Global dimming and brightening: A review
Martin Wild
Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
There is increasing evidence that the amount of solar radiation incident at the Earth’s surface is not stable over the years but undergoes significant decadal variations. Here I review the evidence for these changes, their magnitude, their possible causes, their representation in climate models, and their potential implications for climate change. The various studies analyzing long-term records of surface radiation measurements suggest a widespread decrease in surface solar radiation between the 1950s and 1980s (“global dimming”), with a partial recovery more recently at many locations (“brightening”). There are also some indications for an “early brightening” in the first part of the 20th century. These variations are in line with independent long-term observations of sunshine duration, diurnal temperature range, pan evaporation, and, more recently, satellite-derived estimates, which add credibility to the existence of these changes and their larger-scale significance.
Current climate models, in general, tend to simulate these decadal variations to a much lesser degree. The origins of these variations are internal to the Earth’s atmosphere and not externally forced by the Sun. Variations are not only found under cloudy but also under cloud-free atmospheres, indicative of an anthropogenic contribution through changes in aerosol emissions governed by economic developments and air pollution regulations. The relative importance of aerosols, clouds, and aerosol-cloud interactions may differ depending on region and pollution level. Highlighted are further potential implications of dimming and brightening for climate change, which may affect global warming, the components and intensity of the hydrological cycle, the carbon cycle, and the cryosphere among other climate elements.
Received 14 November 2008; accepted 10 March 2009; published 27 June 2009.
Citation: Wild, M. (2009), Global dimming and brightening: A review,
J. Geophys. Res., 114, D00D16, doi:10.1029/2008JD011470.
I found this passage that parallels a lot of what I’ve been saying about data quality:
The assessment of the magnitude of these SSR (surface solar radiation) variations faces a number of challenges. One is related to data quality. Surface radiation networks with well-calibrated instrumentation and quality standards as those defined in BSRN [Ohmura et al., 1998] need to be maintained on a long-term basis and if possible expanded into underrepresented regions (see Figure 1b).
However in this figure, citing CRU surface temperature, he likely doesn’t understand what data quality issue might have contributed to the trend from 1960-2000
One of the effects of urbanization is the compression of the diurnal temperature variation. I recently was able to demonstrate this between two stations in Honolulu. One is in the middle of the Airport and had a sensor problem, the other was in a more “rural” setting about 4 miles away. Note how the ASOS station at the airport has an elevated temperature overall, but that the biggest difference occurs in the overnight lows, even when the ASOS sensor giving new record highs was “fixed”:
Urbanization affects Tmin more than Tmax. For example, here’s the nighttime UHI signature of Reno, NV that I drove as a measurement transect using a temperature datalogger:
Click for larger image
Even several hours after sunset, at 11:15PM, the UHI signature remained. The net result of urbanization is that it increases Tmin more than Tmax, and thus minimizes the diurnal range, which we see in Wild’s diurnal range graph.
Even the IPCC misses it:
Wild probably has no idea of this type of issue in the CRU data, but again it speaks to data quality which he seems to be keen on. He’s looking for a global solar signature in temperature data, something Basil Copeland and I have done, to the tune of much criticism. The signature is there, but small. But, when diurnal temperature variation is looked at, any solar signature is likely swamped by the urbanization signal. I’m not saying there is no solar component to what Wild is looking at, but it seems fairly clear that UHI/urbanization/land use change plays a significant role also.
Even rural stations can be affected by our modern society, as Dr. John Christy demonstrated in California’s central valley:
A two-year study of San Joaquin Valley nights found that summer nighttime low temperatures in six counties of California’s Central Valley climbed about 5.5 degrees Fahrenheit (approximately 3.0 C) between 1910 and 2003. The study’s results will be published in the “Journal of Climate.”
The study area included six California counties: Kings, Tulare, Fresno, Madera, Merced and Mariposa.
While nighttime temperatures have risen, there has been no change in summer nighttime temperatures in the adjacent Sierra Nevada mountains. Summer daytime temperatures in the six county area have actually cooled slightly since 1910. Those discrepancies, says Christy, might best be explained by looking at the effects of widespread irrigation.
