[luke warm]

 billw55, on 2012-August-08, 06:43, said:

You're funny

rino maybe

[Daniel1960]

Zelandakh,

I know of no scientists who dispute the heat trapping capability of CO2 either, I just did not want to speak for everyone. The feedbacks are highly debatable, and is currently the largest area of dispute among scientists. I have seen very few (but some) who contend that the overall feedback is negative. This is due to saturation, interferences, and the small absorption of incoming solar radiation. The positive feedback is primarily due to water vapor; this is due to the increase in atmospheric water content due to the increase in temperature, but can influenced by the previously mentioned negative feedbacks. Currently, the biggest uncertainty is clouds. This effect is two-fold. First, increased clouds result in decreased water vapor, as the water condenses to form the clouds, reducing the positive water vapor feedback. Secondly, clouds reduce incoming solar radiation, leading to reduced warming. More scientists think that clouds will increase in a warming world due to the increased water content in the atmosphere. However, some think that the increased warmth will lead to a reduction in cloudiness. Recent data have suggested that the two are linked, but the generally thinking is that the reduced cloudiness leads to the temperature increase, not the other way around. This change in cloudiness is thought to be related to the oceanic cycles, but is still an area of contention. How the oceans react to increased warmth is not well understood.

Two other areas which are thought to have a measureable influence are aerosols and albedo. These two factors have more than one source. In the case of aerosols, some are manmade, some are terrestrial, and some are galactic. All research has shown that aerosols reduce incoming solar radiation from reaching the Earth's surface, but the effects on recent temperature changes have been challenged. Albedo changes are mostly manmade; urbanization, deforestation, and agriculture. Urbanization has decreased the Earth's albedo in many ways, leading to increase absorption of incoming solar radiation. Hence, deforestation to build cities leads to higher temperatures. Deforestation for agriculture has the opposite effect, as most crops have a higher albedo than the trees. However, irrigation can reduce the albedo significantly. Global warming can reduce the albedo also, as snow and ice melt, revealing dark land and water.

There is a wide disagreement as to the overall feedback effects. The laboratory results show a 1.1C temperature increase with a doubling of CO2. The first contentions are the negative atmospheric feedback. This value has been quoted as reducing the climate sensitivity by 10-50% (i.e. 0.6 - 1.0 C / doubling). The increase due to water vapor is fairly well known, and equal to ~75% of the initial temperature rise (assuming all the water vapor remains as vapor). The decrease due to water vapor condensing to form clouds has been been reported from negliglible to larger than the increase due to water vapor. Barton Paul Levenson summarized many of the studies which examined climate sensitivity, and found recent values ranging from 0.75 to 4.5 C/ doubling (earlier studies had a higher range).

http://bartonpaullev...ensitivity.html

Realclimate had a discussion about a recent paper which showed that the climate sensitivity based on paleoclimatic restraints since the last glacial maximum has a range of 1.7 - 2.6C/ doubling (1.2 - 2.9 at the 95% confidence level). The biggest issue with this correlation, is that this is based on a temperature/CO2 relationship at the cold end of the temperature spectrum, and may differ on the high end.

http://www.sciencema...t/334/6061/1385

[Zelandakh]

I think you have missed the key uncertainty regarding clouds Daniel. The point is that if we get an increase in low, dense cloud then this is a negative feedback whereas an increase in high, light clouds is a positive feedback. I am interested in your assertion that the effects of aerosols on temperature change have been challenged. The aerosol effect is one of the important inputs to climate models. The effect can be seen quite clearly in the historic record after major volcanic eruptions. One of the more controversial GW solutions I was referring to earlier involves the release of aerosols into the atmosphere, essentially simulating such an eruption over an extended period of time. Under albedo, you missed one of the factors very popular with Green politicians - albedo changes from increased soot.

The rest of your post is about the nett effect of feedbacks. As I wrote previously, most of the models end up quite consistent in this respect even though their individual feedbacks are often quite different. Some skeptics claim this is because they are essentially programmed to produce this response; model supporters say that it shows the robustness of the modelling process. I am not going to discuss what the actual warming effect of CO2 might be in practise as I do not have access to enough data to make such a statement and it is a little while since I made my last full survey of the science. In truth, I was not entirely sure what you were trying to tell me with your post - you did not seem to be disagreeing with me but also not really telling me anything new. Sometimes GW discussions are a bit like that though!

