Multidecadal Changes in Swiss Alps Glacial Mass, North Atlantic Thermohaline Circulation and European Sunshine hours

The Swiss Alps (1), as with many regions across the extra-tropical Northern Hemisphere experienced a significant snow drought in both 2022 and 2023. Many larger glaciers in the Swiss Alps saw as much as 6% reduction in mass in 2022 alone.

Likewise, recent publications have shown that the large temperature rise seen in 2023 was driven to a significant degree by notable reductions in low altitude marine stratiform clouds over the North Atlantic (2).

Here in this article, I would outline a series of arguments from the literature that demonstrates that multi-decadal changes in winter - spring season cloud coverage and sunshine hours over the North Atlantic and across Europe, play a determining role in controlling sea surface temperatures and Swiss Alps glacial ice balance.

To begin this train of thought, Figure 1 is introduced with compares the 100-year mass changes of 30 glaciers in the Swiss Alps with the detrended Atlantic Multidecadal sea surface oscillation (AMO). The anti-correlation between changes in glacial ice mass and the AMO is clearly seen as showing two distinct phases of warming (mass loss) and cooling (mass gain) over the past century.

Unfortunately, Matthias Huss et al (3) does not attempt to address the time dependence or show evidence of causation. However, they do make reference to others who have suggested there is a multidecadal dimming to brightening cycle seen in the Alps over the last century.

Note that the steep rise in North Atlantic ocean surface temperature and the large reduction in Swiss Alps glacial mass loss since the 1980s, coincides with the large increase (decrease) in sunshine hours (cloud coverage) over Europe shown in Figure 2, also beginning around 1980s.

This is the brightening cycle that Matthias Huss et al was referring to in his paper (3).

By definition, 1 sunshine hour equals 1 hour of sunlight at or above 120 Watts per square meter. Therefore, sunshine hours is a measure of the amount of solar energy absorbed by the surface environment, which is in part a function of multidecadal changes in cloud coverage.

Note that Europe, as the birth place of modern science, has the longest running meteorological monitoring stations on the planet and there are extensive records from across the continent for sunshine hours and surface solar radiation intensity.

There is however, no records of the same variables over the North Atlantic. Rather, over the regional ocean there are only sea surface temperature records.

Therefore, when people make comparisons between the AMO and sunshine hours over Europe (Figure 3) or to changes in Swiss Alps glacial ice mass (Figure 1), they are suggesting that multidecadal changes in cloud coverage are driving (causative) these measurable changes in the surface environment.

Andrzej et al's 2023 paper is a case in point where European sunshine duration (hours) is compared against both North Atlantic sea surface temperatures (SST) and thermohaline-circulation (THC).

For those who are not aware of the THC and how it relates to North Atlantic SST, a little refresher is in order. The THC is the rate by which absorbed solar radiation in the North Atlantic subtropics is carried northward by ocean currents as sensible heat into the subpolar regions.

Typically its units are in millions of cubic meters per second.

The pulling force for the THC is called downwelling, where surface water looses buoyancy and sinks to the bottom of the subpolar North Atlantic. The loss of buoyancy is caused by the gradual increase in salinity and density as warm surface water evaporates. The rate of loss of buoyancy is a function of SST; colder water evaporates slower than warmer water.

Thus, THC is seen to vary in time with the AMO.

Again, as long term sunshine monitoring stations are only found in Europe, this author likewise shows that European sunshine hours exhibit similar time dependence to the THC and AMO over the North Atlantic. This is there way of arguing that the regional changes in clouds over Europe are also occurring over the North Atlantic Ocean.

In other words, a multidecadal change in clouds and sunshine exists across this entire climate regime, extending back to the early 20th century.

Thus, it can be said that:

Higher (lower) cloud coverage results in lower (higher) sunshine intensity, lower (higher) evaporation of ocean water and slower (faster) THC over the North Atlantic Ocean.

The real conundrum is, why would Swiss Alps show ice mass loss, while evaporation rates are elevated over the North Atlantic region?

I will leave that question to the conclusions.

Figure 4 is from Martin Wild's 2017 paper that presented findings from a two decade surveillance study from 47 monitoring stations across Europe, which shows that the late winter, spring and early summer are where we find the largest increase in sunshine intensity over the 1983 to 2005 period.

I have extended this same seasonal analysis of the brightening of the winter and spring season using data from UK's Met Office and as shown in Figure 5 in the comparative plot of the undetrended AMO versus the normalized winters + spring sunshine hours, there has been a 30% increase in the amount of absorbed solar radiation in UK since the early 20th century.

In this time series, the smallest value is divided into all others, to emphasize the extend of brightening.

The positive coherence seen between the undetrended AMO and increasing solar radiation over UK strongly supports the idea that the cloud pattern changes over UK are contiguous across the North Atlantic basin.

Looping back around now to data (Figure 6) obtained from studies done specifically within the Swiss Alps, I bring to your attention the study done by D. Lachat et al from the century long Pyrheliometer measurements have been carried out at the Physikalisches-Meteorologisches Observatorium Davos from 1909 to present, which results in the longest stationary direct irradiance record worldwide (4).