Wild’s study is a very interesting and informative paper, I highly recommend reading the entire paper here (PDF 1.4 mb)
h/t and sincere thanks to Leif Svalgaard for bringing this paper to my attention.
Leif,
By high quality I was referring to the improvements over SKY 1 and 2. Also they are no longer stuck in the basement or the bottom of a coal mine. Particle physics in a shirt sleeve environment! But I may be being distracted by the shiny factor, as in – Hey they’ve got a big shiny cloud tank! I bet all the other scientists are jealous! 🙂
Konrad (23:37:36) :
By high quality I was referring to the improvements over SKY 1 and 2.
Why upgrade? Was the outcome of SKY 1 & 2 not what they wanted to see?
Leif,
I think it was always expected that SKY 1 and 2 would not be able to fully test the hypothesis. It should be remembered that CLOUD was proposed before SKY was built. It is clear the SKY experiments did get promising enough results to justify the expenditure on CLOUD, with greater beam time at CERN and a bigger shiny tank.
Leif Svalgaard (21:30:47) :
Not that there are not many claims of that. It is almost so that the more claims there are, the less likely it is that they are true. [why keep trying to show that something is true when it has already been established?]
Too tempting a dictum : I will repeat about tree rings. Science wisdom has it that the 11 year sun cycle was discovered in the change of the width of tree rings in cycles. If this is not a “science myth” it means that the climate changes with the cycles enough to be registered by the trees.
Are you aware of a publication that refutes this, or is the scarcity of publication in the google search a proof of your dictum “something is true so no need to establish it”?
Secondly, on the subject of cosmic rays, there is a publication that connects C14 with solar cycles http://cc.oulu.fi/~usoskin/personal/nature02995.pdf and sunspot counts :
For the Holocene, there is no evidence of considerable oceanic variability,
so we can assume that the short- and mid-term fluctuations of
14C predominantly reflect solar variability. This is supported by the
strong similarity of the fluctuations of 10Be in polar ice cores
compared to 14C, despite their completely different geochemical
history18–20.
from a news release blurb:
The new method works like this: Trees and tree rings contain carbon, which they get from carbon dioxide in the atmosphere. Some of that carbon is the isotope carbon-14 which is created in the Earth’s atmosphere by cosmic rays flying in from outside the solar system.
But those cosmic rays can’t reach Earth when the sun is stormy with sunspots and the solar wind is roaring. So a tree ring containing low carbon-14 is a sign of few cosmic rays in that growth year, which is an indicator of a stormy sun, contend Max-Planck-Institut für Sonnensystemforschung’s Sami Solanki and colleagues.
From fig 3 in the reference I give , one sees large variations in C14 ( percentage wise I suppose) so I wonder how well the variation is taken into account in the model you referenced above.
I think the jury should still be out for cosmic rays. Too little is known yet both from that side and from the magnetic activities of the sun, if Livingston and Penn are right, for example.
Leif Svalgaard (23:20:01)
————————-
[snip] ~ charles the moderator
Gary Strand (14:48:17) :
Allan M R MacRae (13:38:13) :
“So when MacRae (#321) says: “I suspect that both the climate computer models and the input assumptions are not only inadequate, but in some cases key data is completely fabricated – for example, the alleged aerosol data that forces models to show cooling from ~1940 to ~1975. Isn’t it true that there was little or no quality aerosol data collected during 1940-1975, and the modelers simply invented data to force their models to history-match; then they claimed that their models actually reproduced past climate change quite well; and then they claimed they could therefore understand climate systems well enough to confidently predict future catastrophic warming?”, he is close to the truth.”
Would you provide proof of your “the modelers simply invented data” claim? For example, show that the sulfate aerosol forcing data that the IPCC AR4 models used was “invented”, by whom, and how.
Extraordinary claims demand extraordinary evidence; please provide some.
____________________________
Some has already been provided Gary, in my above post:
The pyrheliometric ratioing technique is very insensitive to any changes in calibration of the instruments and very sensitive to aerosol changes.
