9 November 2015

The 700 Year Old Weather Chart That Gives Me Butterflies

Posted by Dan Satterfield

Those buried under Englands greens foliage can no longer tell their stories of ancient tragedy but there are still some trees above them that remember. (Dan's pic St. Mawes, in Cornwall UK.

Those buried under England’s greens foliage can no longer tell their stories of ancient tragedy but there are still some trees above them that remember. (Dan’s pic St. Mawes, in Cornwall UK.

A group of researchers (from over three dozen institutions!) has published a paper in SCIENCE ADVANCES that’s pretty amazing. They used tree ring analysis to reconstruct the summer rainfall maps on a year by year basis for over 1000 years in the past! It’s called the Old World Drought Atlas (OWDA) and it’s based on our modern Palmer Drought Index. If you think this is hoe-hum, then you don’t get it. Read on and you will…

Remember reading about the great famine of 1315 in your history books? You may remember vaguely that It was caused not by drought, but too much rain. It rained, and it rained and it kept raining until the fields turned to mud, which led to massive crop failures, and a deadly famine. A famine so bad that millions starved to death. People turned to cannibalism, and it was a famine that spread across all of Western Europe. It wasn’t something that those who survived it ever forgot. Think your grandmother had a great memory of the Depression in the 1930’s? Yes mine certainly did, and told me many a story, but they did not starve to death This was far worse than that, and the black memories of those years lived through the generations and long enough to be written down in the history books we read in Junior High.

Look at the map below.

There it is. Bottom right.

Screen Shot 2015-11-08 at 11.45.41 PMIs it just me, or does this give you the willies? It’s like looking at that big high pressure over the NW Atlantic on the night of April 14,1912. The Titanic survivors reported the ocean as still as a mill-pond, and I have the surface weather map that proves they were right. That’s how I feel about these rainfall charts. That horrible famine was seven long centuries ago, but the trees still remember, and they tell us that those old faded pieces of parchment were not exaggerating. It was real, and it left millions dead, and millions more in grief.

Oh, and look at 1741, and the terrible drought. The trees are showing the results of the cold and dry spell that began in 1739. This is the year of the great Irish famine, and it killed millions as well. Here’s what the paper has to say about the 1741 map:

The Irish famine of 1740–1741: This event has been attributed to unusually low winter and spring temperatures in 1740, resulting in crop failures and subsequent famine (17). The OWDA is not well suited for determining temperature anomalies because it primarily reflects warm season hydroclimate. However, climate field reconstructions of seasonal precipitation from documentary and early instrumental data (18) indicate that spring-summer rainfall over Ireland in 1741 was well below normal relative to the modern average. Drought over Ireland may therefore have contributed to the severity of the famine through its negative impact on food production in 1741. The OWDA map of 1741  indicates severe drought over Ireland that also extended over England and Wales, consistent with previously reported record rainfall deficits.

This Old World Drought Atlas will have great benefits in climate research, and historians will find them invaluable as well, but they also give us a warning. Our limited 100 years or so of written weather records can be deceiving. We think we know what a bad crop year is, and how long a bad drought can last, but our lifetimes are rather short, and perhaps we are fools. Knowing this makes fooling with our planet’s temperature control even more egregious.

The paper is open access and you can read it all HERE.