The prediction of how much manmade global warming we will see in the future (as well as how much past warming was manmade) depends upon something called "climate sensitivity".
For many years, climate researchers have struggled to diagnose the Earth's climate sensitivity from measurements of the real climate system. It's almost a "holy grail" kind of search, because if we could discover the true value of the climate sensitivity, then we would basically know whether future global warming will be benign, catastrophic, or somewhere in between.
Here I present a new method of satellite data analysis which I believe reveals the climate sensitivity, and I also show why it has been so hard to diagnose from observations.
When the Earth warms, it emits more infrared radiation to outer space. This natural cooling mechanism is the same effect you feel at a distance from a hot stove. The hotter anything gets the more infrared energy it loses to its surroundings.
For the Earth, this natural cooling effect amounts to an average of 3.3 Watts per square meter for every 1 deg C that the Earth warms. There is no scientific disagreement on this value.
Climate sensitivity is how clouds and water vapor will change with warming to make that 3.3 Watts a bigger number (stronger natural cooling, called "negative feedback"), or smaller (weaker natural cooling, called "positive feedback").
While there are other sources of change in the climate system, cloud and water vapor changes are likely to dominate climate sensitivity. The greater the sensitivity, the more the Earth will warm from increasing atmospheric greenhouse gas concentrations being produced by humans through the burning of fossil fuels.
There are three possibilities for climate sensitivity:
1. If clouds and water vapor don't change as we add CO2 to the atmosphere, then the expected warming by 2100 would only be about 1 deg. C, which would not be a very big concern for most people. This is called the "zero-feedback" case.
2. If low clouds decrease, high (cirrus) clouds increase, or water vapor increases, then warming will be magnified. Most, if not all, climate models predict that clouds and water vapor will change like this, resulting in an amplification of the CO2-only warming of 1 deg C to as much as 4.5 deg. C or more. This is called the "positive-feedback" case, and the greater the positive feedback, the greater the warming. (NOTE: If the sum of all positive feedbacks more than cancel out the 3.3 Watt natural cooling, then the climate system is inherently unstable…this is why you sometimes hear of climate change "tipping points".)
3. If the climate modelers are wrong -- and low clouds increase, high clouds decrease or water vapor decreases with warming -- then the effect will be to reduce the warming to less than 1 deg. C. For instance, if that 3.3 Watts of natural cooling mentioned earlier increased to as much as 8 Watts from cloud changes, the warming would be reduced to about 0.5 deg C by 2100. This is called the "negative feedback" case.
Read more from Roy Spencer here: http://www.weatherquestions.com/Climate-Sensitivity-Holy-Grail.htm
In this simplied version of a paper entitled 'Chaotic Radiative Forcing, Feedback Stripes, and the Overestimation of Climate Sensitiviy' submitted on June 25, 2008 to the Bulletin of the American Meteorological Society Dr Spencer goes on to conclude that:
1. Current satellite estimates of climate sensitivity have a spurious bias in the direction of high sensitivity.
2. This bias is probably due to small, natural fluctuations in cloud cover.
3. The true climate sensitivity only shows up during those shorter periods of time when non-radiative forcing (e.g. evaporation) is causing a relatively large source of temperature variability compared to that from cloud variability.
----------------
Read Global Warming for Dummies Part 1 here:
And Global Warming for Dummies Part 2 here:
[...] by the IPCC scientists are similar to those often discussed at this blog, including the issue of cloud feedback and climate sensitivity. There have been recent major breakthroughs in this area by Dr Roy Spencer a so-called climate [...]
Not really. The largest changes are when you look up. For one thing the water vapor concentration and absorptions change radically. There is practically none left at 15 km. That is the lapse rate at work as the saturated vapor pressure of water vapor decreases with temperature. You will notice that there is a lot less emission from CO2 as the altitude increases, and if you look closely you will see that the width of the band decreases.
Looking down you will notice that there is practically no absorption at 100 m, and the CO2 and water bands grow in with altitude. This is because the layers near the surface are practically at the same temperature as the surface so the atmosphere appears transparent with equal amounts of absorption and emission. As one goes higher there is more absorption than emission, so the window closes.
For those who wish, the application to see these things is at
http://geosci.uchicago.edu/~archer/cgimodels/radiation.html
Rabbett:So start at the bottom and work your way up in 1 km increments, look up and down. You might learn something like the radiation from lower levels in the CO2 bands does not get out to space, e.g. it is blocked
It doesn't get blocked it gets diverted some gets used before being radiated off to space e.g. something had to power my sailboat.
What we see in the upward looking chart is that the atmosphere radiates very well in bands where there are polyatomic atmospheric species with resonant vibration modes not so well where there aren't. Without them the atmosphere will take quite a bit longer to cool but then without them the atmosphere would probably not warm as fast or as much.
Without polyatomic my sailboat would probably never have worked but then we would be here either and would it never have been built in the first place.
So start at the bottom and work your way up in 1 km increments, look up and down. You might learn something like the radiation from lower levels in the CO2 bands does not get out to space, e.g. it is blocked
Rabbet "Jan, if you are at 20km looking down almost all of the atmosphere (molecules)is below you. You see about the same thing at 100 km looking down."
I know you "see" the same thing at 70 km looking down but is it really the same think you are looking at. At 20 km you are looking at and seeing in the window the surface radiation barely modified and that would be the similar at 70km but wrt 15micron band we are looking at the radiation from CO2 at different heights to a depth of a few metres because of the atmospheric opacity in that band. Strangely enough the temperature at around 70km is very similar to the temperature at 20 km, so perhaps we aren't really seeing the same thing at all. We can't even see the thermal radiation due to the higher temperature at the stratopause in the 15 m icron band.
Now that rather boring trivially obvious lot is not really relevant. Looking down from 20 km you see the surface radiation in the window which is at the BB equivalent of 268K the upward one shows the same temperature driven radiation from the CO2 absorption band meaning the temperatures are the same. That the downward looking radiation at 20 km for the CO2 band is ~220K hardly surprising as that is about the temperature of the tropopause where the kinetic energy has been converted to potential energy.