New kiwi blog Sir Humphreys opens with an attack on "global dimming" - and in doing so displays a shameful level of scientific illiteracy. The idea that aerosols both increase albedo and promote cloud formation (further reducing the amount of sunlight reaching the earth's surface) is uncontentious. What is contentious is how great the effect is, and how it will feed into other climate effects, such as that of increased CO2 emissions.
Wikipedia has some interesting facts here. The size of the effect has been estimated at:
- 5.3% (9 W/m2) over 1958-85 (Stanhill and Moreshet, 1992)
- 2%/decade over 1964-93 (Gilgen et al, 1998)
- 2.7%/decade (total 20 W/m²) up to 2000 (Stanhill and Cohen, 2001)
- 4% over 1961-1990 (Liepert 2002)
with the largest reductions being found in the northern hemisphere. As for Sir Humphrey's "explanation" - "sunspot activity" -
the value of the solar radiation at the top of the atmosphere has not changed by more than a fraction of this amount
The change is clearly due to the atmosphere, not the sun.
As for consequences, this may help counteract some of the expected global warming (due to increased albedo) - or amplify it due to trapping heat (something clouds are very good at). But I'd like to see some modelling done before dismissing it out of hand.
4 comments:
AL: so your diatribe in a nutshell is that "Wikipedia is drivel". I see. So, is that supposed to mean that aerosols and particulates don't promote cloud formation, that increased cloud cover doesn't increase albedo or trap heat, or that "sunspot activity" explains reduced insolation at the bottom - but not at the top - of the atmosphere?
Or are you simply trying to distract attention from Adolf's manifest ignorance?
Posted by Idiot/Savant : 3/27/2005 03:56:00 PM
> The graph is not 'scientific' at all.
Such a critique I note is applicable to basically any graph. This one is designed to emphasise a specific trend over a period where the driver was in action - following the trend back to 1000 or 1500 might show a cooling trend but all that would indicate is that the carbon burning driver is even more significant to obscure the apparent cooling effect.
the fact that there is global warming is really fairly uncontentious, rather like evolution.
Besides hte obvious statistical information - the mechanism by which it effects the environment is clear as with the subject of this post. What you could dispute, if you wanted, is whether that warming is bad.
Posted by Genius : 3/28/2005 11:37:00 AM
Antarctic Lemur:
"And climate 'modelling'. Such modelling is not science at all, but a mathematical prediction of the future based on our present poor understanding of our atmosphere, Earths internal workings, and external influences."
Why do you say modelling is "not science"? Taking the current understanding of how a physical system works and using that to predict what you would expect to happen to the system in the future seems pretty standard scientific method stuff to me.
Posted by Anonymous : 3/30/2005 01:30:00 PM
> No. In the hard sciences, your graph is designed to illustrate the data, not to repress surrounding data which contradict your thesis. Typically with a time series you would expand the scale of your graph to show extra data at either or both ends.
1) The scientists have a large set of data that becomes increasingly reliable as it aproaches the modern day. The most reliable data is the spike in recent years the next most reliable set is the stuff that goes back to 1800 the stuff before that is even less reliable. there are multiple models for that period.
2) But, you could put hte consensus in a graph and it doesnt change the look all that much. there was a slow cooling trend previously but that was a period but no one disputes that temprature changes, and this was when the CO2 drivers were not in effect. If it had been warming during that period you would have a point because this could bbe a continuation of htat trend but since it was cooling one would think that was even MORE evidence for global warming not evidence against it. One could declare the time axis to be "CO2 in atmosphere" (somthing I have been arguing for) in which case the graph would look rather similar (although probably less steep) and would be better for prediciton and your objection would be meaningless.
3) Worse still the warming trend doesnt resemble the cooling trend in its nature - it is much steeper.
4) When drawing a graph one does so in such a way as to make what would be hard to tell from a pile of statistics, more obvious. thus it is normal procedure to design it in such a way as to make the trend obvious. ie it does not implie sinister motivations.
> The useless temperature 'average' likewise invites the reader to draw the conclusion there is some scientifically-established 'appropriate temperature'.
The appropriate temperature could be argued to be the current temperature because it is change that causes damage (people have to adjsut to the change) more than the absolute temperature. I agree the average temperature like is a bit meaningless.
> As to the global warming datasets, Satellite and balloon data show enough temperature anomalies for me to doubt long-term warming since the 1800's. Global-warming proponents usually rely on ground station measurements and climate 'models' for their dire predictions.
In science you must propose a superior alternative hypothesis to defeat the current hypothesis not jsut shed doubt on the current hypothesis. In addition most of these problems are adressed either in the mthodology or by statistics (ie what are the odds of a random error causing a obvious trend over thousands of readings).
> but that doesn't stop global warming proponents from using the shitty data.
the way statistics works is you take hundreds of examples of shitty data and turn it into good data because it is improbably that all the shitty data will be shitty in the same way.
> In particular we know little about the internal heat generate by the Earth
we know little about anything but that is no reason to throw our hands up.
> Its also important to realise that not a single one of these climate models has been able to take a dataset from a historical period, say 1900-1950, and accurately predict the climate of a later period, say 1975-2000.
for that to have happened it would have had to have occured in 1950-75 obviously, who was concerned about GW then? Besides there is no need to accuratly predict things like that. for example I can say 4x4 kill more people than honda civics on average in car accidents but I cant predict the number of people they will kill next year. that does not make that statistic useless.
Posted by Genius : 3/31/2005 01:08:00 PM
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