6.4.1 Feedback math (p. 106-107) > Consider ice-albedo feedback (Figure 6.8) with strength of feedback expressed as g >g is additional fractional warming produced by one trip through feedback loop per degree of initial warming > In response to initial warming, Ati, first trip through loop produces additional warming GAT, but feedback also operates on this additional warming (AT), and produces additional warming of g(GATI) = 92AT > Subsequent feedbacks operate on additional warming too, leading to gATI > Process continues forever, resulting in final warming AT in Equation 6.4-6.5 (p.106): AT = AT + GATI +92AT + 9%ATI + gATI + ... > Infinite series can be rewritten into Equation 6.6 (p.107): AT = AT /(1-9) - If g = 0 then no feedback and AT = ATI - If g between 0 and 1, then AT > AT and feedback is positive - If g Sum of feedback parameters from individual feedbacks gives Equation 6.7 (p.107): 9 = gia+gw+Gcloud + Gir - where gia = ice-albedo feedback, gw = water-vapor feedback, gcloud = cloud feedback, and gr = lapse-rate feedback (fast feedbacks) - Gw = 0.6, big enough to double initial warming AT - a = 0.1 -= -0.3 cloud = 0.0-0.3 [Note: The value range here contradicts Dessler's previous statement that the current net cloud feedback is negative. My interpretation is that the scientific community expects that the cloud feedback will increasingly favor a positive value as clouds respond to a warming climate system] 6.4.2 Sensitivity (p. 107-108) > Describe climate sensitivity > For doubling of CO2, AT = 1.2 degrees C > Using feedback strengths implied above, AT = 2 to 4 degrees C 6.4.1 Feedback math (p. 106-107) > Consider ice-albedo feedback (Figure 6.8) with strength of feedback expressed as g >g is additional fractional warming produced by one trip through feedback loop per degree of initial warming > In response to initial warming, Ati, first trip through loop produces additional warming GAT, but feedback also operates on this additional warming (AT), and produces additional warming of g(GATI) = 92AT > Subsequent feedbacks operate on additional warming too, leading to gATI > Process continues forever, resulting in final warming AT in Equation 6.4-6.5 (p.106): AT = AT + GATI +92AT + 9%ATI + gATI + ... > Infinite series can be rewritten into Equation 6.6 (p.107): AT = AT /(1-9) - If g = 0 then no feedback and AT = ATI - If g between 0 and 1, then AT > AT and feedback is positive - If g Sum of feedback parameters from individual feedbacks gives Equation 6.7 (p.107): 9 = gia+gw+Gcloud + Gir - where gia = ice-albedo feedback, gw = water-vapor feedback, gcloud = cloud feedback, and gr = lapse-rate feedback (fast feedbacks) - Gw = 0.6, big enough to double initial warming AT - a = 0.1 -= -0.3 cloud = 0.0-0.3 [Note: The value range here contradicts Dessler's previous statement that the current net cloud feedback is negative. My interpretation is that the scientific community expects that the cloud feedback will increasingly favor a positive value as clouds respond to a warming climate system] 6.4.2 Sensitivity (p. 107-108) > Describe climate sensitivity > For doubling of CO2, AT = 1.2 degrees C > Using feedback strengths implied above, AT = 2 to 4 degrees C
