C02 vs Methane: Which is the scariest greenhouse gas?

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Wednesday March 05th David Archer will be addressing this topic in a free public lecture: 

“Because the concentration of methane is lower than that of CO2

in the atmosphere, a molecule of methane has a stronger effect 

than a CO2 molecule on the energy balance of the Earth.  

However, methane is a transient gas in the atmosphere, oxidizing

to CO2 within about a decade.  This behavior limits the

atmospheric concentration, which plateaus unless the emission

flux is continuously accelerated.   In contrast, CO2 released to

the atmosphere essentially accumulates in the “fast” atmosphere

/ ocean / land biosphere carbon cycle, leading to an increase in

atmospheric CO2 concentrations for hundreds of thousands of

years.  The 10-year lifetime of methane is much shorter than the

thousand-year time scale for changing Earth’s temperature,

which is determined by the heat capacity of the deep ocean.

CO2, in contrast, sticks around long enough for Earth’s

temperature to respond completely.  Some components of the

climate system, such as the ice sheets in Antarctica and

Greenland, will respond most strongly to the “long tail” of the

fossil fuel CO2, increasing sea level in the millennial-timescale

future by about 100 times more than the IPCC forecast for the

year 2100.  Therefore mitigation of CO2 emissions seems to me

the highest priority in dealing with climate change, although

mitigating methane emissions as well would have a significant

positive impact on the climate of the next decades…..”

2 responses to “C02 vs Methane: Which is the scariest greenhouse gas?”

  1. agshannon

    I didn’t have a chance to attend this lecture (I wish I’d known about it!) but I’ve encountered some interesting facts about carbon emissions that I think are extremely relevant to any conversation about it. The first is that driving vehicles is not the greatest source, it’s running our homes and businesses (http://www.epa.gov/climatechange/ghgemissions/gases/co2.html). Surprising even to me, industry is third in line. (But I guess a smokestack is an easier icon than something representing the emission of carbon dioxide to produce electricity!) So I’ve start to wonder whether the notion of driving as the root of all carbon-emissions evil is really merited, and I’ve continued to encounter further challenging facts. For example, gas-powered lawnmowers emit as much CO2 as eleven cars (http://www.jocogov.org/dept/health-and-environment/environment/air-quality/clean-air-lawn-care). Or, that another major greenhouse gas, Nitrous Oxide (with a life span of 114 years and a “Global Warming Potential” 300 times that of CO2) is sourced 75% from agriculture (http://www.epa.gov/climatechange/ghgemissions/gases/n2o.html).
    I believe in being efficient with transportation, but attitudes about climate change and carbon emissions tend to demonize cars above all else, and I’ve started to raise an eyebrow. If we really want to affect meaningful change in emissions, we need to have a strong grasp of the real facts, and to face them with realistic and effective action.

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