Based on arduous analyses of the deep-sea sediment cores that yielded the variable-with-depth amounts of three proven proxies for the prior presence of overlying drift-ice, the scientists were able to discern and, with the help of an accelerator mass spectrometer, date a number of recurring alternate periods of relative cold and warmth that wended their way through the entire 12,000-year expanse of the Holocene.  The mean duration of the several complete climatic cycles thus delineated was 1340 years, the cold and warm nodes of the latter of which oscillations, in the words of Bond et al., were "broadly correlative with the so called 'Little Ice Age' and 'Medieval Warm Period'."

The signal accomplishment of the scientists' study was the linking of these millennial-scale climate oscillations - and their imbedded centennial-scale oscillations - with similar-scale oscillations in cosmogenic nuclide production, which are known to be driven by contemporaneous oscillations in the energy output of the sun.  In fact, Bond et al. were able to report that "over the last 12,000 years virtually every centennial time-scale increase in drift ice documented in our North Atlantic records was tied to a solar minimum."  In light of this observation they concluded that "a solar influence on climate of the magnitude and consistency implied by our evidence could not have been confined to the North Atlantic," suggesting that the cyclical climatic effects of the variable solar inferno are experienced throughout the world.

At this point of their paper, the international team of scientists had pretty much verified a number of things we have regularly reported on our website over the past several years, i.e., that in spite of the contrary claims of a host of climate alarmists, the Little Ice Age and Medieval Warm Period were (1) real, (2) global, (3) solar-induced, and (4) but the latest examples of uninterrupted alternating intervals of relative cold and warmth that stretch back in time through glacial and interglacial periods alike.  [For more information on topics 1-3, see Little Ice Age and Medieval Warm Period in our Subject Index; for additional material on topic 3, see Solar Effects (Climate); for information on topic 4, see Climate Oscillations.]

Because these several subjects are of such great significance, particularly to the global warming debate that currently rages over the climate model-predicted consequences of anthropogenic CO2 emissions, Bond and his band of researchers went on to cite additional evidence in support of the implications of their work.  With respect to the global extent of the climatic impact of the solar radiation variations they detected (topics 2 and 3 above, with 1 implied), they made explicit reference to confirmatory studies conducted in Scandinavia, Greenland, the Netherlands, the Faroe Islands, Oman, the Sargasso Sea, coastal West Africa, the Cariaco Basin, equatorial East Africa, and the Yucatan Peninsula, demonstrating thereby that "the footprint of the solar impact on climate we have documented extend[s] from polar to tropical latitudes."  Also in support of topic 3, they noted that "the solar-climate links implied by our record are so dominant over the last 12,000 years ... it seems almost certain that the well-documented connection between the Maunder solar minimum and the coldest decades of the LIA could not have been a coincidence," further noting that their findings support previous suggestions that both the Little Ice Age and Medieval Warm Period "may have been partly or entirely linked to changes in solar irradiance."

Another point reiterated by Bond et al. is that the oscillations in drift-ice they studied "persist across the glacial termination and well into the last glaciation, suggesting that the cycle is a pervasive feature of the climate system."  At two of their coring sites, in fact, they identified a series of such cyclical variations that extended throughout all of the previous interglacial and were "strikingly similar to those of the Holocene."  Here they could also well have cited the work of Oppo et al. (1998), who observed similar climatic oscillations in a sediment core that covered the span of time from 340,000 to 500,000 years before present, and that of Raymo et al. (1998), who pushed back the time of the cycles' earliest known occurrence to well over one million years ago.

So how do the small changes in solar radiation inferred from the cosmogenic nuclide variations bring about such significant and pervasive shifts in earth's global climate?  In answer to this question, which has long plagued proponents of a solar-climate link, Bond et al. describe a scenario whereby solar-induced changes high in the stratosphere are propagated downward through the atmosphere to the earth's surface, where they likely provoke changes in North Atlantic Deep Water formation that alter the global Thermohaline Circulation.  In light of the plausibility of this scenario, they suggest that "the solar signals thus may have been transmitted through the deep ocean as well as through the atmosphere, further contributing to their amplification and global imprint."

Concluding their landmark paper, the authors say the results of their study "demonstrate that the earth's climate system is highly sensitive to extremely weak perturbations in the sun's energy output," noting that their work "supports the presumption that solar variability will continue to influence climate in the future."  It is readily evident, therefore, that the study of Bond et al. provides ample ammunition for defending the premise that the global warming of the past century or so may well have been nothing more than the solar-mediated recovery of the earth from the chilly conditions of the most recent Little Ice Age, and that any further warming of the planet that might occur would likely be nothing more than a continuation of the same solar-mediated cycle that is destined to usher the globe into the next Medieval-like or Modern Warm Period.  Consequently, since there's plenty of precedence for this scenario - it's happened over and over for more than a million years - and none for a warming of the planet as a consequence of atmospheric CO2 enrichment (see CO2-Temperature Correlations in our Subject Index), it would seem the height of folly to implement any energy policy that would restrict anthropogenic CO2 emissions for the avowed purpose of attempting to prevent future global warming.  It's not CO2 that's been causing the earth to warm.  It's the sun!

References
Bond, G., Kromer, B., Beer, J., Muscheler, R., Evans, M.N., Showers, W., Hoffmann, S., Lotti-Bond, R., Hajdas, I. and Bonani, G.  2001.  Persistent solar influence on North Atlantic climate during the Holocene.  Science 294: 2130-2136.

Oppo, D.W., McManus, J.F. and Cullen, J.L.  1998.  Abrupt climate events 500,000 to 340,000 years ago: Evidence from subpolar North Atlantic sediments.  Science 279: 1335-1338.

Raymo, M.E., Ganley, K., Carter, S., Oppo, D.W. and McManus, J.  1998.  Millennial-scale climate instability during the early Pleistocene epoch.  Nature 392: 699-702.