Here are three papers using the technique:
Hoyt, D. V. and C. Frohlich, 1983. Atmospheric transmission at Davos, Switzerland, 1909-1979. Climatic Change, 5, 61-72.
Hoyt, D. V., C. P. Turner, and R. D. Evans, 1980. Trends in atmospheric transmission at three locations in the United States from 1940 to 1977. Mon. Wea. Rev., 108, 1430-1439.
Hoyt, D. V., 1979. Pyrheliometric and circumsolar sky radiation measurements by the Smithsonian Astrophysical Observatory from 1923 to 1954. Tellus, 31, 217-229.
In none of these studies were any long-term trends found in aerosols, although volcanic events show up quite clearly. There are other studies from Belgium, Ireland, and Hawaii that reach the same conclusions. It is significant that Davos shows no trend whereas the IPCC models show it in the area where the greatest changes in aerosols were occurring.
There are earlier aerosol studies by Hand and in other in Monthly Weather Review going back to the 1880s and these studies also show no trends.
___________________________
Repeating: “In none of these studies were any long-term trends found in aerosols, although volcanic events show up quite clearly.”
Doug Hoyt is an authority on these early measurements. I welcome his further comments, and have emailed him of my earlier post on this thread.
Whilst remaining generally supportive of Svensmark’s ideas I remain unconvinced for various reasons:
(i) There are plenty of particulates in the air already.
(ii) The variation in GCRs does not match the timing of temperature changes very well.
(iii) The oceans are a far bigger influence if, as I observe, they change the rate of energy emission to the air for decades at a time.
The observed changes in solar energy reaching the surface would fit well with cloudiness changes induced by ocean SST changes.
1) Warming SSTs first warm the air and initially reduce cloudiness for a while until evaporation catches up. Once evaporation catches up the enhanced water vapour content leads to increased cloudiness and precipitation as the extra energy and vapour is transported to upper levels where condensation occurs. Greater global albedo and less solar energy reaching the surface.
2) Cooling SSTs first cool the air which lies above it resulting in more low level cloudiness for a while but over time the rate of evaporation declines and there is less water vapour content in the air overall and reduced cloudiness and precipitation. Reduced global albedo and more solar energy reaching the surface.
Note that in both cases the response of the hydrological cycle is opposite to the change in ocean SSTs and works to cancel it.
In the case of warming SSTs the air circulation systems move poleward and equatorward for cooling.
The same process cancels the effects of changing GHGs in the air whether they be CO2, water vapour or anything else.
Note that a graph such as the one for Stockholm is not useful due to it being for a single specific location. For a specific location the changes in the amount of energy reaching the surface would be most greatly influenced by the position of that location in relation to the air circulation systems.
For example, in the case of Stockholm it could show more energy reaching the surface in both warming spells (when the mid latitude jets moved to the north) and cooling spells (when the mid latitude jets moved to the south).
The graph seems to confirm that by indicating increased or increasing energy reaching the surface both during the cooling spell of the 50s and 60s and the warming spell of the 80s and 90s.
Diurnal ranges in specific locations would again be primarily affected by that location’s specific position in relation to the movement of the air circulation systems.
Gary Strand (14:48:17) :
Gary, I have read your posts on the earlier “polar bear scientist banned” thread.
I conclude that your comments constitute ignorant baiting, and will have nothing more to do with you. You are a waste of time.
Also, I refuse to duel with an unarmed man.
The thing about artificial dimming to me, is it would seem to have the potential to screw up your trend lines by creating artificial appearance of acceleration of warming over shorter period of times when you clean up the pollution. So that, say, 10 years of warming trend is actually more like 50 years of warming trend that you’ve only been able to detect over the last 10 years. Obviously getting that right makes a big difference in determining what the next 50 years looks like.
Otoh, there’s China to worry about and how much masking they still have going on there.
Stephen Wilde (04:27:02) :
Whilst remaining generally supportive of Svensmark’s ideas I remain unconvinced for various reasons:
(i) There are plenty of particulates in the air already.
(ii) The variation in GCRs does not match the timing of temperature changes very well.
