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Is Natural Variability or Anthropogenic Activity Driving Antarctic Climate?

Paper Reviewed
Jones, J.M., Gille, S.T., Goosse, H., Abram, N.J., Canziani, P.O., Charman, D.J., Clem, K.R., Crosta, X., de Lavergne, C., Eisenman, I., England, M.H., Fogt, R.L., Frankcombe, L.M., Marshall, G.J., Masson-Delmotte, V., Morrison, A.K., Orsi, A.J., Raphael, M.N., Renwick, J.A., Schneider, D.P., Simpkins, G.R., Steig, E.J., Stenni, B., Swingedouw, D. and Vance, T.R. 2016. Assessing recent trends in high-latitude Southern Hemisphere surface climate. Nature Climate Change 6: 917-926.

One of the most debated questions in the field of climate science today is whether or not current trends in various climate indices reflect an anthropogenic component that is driven by increasing atmospheric CO2 concentrations. And if such is found to be the case, scientists seek to know to what extent that component dominates the signal.

Investigating this question with respect to the high latitudes of the Southern Hemisphere, the 25-member research team of Jones et al. (2016) recently compared observed climate trends in surface air temperature (SAT), sea surface temperature (SST) and sea ice from both historical and proxy sources with control and forced simulations from the Fifth Climate Model Intercomparison Project (CMIP5) in an effort to "assess whether recent trends [over the period 1979-2014] are unusual compared with natural variability."

In describing their findings, Jones et al. state that "the longer [proxy] records independently support the conclusion that most of the recent changes for any single [climate] variable largely result from natural variability and are not unprecedented over the past two centuries." Furthermore, they add that "when analyzing specifically the 1979-2014 period, including forced changes and internal variability, models struggle to track the observed trends in SST, SAT and sea-ice cover," which finding, in their words, "suggests either that a singular event associated with internal variability has been able to overwhelm the forced response in observations, or that CMIP5 models overestimate the forced response (potentially partly because of key processes missing in the models), or a combination of both."

Thus, in light of the above, the answer as to whether or not increasing atmospheric CO2 emissions are exerting a discernible influence on high latitude Northern Hemispheric climate is a resounding No! Natural variability is fully capable of explaining the recent trends.

Posted 7 March 2017