Pyrheliometer measurements at stations like that conducted at Davos Switzerland, are intended to quantify the clear sky (cloud free) transmission of short wave length radiation (irradiance) through the entire atmosphere.

The underlying physics use the concept of transmission that follows directly from Lambert's law of extinction (5).

The theoretical upper limit (1,100 Watts / m^2) was defined by pure Rayleigh atmosphere and ozone attenuation, i.e., containing no water vapor or aerosols, at an elevation of 1,600 m.a.s. Lower limits (600 Watts / m^2) were calculated for different integrated water vapor contents derived as seasonal averages of GPS retrievals at Davos.

In essence, as the data coincides with cloud free conditions, any reflection of incoming short wave length radiation (irradiance) is thought to be due to reflection from nanoscopic aerosol particles.

Remember, nanoscopic aerosols function as nucleation sites for cloud droplets.

The higher their density in the troposphere, the greater the tendency towards cloud formation.

Figure 6 shows the seasonally detrended (i.e., 12 month rolling averaged) clear sky irradiance transmission time series, separated into cold and warm seasons, together with their first derivative time series.

This approach to data analysis is argued by the authors, to allow one to identify at which phase of the Seasonal Cycle are changes in tropospheric aerosols occurring, as well as allowing secular changes to be quantified over long intervals.

Figure 6 shows a multidecadal cycle in the cold months, of early 20th century brightening (higher transmission) that peaked in 1940, followed by a decadal dimming that reached a minimum in the 1970s and a return to brightening in the 1980s to the early 2000s.

The authors argue that no clear trend is seen in the warmer months data.

I took the liberty in adding the text to highlight that when the first derivatives of the seasonally detrended transmission time series is positive, it correlated to periods of decadal warming and higher sunshine hours and conversely for periods where the first derivatives are negative.

Conclusion

In conclusion to this study, long term pyrheliometer data from Davos shows that there are fundamental changes occurring, within the colder months of the seasonal cycle, which are giving rise to a multidecadal variation in the density of cloud nucleation aerosols over central Europe.

While many have argued that the Dimming that occurred between the 1940s to the 1970s was driven at first order by increasing pollution aerosol forming emissions (e.g., NOx, SO2), that reversed after the 1980s, this hypothesis ignores the clear Brightening that occurred in the first 40 years of the Davos Switzerland pyrheliometer record.

Instead, I argue that the multidecadal cycle seen in the cold season clear sky transmission data at Davos is part of a much larger hemispheric to global phenomenon that is not just natural, but more than likely is of extraterrestrial origin (i.e., solar system scale processes).

I am of the school of thought that multidecadal modulation of the solar system's magnetosphere (heliosphere), gives rise to changes in the intensity of ionizing cosmic radiation that reached the lower troposphere. In this model, ionization of atmospheric gases by high energy cosmic radiation, functions as aerosol nucleation events and thus acts as seed particles for cloud formation.

A case in point of this established hypothesis in the literature is shown by Nicolas Scaffeta's study (Figure 7) that showed that Northern Hemisphere's auroral records follows a similar multidecadal cycle to the AMO and to cold season atmospheric transmission records at Davos Switzerland. Scaffeta likewise shows that this multidecadal pattern is even observed in the detrended global air temperature anomaly time series.

Note the peak cycles centered around 1940 and 2000.

Scaffeta likewise argues that the multidecadal migration of the solar system's barycenter (center of gravity) is the driving force behind the Sun's magnetospheric control over the auroral intensity cycle seen throughout the 20th century.

This shifting barycenter is driven by gravitational tidal forces of the Gas Giants acting on the Sun's magnetic field generator (internal dynamo), similar to the role of Jupiter's 11 year orbital path around the Sun in modulating the Sun's 11-year Schwab Cycle (6).

This hypothesis suggests that long term changing gravitational tidal forces of the Gas Giants on Sun's internal dynamo acts to modulate both its solar eruptions and large scale heliosphere, where the latter controls the intensity (frequency) of cosmic rays and the Aurora Borealis events.

In closing, I will remind people that snow accumulation in the Swiss Alps will be reduced by higher solar irradiance (transmission) as it has been shown recently that short wavelength radiation can cause water to evaporate without the need for heat (phot-molecular effect). This photo-molecular effect (7) may explain why Swiss Alps glacial mass is seen to decline with higher SSTs across the North Atlantic (Figure 1) and why it shows a negative correlation with the AMO.

Reference:

1. https://planetski.eu/2022/10/02/full-extent-of-summer-swiss-glacier-melt-revealed/
2. https://www.researchgate.net/publication/381006006_Recent_global_temperature_surge_amplified_by_record-low_planetary_albedo
3. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2010GL042616
4. https://boris.unibe.ch/117795/1/704_2012_Article_685.pdf
5. https://reef.atmos.colostate.edu/~odell/AT622/stephens_notes/AT622_section09.pdf
6. https://www.space.com/planets-affect-solar-cycle.html
7. https://news.mit.edu/2024/how-light-can-vaporize-water-without-heat-0423