(iii) The oceans are a far bigger influence if, as I observe, they change the rate of energy emission to the air for decades at a time.
Let us not make once more the mistake of thinking linearly of a chaotic system.
It should be evident that climate is a concert, not a solo input “X” output “temperature”. It is a synergy of a lot of factors entering the equations non linearly.
That is the reason I have been asking repeatedly if the “folk science wisdom” that the tree ring widths are modulated by the sun cycles still holds, and asking for a refuting link.
If it still holds, it is an integration of all factors entering climate in real data , and the question should no longer be if the sun cycles affect climate, but how they do it. I keep finding by googling references that it still holds true, there is a modulation of the sun cycles detectable in tree ring widths, but I would really like to see a review link, for , or against.
anna v (00:39:48) :
Too tempting a dictum : I will repeat about tree rings. Science wisdom has it that the 11 year sun cycle was discovered in the change of the width of tree rings in cycles.
This may be a case of bad translation. The solar cycle was ‘discovered’ by looking at the Sun not at tree rings. You may mean that the cycle can also be seen [‘discovered’] in tree rings.
If this is not a “science myth” it means that the climate changes with the cycles enough to be registered by the trees.
Are you aware of a publication that refutes this, or is the scarcity of publication in the google search a proof of your dictum “something is true so no need to establish it”?
Perhaps also simply a reflection of the lack of evidence in the first place.
Secondly, on the subject of cosmic rays, there is a publication that connects C14 with solar cycles
This is well established and there is no doubt about the basics [although there are questions about how much the climate itself influences the deposition process]
I think the jury should still be out for cosmic rays. Too little is known yet both from that side and from the magnetic activities of the sun, if Livingston and Penn are right, for example.
My problem is not with the jury being still out, but with the people who claim that it is not.
dennis ward (22:45:42) :
So because solar radiation has been decreasing since about 1945, does this discredit the theory that the sun has had anything to do with earth’s global warming for the last 65 years?
Hi Dennis. Although sunspot maximum amplitudes declined after the 1960 record breaker, they were still pretty high by historical standards. Although you are correct that the maximum amplitudes diminished as temperature rose, and a superficial analysis might conclude that therefore solar activity doesn’t correlate with temperature, a deeper look at the data reveals something else.
The run of high but diminishing amplitude cycles in the late C20th were shorter than average, with less lengthy low counts at minimum. If you plot a cumulative total of the difference between the monthly sunspot count or total sunspot area and the long term average for the monthly sunspot count, you’ll get a graph which looks like this:
http://s630.photobucket.com/albums/uu21/stroller-2009/?action=view¤t=sst-nino-ssa.jpg
Although my work is preliminary at this point, and Dr Svalgaard has not been encouraging, I think it may shed some light on the solar-climate link, when it is considered that the oceans store heat in the Pacific warm pool in ways which are not measured by SST series. To me, accumulation of heat energy in the PWP means it is reasonable to look at sunspot counts in a cumulative way. When the effects of positive and negative phases of ENSO are subtracted from the equation, the residual looks to me like a reasonably good correlation.
“anna.v
Let us not make once more the mistake of thinking linearly of a chaotic system”.
Let us not make the mistake of assuming that a chaotic system cannot be underlain by a linear change over time. When all is said and done the sun is the sole source of energy for the Earth and it’s energy output varies in a linear fashion.
Tree rings would be affected by solar changes but only indirectly via temperature and precipitation changes. Many other parameters would add to the difficulty of seeking a reliable link between tree rings and solar changes.
Overall the tree ring/solar relationship would be too varaible for diagnostic purposes.
It is for that reason that I think too much reliance has been placed on the bristle cone pine for the purposes of climate speculation.
And what Leif says.
anna v (07:07:53) :
That is the reason I have been asking repeatedly if the “folk science wisdom” that the tree ring widths are modulated by the sun cycles still holds, and asking for a refuting link.
http://www.treeringsociety.org/TRBTRR/TRBvol32_19-33.pdf
“The results show no evidence of significant, consistent relationships between tree-ring data and sunspot numbers”
Tree-ring data are NOT the 14C contents, but the width and appearance of the rings.
