The Daily Parker

Politics, Weather, Photography, and the Dog

New evidence of the Mayans' fate

Sediment under Lake Chichancanab on the Yucatan Peninsula has offered scientists a clearer view of what happened to the Mayan civilization:

Scientists have several theories about why the collapse happened, including deforestation, overpopulation and extreme drought. New research, published in Science Thursday, focuses on the drought and suggests, for the first time, how extreme it was.

[S]cientists found a 50 percent decrease in annual precipitation over more than 100 years, from 800 to 1,000 A.D. At times, the study shows, the decrease was as much as 70 percent.

The drought was previously known, but this study is the first to quantify the rainfall, relative humidity and evaporation at that time. It's also the first to combine multiple elemental analyses and modeling to determine the climate record during the Mayan civilization demise.

Many theories about the drought triggers exist, but there is no smoking gun some 1,000 years later. The drought coincides with the beginning of the Medieval Warm Period, thought to have been caused by a decrease in volcanic ash in the atmosphere and an increase in solar activity. Previous studies have shown that the Mayans’ deforestation may have also contributed. Deforestation tends to decrease the amount of moisture and destabilize the soil. Additional theories for the cause of the drought include changes to the atmospheric circulation and decline in tropical cyclone frequency, Evans said.

What this research has to do with the early 21st Century I'll leave as an exercise for the reader.

Mexican villages about to get destroyed by climate change

Hurricane Patricia, which will slam into the Mexican coastal villages of San Patricio and Barra de Navidad in just a few hours, is the strongest hurricane ever observed:

Packing 200 mph winds, the U.S. National Hurricane Center described Patricia as the "strongest hurricane on record" in the Atlantic and eastern North Pacific Basins.

At 8 a.m. ET, Patricia was about 230 km southwest of Manzanillo, and about 340 km south of Cabo Corrientes.

Hurricane warnings stretched from San Blas to Punta San Telmo, an area that includes Puerto Vallarta and Manzanillo. CONAGUA, the Mexican national water commission, predicted waves about 40 feet at landfall.

Up to 20 inches of rain was predicted for the Mexican states of Jalisco, Colima, Michoacan and Guerrero through Saturday, the NHC said.

The NHC estimates landfall this evening.

As for the climate-change aspect of the story, the Washington Post has it covered:

Certainly, record-breaking hurricanes raise questions about longstanding predictions that global warming, by raising ocean temperatures, should also strengthen these storms. The issue, however, is beset by data-related difficulties, since storm measurement techniques are continually improving (creating a kind of apples-and-oranges problem when comparing past strong storms with present ones) and are also highly variable around the world — thus, hurricane hunter flights are far more common in the Atlantic than in the Northeast Pacific, where Patricia formed.

Still, there have been widespread predictions that hurricanes should become stronger, on average, in a warmer world. Summarizing the current research, the Geophysical Fluid Dynamics Laboratory of the National Oceanic and Atmospheric Administration puts it this way: “Anthropogenic warming by the end of the 21st century will likely cause tropical cyclones globally to be more intense on average….This change would imply an even larger percentage increase in the destructive potential per storm, assuming no reduction in storm size.”

Yes, because it turns out, when you put energy into a system at a constant rate but decrease the rate that the energy can leave the system, the system has more energy. And half a century of dithering on climate-change policy has caught up with us.