There has been one new paper about climate in the past week that caught my attention (the Gleick story did catch my attention, but I am passing on it). The collapse of the Mayan civilization 1000 years ago is now being tied to climate change. Most news isn’t making the direct argument that global warming was the cause, but there is at least one newspaper that raises the speculation that global warming caused the downfall of the Mayans. Normally silly things like this get ignored, but I found a couple of genuinely interesting things buried under the propaganda.
The Mayan civilization was the most technically advanced in the America’s prior to European colonization. They are perhaps best known for their very accurate calendar which flips over later this year. While there is a common perception that the calendar ends this year, it really operates more like a car odometer and it simply “flips” over this year. Such flips take place every ~400 years. The big calendar flip takes place in ~2700 years.
The high point of the Maya was from 250 to 900 AD. This is when most of the large construction and the greatest extend of their urbanization occurred. It was during this period that their society optimized their farming and food production to sustain a large non-farming population. All such urban societies require an efficient system of farming, storage and transportation to maintain an urban population. That they were able to maintain such a civilization for > 600 years is impressive, especially when considering that the modern industrial civilization is at best 300 years old now.
It has long been theorized that an extended drought is what caused their downfall. An article in Science published in 2001 discusses a 200 year variation in solar output that triggered an extended drought that lasted from 750 to 850 AD. Such a drought would have disrupted the highly optimized food system that was needed to sustain the urban populations that the Maya had up till that point. While a 7,000 year record of that region shows many droughts, it was the one from 750 to 850 AD that was the largest drought.
The new article that ties global warming to the fall of the Mayans is along the same line of thought that it was a drought caused the collapse. This raises the obvious question of how in the world did global warming cause the drought? Obviously 800 AD is part of the pre-industrial era when the CO2 level was < 300ppm, which means that there was no global warming at the time. So how does this tie in?
Enter the straw man. From the mostly good article here:
The scientists noted that the droughts they saw during the demise of the ancient Mayan civilization were similar in severity to those projected by the Intergovernmental Panel on Climate Change (IPCC) for the near future in the same region. [10 Surprising Results of Global Warming]
“There are differences too, but the warning is clear — what seems like a minor reduction in water availability may lead to important, long-lasting problems,” Medina-Elizalde said. “This problem is not unique to the Yucatan Peninsula, but applies to all regions in similar settings where evaporation is high. Today, we have the benefit of awareness, and we should act accordingly.”
What they are in fact saying, is that global warming will cause the Earth to behave in the same way that it did 1,000 years ago when the CO2 level was < 300 ppm. Both the article from 2001 and 2012 both state that there have been many periods of extensive droughts in that region of the world, but the new one goes onto say that when they happen in the future, they won’t be natural because that is what the IPCC said would happen.
The actual information that serious droughts and climate shifts have happened recently while CO2 was low and stable perfectly fits in with the natural cycles that the Earth experiences. None of this is a surprise to me. Far more important to me is the idea that what got the Mayan civilization into trouble was a disruption in the “average” climate. That anomaly from average was sufficient to disrupt their supply chain enough to cause their civilization to collapse.
I make the point several times in my book that world today is even more delicately balanced. While our resources are vastly larger and our ability to adjust is much, much higher. So are the demands for food. In the future there will be large changes to the Earth’s climate. A failure of 50% of the world’s food crops for decades on end would be beyond catastrophic for the much of the world today. The real problem is not CO2, but our foolish idea that the Earth will stay the way that it is today. That same idea is what brought down one of the most advanced civilizations in history.
Federico has a good point. The calendar that gets attributed to the Mayan is not their calendar. It seems that I am not the only one that makes this mistake. There is a lot of weirdness with the Mayan Calendar which ends up generating lots of bad information. Hopefully I got it right this time.