(Manuscript received 17 September 2011; revised 11 April 2012; accepted 7 May 2012) © The Korean Meteorological Society and Springer 2012
Abstract: The apparent leveling of the global temperature time series at the end of the 1990s may represent a break in the upward trend. A study of the time series measurements for temperature, carbon dioxide, humidity and methane shows changes coincident with phase changes of the Atlantic and Pacific Decadal Oscillations. There are changes in carbon dioxide, humidity and methane measurement series in 2000. If these changes mark a phase change of the Pacific Decadal Oscillation then it might explain the global temperature behavior.
One of the most useful analytical techniques where there is timing information is the use of coincidence to separate signal from noise. This can be seen looking at the timing of changes in temperature, CO2, humidity for the period 1959 to 2010 and from 1983 to 2010 for methane. Figure 9 shows the timing of breaks in the various time series identified from the Chow break analysis where the Chow statistic indicates greater than 98% significance. This analysis has identified a series of coincident changes that are unlikely to be a random coincidence of events since it is possible to understand that the Pacific and Atlantic Decadal Oscillations cause breaks in global tempera- tures, a rebalancing of ocean and atmosphere exchanges of CO2, consequent changes in humidity and indirectly changes in the annual increases of atmospheric methane. Some random breaks might be expected to arise from the number of data points analyzed with a 98% probability level. The break identified in the Southern Hemisphere Atlantic Ocean humidity time series (Fig. 7) in 1972 may simply be a random break.
This analysis shows:
· coincident changes in temperature, CO and humidity at the time of the Atlantic Decadal Oscillation phase change in 1995. There is also a hint of the change in 1965 from the atmospheric CO2 measurements;
· coincident changes in temperature, CO2 and humidity at the time of the Pacific Decadal Oscillation phase change in 1976-77, the time of the Great Pacific Climate Shift; and
· coincident changes of CO , humidity and methane for 2 1999-2002. If these changes mark a phase change of the Pacific Decadal Oscillation then it could explain the global temperature behaviour. There is a strong set of coincident events at or around 2000 that suggest the onset of a cool phase of the Pacific Decadal Oscillation. This is supported by the decreasing humidity in the Northern Pacific Ocean after the break in 2000 (Fig. 6) where the probability of the straight line fit showing no de- crease is 3%. However for the global surface temperature this analysis has not established whether the cool phase of the Pacific Decadal Oscillation dominates the warm phase of the North Atlantic Decadal Oscillation. The variations in global temperature, atmospheric CO2, water vapour and atmospheric methane all indicate the importance of the Atlantic and Pacific Decadal Oscillations. This is not easily taken into account in General Circulation Models and until there is a better under- standing of the long term behaviour of the oceans, it must be a significant difficultly in projecting future temperatures.
Acknowledgements. I have benefited greatly from discussions with William Kininmonth and in particular, David Stockwell who introduced me to the Chow Break Test.