from EIA here), coal-fired generation accounted for 2,016,456,000 of 4,156,745,000 Megawatthours (MWh) U.S. electric power generation (~48.5%). Thus 2,419,747,200mt CO2 emission from U.S. coal-fired generation (rounded up to 2.42 billion mt).
For simple expedience using CDIAC’s FAQ :
“Q. What percentage of the CO2 in the atmosphere has been produced by human beings through the burning of fossil fuels?”
A. “Atmospheric CO2 concentrations rose from 288 ppmv in 1850 to 369.5 ppmv in 2000, for an increase of 81.5 ppmv, or 174 PgC. In other words, about 40% (174/441.5) of the additional carbon has remained in the atmosphere, while the remaining 60% has been transferred to the oceans and terrestrial biosphere.
[Note for those not familiar with the units: PgC are petagrams of carbon, petagrams are one billion metric tons and carbon, with an atomic weight of 12, combined with 2 oxygen, atomic weight 16 (12 + 16 + 16 = 44) is 12/44 of the mass of carbon dioxide. We are only interested in the percentage emission accumulating in the atmosphere here.]
Atmospheric accumulation from U.S. coal-fired generation is then 2.42 (emission) x 0.4 (persistence) = 0.968 billion metric tons carbon dioxide (2007).
Again using CDIAC’s FAQ :
“Q. In terms of mass, how much carbon does 1 part per million by volume of atmospheric CO2 represent?”
A. Using 5.137 x 1018 kg as the mass of the atmosphere (Trenberth, 1981 JGR 86:5238-46), 1 ppmv of CO2 = 2.13 Gt of carbon.”
[note: I believe they are using Gt (gigaton) for 1 billion metric tons here since their calculation begins with mass in kilograms.]
And converting the carbon value to carbon dioxide: 2.13 * 44/12 = 7.81 billion metric tons carbon dioxide = 1 ppmv of the atmosphere.