Dear Sridhar:

I'll be very brief and possible mistaken. I usually do analysis without changing CO2 concentration and using CO2 concentration changes predicted by some emission scenario. That should encompass the extremes, if we don't take into account nonlinear interactions effects between CO2 and O3 concentrations in plant behaviour and other minor nuissances. Both extremes should give you a measure of uncertainty. Differences between both kind of simulations should be little in C4 species but could be large in C3 ones. There will be differences also with different management procedures (irrigated or rainfed crops, sowing dates, use of fertilisers and such).

In the end, the magnitude of the positive expected influence of CO2 fertilization effect can't be analysed without analysing the expected magnitude of climate change itself. As far as I know the CO2 fertilisation effect is physiologically limited but the accompanying climate change can be rather large depending of the global climate model which you used to predict your climate change scenario.

Sincerely yours,

Roger E. Rivero Vega
  ----- Original Message ----- 
  From: Sridhar Gummadi 
  To: [log in to unmask] 
  Sent: Saturday, March 04, 2006 1:33 AM
  Subject: CO2 and Climate Change


  Dear All,

     While assessing the impact of climate change on agricultural crops in
  India conditions, I am using PRECIS (RCM) data. My question is whether
  the CO2 ppm should be changed to 550 ppm or it should be kept at 350
  ppm. When I am trying to assess the impact of climate change in A2 and
  B2 scenarios with CO2 at 550 ppm, I found that yields are increasing
  even though temperatures are raising by 4-5 oC. Can anyone let me know,
  whether we have to change CO2 ppm or not in assessing climate change
  impact on agricultural crops.

  Regards,

  Sridhar Gummadi
  Sr.Engg GIS,
  RMG, RMSI,
  Noida, India.

  Ph:=919818399948.