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Global warming: Study confirms greenhouse gas ‘fingerprint’ in distinct patterns of temperature change

Study links regional atmospheric warming with greenhouse gases. Photo courtesy NASA.

Study will anchor new IPCC climate change assessment

By Summit Voice

FRISCO — Just as thousand of delegates gather in Doha, Qatar for the UN’s annual climate talks, researchers are releasing a wealth of new observational data that verifies the output from existing climate models.

In recent example, a team of climate scientists from the Lawrence Livermore National Laboratory and colleagues from 16 other organizations compared simulations from 20 different computer models to satellite observations, finding that tropospheric and stratospheric temperature changes are clearly related to human activities.

“It’s very unlikely that purely natural causes can explain these distinctive patterns of temperature change,” said Lawrence Livemore National Laboratory atmospheric scientist Benjamin Santer, who is lead author of the paper appearing in the Nov. 29 online edition of the journal, Proceedings of the National Academy of Sciences. “No known mode of natural climate variability can cause sustained, global-scale warming of the troposphere and cooling of the lower stratosphere.”

The team looked at geographical patterns of atmospheric temperature change over the period of satellite observations with the goal of determining whether previous findings of a “discernible human influence” on tropospheric and stratospheric temperature were sensitive to current uncertainties in climate models and satellite data.

The troposphere is the lowest portion of earth’s atmosphere. The stratosphere sits just above the troposphere, between 6 and 30 miles above earth’s surface.

The satellite temperature data sets were produced by three different research groups, and rely on measurements of the microwave emissions of oxygen molecules. Each group made different choices in processing these raw measurements, and in accounting for such complex effects as drifts in satellite orbits and in instrument calibrations.

The new climate model simulations analyzed by the team will form the scientific backbone of the upcoming 5th assessment of the Intergovernmental Panel on Climate Change, which is due out in 2014.

In both satellite observations and the computer model simulations of historical climate change, the lower stratosphere cools markedly over the past 33 years. This cooling is primarily a response to the human-caused depletion of stratospheric ozone. The observations and model simulations also show a common pattern of large-scale warming of the lower troposphere, with largest warming over the Arctic, and muted warming (or even cooling) over Antarctica. Tropospheric warming is mainly driven by human-caused increases in well-mixed greenhouse gases.

The team analyzed results from climate model simulations with specified historical changes in human and natural external factors, and from simulations with projected 21st century changes in greenhouse gases and anthropogenic aerosols. They also looked at simulations with no changes in external influences on climate, which provide information on the year-to-year and decade-to-decade “noise” of internal climate variability, arising from such natural phenomena as the El Niño/Southern Oscillation and the Pacific Decadal Oscillation.

The team used a standard “climate fingerprint” method to search for the model signal pattern (in response to human influences, the sun and volcanoes) in the satellite observations. The method quantifies the strength of the signal in observations, relative to the strength of the signal in natural climate noise.

Other contributors include researchers from Remote Sensing Systems of Santa Rosa; the Centre for Australian Weather and Climate Research, Melbourne, Australia; the Canadian Centre for Climate Modeling and Analysis, Victoria, Canada; the National Oceanic and Atmospheric Administration (NOAA) Geophysical Fluid Dynamics Laboratory, Princeton; the University of Colorado, Boulder; the Massachusetts Institute of Technology, Cambridge; the U.K. Met. Office Hadley Centre, Exeter, U.K.; the Centre National de la Recherche Scientifique, Toulouse, France; North Carolina State University; the National Climatic Data Center, Asheville; Lawrence Berkeley National Laboratory; the National Center for Atmospheric Research, Boulder; the University of Adelaide, South Australia; the University of Reading, U.K.; and the Center for Satellite Applications and Research, Camp Springs. The paper is Santer’s inaugural article as a member of the U.S. National Academy of Sciences.

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3 Responses

  1. Oh no not the dreaded ‘fingerprint’ thingy again. About every year at this time, the fingerprint thingy appears and it hits the blogosphere and news media, then it vanishes again.

    • You understand what’s going on, right? Now, studies based on 20 years of observational data are showing that, in many (not all) cases, the models have been pretty accurate.

  2. Firstly the paper actually reports that the models do not agree with observations to the extent that they cannot reasonably draw the conclusions they did. and secondly previous similar papers from Santer seem to have invented signals and ignored bad data, which even uber-warmist Kevin Trenberth (privately) took issue with. See below:

    http://pielkeclimatesci.wordpress.com/2012/08/27/ye-old-boys-club-an-example-with-ben-santer-and-kevin-trenberth/

    I expect a rebuttal comment will follow soon.

    Also a recent paper by Santer discussed here :

    http://pielkeclimatesci.wordpress.com/2011/09/07/comments-on-the-new-paper-separating-signal-and-noise-in-atmospheric-temperature-changes-the-importance-of-timescale-by-santer-et-al-2011/

    had admitted at last that the last decade had no global warming (its actually 16 years of non trop warming now and 18 years of non cooling in the stratosphere). He blithely ignores this but the last decade has seen one third of all manmade carbon dioxide released. If anthropogenic warming is as stark and obvious then the warming should not have paused. It is difficult to accept the contradictory idea that weak natural variation is still consistent with a pause in warming: ie what else caused the pause? Magic pixies? The idea that CO2 somehow produces a staircase rise so we should ignore the current non-warming is pure speculation with no actual theory introduced to explain it and presents us with a paradox that the exponential increase in CO2 to date must have been muted by an ever-increasing yet at the same time totally absent (according to Santer) natural cooling. Whither art thou Occams razor.

    I’m afraid the climate change activists like Santer raise speculation to an artform. Good science it is not!

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