The key conclusions of working group I of the intergovernmental panel on climatechang (IPCC) the fourth assessment report (AR4) were:a).warming of the climatic system is unequivocal : b).anthropogenic warming will probably continue for centuries due to the timescales associated with climate processe and feedback; c).the surface air warming in the 21st century by best estimate will range from 1.1 to 2.9°c for a "low scenario" and of 2.4 to 6.4°c for a " high scenario".