A new paper predictably makes a big splash in this week’s Nature magazine:
Katharine M. Willett1,2, Nathan P. Gillett1, Philip D. Jones1 & Peter W. Thorne2
Climatic Research Unit, School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK
Met Office Hadley Centre, FitzRoy Road, Exeter EX1 3PB, UK
Water vapour is the most important contributor to the natural greenhouse effect, and the amount of water vapour in the atmosphere is expected to increase under conditions of greenhouse-gas-induced warming, leading to a significant feedback on anthropogenic climate change. Theoretical and modelling studies predict that relative humidity will remain approximately constant at the global scale as the climate warms, leading to an increase in specific humidity. Although significant increases in surface specific humidity have been identified in several regions and on the global scale in non-homogenized data, it has not been shown whether these changes are due to natural or human influences on climate. Here we use a new quality-controlled and homogenized gridded observational data set of surface humidity, with output from a coupled climate model, to identify and explore the causes of changes in surface specific humidity over the late twentieth century. We identify a significant global-scale increase in surface specific humidity that is attributable mainly to human influence. Specific humidity is found to have increased in response to rising temperatures, with relative humidity remaining approximately constant. These changes may have important implications, because atmospheric humidity is a key variable in determining the geographical distribution and maximum intensity of precipitation, the potential maximum intensity of tropical cyclones, and human heat stress16, and has important effects on the biosphere and surface hydrology.
Also in Nature News:
Study models rises in atmospheric water vapour.
Human activity is behind the rising levels of water vapour in the lower atmosphere over the past few decades, climatologists have concluded. The rises in humidity could affect patterns of extreme storms, they warn.
Nature’s editor likes it too:
………using a new data set of surface specific humidity observations, along with output from a coupled climate model, Willett et al. identify a significant increase in global mean surface specific humidity during the late twentieth century that is mainly attributable to human influence.
Luke Walker thinks the paper is significant and sent a link to ABC’s predictable take:
We also had this report from the BBC in November 2005:
“Water vapour rather than carbon dioxide in the atmosphere is the main reason why Europe’s climate is warming, according to a new study.”
The BBC are up to speed with the new Nature paper:
I wonder how evaporation equalling precipitation globally over the past 20 years fits into this?
The paper also tries to make a link with increased tropical cyclones, but the case for a link is weak.
Scant publicity by comaprison for the recent Spencer et al paper ‘Cloud and radiation budget changes associated with tropical intraseasonal oscillations’. Geophys. Res. Lett., Vol. 34, No. 15, 9 August 2007.
Read the article ‘Global Warming and Nature’s Thermostat’ by Roy W. Spencer:
August 9, 2007 RESEARCH UPDATE!: Our peer-reviewed paper showing the natural cooling behavior of tropical cirrus clouds in response to warming has been published today in Geophysical Research Letters. (The UAH news release is here.) This natural cooling mechanism constitiutes a strong “negative feedback” (reducing warming tendencies), while all leading climate models have cirrus clouds behaving in a positive feedback manner (amplifying warming tendencies). As is usually the case in this business, however, there is no way to know with any level of confidence whether this mechanism is operating in the context of manmade global warming………