Well, I messed up my post on methane, giving it far greater weight as a contributor to human influences on the climate than does the IPCC.
Since I couldn’t find what I was looking for (a stacked bar chart showing in Column A all positive human contributions and in Column B all negative contributions, I am trying to do it myself.
Radiative forcing has been used as a proxy to express the climate response of different GHGs. It is a hypothetical figure, as it doesn’t include the response of the rest of the climate’s components or natural variability. Increased warmth, for example, has produced a quick response in vegetative cover increase, which should reduce CO2 in the atmosphere, affect precipitation in the immediate region and have an effect on surface albedo as well. None of those is captured by radiative forcing estimates, an indication that physicists have superimposed their concept of the world on us all. All hail our new physicist overlords! (I suspect that biology and chemistry will eventually find their voice.)
My source is IPCC AR4 (I couldn’t find it in AR5), but the physics shouldn’t change that much in a handful of years, right?
So here’s about half the picture in my handmade chart:
According to the IPCC, human emissions of CO2 comprise 56.6% of the relevant gas emissions.
The total net forcing (subtracting the negative contributions of land use and cloud albedo) is 1.8 Watts per square meter. The total forcing of the elements listed in the chart above are 2.64 Watts per square meter, I think.
Here’s their chart:
There are a lot of things I don’t understand.
For example, their separate figure for deforestation. Much of the effects of deforestation is the liberation of CO2 from dead trees. Some of it is from the changed albedo of the cleared land. Is the separate figure for deforestation accounting for either, both or something else?
But I guess my major sticking point is black carbon. I’m not sure why they list black carbon is given by the IPCC as a negligible forcing of 0.1 W/m2. In a report by the EPA to Congress, the EPA writes,
“BC influences climate through multiple mechanisms: – Direct effect: BC absorbs both incoming and outgoing radiation of all wavelengths, which contributes to warming of the atmosphere and dimming at the surface. In contrast, GHGs mainly trap outgoing infrared radiation from the Earth’s surface. – Snow/ice albedo effect: BC deposited on snow and ice darkens the surface and decreases reflectivity (albedo), thereby increasing absorption and accelerating melting. GHGs do not directly affect the Earth’s albedo. – Other effects: BC also alters the properties and distribution of clouds, affecting cloud reflectivity and lifetime (“indirect effects”), stability (“semi-direct effect”), and precipitation. These impacts are associated with all ambient particles, but not GHGs. y The direct and snow/ice albedo effects of BC are widely understood to lead to climate warming. Based on the studies surveyed for this report, the direct and snow/ice albedo effects of BC together likely contribute more to current warming than any GHG other than CO2 and methane (CH4).”
The EPA gives the potential forcing of black carbon as “+0.34 to 1.0 W m-2 direct forcing +0.05 W m-2 (snow/ice albedo forcing) ± ? (cloud interactions) Net effect: uncertain, but likely warming.”
Way back in 2001, Mark Jacobson (Yes, him) published a paper in Nature saying “Soot - or black carbon may be responsible for 15 to 30 percent of global warming, yet it’s not even considered in any of the discussions about controlling climate change,” says Stanford Professor Mark Z. Jacobson, author of the Feb. 8 Nature study.
Since then, the Guardian has published a story saying “The global warming effect of ‘black carbon’, or soot, has been greatly exaggerated due to mistaken assumptions about the atmospheric altitude at which its particles are concentrated, according to a new study” based on a paper by the Centre for International Climate and Environmental Research-Oslo.
The BBC countered with “Scientists say that particles from diesel engines and wood burning could be having twice as much warming effect as assessed in past estimates. They say it ranks second only to carbon dioxide as the most important climate-warming agent. The research is in the Journal of Geophysical Research-Atmospheres. Black carbon aerosols have been known to warm the atmosphere for many years by absorbing sunlight. They also speed the melting of ice and snow.
This new study concludes the dark particles are having a warming effect approximately two thirds that of carbon dioxide, and greater than methane. “The large conclusion is that forcing due to black carbon in the atmosphere is larger,” lead author Sarah Doherty told BBC News. “The value the IPCC gave in their 4th assessment report in 2007 is half of what we are presenting in this report – it’s a little bit shocking.”
I guess I’m not the only puzzled by all this.