Post by william on Jan 23, 2010 14:10:11 GMT
ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F2009JCLI3461.1
A doubling of CO2 is theoretically estimated to cause an increase in forcing of 3.8 W/m^2. Note it is not a fact that there will be 3.8 W/m^2 forcing. That is a theoretical calculation. It is possible the forcing due to a doubling of CO2 is less than 3.8 W/m^2.
Now if the planetary feedback is negative planetary cloud cover will increase as the planet warms in response to the 3.8 W/m^2 of CO2 warming. An increase in planetary cloud cover will result in an increase in amount of sunlight reflected into space.
Negative feedback is a good thing not a bad thing from the standpoint of stability of the earth's biosphere. If there is a massive volcanic eruption which cools the planet, cloud cover will reduce to counteract the cooling.
Likewise if there is a massive CH4 release from Methane clathrate from the deep ocean, planetary clouds will increase to protect the planet from over heating.
Now if the planetary feedback is positive then there is a greater change in planetary temperature which amplifies the original forcing change. Positive forcing is a bad thing in physical systems as the system becomes unstable and will oscillate as there are lag times in system response. Positive feedback will also cause system to continue to increase until the system reaches a physical limit.
It should be noted that the CO2 forcing is logarithmic not exponential. The first increase in forcing from 280 ppm to 300 ppm had the greatest effect. Each incremental increase in CO2 has less and less and affect on the planetary temperature than than the last 20 ppm increase. The forcing asymptotically reaches a limit. It saturates.
Venus is different than the earth because its atmospheric pressure is 90 times that of the earth. Gases under very high pressure start to act like liquids. Under 90 atmosphere the CO2 no longer absorbs a very narrow frequency which explains the high temperature of Venus.
If planetary feedback is zero, the planet warms around 1.5C to the 3.8W/m^2 increase due to doubling of CO2.
Now the IPCC is predicting 3C to 5C warming for the 3.8W/m^2 of forcing due to a doubling of CO2.
Now for those who are not following the details of planetary temperature change. The question is not is the planet warming? but rather how much has the planet warmed due to the 39% increase in CO2 from 0.028% to 0.0389%.
As noted below the planetary temperature rise due to a 40% increase in CO2 is less than 40% of what is predicted by the IPCC, assuming 100% of the 20th century temperature rise was due to CO2.
As it appears even if 100% of the twentieth century warming was due to CO2, the actual measured temperature increase is less than 40% of what the IPCC predicts.
That would support negative feedback (increase in planetary cloud cover) rather than positive feedback which is a good thing.
Why Hasn't the Earth Warmed as Much as Expected? Stephen E. Schwartz, Robert J. Charlson, Ralph A. Kahn, John A. Ogren, Henning Rodhe Issued January 19th, 2010
The observed increase in global mean surface temperature (GMST) over the industrial era is less than 40% of that expected from observed increases in long-lived greenhouse gases together with the best-estimate equilibrium climate sensitivity given by the 2007 Assessment Report of the Intergovernmental Panel on Climate Change. Possible reasons for this warming discrepancy are systematically examined here. The warming discrepancy is found to be due mainly to some combination of two factors: the IPCC best estimate of climate sensitivity being too high and/or the greenhouse gas forcing being partially offset by forcing by increased concentrations of atmospheric aerosols; the increase in global heat content due to thermal disequilibrium accounts for less than 25% of the discrepancy, and cooling by natural temperature variation can account for only about 15%. Current uncertainty in climate sensitivity is shown to preclude determining the amount of future fossil fuel CO2 emissions that would be compatible with any chosen maximum allowable increase in GMST; even the sign of such allowable future emissions is unconstrained. Resolving this situation, by empirical determination of Earth's climate sensitivity from the historical record over the industrial period or through use of climate models whose accuracy is evaluated by their performance over this period is shown to require substantial reduction in the uncertainty of aerosol forcing over this period.
The observed increase in global mean surface temperature (GMST) over the industrial era is less than 40% of that expected from observed increases in long-lived greenhouse gases together with the best-estimate equilibrium climate sensitivity given by the 2007 Assessment Report of the Intergovernmental Panel on Climate Change. Possible reasons for this warming discrepancy are systematically examined here. The warming discrepancy is found to be due mainly to some combination of two factors: the IPCC best estimate of climate sensitivity being too high and/or the greenhouse gas forcing being partially offset by forcing by increased concentrations of atmospheric aerosols; the increase in global heat content due to thermal disequilibrium accounts for less than 25% of the discrepancy, and cooling by natural temperature variation can account for only about 15%. Current uncertainty in climate sensitivity is shown to preclude determining the amount of future fossil fuel CO2 emissions that would be compatible with any chosen maximum allowable increase in GMST; even the sign of such allowable future emissions is unconstrained. Resolving this situation, by empirical determination of Earth's climate sensitivity from the historical record over the industrial period or through use of climate models whose accuracy is evaluated by their performance over this period is shown to require substantial reduction in the uncertainty of aerosol forcing over this period.
A doubling of CO2 is theoretically estimated to cause an increase in forcing of 3.8 W/m^2. Note it is not a fact that there will be 3.8 W/m^2 forcing. That is a theoretical calculation. It is possible the forcing due to a doubling of CO2 is less than 3.8 W/m^2.
Now if the planetary feedback is negative planetary cloud cover will increase as the planet warms in response to the 3.8 W/m^2 of CO2 warming. An increase in planetary cloud cover will result in an increase in amount of sunlight reflected into space.
Negative feedback is a good thing not a bad thing from the standpoint of stability of the earth's biosphere. If there is a massive volcanic eruption which cools the planet, cloud cover will reduce to counteract the cooling.
Likewise if there is a massive CH4 release from Methane clathrate from the deep ocean, planetary clouds will increase to protect the planet from over heating.
Now if the planetary feedback is positive then there is a greater change in planetary temperature which amplifies the original forcing change. Positive forcing is a bad thing in physical systems as the system becomes unstable and will oscillate as there are lag times in system response. Positive feedback will also cause system to continue to increase until the system reaches a physical limit.
It should be noted that the CO2 forcing is logarithmic not exponential. The first increase in forcing from 280 ppm to 300 ppm had the greatest effect. Each incremental increase in CO2 has less and less and affect on the planetary temperature than than the last 20 ppm increase. The forcing asymptotically reaches a limit. It saturates.
Venus is different than the earth because its atmospheric pressure is 90 times that of the earth. Gases under very high pressure start to act like liquids. Under 90 atmosphere the CO2 no longer absorbs a very narrow frequency which explains the high temperature of Venus.
If planetary feedback is zero, the planet warms around 1.5C to the 3.8W/m^2 increase due to doubling of CO2.
Now the IPCC is predicting 3C to 5C warming for the 3.8W/m^2 of forcing due to a doubling of CO2.
Now for those who are not following the details of planetary temperature change. The question is not is the planet warming? but rather how much has the planet warmed due to the 39% increase in CO2 from 0.028% to 0.0389%.
As noted below the planetary temperature rise due to a 40% increase in CO2 is less than 40% of what is predicted by the IPCC, assuming 100% of the 20th century temperature rise was due to CO2.
As it appears even if 100% of the twentieth century warming was due to CO2, the actual measured temperature increase is less than 40% of what the IPCC predicts.
That would support negative feedback (increase in planetary cloud cover) rather than positive feedback which is a good thing.