«An increase by only a factor of 4 in global aerosol background concentration may be sufficient to reduce the surface temperature by as much as 3.5 ° K.» (skepticalscience.com)
In fact, when you get to very small amounts of CO2 (on the order of a few parts per million), the radiative forcing is much faster than logarithmic since you're opening up new opacity in the central 15 micron band where Earth is strongly emitting (it is for this reason methane changes are commonly cited as being «more powerful than CO2,» which is only true molecule - for - molecule in the modern atmosphere, as methane is starting off at much lower background concentrations. (skepticalscience.com)
Although background concentrations of gold in vegetation are typically less than 2 parts per billion (ppb), dried leaves from the trees growing above the ore deposit — but not those 200 meters away — had gold levels up to 80 ppb, says team member Mel Lintern, a geochemist at CSIRO's Earth Science and Resource Engineering division in Kensington, Australia. (sciencemag.org)