Earth's Climate Follows The Sun's UV Groove
That large changes in solar radiation can affect Earth's climate is widely accepted. However, the hypothesis of solar-induced centennial to decadal climate changes, which suggests feedback mechanisms in the climate system amplifying even small solar variations, has not found acceptance among orthodox climate scientists. The climate change clique would rather place their money on greenhouse gasses—human generated CO2 in particular. It is true that satellite-based measurements of total solar irradiance show that mean variations during solar cycles do not exceed 0.2 W m−2 (~ 0.1% of the Sun's energy output). It has also been noted that relatively large variations of 5–8% in the ultraviolet (UV) frequencies can occur, though how this could change global climate remained a puzzlement—but perhaps no longer. From studying a significant climate shift 2,800 years ago, a group of scientists have concluded that large changes in solar UV radiation can, indeed, affect climate by inducing atmospheric changes.
Ask a rational and scientifically literate person what might be the primary cause of climate change and they would be well justified in pointing out the large bright object that passes overhead daily. Humanity noticed that warmth came from the Sun long before it started keeping written records. A number of primitive cultures even worshiped the Sun as a deity. Fittingly, the Sun's possible influence on climate has not been ignored (see “Atmospheric Solar Heat Amplifier Discovered”). Climate scientists, however, have been loath to grant the local star primacy of place, at least when it comes to relatively short term climate variation.
It has been suggested by several scientists that centennial-scale climate variability during the Holocene epoch has been controlled by the Sun. While this sounds reasonable the problem has always been that the amplitude of solar forcing is small when compared with the climatic effects. Satellite measurements taken at the top of Earth's atmosphere indicate that observed solar fluctuations amount to less than 1/10th of a percent of total irradiance, though the data are limited and not reliable beyond the past 30 years or so. Without more extensive and reliable data, it is unclear which feedback mechanisms could have amplified the influence. That situation may have recently changed.
As reported in Nature Geosciences, “Regional atmospheric circulation shifts induced by a grand solar minimum,” Celia Martin-Puertas et al. took a meticulous look at annual sediment deposits in a German lake from 3,300 to 2,000 years ago. They analyzed the sediment layers—called varve—carefully measuring proxies for solar irradiance. This is what they found and their major conclusion:
Here we analyse annually laminated sediments of Lake Meerfelder Maar, Germany, to derive variations in wind strength and the rate of 10Be accumulation, a proxy for solar activity, from 3,300 to 2,000 years before present. We find a sharp increase in windiness and cosmogenic 10Be deposition 2,759 ± 39 varve years before present and a reduction in both entities 199 ± 9 annual layers later. We infer that the atmospheric circulation reacted abruptly and in phase with the solar minimum. A shift in atmospheric circulation in response to changes in solar activity is broadly consistent with atmospheric circulation patterns in long-term climate model simulations, and in reanalysis data that assimilate observations from recent solar minima into a climate model. We conclude that changes in atmospheric circulation amplified the solar signal and caused abrupt climate change about 2,800 years ago, coincident with a grand solar minimum.
The methodology involved employed a number of proxy sources aside from counting layers of sediment. 10Be is a so called cosmogenic radionuclide, an isotope of beryllium who's abundance is regulated by incoming cosmic radiation. Since the level of solar activity regulates the amount of incoming cosmic radiation, 10Be can be used as a gauge of the Sun's activity in times gone by.
“A less active Sun implies high cosmogenic radionuclide production rates in the atmosphere related to weaker shielding against galactic cosmic ray fluxes,” the authors state, “thus, the steep increase in 14C content of the atmosphere from 2,800–2,650 cal yr BP and the rise in the cosmogenic radionuclide 10Be flux archived in Greenland ice cores both point to a long-term (centennial) solar minimum from about 2,750–2,550 cal yr BP known as the Homeric minimum.”
What they were looking for were indications of “top-down” mechanisms that could translate long-term solar fluctuations into changes in climate. To accomplish this required very accurate dating, along with high resolution proxy readings for temperature and precipitation. Then they added in data for other climate parameters such as wind strength. An illustration of some of the measurements used in the study are shown below:
Lake Meerfelder Maar proxy data.
