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New excuse #56 for the ‘pause’ in global warming: Satellites underestimate cooling from volcanic aerosols – Published in Geophysical Research Letters

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New excuse #56 for the “pause” in global warming: Satellites underestimate cooling from volcanic aerosols

http://hockeyschtick.blogspot.com/2014/10/new-excuse-56-for-pause-in-global.html

A paper published today in Geophysical Research Letters states, “Understanding the cooling effect of recent volcanoes is of particular interest in the context of the post-2000 slowing of the rate of global warming” and finds “recent volcanic events are responsible for more post-2000 cooling than is implied by satellite databases” which “translates into an estimated global cooling of 0.05 to 0.12 °C.” By way of comparison, the IPCC formula claims post-2000 warming from CO2 was 5.35*ln(400/369) = 0.43W/m2 *(3C/3.7Wm-2) = 0.35C warming, which is at least three times larger than the estimated volcanic cooling found from this paper. Therefore, volcanic cooling would not be sufficient to account for the zero degrees global warming post-2000 (actually post-1996). This implies that either this new paper is incorrect regarding volcanic cooling account for the “pause,” or that the IPCC exaggerates climate sensitivity to CO2. Further, even James Hansen admits there have been no large volcanic eruptions post-2000: “Remarkably, and we will argue importantly, the airborne fraction [of man-made CO2] has declined since 2000 (figure 3) during a period without any large volcanic eruptions.” and as demonstrated by the stratospheric aerosol index of volcanic eruptions: How can volcanic aerosols explain the post-2000 “pause” without an increase of volcanic activity?Total volcanic stratospheric aerosol optical depths and implications for global climate changeD. A Ridley et al Understanding the cooling effect of recent volcanoes is of particular interest in the context of the post-2000 slowing of the rate of global warming. Satellite observations of aerosol optical depth (AOD) above 15 km have demonstrated that small-magnitude volcanic eruptions substantially perturb incoming solar radiation. Here we use lidar, AERONET and balloon-borne observations to provide evidence that currently available satellite databases neglect substantial amounts of volcanic aerosol between the tropopause and 15 km at mid to high latitudes, and therefore underestimate total radiative forcing resulting from the recent eruptions. Incorporating these estimates into a simple climate model, we determine the global volcanic aerosol forcing since 2000 to be −0.19 ± 0.09 Wm−2. This translates into an estimated global cooling of 0.05 to 0.12 °C. We conclude that recent volcanic events are responsible for more post-2000 cooling than is implied by satellite databases that neglect volcanic aerosol effects below 15 km.

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