[Daniel1960]

Zelandak,
Yes, there is a difference in cloud layer. However, there is no indication that either cloud formation is favored over the other, and an increase in both points to a net negative feedback. While aerosols have been shown to decrease incoming solar radiation on a qualitative basis, there has been some dispute as to how much cooling was caused by galactic cosmic rays, volcanic eruptions, and manmade emissions. This is an important climate model input. I incorporated the soot albedo change into urbanization for simplicity, but it is a an inportant aspect.

I am not really disagreeing with you, although I am not fully agreeing with you either. If models are programmed to produce the observed response, it is hard to argue robustness. That said, I am not sure that all the models agree to that extent, especially as most models have over-predicted the current temperature rise. Model supporters have argued that the recent temperature measurements fall within the model uncertainties, but the low end of the model predictions is a 0.2C decline in global temperatures since 2000. The following is from realcllimate, one of the most fervent supporters of climate modeling.

http://www.realclima...ges/model11.jpg

All-in-all, it is too soon to say whether the models are accurate or not.

[Al_U_Card]

Depends on which parameter and just how important it might be as a forcing.
Water vapor is expected to increase GHG-warming by three times.
So clearly, the water vapor in the atmosphere must be well-understood and accurately modeled?

Or... from Miller et al one of many that show just how poorly the models are...



and the whys and wherefores from just more of the same...

but then again there is:

A paper published today in the Journal of Geophysical Research finds that current global climate models make "very large" errors in determining solar radiation at the surface of the Earth "due to ignoring the effects of clouds." According to the authors, these very large errors can exceed 800 Watts per meter squared, which by comparison is about 216 times more than the alleged effect of doubling CO2 concentrations [3.7 W m-2].


JOURNAL OF GEOPHYSICAL RESEARCH, doi:10.1029/2012JD017557

and

New paper finds clouds act as a negative feedback and cause significant cooling
A paper published today in the Journal of Geophysical Research finds that a natural atmospheric oscillation, the Southern Annular Mode, is correlated to significant increases in cloud cover resulting in "large scale" local cooling of approximately -2.5C. All climate models falsely assume clouds result in net positive feedback and increased temperatures, however this new paper and several others show clouds instead result in net negative feedback and cooling.

Large localized reductions in temperature result from increased clouds with a ~1 day time lag
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 117, D13103, 7 PP., 2012
doi:10.1029/2012JD017626

and

New paper shows clouds have a large negative-feedback cooling effect
A paper published last week in the journal Meteorological Applications undermines a key assumption of the theory of man-made global warming, finding that the cooling effect of clouds far outweighs a supposed 'greenhouse' warming effect. Alarmists claim clouds have an overall 'positive-feedback' warming effect upon climate due to 'back-radiation' of the 'greenhouse' gas water vapor. This new paper based on satellite measurements finds instead that clouds have a large net cooling effect by blocking solar radiation and increasing radiative cooling outside the tropics. The cooling effect is found to be -21 Watts per meter squared, more than 17 times the supposed warming effect from a doubling of CO2 concentrations [1.2 W/m2]. Another key assumption of the AGW theory topples in the face of real-world data showing the net feedback from clouds is strongly negative.

Combining satellite data and models to estimate cloud radiative effect at the surface and in the atmosphere

Richard P. Allan

Abstract: Satellite measurements and numerical forecast model reanalysis data are used to compute an updated estimate of the cloud radiative effect on the global multi-annual mean radiative energy budget of the atmosphere and surface. The cloud radiative cooling effect through reflection of short wave radiation dominates over the long wave heating effect, resulting in a net cooling of the climate system of − 21 Wm−2. The short wave radiative effect of cloud is primarily manifest as a reduction in the solar radiation absorbed at the surface of − 53 Wm−2. Clouds impact long wave radiation by heating the moist tropical atmosphere (up to around 40 Wm−2 for global annual means) while enhancing the radiative cooling of the atmosphere over other regions, in particular higher latitudes and sub-tropical marine stratocumulus regimes. While clouds act to cool the climate system during the daytime, the cloud greenhouse effect heats the climate system at night. The influence of cloud radiative effect on determining cloud feedbacks and changes in the water cycle are discussed.

