New Evidence Suggests 'Medieval Warming Period' Was Global: Proof of Naturally-Occurring Global Warming?

• Research from Syracuse University has established another metric for analyzing historical climate conditions -- a rare mineral called ikaite.
• Ikaite exists in cold water but it melts at warmer conditions. 
• During warming and cooling periods oxygen-16 and oxygen-18, respectively, accumulate in the water and by studying these levels trapped in the crystals researchers can approximate climate conditions. 
• The Syracuse researchers found a direct correlation between a rise and fall in oxygen-18 isotopes in ikaite in both Greenland and Antarctica for a period known as the Medieval Warming Period, which was followed by a "little ice age."
• The Medieval Warming Period to some in the scientific community is held to be an isolated event in Europe and Greenland but this correlation may show it was global.
• If it was a global event, the evidence could suggest natural warming and cooling cycles. 

A new study from researchers at Syracuse University might call into question man-made global climate change as it is related to cyclical warming and cooling periods.

The study establishes a new, reliable metric for analyzing past climate conditions, and in doing so suggests that a period of warming once thought isolated to Europe, known as the Medieval Warming Period, may not have been so isolated after all. It may have been global.

Forbes provides some background on the Medieval Warming Period and why this study is important for today's climate science:

To give a little background: we know very well that Europe was as warm if not warmer than it is now some 800, 900 years ago. Grapes grew further north than they do now for example, Greenland (the warmth extended that far at least) could be used in part to grow wheat and so on. So many have been saying, well, if it was this warm or warmer before, what’s all the fuss about this climate change then?

The answer has always been, well, so far as we know that warming was local, not global, and now we’re having global warming which is a very different thing. This research brings that explanation into question.

According to the U.S. Environmental Protection Agency, the temperature of the last 2,000 years has been relatively stable aside from three events: the ice age, the "Medieval Climate Anomaly" (aka Medieval Warming Period) and the Industrial Era. EPA describes the "Medieval Climate Anomaly" as falling roughly between 900 and 1300 AD and with evidence suggesting Europe, Greenland and Asia experienced relative warmth. EPA does acknowledge historical accounts and other evidence that cite warmth occurring in other regions but states "the geographical extent, magnitude and timing of the warmth during this period is uncertain."

The research from Syracuse could help provide more certainty. The Syracuse press release states that the research, which will be published in the journal Earth and Planetary Science Letters, by geochemist Zunli Lu and his colleagues found ikaite, a rare mineral that exists in cold water, in both Antarctica and Greenland. What does this mean for climate change and the Medieval Warming Period? The release explains further:

"Ikaite is an icy version of limestone,” say Lu, assistant professor of earth sciences in SU’s College of Arts and Sciences. “The crystals are only stable under cold conditions and actually melt at room temperature.”

It turns out the water that holds the crystal structure together (called the hydration water) traps information about temperatures present when the crystals formed.

[...]

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.

“We showed that the Northern European climate events influenced climate conditions in Antarctica,” Lu says. “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.”

Forbes's Tim Worstall explains that this doesn't mean there is nothing to worry about in a warming climate. He states it is still uncertain how the higher recorded levels of carbon dioxide will affect the climate but notes that this study shows potential evidence of the warming "[stopping] of its own accord":

From which the takeaway point is that perhaps climate sensitivity is lower than currently thought and thus climate change is less dangerous than currently thought.

Although there’s one terribly important word we have to add here: maybe.

The Register points out that Lu's findings are contrary to the International Panel for Climate Change's current stance that the Medieval Warming Period was a localized event and that other areas globally were cooler. It is this thought that is used to help draw the correlation that warming data collected more recently is related to human activity.

[H/T Daily Mail]