The methodology used here is not new or groundbreaking, but the conclusion the investigators reached is: they suggest a link between UV variability and atmospheric conditions. The report notes that significant shifts at the 200–300 nm (ie UV) part of the solar emission spectrum can have significant effects on heating and ozone chemistry in the middle atmosphere. This can induce indirect dynamical effects in the atmosphere down to the Earth’s surface and that could affect climate. Specifically:
This acts through disturbances of the stratospheric polar vortex that propagate by means of wave–mean flow interactions downwards, influence the tropospheric jet streams, which are connected to the Arctic Oscillation/North Atlantic Oscillation at Northern Hemisphere mid-latitudes and affect European winter variability. Other mechanisms for solar influence on climate concern the role of energetic particles from the Sun or galactic cosmic rays, but they are energetically smaller and their climate impact is much less understood than the mechanisms connected to electromagnetic radiation.
Anyone in the US who experienced this past winter's mild temperatures and is now suffering through the Midwest's sweltering summer can attest to the influence of upper-level air currents like the jet stream. The same can be said for the record cold in some parts of eastern Europe, a weather pattern blamed on the Arctic Oscillation and North Atlantic Oscillation being stuck in their plus phases. This winter’s AO/NAO pattern stands in stark contrast to what occurred the previous two winters, when we had the most extreme December jet stream patterns on record, caused by a strongly negative AO/NAO. The negative AO conditions suppressed westerly winds over the North Atlantic, allowing Arctic air to spill southwards into eastern North America and Western Europe, bringing unusually cold and snowy conditions.
“Climate models are generally too crude to make skillful predictions on how human-caused climate change may be affecting the AO, or what might happen to the AO in the future,” states Dr. Jeff Master on his WunderBlog. “There is research linking an increase in solar activity and sunspots with the positive phase of the AO. Solar activity has increased sharply this winter compared to the past two winters, so perhaps we have seen a strong solar influence on the winter AO the past three winters.”
Even NASA—at least the part not filled with climate change doomsayers like James Hansen—recognizes that UV radiation can have a big impact on the upper atmosphere. The National Center for Atmospheric Research (NCAR) in Boulder, Colorado, put out a NASA funded report that implicated solar UV radiation in expanding and contracting the upper atmosphere, possibly hastening the decay of satellite orbits.
As background, Martin-Puertas et al. cite an earlier paper by Sarah Ineson et al., “Solar forcing of winter climate variability in the Northern Hemisphere,” also published in Nature Geoscience. In that paper it was proposed that solar UV variation contributes a substantial fraction of typical year-to-year variations in near-surface circulation, with shifts of up to 50% of the interannual variability. That report concluded:
Our result has important implications for regional climate prediction in the northern extratropics. Fluctuations in the NAO often dominate the seasonal and decadal winter climate but its predictability on seasonal and decadal timescales is low. If the recent satellite data are typical of the variation in ultraviolet fluxes in other solar cycles then our results suggest shifts in the NAO of a sizeable fraction of the interannual variability. Given the quasiregularity of the 11-year solar cycle, our results therefore suggest significant decadal predictability in the NAO.
Here is recent research by two independent groups of investigators that have suggested plausible mechanisms for variation in the Sun's ultraviolet radiation to affect climate. This should surprise no one who is aware of the Maunder Minimum and the corresponding Little Ice Age—a time of advancing mountain glaciers in the Alps, failed crops and cold weather around the world. It is generally agreed that there were three temperature minima, occurring around 1650, 1770, and 1850. Each minima separated by slight warming intervals. These periods coincide closely with times of solar inactivity, with some of the worst weather occurring squarely during the Maunder Minimum. Of course, this blog has reported on such findings before, but as usual, the warm-mongering climate alarmists have ignored these data.
A NASA video of the Sun in UV—this is what changes Earth's climate.
Science has linked UV radiation to both decadal and century long timescales, yet the climate science establishment continues to pursue GHG emissions as the primary cause for recent climate change. It should be noted that not knowing the precise mechanisms by which GHG emissions amplify the Sun's power to cause global warming has not silenced the climate change alarmists. Lack of linkage has in no way diminished the shrillness or fervor with which they trumpet their unsubstantiated claims. We now know that the Sun calls the tune for earthly climate change, so the eco-extremist crowd can no longer blame global warming primarily on humans.
Let me emphasize the research paper's central conclusion: “changes in atmospheric circulation amplified the solar signal and caused abrupt climate change.” In other words, small changes in the Sun's output can and have driven rapid climate change in the recent past. Too bad for the warmists, because science has shown that Earth's climate does groove to the Sun's UV tune. No CO2 emissions need apply.
Be safe, enjoy the interglacial and stay skeptical.