A comprehensive bibliography of tree-ring research can be found here: http://www.treeringsociety.org/TRBTRR/TRBTRR.htm
These people are enthusiasts so will leave no stone unturned.
The Sun is downing its emissions of energy, but at a very low extent:
5320 BP: 1367.84 W/m^2
Today: 1365.92 W/m^2
% of dimming = 0.15
The next graph shows the Sun is not the same “giant” than it was 11000 years ago:
http://www.biocab.org/Extrapolated_TSI.jpg
The margins of error on the extrapolation (from HSG proxy) are -0.3 W/m^2, 0.3 W/m^2
Leif Svalgaard (08:47:55) :
Thanks for the links.
I have one recent with positive results: http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VHB-4NDDM72-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=942050960&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=d6327d573e47213f5d4ad7451d25ecb6
We have investigated the solar activity signal in tree ring data from two locations in Chile. The tree ring time series extended over a period of not, vert, similar400 yr. Spectral and wavelet analysis techniques were employed. We have found evidence for the presence of the solar activity Schwabe (not, vert, similar11 yr), Hale (not, vert, similar22 yr), fourth-harmonic of the 208-yr Suess cycle (not, vert, similar52 yr) and Gleissberg (not, vert, similar80 yr) cycles. The Gleissberg cycle of tree ring data is in anti-phase with solar activity. Wavelet and cross-wavelet techniques revealed that the periods found are intermittent, possibly because solar activity signals observed in tree rings are mostly due to solar influence on local climate (rainfall, temperature, and cloud cover) where trees grow up. Further, cross-wavelet analysis between sunspot and tree ring time series showed that the cross power around the 11 yr solar cycle is more significant during periods of high solar activity (grand maximum) than during periods of low solar activity (grand minimum). As Glaciar Pio XI is practically at the Pacific Ocean level, the tree-ring response may be stronger due to the heating of the Pacific Ocean water following an increase of the solar radiation incidence rather than at the higher altitudes of Osorno region.
it is behind a pay barrier.
Tree-ring data are NOT the 14C contents, but the width and appearance of the rings.
Yes, of course. I was using the reference for the level of cosmic rays and the correlation with sun cycles with cosmic rays. That was a second point.
anna v (09:57:51) :
I have one recent with positive results:
“Wavelet and cross-wavelet techniques revealed that the periods found are intermittent,”
They find all kinds of periods on and off. Not very positive to me. But it is a myth that is hard to kill.
The tree-ring society http://www.treeringsociety.org/TRBTRR/TRBTRR.htm
has in their extensive bibliography only that one paper with the words sunspot, sun, or solar in the title. I’ll tend to go with the professionals here.
BTW, one of the authors [Echer] of the paper you quoted is a good friend of mine with a propensity for trying to find wavelet cycles everywhere, e.g. here http://www.leif.org/research/Asymmetric%20Rosenberg-Coleman%20Effect.pdf
Sometimes he is a bit too enthusiastic.
Allan M R MacRae (03:23:07)
FABRICATION OF AEROSOL DATA USED FOR CLIMATE MODELS:
The pyrheliometric ratioing technique is very insensitive to any changes in calibration of the instruments and very sensitive to aerosol changes.
Here are three papers using the technique:
Hoyt, D. V. and C. Frohlich, 1983. Atmospheric transmission at Davos, Switzerland, 1909-1979. Climatic Change, 5, 61-72.
Hoyt, D. V., C. P. Turner, and R. D. Evans, 1980. Trends in atmospheric transmission at three locations in the United States from 1940 to 1977. Mon. Wea. Rev., 108, 1430-1439.
Hoyt, D. V., 1979. Pyrheliometric and circumsolar sky radiation measurements by the Smithsonian Astrophysical Observatory from 1923 to 1954. Tellus, 31, 217-229.
In none of these studies were any long-term trends found in aerosols, although volcanic events show up quite clearly. There are other studies from Belgium, Ireland, and Hawaii that reach the same conclusions. It is significant that Davos shows no trend whereas the IPCC models show it in the area where the greatest changes in aerosols were occurring.
