How much of the current climate change is attributable to Anthropogenic GHG’s?

... and how do you demonstrate this?
If you'd like to reference measurements in your response, then there are some handy links below.

2011-08-11T20:33:14Z

CO2. Mauna Loa since 1958. ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/co2_mm_mlo.txt

Global Surface (inc oceans) temperature anomaly since 1850. HadCRUT3: http://hadobs.metoffice.com/hadcrut3/diagnostics/global/nh+sh/monthly

Mean Sea Level Anomaly since 1992. University of Colorado.: http://sealevel.colorado.edu/current/sl_ib_global.txt

Total Ocean Heat Content anomaly since 1955. NODC. http://climexp.knmi.nl/data/inodc_heat700_0-360E_-90-90N_n.dat

2011-08-14T05:32:56Z

The Meehl paper is very interesting. The natural forcings they model are; Solar and Volcanic. The anthropogenic forcings considered are GHG’s and sulphates (actually, only SO4). They also model ozone over the same period... but is stays essentially the same, so for simplicity we might ignore it. The ‘observations’ in this paper are from the ‘CRU’ dataset. This is superseded by HadCRUT3, but exhibits substantially the same pattern over time.

The first thing that strikes me is that none of the forcings considered exhibits an increase in the periods 1940+/-8 years and 1960 +/- 5 years that accounts for those two warm periods. Unfortunately this tells me straight away that the model is substantially incomplete.

The second thing I notice is that the cool period in the 1970’s, which is normally attribute to increased atmospheric sulphates, does not actually have a correspondingly increased negative sulphate forcing in this time period. The cooling forcing from sulphates falls in a mostly

2011-08-14T05:34:20Z

linear manner through that period.

The third thing I see is how strongly GHG’s and observations correlate from about 1978 to 1999, but NOT in the three time periods I have mentioned above.

Of the forcings considered, only GHG’s exhibits a positive change over the study period. Thus, if the model is complete, then only GHG’s can account for the increased ‘observation’... and towards the end of the study period the summing of the forcings does appear to correspond to the ‘observation’. See fig2, c and d.

However, this study ends at 1999. We know that the Keeling curve continues uninterrupted 2000 to present, thus the Anthropogenic forcing in this model would continue to rise strongly. We also know that the ‘observation’ does not rise at all in this period.

If this study were repeated using current data, then the combined forcings would dramatically fail to match ‘observations’ in the period 2000-2011. Here’s a chart I’ve shown previously that illustrates the issue. http://farm7.sta

2011-08-14T05:35:23Z

http://farm7.static.flickr.com/6136/5917099494_aba725cf32_z_d.jpg

The Meehl paper is a nice read, but as you see, the model they use is so incomplete as to bring into doubt the conclusions they draw.

For Darwinist. Here’s how to add a second y scale to your charts. http://office.microsoft.com/en-us/excel-help/add-or-remove-a-secondary-axis-in-a-chart-HP001234165.aspx

2011-08-14T19:49:30Z

Edit Andy. Do you have a data source for atmospheric water vapour?

Anonymous2011-08-11T23:06:46Z

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My source is the following paper by Gerald A. Meehl et al, particularly figure 2a.
http://www.cgd.ucar.edu/ccr/publications/meehl_additivity.pdf

Eyeballing the graph, it would appear that the warming from 1900-2000 is approximately 30% natural and 70% anthropogenic. The warming from 1950-2000 appears to be approximately -5% natural and 105% anthropogenic. These odd looking figures are due to the fact that natural forcings have been exerting a net cooling effect on the Earth since 1950.

<If this study were repeated using current data, then the combined forcings would dramatically fail to match ‘observations’ in the period 2000-2011. Here’s a chart I’ve shown previously that illustrates the issue.>

The only forcing shown in the link is CO2. The Meehl study considers the effects of volcanoes, the Sun, sulfate aerosols and ozone. Since 1999, there has been a sharp drop in solar activity
http://science.nasa.gov/science-news/science-at-nasa/2009/01apr_deepsolarminimum/
and there has been a sharp increase in sulfate aerosols due to China opening new coal fired power plants almost weekly.
http://www.nasa.gov/vision/earth/environment/brown_cloud.html

An update to the Meehl study would be very interesting, but I doubt that the laws of physics have changed since then. An update would still show that most of the warming is due to human activity.

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andy2011-08-14T01:36:39Z

Worse case if you use the average before the Industrial revolution of 290 and round down to the nearest ten of the current value (392) to 390 you have an increase of 34.5% total. Now the average climate scientist will say this whole amount of increase is due to man even if it comes from natural sources. The average "denier" will say that our amount of increase in CO2 is some what less then this. What both sides DO agree with is that most of the water vapor is natural, 95% versus man made, 5% yet water vapor has doubled over the last 160 years and absorbs 11 wave lengths of energy versus only 2 for CO2.

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Darwinist2011-08-12T22:24:50Z

Well, just for the exercise, ( I need the practice) here is a graph based on your links, from 1955 to 2010.

Don't worry too much about the Y axis, I just wanted to get them all on the one graph!

http://www.flickr.com/photos/darwin_leigh/6036321092/in/photostream

Clearly they are all increasing; from the spreadsheet, ocean heat content by 0.15GJ/m2/700m/decade (I think that's right), mean sea level by 30.3mm/decade, Global average temps by 0.13C/decade and CO2 by 14.4ppm/decade.

As for how much is attributable to anthropogenic GHG’s? I think jyuschyshyn is spot on! If we were looking at nature alone, we would be cooling slightly!

How do I demonstrate this? I don't claim to be able to prove that it's all down to GHG's, it's just that's the best explanation. It's an Occam's Razor sort of thing.

http://en.wikipedia.org/wiki/Occam's_razor

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virtualguy921072011-08-13T16:56:40Z

Geez, Z

"About half of our emissions get absorbed by the ocean that dwarfs what is in the atmosphere."

No. Half of our emissions getting absorbed by the ocean means that what goes into the ocean is approximately the same amount as what goes into the atmosphere. The size of the deep ocean reservoir has no more to do with how much gets absorbed than the size of the coal reserves has to do with how much gets burned.

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JimZ2011-08-13T00:00:32Z

The answer is quite simple. We don't know how much is attributable to human emissions of GHGs. I wouldn't pretend to know things that I don't so I can't honestly answer the question. Graphs have inherent uncertainties. For example, the graph of CO2 from Mauna Loa doesn't prove that humans emissions were responsible for that trend. About half of our emissions get absorbed by the ocean that dwarfs what is in the atmosphere. We don't know what the CO2 concentrations would be without human emissions in spite of alarmists shrill cries to the contrary. Stomata climate proxies indicate a much greater variability than alarmism can accept so it is ignored and hidden when in fact it is the most precise indicator of historic CO2 concentrations.

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