Recession pulled US greenhouse gases down in 2009

By Martin Leggett - 01 Apr 2011 15:22:0 GMT
Recession pulled US greenhouse gases down in 2009

The headline numbers for US greenhouse gas emissions look great - a nearly 6% fall in CO2 equivalents between 2008 and 2009. But the US EIA (Energy Information Administration) report on greenhouse gas emissions caught the snapshot of an economy in sharp decline. So it will be the 2010 figures which will show whether falls can coexist with a return to economic growth. Still, the detailed breakdown for 2009 does throw some interesting light on the changing picture of man-made greenhouse gas emissions in the US.

Greenhouse gases are those gases which play a role in trapping some of the heat of the sun. In fact they are vital in keeping the Earth in its 'Goldilocks' sweet-spot - not too hot, not too cold. The problem is that man's activities are releasing these gases in increasing quantities - and many hang around in the atmosphere for decades or centuries. That is increasing their concentration, resulting in a gradual rise in temperatures globally - and in increasingly erratic climate change as a consequence.

The US has historically been one of the major emitters of greenhouse gases (although China is usurping that dubious honor), so the EIA annual emissions tally is keenly watched. The numbers for each of the main gases (CO2, methane, nitrous oxide and high-global warming potential gases) are converted to the equivalent amount of CO2 that would produce warming - so allowing them to be compared and added together. The fall being reported for 2009, from nearly 7,000 million metric tonnes CO2 equivalent, to 6,600 MMTCO2e is the largest recorded since detailed records began in 1990.

Most of that fall comes from CO2 itself , which accounts for over 80% of greenhouse gas warming. Emissions plummeted by over 300 MMTCO2e. The EIA report points to the recession as the trigger, which saw the worst losses of production in high-emitting industries. There was also a switch to lower-priced natural gas, from higher carbon emitting coal, for electricity generation, which helped in pulling the numbers down.

For methane, it was a mixed picture. It accounts for 10% of US emission warming-potential, and there were increased releases from underground coal mining. But these were mainly offset by reduced methane from farming, producing a 1% rise overall, to 730 MMTCO2e. Nitrous oxide emissions, which comes from industry, farming and general energy use, fell by nearly 2%. But it only accounts for some 3% of overall greenhouse gas warming.

One to watch is the so-called 'high-global warming potential gases' - which includes chemicals such as hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride. These are only a small player, at 3% of warming emissions, but they rose sharply by 5%. But besides the shifting mix amongst these different gases, and the influence of the recession on them, the one promising note was the reduction in 'greenhouse gas intensity'. This measures how much CO2 equivalent is pumped out for each dollar of growth. It fell in 2009 by 2%. However, at this rate, the time to reach the holy grail of a zero-carbon economy is going to be a long haul.