Cross posted at The Examiner.com
For this green diary we'll take a trip back in time to a very different world. One-thousand years ago the seeds of bloody Crusade were being laid. Far across the Atlantic, the horse, so intimately associated with later paleo-indian cultures, had been absent for ten millennia and would not reappear in the North American wilderness for another 500 years. And in far northwest Europe, fierce and fearless Norse tribesmen were enjoying their golden age. But new evidence written in ancient lagoons suggest that that era had at least two things in common with our own: a warming climate and lots of hurricanes.
Research on ancient storms is one of climatology's newest ventures and one of the pioneers of this nascent field is Professor Michael Mann, co-creator of the paleo-climate record, better known as the Hockey Stick Graph. But how does a scientist go about detecting something as fleeting as an ancient hurricane that happened centuries ago, in what was then a remote wilderness with few witnesses and no written records?
"You look for storm debris," said Prof. Mann. "Distinctive sediments washed from beaches into coastal lagoons a little further inland, separated by dunes or distance or other features in the landscape which prevent normal waves from entering, but close enough that they're soaked by the powerful waves and storm surges produced by hurricanes at landfall. Then we compare that overwash data taken from the east coast, gulf coast, and the Caribbean -- gathered by my intrepid colleagues wading in mud and muck up to their armpits -- to estimates of variables at that time associated with modern cyclone activity today; like sea surface temperatures, El Nino's, and periodic changes in Atlantic."
Sounds simple in theory. In practice, it's dirty, messy, time consuming work and as much experience and instinct as science. Did that inland lagoon even exist a thousand years ago? Was the beach in the same place, has the coastline eroded since, has the sea level changed, or was there a short-lived barrier island or a series of sandbars in that spot at one time?
After all that has been addressed and samples collected with overwash in them, one result is the graph to the left. The green line represents overwash data gathered from as far north as Cape Cod and as far south as Puerto Rico (The blue line is an aggregate of cyclone conducive variables created by proxies). That sustained green hump beginning at about 1000 AD represents clear evidence that the tropical Atlantic experienced a measurable increase in the number of cyclones making landfall.
"No one is proposing that this increase in storm activity was produced by human activity a thousand years ago," explained Mann. "What it does help us understand is the relationship between warmer sea surface temperatures and other climate factors and intense hurricanes. The inference for us is it doesn't matter to hurricanes if those more conducive conditions arise from a so-called medieval warm period, or anthropogenic climate change driven by greenhouse gas emissions."
Understanding that inferred relationship is critical. Consider the northern hemisphere paleoclimate record for the last one-thousand years shown right. It's called the hockey stick because of that sharp rise at the right end where global temperatures surge. On that same graph, the medieval warm period is barely noticeable, a few gentle bumps at the far left, and even the sharp cooling trend known as the little ice age is a comparatively minor feature next to the dramatic modern uptick. Mann notes that the peak in tropical cyclone activity was the result of a 'perfect storm' of conditions which included not only a warm tropical Atlantic ocean, but a "La Nina" pattern in the tropical Pacific, also conducive to enhanced tropical cyclone activity. Nonetheless, the long-term relationship between tropical Atlantic sea surface temperatures and Atlantic tropical cyclone activity is fairly clear. And if those small bumps beginning in 1000 AD spell a warming period capable of producing an increase in tropical Atlantic cyclones so remarkable it can be detected a thousand years later, what might the business end of the stick spell for Atlantic storms in the 21st century?
A global change of just a fraction of a degree was amplified in the land of the midnight sun a thousand years ago and gave rise to a bold band of warriors and explorers the likes of which the planet had never seen. But the Vikings had no way to know their temperate medieval epoch was on the wane. Nor could they have done anything about if it they did. Soon the climate of northwest Europe snapped back with a vengeance. In the rugged fjords of Scandinavia, winter stretched longer and colder, summers came cool and short, crops failed, southern armies ganged up on the pirates, and the impressive Norse expansion -- which tiptoed across the edge of the Arctic Circle all the way to North America centuries before Columbus -- utterly collapsed.
Our global civilization was forged on that cooler world, and this modern economy is far more interdependent on all its parts than medieval Europe could ever be. Unlike the Vikings we have a choice. But if cooler heads don't prevail, or at least prepare, our civilization as we know it might soon face a climate threat far worse than the one that sunk the Norse. And if we don't deal with it, perhaps our civilization will one day join the fallen Einherjar in the pages of history. Maybe there's room for all of us in the Hall of Valhalla.
GreenRoots is a new environmental series created by Meteor Blades and Patriot Daily for Daily Kos. This series provides a forum for the discussion of all environmental issues, including the need for sustainability and the interrelationship between environment and salient issues of our lives, including health care, family, food, economy, jobs, labor, poverty, equal justice, human rights, political stability, national security and war.
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