from The American Heritage® Dictionary of the English Language, 4th Edition
- abbr. parts per million
from Wiktionary, Creative Commons Attribution/Share-Alike License
- Parts per million. (10000 ppm = 1%)
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The majority of samples (128 out of 187) had measurable levels of total hydrocarbons and 28 had levels greater than 10 ppm, which is the level of concern EPA is using for Volatile Organic Compounds (VOCs).
Human emissions have increased the atmospheric CO2 concentration to 385 ppm, which is 4.0 kg per square metre, or an extra 1.1 kg per square metre.
One intermediate action they're contemplating is lowering the discharge requirement on existing platforms to 15 ppm, which is easily doable 95% of the time, but the last 5% will be very tricky for platforms.
A few years ago, scientists thought that a doubling of carbon concentrations over preindustrial times, to 550 parts per million, was a reasonable line in the sand; in recent years they've revised that figure downward, to 450 ppm, which is what Copenhagen (and the Waxman-Markey bill) aim for.
Thus, R400, the most toxic formulation, killed all cells at 20 ppm, which is equivalent to 8ppm in G.
A level of 450 ppm CO2 is a mere ~40 ppm below the upper boundary of ~500 ppm, which is the upper limit of stability of the Antarctic ice sheet, formed about 34 million years ago.
I note that the Matsui + Pielke paper uses a current value for CO2 of 336 ppm, which is significantly out-of-date, and that biases their estimate of GHG radiative forcing down by about 0.6 W/m2.
The late Ordovician had an ice age despite CO2 levels of 4,000 ppm, which is over ten times the current level.
Concentrations of CO2 are now 380 ppm -- in other words, off the chart.
We have already surpassed 350 ppm, which is considered by the NOAA to be the "upper safety limit" for atmospheric CO2.
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