Here we go again. Regular readers will remember that a couple of weeks ago Christopher Columbus was being blamed for the Little Ice Age (AD 1300 to 1850). Now, a new computer "study" announced that volcanoes caused the Little Ice Age! A research team led by Gifford Miller of the University of Colorado says eruptions of four volcanoes just before AD 1300 spewed huge amounts of sulphates into the air, which cooled the Arctic and "grew" the Arctic ice sheets and glaciers.
I find a few problems with this "news," starting with the reality that the Little Ice Age lasted about 550 years! How do volcanic eruptions--even from four very big volcanoes--throw up enough space dust to cool the planet for five centuries!? Two years, certainly, perhaps even ten years for an awesome eruption such as Krakatoa in 1883--but not 500. Climate historian Hubert Lamb notes that "in 1783, when there were two very great eruptions--in Iceland and in Japan--in the same year, the combined effect may have been a cooling of the northern hemisphere by 1.3 degrees C, gradually tailing away to zero over the following four or five years."
My second problem is that Dr Miller doesn't know which volcanoes erupted! His team suspects the spewing mountains were in the tropics. Their global computer model told them that the Little Ice Age must have been touched off by volcanic eruptions. So, even though they haven't found the culprit mountains, we are expected to accept the theory. These are the global climate models that have already predicted far more global warming than we've gotten, and whose programmers forgot to put in the Medieval Warming. Now they're inventing volcanic eruptions whose residues have not been found in the volcanic sediment record.
Third, how do we explain the hundreds of previous "little ice ages" found in the seabed sediments from the past million years? Those cycles have also been confirmed from ice cores, boreholes, fossil pollen and glacier cycling. How do volcanoes explain cyclical events, which have a 79 percent correlation with the sunspot cycles?
How does Dr. Miller explain the archaeology and sediment records that show what's now Iraq has been through seven "little ice ages" over the past 5500 years? Each time, the abrupt climate change started with a 300-year drought, not with any known big volcanic eruption. Egypt went through six famine collapses, at the same times as the awful Iraq droughts. Egyptians were recorded at the time as eating their own children! This all happened because the tropic rain belts shift 500 miles north and south during the 1,500-year cycles, with often-disastrous results.
The evidence shows it's the sun, not volcanoes that have caused the "little ice ages." The real trick now is to predict the onset of the next "little ice age" enough in advance to stock up on grain and long underwear. That next intense cold period is when we'll find out firsthand why we should appreciate our current "global warming." Human numbers tripled during the Medieval Warming; then half of that expanded population died in the famines and disease epidemics of the Little Ice Age.
The 1,500-year cycle has been extremely regular during the big Ice Ages, at roughly 1470 years. During the warm periods like our Holocene, it is less regular, but has still dominated our climate. The Medieval Warming lasted only 350 years, while the Roman Warming lasted 800 years. We can't predict accurately yet when the next "little ice age" will arrive, but there is no question that it will be a real test of sustainability for human societies. Or we may get the next full Ice Age. I wonder which volcano will cause that.