By Dr. Sebastian Lüning and Prof. Fritz Vahrenholt
(German text translated, edited by P Gosselin)
It was stated in our 2012 climate science skeptical book “Die kalte Sonne” and was massively criticized. Today it is accepted: the systematic impact of ocean cycles on climate events.
The latest example: Meehl et al. from August 2016 in Nature Climate Change:
Contribution of the Interdecadal Pacific Oscillation to twentieth-century global surface temperature trends
Longer-term externally forced trends in global mean surface temperatures (GMSTs) are embedded in the background noise of internally generated multidecadal variability1. A key mode of internal variability is the Interdecadal Pacific Oscillation (IPO), which contributed to a reduced GMST trend during the early 2000s1, 2, 3. We use a novel, physical phenomenon-based approach to quantify the contribution from a source of internally generated multidecadal variability—the IPO—to multidecadal GMST trends. Here we show that the largest IPO contributions occurred in its positive phase during the rapid warming periods from 1910–1941 and 1971–1995, with the IPO contributing 71% and 75%, respectively, to the difference between the median values of the externally forced trends and observed trends. The IPO transition from positive to negative in the late-1990s contributed 27% of the discrepancy between model median estimates of the forced part of the GMST trend and the observed trend from 1995 to 2013, with additional contributions that are probably due to internal variability outside of the Pacific4 and an externally forced response from small volcanic eruptions5. Understanding and quantifying the contribution of a specific source of internally generated variability—the IPO—to GMST trends is necessary to improve decadal climate prediction skill.”
The cycles always pop up with new names, but in the end they are all relatives of the PDO and AMO, which are also coupled with one another with a time lag.
Now that this factual basis has become accepted, suddenly there have been a shower of publications. For example Chikamoto et al. from the Geophysical Research Letters in July 2016:
Potential tropical Atlantic impacts on Pacific decadal climate trends
The tropical Pacific cooling from the early 1990s to 2013 has contributed to the slowdown of globally averaged sea surface temperatures (SSTs). The origin of this regional cooling trend still remains elusive. Here we demonstrate that the remote impact of Atlantic SST anomalies, as well as local atmosphere-ocean interactions, contributed to the eastern Pacific cooling during this period. By assimilating observed three-dimensional Atlantic temperature and salinity anomalies into a coupled general circulation model, we are able to qualitatively reproduce the observed Pacific decadal trends of SST and sea level pressure (SLP), albeit with reduced amplitude. Although a major part of the Pacific SLP trend can be explained by equatorial Pacific SST forcing only, the origin of this low-frequency variability can be traced back further to the remote impacts of equatorial Atlantic and South Atlantic SST trends. Atlantic SST impacts on the atmospheric circulation can also be detected for the Northeastern Pacific, thus providing a linkage between Atlantic climate and Western North American drought conditions.”
Incorporating ocean cycles in the climate models has now taken on top priority as the earlier models have failed miserably, just as has been shown by Peings et al. in March 2016 in the Journal of Geophysical Research.
Let’s ignore the past for now and direct our focus instead on the new, improved models.
Also a team led by Monika Barcikowska succeeded in integrating the ocean cycles in model simulations as explained on 20 October 2016 in the Journal of Climate. And suddenly, lo and behold, the warming hiatus made sense and cooling looks likely for the future:
Observed and simulated fingerprints of multidecadal climate variability, and their contributions to periods of global SST stagnation
This study investigates spatio-temporal features of multidecadal climate variability, using observations and climate model simulation. Aside from a long-term warming trend, observational SST and atmospheric circulation records are dominated by a ~65yr variability component. Though its center of action is over the North Atlantic, but it manifests also over the Pacific and Indian Oceans, suggesting a tropical inter-basin teleconnection maintained through an atmospheric bridge.
Our analysis shows that simulated internal climate variability in a coupled climate model (CSIRO-Mk3.6.0) reproduces the main spatio-temporal features of the observed component. Model-based multidecadal variability comprises a coupled ocean-atmosphere teleconnection, established through a zonally oriented atmospheric overturning circulation between the tropical North Atlantic and eastern tropical Pacific. During the warm SST phase in the North Atlantic, increasing SSTs over the tropical North Atlantic strengthen locally ascending air motion and intensify subsidence and low-level divergence in the eastern tropical Pacific. This corresponds with a strengthening of trade winds and cooling in the tropical central Pacific.
The model’s derived component substantially shapes its global climate variability and is tightly linked to multidecadal variability of the Atlantic Meridional Overturning Circulation (AMOC). This suggests potential predictive utility and underscores the importance of correctly representing North Atlantic variability in simulations of global and regional climate.
If the observations-based component of variability originates from internal climate processes, as found in the model, the recently observed (1970s-2000s) North Atlantic warming and eastern tropical Pacific cooling might presage an ongoing transition to a cold North Atlantic phase with possible implications for near-term global temperature evolution.”
And because it is so nice, here’s another paper on the subject by Dai et al. 2015 from Nature Climate Change:
Decadal modulation of global surface temperature by internal climate variability
Despite a steady increase in atmospheric greenhouse gases (GHGs), global-mean surface temperature (T) has shown no discernible warming since about 2000, in sharp contrast to model simulations, which on average project strong warming1, 2, 3. The recent slowdown in observed surface warming has been attributed to decadal cooling in the tropical Pacific1, 4, 5, intensifying trade winds5, changes in El Niño activity6, 7, increasing volcanic activity8, 9, 10 and decreasing solar irradiance7. Earlier periods of arrested warming have been observed but received much less attention than the recent period, and their causes are poorly understood. Here we analyse observed and model-simulated global T fields to quantify the contributions of internal climate variability (ICV) to decadal changes in global-mean T since 1920. We show that the Interdecadal Pacific Oscillation (IPO) has been associated with large T anomalies over both ocean and land. Combined with another leading mode of ICV, the IPO explains most of the difference between observed and model-simulated rates of decadal change in global-mean T since 1920, and particularly over the so-called ‘hiatus’ period since about 2000. We conclude that ICV, mainly through the IPO, was largely responsible for the recent slowdown, as well as for earlier slowdowns and accelerations in global-mean T since 1920, with preferred spatial patterns different from those associated with GHG-induced warming or aerosol-induced cooling. Recent history suggests that the IPO could reverse course and lead to accelerated global warming in the coming decades.”
The summary sentence with suspected warming linked to ocean cycles over the coming years is mysterious, though. Perhaps the authors here are thinking about the time after 2035…
If any journalist, who got all excited about our “crude” ocean cycle theory when we published our book in 2012, wishes to contact us — they’re welcome to do so. We are not resentful when the apology comes from the heart.