[luke warm]

 Al_U_Card, on 2012-August-16, 16:42, said:

A paper published today in the Journal of Geophysical Research

well that was inconvenient

[phil_20686]

 Al_U_Card, on 2012-August-16, 16:42, said:

Depends on which parameter and just how important it might be as a forcing.
Water vapor is expected to increase GHG-warming by three times.
So clearly, the water vapor in the atmosphere must be well-understood and accurately modeled?

Or... from Miller et al one of many that show just how poorly the models are...

So I looked up the source for your graph, via the link above, and honestly, i think you just don't understand modelling. When you model a climate system, I do not expect my model to be right in every way, and even if it was It would still diverge erratically in prediction periods as short as one year, since climate is chaotic. But it is chaotic around the equilibrium, so long term predictions are better than short term predictions.

Moreover, models can be right in different ways. There can be affects that you model for that don't really effect the outcome, in which case, you would expect different viable models to have results that diverge wildly from reality. The correct conclusion is that water density in the atmosphere over the Sahara desert is probably not all the important for the global outcomes. Perhaps these models thought russia will be wetter and the sahara will be drier than in reality. Why does that matter? The oscillations around the equilibrium are chaotic and unpredictable. Trying to use them as a weather forecast for small regions of the globe is completely absurd.

The models, by construction, fit the data for the past 150 years, the past 60 of which is extremely detailed. The only way they can be wrong is if there is some effect which doesn't apply in the past, but becomes significant in the future. If it didn't matter to the results in the past it is unlikely that the data constrains the models. However, this is quite unlikely. If they fit 150 years of past data, why would they diverge wildly in the next thirty years? It doesn't matter that there are trade offs in teh science when we fit the data. There are chains of effects where I can up the effect of process A and decrease the effects of process B and the results stay within the acceptable bands. That is why there are 60 different climate models all of which predict broadly the same warming.

[Daniel1960]

Phil,
The models fit the data for the past 150 years, because they have been hindcast to fit that data. However, past performance is no guarantee of future success. One of the earliest models was reported by Hansen in 1988.

http://pubs.giss.nas...Hansen_etal.pdf

At the time of his prediction, temperatures were ~0.3C above the long term average. In his scenario A (business as usual), he predicted that temperatures would rise to an anomaly of 0.9C by the year 2000, and reach +1.2C by 2012. In scneario C, where greenhouse gases are reduced to zero by the year 2000 (did not happen), the corresponding temperatures rises would be 0.5C by the year 2000 and rise slightly to 0.6C today, where they would remain. While individual months, and even years, have surpassed those numbers, the 5-yr average for 2000 was +0.44C, and today it stands at +0.53C (FYI, July just came in at +0.47C). Clearly, his scenario A was much too high, but scenario C was quite close. Unfortunately, CO2 levels rose more than his scenario A forecast of 1.5% annually.

Now I know that this was an early version, but the IPCC AR4 report in 2007 indicated that under a similar "business as usual" scenario, global temperatures would rise at a rate of 0.3C/decade from the year 2000 forward. Using the aforementioned +0.44C for 2000, that would indicate +0.74C for 2010, and +0.80C today. Thus far, all climate models have predicted greater warming than has occurred. Granted, the climate is chaotic, and large fluctuations are expected to occur.

http://www.ipcc.ch/p...ections-of.html

Today's models may be more accurate at forcasting future temperature changes. You ask why models would diverge in the next 30 years, if they correctly model the past 150. Your answer is in your previous statement; some effect which wasn't applied to the past. Several different explanations have been given to the lack of warming thus far this century; lower solar output, a predominacne of La Nina conditions, volcanic eruptions, high sulfate output from China, etc. Better incorporation of these parameters, may serve to enhance model accuracy in the future. On the other hand, the climate may be more chaotic than we imagine, and current conditions may just be at the low end of predictions temporarily, resulting in oscillations to the higher side in the near future.

