If everyone agreed that our atmosphere were to warm only 0.0001 degree C for every doubling of carbon dioxide concentration, nobody would give a hoot about anthropogenic global warming. If everyone agreed that it would warm 20 degrees C for every doubling, everybody would be in full panic mode.

But nobody believes either of those, and the real matter for debate about global warming is precisely this: How much will Earth’s near-surface temperature rise from a given increase in atmospheric carbon dioxide concentration?

The United Nations Intergovernmental Panel on Climate Change claims a mid-range estimate of 3 degrees C (4.5 degrees F) from doubled CO2 and a minimum of 1.5 (2.25 F).

Those estimates assume strong net positive feedback by the climate system on the much smaller amount of warming that would be directly attributed to doubled CO2. The latter is about 1.2 C (2.16 F). To get 3 C feedback must add 150%; even to get 1.5 C, it must add 25%.

Recent observations of changes in radiative energy outflow from Earth’s atmosphere, however, strongly indicate that the assumption of strong net positive feedback is wrong—not just in magnitude, but in sign. That is, not only do the feedbacks not add from 25% to 150% to CO2’s basic radiative warming. Instead, they diminish the warming. They are strongly net negative, not positive.

Dr. Roy W. Spencer, principal research scientist in climatology at the University of Alabama, Huntsville, and a lead scientist in NASA’s satellite remote atmospheric sensing experiments, reports in a blog entry that satellite measurements of outgoing infrared radiation indicate that feedbacks reduce GHG warming rather than increasing it. The result? Net warming from doubled CO2, after feedbacks, of about 0.5 C (0.9 F).

And that amount of warming in response to doubled CO2 would, according to the best ecological and economic modeling, cause significant net benefit to human economy and health and to the rest of Earth’s ecosystems.

Spencer and co-author William D. Braswell report their findings in a forthcoming article in the Journal of Geophysical Research, which we at the Cornwall Alliance will be sure to link in our newsletter as soon as it’s available.