New Papers: North Atlantic, Pacific, And Southern Oceans Are Cooling

  • Date: 11/09/17
  • P. Gosselin, No Tricks Zone

Contrary to expectations, climate scientists continue to report that large regions of the Earth have not been warming in recent decades.

Graph Source Duchez et al., 2016

According to Dieng et al. (2017), for example, the global oceans underwent a slowdown, a pause, or even a slight cooling trend during 2003 to 2013.  This  undermines expectations from climate models which presume the increase in radiative forcing from human CO2 emissions should substantially increase ocean temperatures.

The authors indicate that the recent trends in ocean temperatures “may just reflect a 60-year natural cycle“, the AMO (Atlantic Multidecadal Oscillation), and not follow radiative forcing trends.

Dieng et al., 2017    We investigate the global mean and regional change of sea surface and land surface temperature over 2003–2013, using a large number of different data sets, and compare with changes observed over the past few decades (starting in 1950). … While confirming cooling of eastern tropical Pacific during the last decade as reported in several recent studies, our results show that the reduced rate of change of the 2003–2013 time span is a global phenomenon. GMST short-term trends since 1950 computed over successive 11-year windows with 1-year overlap show important decadal variability that highly correlates with 11-year trends of the Atlantic Multidecadal Oscillation index. The GMST 11-year trend distribution is well fitted by a Gaussian function, confirming an unforced origin related to internal climate variability.

We evaluate the time derivative of full-depth ocean heat content to determine the planetary energy imbalance with different approaches: in situ measurements, ocean reanalysis and global sea level budget.  For 2003–2013, it amounts to 0.5 +/− 0.1 W m−2, 0.68 +/− 0.1 W m−2 and 0.65 +/− 0.1 W m−2, respectively for the three approaches.    Although the uncertainty is quite large because of considerable errors in the climate sensitivity parameter, we find no evidence of decrease in net radiative forcing in the recent years, but rather an increase compared to the previous decades.

We can note that the correlation between GMST [global mean surface temperature] trends and AMO trends is quite high. It amounts 0.88 over the whole time span. At the beginning of the record, the correlation with PDO trends is also high (equal to 0.8) but breaks down after the mid-1980s.  The GMST and AMO trends shown in Figure 6 show a low in the 1960s and high in the 1990s, suggestive of a 60-year oscillation, as reported for the global mean sea level by Chambers et al. (2012). Thus the observed temporal evolution of the GMST [global mean surface temperature] trends may just reflect a 60-year natural cycle driven by the AMO.

Subpolar North Atlantic Cooling Rapidly Since 2005

According to Piecuch et al. (2017) there has been no net warming of the North Atlantic Ocean in the last quarter century.  The warming that occurred in the 10 years from 1994-2004 has been completely negated by an even more pronounced cooling trend since 2005.   The predominant (87%) cause of the warming was determined to be of the same natural (non-anthropogenic) origin as the subsequent cooling: advection, the movement/circulation of heat via internal processes.   In fact, human CO2 emissions are never mentioned as even contributing to the the 1994-2004 warming.

Piecuch et al., 2017    The subpolar North Atlantic (SPNA) is subject to strong decadal variability, with implications for surface climate and its predictability. In 2004–2005, SPNA decadal upper ocean and sea-surface temperature trends reversed from warming during 1994–2004 to cooling over 2005–2015. … Over the last two decades, the SPNA has undergone a pronounced climate shift. Decadal OHC and SST trends reversed sign around 2004–2005, with a strong warming seen during 1994–2004 and marked cooling observed over 2005–2015. These trend reversals were pronounced (> 0.1 °C yr−1 in magnitude) in the northeastern North Atlantic (south and west of Iceland) and in the Labrador Sea. … To identify basic processes controlling SPNA thermal variations, we diagnose the SPNA heat budget using ECCOv4. Changes in the heat content of an oceanic control volume can be caused by convergences and divergences of advective, diffusive, and surface heat fluxes within the control volume.  [Advective heat convergence] explains 87% of the total [ocean heat content] variance, the former [warming] showing similar decadal behavior to the latter [cooling], increasing over 1994–2004, and decreasing over 2005–2015. … These results demonstrate that the recent SPNA decadal trend reversal was mostly owing to advective convergences by ocean circulation … decadal variability during 1993–2015 is in largest part related to advection by horizontal gyres.

Yeager and Robson (2017) also point out that, like it did from the 1960s to 1980s, the North Atlantic “has again been cooling”, a trend which they and others expect to continue.   Sea surface temperatures are no warmer today than they were in the 1950s.

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