The Physical Evidence of Earth's Unstoppable 1,500-Year Climate Cycle
Friday, September 30, 2005
by S. Fred Singer & Dennis T. Avery
Table of Contents
The Ice Cores
In the 1980s scientists got the first unequivocal evidence of a continuing, moderate natural climate cycle.The 1,500-year climate cycle emerged almost full-blown from Greenland in 1983.
Denmark’s Willi Dansgaard and Switzerland’s Hans Oeschger were among the first people in the world to see two mile-long ice cores that brought up 250,000 years of the Earth’s frozen, layered climate history. Over the previous dozen years, the two researchers had pioneered ways to pry information from the ice cores. They had learned, among other things, that the ratio of oxygen-18 isotopes to oxygen-16 isotopes in ice could reveal the air temperature at the time when the snowflakes that made the ice fell to earth. The correspondence of the change in the isotope ratios to the recent Medieval Warming Period (MWP) and Little Ice Age (LIA) is shown in Figure II.3
Dansgaard and Oeschger expected to see the big 90,000-year Ice Ages in the cores, and they did. But they were startled to find, superimposed on the big Ice Age swings, a smaller, moderate and more persistent temperature cycle. They estimated the average cycle length at 2,550 years. They dismissed volcanoes as a causal factor because there’s no such cycle in volcanic activity. The timing of the cycles seemed to match closely with the known history of recent glacier advances and retreats in northern Europe.
The report that Dansgaard and Oeschger wrote in 1984, “North Atlantic Climatic Oscillations Revealed by Deep Greenland Ice Cores,” was, in retrospect, almost eerie in its accuracy, its completeness and its logical linking of the climate cycles to the sun.4 The only major correction imposed by subsequent research is that the cycles were more frequent than they thought. The average length of the cycles has now been shortened by almost half — from their original estimate of 2,550 years to 1,500 years (plus or minus 500 years).
"Ice cores from Antarctica show the same climate cycle."
Dansgaard and Oeschger were correct when they told us that the climate shifts were moderate, rising and falling over a range of about 4°C in northern Greenland, with very little temperature change at the equator — and only half a degree when averaged over the northern hemisphere.
The cycles were confirmed by 1) their appearance in two different ice cores drilled more than 1,000 miles apart; 2) their correlation with known glacier advances and retreats in northern Europe; and 3) independent data in a seabed sediment core from the Atlantic Ocean west of Ireland.5
They noted that the cycle shifts were abrupt, sometimes gaining half of their eventual temperature change in a decade or so. That suggested an external forcing, perhaps amplified and transmitted globally by the ocean currents and winds. (In the mid-19th century, the Upper Fremont Glacier in Wyoming went from Little Ice Age to Modern Warming in about 10 years.6 That implies a climate driver from outside our planet, almost certainly involving the sun.)
However, Dansgaard and Oeschger noted, “Since the solar radiation is the only important input of energy to the climatic system, it is most obvious to seek an explanation in solar processes. Unfortunately we know much less about the solar radiation output than about the emission of solar particulate matter in the past.”
The two scientists did know, however, that both carbon-14 and beryllium-10 isotopes vary inversely with the strength of the solar activator. The isotopes of both elements in their Greenland ice cores showed historic temperature lows during what solar scientists term the Maunder sunspot minimum (1645–1715) — the absolute coldest point of the Little Ice Age and a period when sunspots virtually disappeared.
"Climate cycles coincide with sunspots and variations in solar energy output."
Today, we can measure variations in the sun’s irradiance from satellites out beyond the obscuring atmosphere of our own planet. The solar constant isn’t — constant, that is. We also know that when the sun is less active, its solar wind weakens and provides less shielding for the Earth from the cosmic rays that bounce around space. With a weaker sun, more of the cosmic rays hit the Earth, creating more charged particles in the atmosphere, which then become low, wet clouds reflecting more heat back into space. A less active sun thus means a cooler Earth.7
The importance of the 1,500-year cycles found in the Greenland ice cores increased dramatically four years later when they were also found at the other end of the world — in an ice core from the Antarctic’s Vostok Glacier. The Vostok ice core went back 400,000 years, and showed the 1,500-year cycle through its whole length.8
The scientific world had known about the sunspot connection to Earth’s climate for some 400 years. British astronomer William Herschel claimed in 1801 that he could forecast wheat prices by sunspot numbers, because wheat crops were often poor when sunspots (and thus solar activity) were low. Not only did the Maunder minimum (1645-1715) coincide with the coldest period of the Little Ice Age, the Sporer minimum (1450–1543) aligned with the second-coldest phase of that period.
In 1991, Eigel Friis-Christensen and Knud Lassen noted that the correlation between solar activity and Earth temperatures is even stronger if we use the length of the solar cycle to represent the sun’s variations instead of the number of sunspots.9 (The solar cycles average about 11 years in length, but actually vary between eight and 14 years.) Their paper in Science concluded that the solar connection explained 75 to 85 percent of recent climate variation.