It is pretty close to TempC change = -0.0135 ln(CO2) +0.0807

Or right now, the tempC is increasing at 0.030C per ppm(CO2) and this will fall to 0.021C per ppm by the time CO2 reaches the first doubling level of 560 ppm in about 2060.

Climate models are using 0.04C per ppm right now which will fall to 0.0287C by the same 2060.

Yes, I agree about the confusion part. If CO2 were increasing linearly then dF/dt would decrease over time. The problem is that atmospheric CO2 isn’t increasing linearly. I can get a really good fit of the Muana Loa CO2 data with an exponential function with an exponent coefficient that increases linearly with time. Specifically: [CO2(t)]=[CO2(to)]*EXP((0.002625+2.98E-05*t)*t) where t is years since 1959 and [CO2(to)] is 316 ppmv. As long as that continues, the dF/dt will increase with time. That should result in some increase in global heat content. How much, though, is anyone’s guess. I use ‘guess’ advisedly as I don’t trust the model results and I trust the economic scenarios used to drive them not at all. For example, in 17 of the 40 scenarios, world wide petroleum consumption in 2100 will be greater than in 2000. Even most of the optimists in the oil patch don’t believe there’s enough oil in the ground for that to be possible. The pessimists say we’ve already seen peak oil production.

Neither of the functions you list is particularly interesting or relevant in this context. dF/d(ln[CO2]) is more like it.

You’re right, the second expression should have been F(2[CO2])-F([CO2]), which is approximately constant. Then dF/d(ln [CO2]) = a (constant), consistent with the MODTRAN results you posted. That is, each further doubling will does about the same as the previous doubling.

Meanwhile, hunter said this:
“Mr. Payne,
So CO2 is not diminishing in its ability to act as a GHG as its concentration increases?”

In a sense, CO2 is diminishing in its ability, since dF/d([CO2]) is decreasing with [CO2]. This may be a source of misunderstanding about future “forcing levels.”

Neither of the functions you list is particularly interesting or relevant in this context. dF/d(ln[CO2]) is more like it. I did that curve once for CO2 from 0.1 ppmv to 1000 or 10,000 ppmv, but apparently I didn’t save it. Needless to say, it’s not a straight line. I may still have the data in my notebook. If I find it , I’ll post a link to the graph.

hunter,
I was demonstrating that, contrary to the specific statement about radiative forcing made by tetris, forcing from doubling CO2 continues to be approximately constant…over a wide range of concentration higher than present. Forcing being defined as the reduction in emitted radiation from a change in CO2 with everything else held constant.

*raises hand from the peanut gallery*

There is a big difference between dF/d([CO2]) and F(2*[CO2])/F([CO2]) that you guys ought to be clear about before arguing further on this.

http://linux.com/news/embedded.....re-venture

As a point in your favour, the current rainfall in Victoria does not match the model predictions. If the models are right, then this must be natural variability.

Here is some information on the proxy data for Australia.

The only bit related to Victorian rainfall, though, is this:

“Another record of interest has been derived from crater lakes in south-western Victoria. These lakes are very deep and have catchments of at most a few square kilometres (with the lake surface itself occupying most of the catchment), so the lake level is almost entirely determined by the rainfall-evaporation balance, with runoff and land use change having little or no influence. The lakes studied all show a marked decline in level from about 1840 after having been relatively stable for several centuries. This indicates a marked shift in the rainfall-evaporation balance in the decades around 1840, with a decrease in rainfall being the most likely factor, although changes in evaporation (which could arise from cloudiness, temperature, wind or a combination of these) may also have been involved.”

I guess it depends on the timescales you are looking at. For the direct rainfall records that we have, the current situation in Victoria is unprecedented. I am unsure of what proxy data we have for Victoria, though.

re Victoria, this has been a record low-rainfall period. While records are made to be broken and natural climate variability may well break all records over long enough periods, it seems pretty clear to the BOM that we are looking at something special here.

I was demonstrating that, contrary to the specific statement about radiative forcing made by tetris, forcing from doubling CO2 continues to be approximately constant (actually it increases with increasing concentration, but not by enough to have a significant effect at current concentrations) over a wide range of concentration higher than present. Forcing being defined as the reduction in emitted radiation from a change in CO2 with everything else held constant. Climate sensitivity, or how much the average temperature changes for a given forcing, is a completely separate issue. Confusing the two does not lead to constructive conversations.

tetris,

Canard is a French word for a duck, and is often used in English to refer to a deliberately false story, originating from an abbreviated form of an old French idiom, “vendre un canard à moitié,” meaning “to half-sell a duck.” [Wikipedia]

CO2 is not at all like paint. Explaining why would take too much space. I suggest consulting a good textbook on atmospheric radiative transfer like A First Course in Atmospheric Radiation by Grant W. Petty

CO2 ppmv concentrations alone can neither explain nor serve as the main predictor of temperature increases. A different and significant forcing is required without which the entire AGW/ACC story does a lawn dart, and it is becoming pretty obvious that the GCMs have the sign on the most significant forcing wrong, which is why their predictive value is essentially zero [Schmidt and a few others have recently, more or less reluctantly, intimated as much.]