There are earlier aerosol studies by Hand and in other in Monthly Weather Review going back to the 1880s and these studies also show no trends.
___________________________
Repeating: “In none of these studies were any long-term trends found in aerosols, although volcanic events show up quite clearly.”
___________________________
Here is an email just received from Douglas Hoyt [my comments in square brackets]:
It [aerosol numbers used in climate models] comes from the modelling work of Charlson where total aerosol optical depth is modeled as being proportional to industrial activity.
[For example, the 1992 paper in Science by Charlson, Hansen et al]
http://www.sciencemag.org/cgi/content/abstract/255/5043/423
or [the 2000 letter report to James Baker from Hansen and Ramaswamy]
http://74.125.95.132/search?q=cache:DjVCJ3s0PeYJ:www-nacip.ucsd.edu/Ltr-Baker.pdf+%22aerosol+optical+depth%22+time+dependence&cd=4&hl=en&ct=clnk&gl=us
where it says [para 2 of covering letter] “aerosols are not measured with an accuracy that allows determination of even the sign of annual or decadal trends of aerosol climate forcing.”
Let’s turn the question on its head and ask to see the raw measurements of atmospheric transmission that support Charlson.
Hint: There aren’t any, as the statement from the workshop above confirms.
__________________________
IN SUMMARY
There are actual measurements by Hoyt and others that show NO trends in atmospheric aerosols, but volcanic events are clearly evident.
So Charlson, Hansen et al ignored these inconvenient aerosol measurements and “cooked up” (fabricated) aerosol data that forced their climate models to better conform to the global cooling that was observed pre~1975.
Voila! Their models could hindcast (model the past) better using this fabricated aerosol data, and therefore must predict the future with accuracy.
That is the evidence of fabrication of the aerosol data used in climate models that predict catastrophic humanmade global warming.
And we are going to spend trillions and cripple our Western economies based on this fabrication of false data, this model cooking, this nonsense?
*************************************************
Allan M R MacRae (10:41:55) :
There are actual measurements by Hoyt and others that show NO trends in atmospheric aerosols, but volcanic events are clearly evident.
So, you are saying that since there is no trend in aerosols, the climate changes must be anthropogenic. A lot of people, even scientists [didn’t I see somewhere that 30,000 of those critters supports the IPCC’s assessments…] would agree with that, voting for this government.
Once the Western economies are crippled and the bulk of industrial output is shifted to the East, the world will be saved from the austerity of the skies clearing and global warming frying the planet. Asia will never stop burning coal until there isn’t any more to burn.
They call it saving the planet from impending disaster.
I call it capitulation.
As capital, output and might shift to the non-free world, the balance of power will be upset, and the inevitable consequences of the weakening of the Free World will be felt.
All because of fabricated models.
Just have a look at the video of Global Dimming. What you do hear is the increase of daytime temps. What I do not hear is what happened to the nighttime temps as a result of a clearing atmosphere.
Did the diurnal range simply widen at both ends, or on one end?
The assumed ‘brightening’ at Stockholm in recent years does not agree with other global dimming reports.
http://en.wikipedia.org/wiki/Global_dimming
Leif Svalgaard (11:31:22) :
Allan M R MacRae (10:41:55) :
There are actual measurements by Hoyt and others that show NO trends in atmospheric aerosols, but volcanic events are clearly evident.
So, you are saying that since there is no trend in aerosols, the climate changes must be anthropogenic. A lot of people, even scientists [didn’t I see somewhere that 30,000 of those critters supports the IPCC’s assessments…] would agree with that, voting for this government.
——————–
No Leif, as you know, I’m not saying that.
There are many other causative variables for climate, such as clouds, oceans, volcanoes, etc.
But increased atmospheric CO2 is NOT a significant driver of global warming – that much is obvious by now.
The sensitivity of global temperature to increased atmospheric CO2 is so small as to be inconsequential – much less than 1 degree C for a doubling of atmospheric CO2. CO2 feedbacks are negative, not positive. Climate model hindcasting fails unless false aerosol data is used to “cook” the model.
