Challenging climate sensitivity: 'Observational Quantification of Water Vapor Radiative Forcing' #AGU16 presentation

By Willis Eschenbach and Anthony Watts

Today at the American Geophysical Union Convention, Willis Eschenbach and Anthony Watts will be presenting at 1:10PM in Moscone South.

FOR IMMEDIATE RELEASE

Study at AGU 2016 challenges conventional wisdom on climate sensitivity

‘Observational Quantification of Water Vapor Radiative Forcing’

December 14^th, 2016 – San Francisco, CA – A new study about the role of water vapor in climate sensitivity is being presented at the 2016 Fall Meeting of the American Geophysical Union today by Willis Eschenbach and Anthony Watts in session A33B: Climate Sensitivity and Feedbacks: Advances and New Paradigms, in Moscone South Poster Hall at 1:10PM to 6PM December 14^th, position A33B-0226.

The study, using satellite measured water vapor data obtained from Remote Sensing Systems (RSS) of Santa Rosa, CA, suggests that the global climate sensitivity to increased carbon dioxide, and the potential feedback mechanism of increased water vapor in Earth’s atmosphere, is actually far less than postulated by the IPCC.

An investigation was conducted utilizing the Remote Sensing Systems (RSS) 1°x1° gridded total precipitable water (TPW) dataset to determine the magnitude of upwelling long-wave infrared radiation from Earth’s surface since 1988. TPW represents the mass of water vapor in a 1 meter by 1 meter column from the surface to the top of the atmosphere. As referenced in IPCC AR5 WGI Box 8.1, the radiative effect of absorption by water vapor is roughly proportional to the logarithm of its concentration. Therefore it is the fractional change in water vapor concentration, not the absolute change, that governs its strength as a climate forcing mechanism. A time-series analysis utilizing a Loess decomposition filter indicated there is a clear upward trend in the RSS TPW data since 1988. The observed total change over the period is ~ 1.5 kg/m^2, centered around the long-term mean of 28.7 kg/m^2. Utilizing the observed relationship between water content and atmospheric absorption, the RSS TPW data indicates an increase in downwelling longwave radiation of 3.3 W/m2 over the period 1988 – 2015.

Key finding:

The finding of an observationally measured increase in downwelling radiation of 3.3W/m2 since 1988, in addition to the increase in downwelling radiation over the period as calculated by the IPCC, with little corresponding change in temperature, calls into question the applicability of the concept of “climate sensitivity”.

Corresponding author: Willis Eschenbach willis@surfacetemps.org