[hrothgar]

 phil_20686, on 2012-August-17, 04:17, said:

The models, by construction, fit the data for the past 150 years, the past 60 of which is extremely detailed. The only way they can be wrong is if there is some effect which doesn't apply in the past, but becomes significant in the future. If it didn't matter to the results in the past it is unlikely that the data constrains the models. However, this is quite unlikely. If they fit 150 years of past data, why would they diverge wildly in the next thirty years? It doesn't matter that there are trade offs in teh science when we fit the data.

One quick technical note:

You seem to be stating that latent or hidden variables is the only possible way to construct a predictive model that is extremely accurate in modeling the training set but has poor predictive accuracy.

In my experience, over training/ over fitting is a much more likely explanation.

[Daniel1960]

hrothgar,

You may be right on the over-fitting. In any regard, the predictive power of the model is most important.

[phil_20686]

 hrothgar, on 2012-August-17, 12:53, said:

One quick technical note:

You seem to be stating that latent or hidden variables is the only possible way to construct a predictive model that is extremely accurate in modeling the training set but has poor predictive accuracy.

In my experience, over training/ over fitting is a much more likely explanation.

I thoguht if this was a danger it would be evident in the high correlation in short time spans, and that when the models are better on larger time scales than smaller ones, it hard to imagine that they are over-fitted.

[hrothgar]

 phil_20686, on 2012-August-20, 06:44, said:

I thoguht if this was a danger it would be evident in the high correlation in short time spans, and that when the models are better on larger time scales than smaller ones, it hard to imagine that they are over-fitted.

More importantly, the models in question use techniques like cross validation to protect against over fitting.

I was merely pointing out that in my experience, this type of behavior typically suggests overfitting.

[Al_U_Card]

Dr. Trenberth, please come to the out-patient clinic, stat. Dr. Santer is having trouble walking...

And this was one of the biggies as far as attribution by the IPCC was concerned. What a joke.

[PassedOut]

Sea Ice in Arctic Measured at Record Low

Quote

The amount of sea ice in the Arctic has fallen to the lowest level on record, a confirmation of the drastic warming in the region and a likely harbinger of larger changes to come.

Satellites tracking the extent of the sea ice found over the weekend that it covered about 1.58 million square miles, or less than 30 percent of the Arctic Ocean’s surface, scientists said. That is only slightly below the previous record low, set in 2007, but with weeks still to go in the summer melting season, it is clear that the record will be beaten by a wide margin.

And little is being done to reduce the billions of tons of CO2 that mankind dumps into the air each year...

[luke warm]

 PassedOut, on 2012-August-27, 13:02, said:

And little is being done to reduce the billions of tons of CO2 that mankind dumps into the air each year...

with any luck there will be billions more, after we start drilling/fracking in earnest

[Al_U_Card]

 PassedOut, on 2012-August-27, 13:02, said:

Sea Ice in Arctic Measured at Record Low


And little is being done to reduce the billions of tons of CO2 that mankind dumps into the air each year...

Thank goodness.

[PassedOut]

Ice age study delivers blow to global-warming skeptics

Quote

Rising levels of carbon dioxide drove much of the global warming that thawed Earth at the end of the last ice age.

That's the conclusion a team of scientists has drawn in a new study examining the factors that closed the door on the last ice age, which ended about 20,000 years ago.

The result stands in contrast to previous studies that showed temperatures rising ahead of increases in atmospheric CO2 levels. This has led some skeptics of human-triggered global warming to argue that if warming temperatures came first, CO2 wasn't an important factor then and so can't be as significant a factor today as most climate scientists calculate it to be.

But, of course, there is now no doubt of its significance. We're feeling the effects today.

Quote

The results also hold notes of caution for today, notes Jeremy Shakun, a climate researcher at Harvard University in Cambridge, Mass.

He notes that during the 10,000 years from the end of the last ice age to the beginning of the current “interglacial” climate, atmospheric CO2 concentrations rose 40 percent, from 180 molecules per million in the atmosphere to 260 parts per million. During the past 100 years, concentrations have risen 34 percent, from 292 ppm to 392 ppm – and continue to rise.

