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A second question is the very limited differentiation of the warming influence of greenhouse gases versus the offsetting cooling influences of aerosols (both long term sulfate loading from SO2 emissions and intermittent volcanic injections). I would also add that the baseline temperature being used internationally to define the 2 C threshold is from preindustrial levels (the recovery from Little Ice Age being a natural cycle is primarily wishful thinking). Now, timing can make a difference–if the GHGs are offset by sulfate aerosols for all but the last year, there would be a different heat uptake than if aerosols were controlled in the 19th century and GHGs were not affected the whole time. Just looking at present conditions to try to do the analysis instead of the path of the change is just not likely to give the right answer.

It is nice to try a simple schematic approach, but the world is pretty complex. You might try looking at/using the MAGICC model (easy to get on the Web) and actually do the time dependent calculation.

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Mike MacCracken

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I read recently an argument that went roughly as follows,
Recent probes have found that at 1Bar on Venus , the temperature is comparable to Earth’s, and that Mars surface temperature extrapolated to to 1 Bar is again similar to Earth’s regardless of the high CO2 content of their atmospheres, so in fact basic gas laws account for temperature regardless of GHG’s,
any comments?

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You’ve asked a number of good questions. I’ve paraphrased some and answered them below.

1) Where does the carbon go?

The oceans play a role, however; rain is more important relative to scrubbing CO2 from the atmosphere. Biology sequesters a sizable fraction of the carbon it consumes. Most of this is in the form of biomass falling to the ocean bottom where it decomposes in an oxygen depleted environment, ultimately producing methane ices and after millions of years, fossil fuels. If not enough CO2 is being returned to the atmosphere to replace that sequestered by biology, CO2 levels will fall. When temperatures are falling, the ecosystem shrinks due to habitat shrinkage. Because of the higher CO2 levels from when the temperatures were higher, the remaining biomass will will be consuming and sequestering CO2 at the same higher rate as before, but the CO2 returned through decomposition will not be enough to keep up, ultimately causing CO2 levels to drop and biomass to drop further, until a new steady state level is achieved. The opposite happens as the temperatures rises. This predicts that the delay between temperature changes and CO2 changes will be larger when the temperature is falling, which is consistent with the ice core record. Keep in mind that the steady state atmospheric CO2 concentration level is a function of 2 relatively large fluxes, CO2 entering the system and CO2 being consumed by the system.

2) How do you handle the ocean?

The oceans are divided into 3 parts. The deep ocean, the thermocline and the upper layer. If you draw an isotherm whose temperature is the average temperature of the Earth (about the same as the average surface temperature), this will bisect the thermocline. This surface also divides the Earth’s stored thermal energy into 2 energy pools, a warm pool and a cool pool. The average temperature of the warm pool is about the same as the temperature at the boundary between the thermocline and the upper ocean. The average temperature of the cool pool is about the same as the temperature at the boundary between the thermocline and the deep ocean. The thermocline is acting as a layer of insulation between them, which is consistent with the tiny energy flow through it. In fact, the energy flowing down is equal and opposite to the energy flowing up from the Earth’s internal heat which could be coincidental, but is more likely the result of a convection current. The consequence is that because only a tiny fraction of the ocean is involved in storing heat (as opposed to storing cold), the oceans respond far faster to energy changes than the long term feedbacks assumed by AGW require. A final point is that the total number of joules stored in the warm and cool portions want to be the same, which should be recognized as an additional constraint on any thermodynamic model and dictates that the cool pool is much larger than the warm pool. The temperature of the cold pool is far less variable than that of the warm pool. This is due to the density profile of water, relative to temperature and pressure and that the bulk of the Earth’s thermal mass is in the oceans.

3) What about CO2 feedback?

