|Title||The North Atlantic Oscillation and greenhouse-gas forcing|
|Publication Type||Manual Entry|
|Year of Publication||2005|
|Authors||Kuzmina, S. I., L. Bengtsson, O. M. Johannessen, H. Drange, L. P. Bobylev, and M. W. Miles|
|Geophysical Research Letters|
|Type of Article||Journal Article|
 The results of 12 coupled climate models participating in the Coupled Model Intercomparison Project (CMIP2) are compared together with observational data in order to investigate: 1) How the current generation of climate models reproduce the major features of the winter North Atlantic Oscillation (NAO), and 2) How the NAO intensity and variability may change in response to increasing atmospheric CO2 concentration. Long-term changes in the intensity and spatial position of the NAO nodes (Icelandic Low and Azores High) are investigated, and different definitions of the NAO index and the Arctic Oscillation (AO) are considered. The observed temporal trend in the NAO in recent decades lies beyond the natural variability found in the model control runs. For the majority of the models, there is a significant increase in the NAO trend in the forced runs relative to the control runs, suggesting that the NAO may intensify with further increases in greenhouse-gas concentrations.
This paper has a nice discussion of the definition of the Arctic Oscillation as compared to the North Atlantic Oscillation and the Northern Annular Mode as well as nuances of those definitions.
The paper examines CMIP-2 models which is two generations before the CMIP-5 models used in the IPCC assessment report which should be released in 2013. Hence, update with current models is needed.
The paper substantiates that the already observed changes in the North Atlantic Oscillation has a discernable greenhouse gas signal and suggests that this trend will continue into the future with the positive mode becoming more common.
There are differences in the trend based on the definition of the index.
Physical mechanisms are linked, at this writing, to changes in tropical sea surface temperature and modulation due to stratospheric processes.