“Clearly, it's not a small amount,” says Dr. Shakun, referring to the increases during the past century. “Rising CO2 at the end of the last ice age had a huge effect on global climate. We've raised it as much in the last century.”

You can read the Nature article here: Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation

[Daniel1960]

Not sure that study is the big blow you envision. The article also states, "This finding suggests that CO2 was not the cause of initial warming."

Followed by, "In any event, we suggest that these spatiotemporal patterns of temperature change are consistent with warming at northern mid to high latitudes, leading to a reduction in the AMOC at ~19 kyr ago, being the trigger for the global deglacial warming that followed, although more records will be required to confirm the extent and magnitude of early warming at such latitudes. A possible forcing model to explain this sequence of events starts with rising boreal summer insolation driving northern warming28. This leads to the observed retreat of Northern Hemisphere ice sheets26 and the increase in sea level29 commencing ~19 kyr ago (Fig. 3a, b), with the attendant freshwater forcing causing a reduction in the AMOC that warms the Southern Hemisphere through the bipolar seesaw30."

And finally, "Recent studies of the deglaciation31, 32 have shown a strong correlation between times of minima in the AMOC and maxima in CO2 release, consistent with our ΔT proxy for AMOC strength (Fig. 4d), suggesting that a change in the AMOC may have also contributed to CO2 degassing from the deep Southern Ocean though its influence on the extent of Southern Ocean sea ice33, the position of the southern westerlies34 or the efficiency of the biological pump35. Further insight into this relationship is provided by meridional differences in the timing of proxy temperature change following the reduction in AMOC after ~19 kyr ago. A near-synchronous seesaw response is seen from the high northern latitudes to the mid southern latitudes, whereas strong Antarctic warming and the increase in CO2 concentration lag the AMOC change36 (Figs 2a and 5b). This lag suggests that the high-southern-latitude temperature response to an AMOC perturbation may involve a time constant such as that from Southern Ocean thermal inertia23, 37, whereas the CO2 response requires a threshold in AMOC reduction to displace southern winds or sea ice sufficiently38 or to perturb the ocean’s biological pump35."

After all that, they claim that their modelling indicates that the CO2 rise was a key mechanism in the continued rise of global temperatures. Not exactly the headliner that you make ti seem.

[Al_U_Card]

Modern Times

From the abstract (bolding mine):


Using data series on atmospheric carbon dioxide and global temperatures we investigate the phase relation (leads/lags) between these for the period January 1980 to December 2011. Ice cores show atmospheric CO2 variations to lag behind atmospheric temperature changes on a century to millennium scale, but modern temperature is expected to lag changes in atmospheric CO2, as the atmospheric temperature increase since about 1975 generally is assumed to be caused by the modern increase in CO2. In our analysis we use eight well-known datasets; 1) globally averaged well-mixed marine boundary layer CO2 data, 2) HadCRUT3 surface air temperature data, 3) GISS surface air temperature data, 4) NCDC surface air temperature data, 5) HadSST2 sea surface data, 6) UAH lower troposphere temperature data series, 7) CDIAC data on release of anthropogene CO2, and 8) GWP data on volcanic eruptions. Annual cycles are present in all datasets except 7) and 8), and to remove the influence of these we analyze 12-month averaged data. We find a high degree of co-variation between all data series except 7) and 8), but with changes in CO2 always lagging changes in temperature.

[Daniel1960]

Al,

From the following paper:

http://www.sciencedi...8112001658?v=s5

► The overall global temperature change sequence of events appears to be from 1) the ocean surface to 2) the land surface to 3) the lower troposphere. ► Changes in global atmospheric CO2 are lagging about 11–12 months behind changes in global sea surface temperature. ► Changes in global atmospheric CO2 are lagging 9.5-10 months behind changes in global air surface temperature. ► Changes in global atmospheric CO2 are lagging about 9 months behind changes in global lower troposphere temperature. ► Changes in ocean temperatures appear to explain a substantial part of the observed changes in atmospheric CO2 since January 1980. ► CO2 released from use of fossil fuels have little influence on the observed changes in the amount of atmospheric CO2, and changes in atmospheric CO2 are not tracking changes in human emissions.