The only CO2 and temperature specific feedback is the change in ocean solubility caused by changing temperatures. The pre-feedback effect of incremental CO2 on the temperature is quite small. Even using the inflated 3.7 W/m^2 of incremental forcing for doubling CO2, it’s still only about 0.66C. A CO2 related feedback effect would need to double the CO2 by many more times in order to get the prescribed 3C increase. The feedback quantified by the climate sensitivity metric is not specific to CO2, but the feedback effect of a temperature change on a future temperature change. The accepted value of 0.8 means that if the temperature increases by 0.66C, an additional future temperature increase of 2.33C should be expected. Note that biology is a negative feedback. As CO2 accumulates in the atmosphere and biomass expands, more energy goes in to building biomass and less is available to heat the planet, causing cooling.

4) Don’t orbital variations cancel out over a year?

No they don’t and this is one of the biggest assumptive mistakes made in models. The 2 hemispheres respond quite differently to energy, as the satellite data shows. This is largely the result of the dynamic reflectivity of ice and snow. Any paleo simulation with a time step greater than or equal to 3 months will not model the asymmetry properly and would explain why the sensitivity doesn’t seem to be there. This is a discrete time model so the Nyquist rate matters. The asymmetry acts over a period of 6 months at the equator and 12 months elsewhere. To resolve the 6 month effect, the sample period must be less than 3 months, but not so small that the chaos of weather must be accurately modeled.

5) Did orbital variability cause the Younger Dryas and not a shutdown of the thermohaline circulation?

Yes. This would also be more consistent with the difference between the southern and northern hemispheres timing of the event.

6) How are the hemispheric and equatorial regions defined?

I always use equal angle latitude slices to divide up the planet because that’s how the satellite data I correlate the model to is aggregated. For the slide you mentioned, there are 3 60 degrees slices and all the appropriate weights are handled. In my model, I maintain concurrent representations for all combinations of equal slice widths from, 72 2.5 degree slices to a single 180 degree slice, all of which must be hierarchically consistent with each other.

7) Doesn’t more of the energy absorbed by CO2 end up reflected to the surface than is radiated into space?

This question has 2 answers, depending on your temporal perspective. In the very short term, the biggest effect of increasing CO2 is that 15u photons are captured closer to the surface and as the levels increase a slightly higher fraction is returned to the surface. If you consider a time scale of hours to days, then the answer is no since the energy returned to the surface is re-radiated at other frequencies, some of which pass through the transparent regions of the atmospheric absorption spectrum. Ultimately, most of the energy reflected by CO2 to the surface ends up leaving the planet within a day or so. It’s this delayed release, summed up over time, which quantifies the effect of GHG’s on the surface temperature.

8 ) Don’t GHG’s have a slow accumulative effect on the climate?

No. This is another incorrect assumption found in many models. Most of the effects of changing GHG concentrations are almost immediate. Only ice related feedback (which applies to any change in the surface temperature) acts over a time frame long enough to even see in the ice cores. The idea that energy hides for a while before affecting the surface temperature arose to explain why the data isn’t cooperating with AGW theory, but has no physical basis and no support from the data. The reason is that the Earth’s energy imbalance is not monotonic. It’s clear from the satellite data that during half of the year, the net imbalance is positive and temperatures increase. During the other half, the imbalance is negative and temperatures drop. It’s also important to remember that the net imbalance is the difference between 2 very large fluxes.

9) How does the data rule out CO2 as a forcing influence.

There are several aspects to this. The cross correlation analysis between temperature and CO2 effectively subtracts out the orbital effects. This is evident from the lack of correlation peaks corresponding to the known periods of orbital variability. The only correlation peak in the cross correlation analysis are due to the delay between temperature and GHG levels and shows unambiguously that temperature changes first, CO2 levels follow and CH4 lags by more, with a timescale on the order of centuries. Note that autocorrelating temperature, CO2 or CH4 produces the same correlation peaks corresponding to the known orbital forcing periods. This is clear evidence that CO2 and CH4 levels are dependent on the same orbital forcings as the temperature. Unless you can tell me why orbital variability would affect CO2 levels independent of the temperature, you can’t support the claim that CO2 levels driving temperature is dominant. More evidence is that prior interglacials were far warmer than today, even with significantly lower CO2 levels.

