Global Warming and Chaos Theory

[vanesch]

Water vapour is the lion's share of your 200% to 800% feedback, which is already included in MODTRAN.

Mmm, maybe I misunderstood you. Maybe you are implying that the modest amount of CO2 is the reason why there is a certain amount of water vapor in the atmosphere. If we would remove all CO2, then all or a large fraction of the water vapor would also disappear (for an amplification factor close to 8). Well, the simple case is implemented in MODTRAN where relative humidity is used instead of constant water vapor.
For our tropical atmosphere, we go from 280 ppm and 289.2 W/m2 to 560 ppm and 286 W/m2 at 300 K (that's our famous 3.2 W/m2 forcing for a CO2 doubling), and we now have to increase the surface temperature not by 0.8K but by 1.5K (because heating up gives more water vapor in the atmosphere and hence more greenhouse effect).

So we get about a 87% extra feedback this way, true. That's not the 800%. It comes close to the 200%, if this relative humidity doesn't do anything else. But increasing the absolute water vapor pressure increases things like convection (it is the working principle of a cooling tower!). So it is not even said that this feedback is really there.

So using this feature, we get a cllimate sensitivity of not 0.8K but of 1.5K. And that's the highest modtran can do.

 

[Andre]

Mmm, maybe I misunderstood you. Maybe you are implying that the modest amount of CO2 is the reason why there is a certain amount of water vapor in the atmosphere. If we would remove all CO2, then all or a large fraction of the water vapor would also disappear (for an amplification factor close to 8). Well, the simple case is implemented in MODTRAN where relative humidity is used instead of constant water vapor.
For our tropical atmosphere, we go from 280 ppm and 289.2 W/m2 to 560 ppm and 286 W/m2 at 300 K (that's our famous 3.2 W/m2 forcing for a CO2 doubling), and we now have to increase the surface temperature not by 0.8K but by 1.5K (because heating up gives more water vapor in the atmosphere and hence more greenhouse effect).

So we get about a 87% extra feedback this way, true. That's not the 800%. It comes close to the 200%, if this relative humidity doesn't do anything else. But increasing the absolute water vapor pressure increases things like convection (it is the working principle of a cooling tower!). So it is not even said that this feedback is really there.

So using this feature, we get a cllimate sensitivity of not 0.8K but of 1.5K. And that's the highest modtran can do.

Would you please substract the energy, required for the enhanced evaporation rate to maintain the higher humidity, from the energy available to heat the surface?

 

[vanesch]

Would you please substract the energy, required for the enhanced evaporation rate to maintain the higher humidity, from the energy available to heat the surface?

Why would I ? Once the quantity of water is in the atmosphere, the latent heat of evaporation will equal the latent heat gained back during precipitation, no ? If a closed bottle containing water and air is brought to a higher temperature, then of course during the initial heating, you have to take into account the heat capacity and the latent heat of evaporation, but once equilibrium is reached, there's no need anymore for a power influx to maintain a higher partial pressure of water vapor.

 

[Andre]

Why would I ? Once the quantity of water is in the atmosphere, the latent heat of evaporation will equal the latent heat gained back during precipitation, no ?

No, you basically accellerate the water cycle. Precipitation is colder than the ambient temperature during falling into lower warmer levels (lapse rate). So it doesn't bring energy back to the surface. The increased latent heat released at altitude is emitted and partially escapes into space, not helping the required higher evaporation rate to sustain the quicker water cycle.

Also think in daily cycles. In many parts of the world, there is cumulus type clouds at daytime and no clouds at night time, During the day the decreasing albedo is restricting the temperature rise at the Earth surface. If the water cycle is acceralerated, the increase in cloudiness will limit the temperature rise even more as a substantial negative feedback, while at night time out radiation is changed only very little(assuming a small decrease in optical depth for IR radiation) It's just as if you turn the air conditioner to more cooling.

 

[vanesch]

No, you basically accellerate the water cycle. Precipitation is colder than the ambient temperature during falling into lower warmer levels (lapse rate). So it doesn't bring energy back to the surface. The increased latent heat released at altitude is emitted and partially escapes into space, not helping the required higher evaporation rate to sustain the quicker water cycle.

Also think in daily cycles. In many parts of the world, there is cumulus type clouds at daytime and no clouds at night time, During the day the decreasing albedo is restricting the temperature rise at the Earth surface. If the water cycle is acceralerated, the increase in cloudiness will limit the temperature rise even more as a substantial negative feedback, while at night time out radiation is changed only very little(assuming a small decrease in optical depth for IR radiation) It's just as if you turn the air conditioner to more cooling.

Yes, but these are more complicated mechanisms, which are part of more involved models taking into account cloud formation, convection, albedo changes etc...

I was talking about the simple model of a static (no air movement, no convection) monophase (no clouds) optical model as done in modtran. In such a model, one doesn't need to subtract the evaporation latent heat once equilibrium with the new radiative forcing is established.

 

[Robert Elliso]

‘The climate system is particularly challenging since it is known that components in the system are inherently chaotic; there are feedbacks that could potentially switch sign, and there are central processes that affect the system in a complicated, non-linear manner. These complex, chaotic, non-linear dynamics are an inherent aspect of the climate system.’ (IPCC TAR s14.2.2.1 - http://www.ipcc.ch/ipccreports/tar/wg1/504.htm)

‘Modern climate records include abrupt changes that are smaller and briefer than in paleoclimate records but show that abrupt climate change is not restricted to the distant past.’ (Abrupt Climate Change: Inevitable Surprises, 2002, NAP, p19 - http://books.nap.edu/openbook.php?record_id=10136&page=19).

A dynamic theory of ocean/climate states (http://www.nosams.whoi.edu/PDFs/papers/tsonis-grl_newtheoryforclimateshifts.pdf ) confirms that climate on decadal timescales is an emergent property of complex and dynamic Earth systems. "You go from a cooling regime to a warming regime or a warming regime to a cooling regime. This way we were able to explain all the fluctuations in the global temperature trend in the past century," Anastasios Tsonis said.