The group of scientists from the Syracuse University in New York state, led by geochemist Zunli Lu, found that the period known as the "Medieval Warm Period"
occurred about 500 to 1,000 years ago and was not limited only to Europe as previously thought, but covered almost the entire world, including the Antarctica.
The significance of their work, as Daily Mail
points out, is that the world has experienced global warming in the past, even in the absence of the current CO2 emissions that many scientists have blamed for the current pattern of global warming.
The consensus among scientists that the Earth is warming up due to CO2 emission, according to The Register
, comes largely from the work of Michael Mann and Phil Jones, with its conclusions upheld by the IPCC. The Intergovernmental Panel on Climate Change (IPCC)
says that the Medieval Warm Period was only in Europe and that, therefore, the global warming we are experiencing now is caused by greenhouse gases emitted by man's industrial activities.
reports that the U.S. Environmental Protection Agency
cautiously aligns with the IPCC view that the Medieval Warm Period was a local anomaly. EPA says temperatures have been relatively stable in the last 2,000 years apart from the periods of the Little Ice Age
and what it terms the "Medieval Climate Anomaly," that is, the Medieval Warming Period, and now finally the temperature increase of the Industrial Era
believed to be caused by greenhouse gas emissions
. According to The Blaze
, EPA acknowledges the fact of the Medieval Warm Period but says that “the geographical extent, magnitude and timing of the warmth during this period is uncertain.”
But in their study recently published online in the journal Earth and Planetary Science Letters
, and titled "An Ikaite record of late Holocene climate at the Antarctic Peninsula,"
Professor Lu and his colleagues argue that there is evidence that the Medieval Warm Period was a global phenomenon. According to Lu, the clinching evidence that the Medieval Warm Period was global comes from study of the rare mineral ikaite which is formed in cold waters. According to The Register
, Lu described ikaite as "an icy version of limestone. The crystals are only stable under cold conditions and actually melt at room temperature.”
reports that the researchers, in their study, showed that ikaite is a reliable way to study past conditions of the Earth's climate. Studies of the rare mineral derived from sediment cores off the coast of Antarctica deposited over 2,000 years ago includes those deposited in the so-called "Little Ice Age" about 300 to 500 years ago. The Little Ice Age occurred after the Medieval Warm Period. Previous studies have documented both the Medieval Warm Period and the Little Ice Age in Northern Europe but it was never established with certainty that the conditions extended beyond Northern Europe.
Lu and his colleagues explain that hydration water that holds the crystal structure of this rare mineral together can give clues about temperature levels at the time when the crystals were formed. According to a Syracuse University release
: "Ikaite crystals incorporate ocean bottom water into their structure as they form. During cooling periods, when ice sheets are expanding, ocean bottom water accumulates heavy oxygen isotopes (oxygen 18). When glaciers melt, fresh water, enriched in light oxygen isotopes (oxygen 16), mixes with the bottom water. The scientists analyzed the ratio of the oxygen isotopes in the hydration water and in the calcium carbonate. They compared the results with climate conditions established in Northern Europe across a 2,000-year time frame. They found a direct correlation between the rise and fall of oxygen 18 in the crystals and the documented warming and cooling periods."
In other words, the team looked at the amount of heavy oxygen isotopes found in the crystals and found that during cool periods there were high concentrations of the isotopes and during warm periods there were low concentrations of the isotopes. Using the evidence from levels of heavy oxygen isotopes in the crystals from the Antarctica, Lu and his colleagues were able to show that the Medieval Warm Period was a global phenomenon.
reports Lu said: "We showed that the Northern European climate events influenced climate conditions in Antarctica. More importantly, we are extremely happy to figure out how to get a climate signal out of this peculiar mineral. A new proxy is always welcome when studying past climate changes."
The importance of showing that the Medieval Warm Period was a global phenomenon rests on the fact that a major debate in the global warming controversy is that the Medieval Warm Period and Little Ice Age were only regional. The Medieval Warm Period occurred approximately between 900 AD and 1250 AD and according to scientists temperature levels during this period were as high as what we are now experiencing. Evidence that the phenomenon was global would, of course, call the current global warming theories based on effects of CO2 concentrations into question and suggest that global warming is a natural process that occurs periodically.
Tim Worstall points out a subtle fact that opponents of the current theories of global warming will miss, the fact that while global warming might have occurred in the past, a new complicating factor has been introduced into the phenomenon in the Industrial Era, and that is rising CO2 levels. The Register
notes that the present CO2 levels in the atmosphere is 0.04 per cent "and may climb to 0.07 per cent in the medium term." These are projections of significant changes in CO2 levels which complicate the simpler picture of what happened in the medieval. It is too early to say with certainty that the present pattern of climate change will behave exactly as it did in the medieval when global warming gave way to a "mini ice age." Lu's findings suggests the need to build new models of climate change which incorporate the new findings that global warming may occur independent of industrial emissions and then attempt to predict the impact of greenhouse gas emissions on the current trend we are witnessing.