Enough for now, I have things to do today …

George

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The Little ice age didn’t have to be global. It just had to be where most of the thermometers were, if you get the point. There seems to be good evidence for the other periodic warmings which clearly didn’t have much to do with human activity. You have not explained those.

The AGW arguments seem highly contrived at best. After several years of reading about this I’m convinced there’s nothing terribly significant happening, natural or human caused. Even if the AGW people are correct that there is some human caused global warming due to CO2 the worst case seems to be 1 deg C or so and we’ll be arguing for a long time whether it is 0.3 or 1.1 deg as I see it.

For this you are proposing a wholesale rearrangement of the world economic system with the creation of energy ” sacred cows”, the burning of fossil fuels. This would be far more convincing if The Climate Institute was advising governments on how to move to nuclear electricity generation.

I’m not an economics expert but my understanding is that Stern’s discount rate assumptions are a joke.

Your preferred plan seems to be “lets do something, something might be happening!”. The human race has certainly suffered from mass delusions before (religion in various supernatural or political guises) so this doesn’t seem all that unusual. It’s just difficult to do business with the insane and/or evil.

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And similarly on the policy side. There are many different views about the likely cost of changing, and a very interesting paper of a decade or so ago looked at how the different economic analyses were getting such different results (from nearly no influence to building up to a few percent of the GDP–that is about a one year delay in per capita wealth to save the world). The key reason for the differences was the assumptions that were made, whether the benefits of limiting climate change were accounted for, how the revenues from taxes or permits were utilized and distributed, and more–for Nordhaus and Stern, it is how to weigh the future, so differences in discount rates–so the assumptions are the main difference. Hence, we need to be careful of what we assume.

And then there is the issue of one’s framing of the question–is what is happening natural until there is some sort of 99% confidence or more that it is not. That is a nice traditional hypothesis testing view. If a business person took that view, they’d be left way behind in the marketplace–that is not how public policy and economic decisions are typically made, and it results in taking a tremendous risk with a very valuable asset, namely our Earth.

I am not saying it is wrong to do this–only that I think that you (like all the rest of us) have an obligation to then explain to everyone that that is the decision framework that you are using so that they can decide if they want to use the same decision framework. IPCC has tried to carefully explain what its words mean so that those reading its results can then make their own judgments if the science is well-enough understood to make a decision. I do imagine that you have fire insurance on your home, though that risk is quite uncertain and you would not want to wait until you were certain your house were on fire before getting it.

So, I would only say that it is important to be careful of one’s assumptions (be equally skeptical of everything) and explain one’s decision framework. We should all try to do this.

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What about the Minoan, Roman and Medieval warm periods? What caused them? Do your models account for them? Or are you denying past warmer periods in the Holocene? The Holocene optimum?

As it seems there is still a large amount of dispute over the temperature rise that extra CO2 will cause(feedbacks), your linking of the magnitude of the current alleged rise(I say alleged because of the known measurement problems and lack of consistent long term measurements)to increased CO2 levels seems disingenuous at best. I don’t think most of the people here are that gullible.

Now that’s the first time I’ve heard that sea level has been virtually constant for millenia. I guess compared to the changes that occur when entering and exiting glaciations it is, but that also applies to the present rise. I live at 2100 feet above sea level,not because I think the seas will rise, (a surf beach at the bottom of the hill would be nice, though) but I believe Al Gore recently bought waterfront property in San Francisco and Kevin Rudd, the Australian Prime Minister, bought beachfront property on the Sunshine Coast north of Brisbane. I guess they are both not worried about sea level rise then? Both seem very keen on Emissions Trading Schemes.

As for a few Inuit villages, relocating them will be extremely cheap compared to what you’re planning to do to the world economy and in any case it isn’t at all clear that the coastal erosion you are talking about has anything to do with a little extra CO2 in the atmosphere. That is just an assumption you keep making.

I sure hope LLNL’s nuclear weapons designers are better than their climate scientists. They seem potentially less harmful anyway.

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