Regards, Allan
P.S. I’m sorry about the death of your friend Jack Eddy.
_____________________________
Here is a reasonable summary for anyone who is interested:
http://scienceandpublicpolicy.org/a_proper_focus_in_the_climate_change_debate.html
A Proper Focus in the Climate Change Debate
The Debate Is Not Over. Early in 2007 there was a concerted, international effort among climate alarmists to suggest that the science was so certain that debate was no longer possible. That effort had no impact on the scientific community, which continues to debate climate change vigorously and sometimes even acrimoniously in the peer-reviewed, learned journals. The debate continues.
Climate change has always been real, but the fact of climatic variability tells us nothing of its cause. The more the climate is researched, the less likely it appears that humankind has had any significant climatic impact.
Climate change is not unprecedented. The mediaeval warm period was warmer than the present. Even now, melting glaciers in the Alps are revealing mediaeval trackways, silver-mines and even entire forests that have been buried under ice since the Middle Ages. Some of the Viking settlements in Greenland are still under permafrost to this day.
The chicken and the egg: The temperature changes that led to the ice ages and interglacial period preceded changes in CO2 concentration.
The central calculation: The UN says a doubling of CO2 concentration will push global temperatures up by 3C. Others say less than 1C.
Will warming be harmful? Almost certainly not. Warming is better than cooling. We now know that neither droughts nor floods nor storms have increased or are likely to increase as a result of anthropogenic warming; these events come and go in natural cycles which have scarcely altered over the past 100 years.
What is the cause of the present warming? Even if one assumes that the UN’s estimates of recent warming are not themselves an exaggeration, observations do not confirm the presence, in any climatically-significant degree, of the characteristic signature of anthropogenic warming – namely, a greater rate of increase in temperature at altitude, particularly at low latitudes, than at the surface. These results provide proof that much of the present warming is not anthropogenic but natural, caused partly by millennial alterations in patterns of ocean circulation and partly by the Sun, which has been more active, and for longer, in the past 70 years than at almost any time in at least the past 11,400 years (Solanki et al., 2005).
Will proposed mitigative measures cost more than they achieve? Now that the predictions of the extremists have been discredited even by the UN, it is near-certain that the cost of almost any measure to mitigate the volume of anthropogenic CO2 emissions will outweigh the effectiveness and economic benefit of that measure. Most proposed measures would not make any significant climatic difference even if implemented. The few measures that might have some impact would have only a small impact, but will prove impossible both politically and economically, and will not be achieved, though much money will be wasted in the attempt. It is the poorer nations who will suffer most grievously by the proposed restrictions on CO2 emissions.
What is the real problem? Energy is the real problem. Primary energy sources, particularly fossil fuels, are becoming scarce and expensive, and are increasingly in the hands of unstable regimes that are unfriendly to the West. Energy prices are already rising, but could rise very much more quickly in the coming years.
*****************************
Allan M R MacRae (12:54:27) :
“There are actual measurements by Hoyt and others that show NO trends in atmospheric aerosols, but volcanic events are clearly evident.”
But increased atmospheric CO2 is NOT a significant driver of global warming – that much is obvious by now.
But what has that to do with aerosols?
No Leif, as you know, I’m not saying that.
You may not have meant it that way, but you were saying that.
partly by the Sun, which has been more active, and for longer, in the past 70 years than at almost any time in at least the past 11,400 years (Solanki et al., 2005).
There is no good evidence for that. Solanki’s ‘result’ is partly based on a now [generally accepted] refuted doubling of the Sun’s open magnetic flux, and partly on wrongly calibrated group sunspot number.
Another example of bias [anything goes to defeat that damn AGW, even dubious ‘results’ as long as it works, a la Carlin].
Leif Svalgaard (13:21:18) :
There is no good evidence for that. Solanki’s ‘result’ is partly based on a now [generally accepted] refuted doubling
It is the refutation that is generally accepted by now, even by Lockwood and by me [we were the ones culpable of advocating that notion in the past].