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The Radiative Forcing for 2xCO2 predicted by CAM

K

kittybuy@yahoo_com

New Member
Has anyone checked this out before?

I did the CAM 5 year run with 2xCO2 (CO2VMR=7.1e-4). The radiative forcing at surface is only ~1 w/m2 based on the normal CO2 (default 3.55e-4) case. This is way lower than the 4 w/m2 expected. Any thoughts? Has anybody done the similar study? What is your result? Thanks in advance.

In both runs, climatology values of surface temperature are used. All namelist variables are by default except for the CO2VMR in the 2xCO2 case.
 
B

brianpm

Active Member
I am also getting a very small response in a simplified configuration of CAM. I increase CO2 using CO2VMR in the namelist, but the climate basically doesn't change.

Is it possible that the CAM doesn't adjust to CO2VMR alone, that something has to be done to BNDTVGHG? This is my present concern, since I'd expect a more significant response.

Any advice would be very welcome.
 
B

brianpm

Active Member
Well, I guess I should have looked at the default BNDTVGHG before I said that. It is apparently for ramping the CO2.

I'm still puzzled by this small response though.

brianpm said:
Is it possible that the CAM doesn't adjust to CO2VMR alone, that something has to be done to BNDTVGHG? This is my present concern, since I'd expect a more significant response.
Click to expand...
 
S

sandeep_sahany@indiatimes_com

Member
brianpm said:
Well, I guess I should have looked at the default BNDTVGHG before I said that. It is apparently for ramping the CO2.

I'm still puzzled by this small response though.
Click to expand...

Hi Brian,
Did you get the reason ? I am working on a similar kind of problem for which I need to give a long run so it is advisable in my part to ask you the reason behind the small response. Is it due to (1) In only atmospheric model it should unlike the slab ocean/coupled model ? (2) Did you make any mistake in doing the simulation ?

Anticipating your reply and thanking you in advance
Saroj
 
R

rneale

Rich Neale
CAM Project Scientist
Staff member
2xCO2 climate sensitivity runs performed with CAM usually use the slab ocean model since only land surface temperatures can respond to radiative balance changes in a fixed SST run. With a slab ocean CAM3 has an intital top of atmosphere imbalance of about 2.5W/m^2 and the climate sesnitivity works out at about 2.5 deg C for 2xCO2
 
S

sandeep_sahany@indiatimes_com

Member
rneale said:
2xCO2 climate sensitivity runs performed with CAM usually use the slab ocean model since only land surface temperatures can respond to radiative balance changes in a fixed SST run. With a slab ocean CAM3 has an intital top of atmosphere imbalance of about 2.5W/m^2 and the climate sesnitivity works out at about 2.5 deg C for 2xCO2
Click to expand...

Dear Neale,
Thanks a lot.
Wishes,
Saroj
 
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