The Medieval Climate Anomaly

                                          Marlin Turby, member from Dillsburg, PA

To declare that climate change is due from natural climate variability acknowledges that there is observed global warming and the consequent change in climate. Does it not? The argument therefore is not concerning global warming and climate change as a physical reality; rather, it is whether it is of natural or human (anthropocentric) origin?

For each side of the argument the following is true: climatologists -- working as peer reviewed scientists and abiding by the scientific method -- have accurately measured the temperature of the planet, as well as the warming in the past century, and verified the change in world climates. 

I conclude that all people, institutions, and think tanks, which say that global warming and climate change are merely natural climate variability, are fully acknowledging that the planet is warming and the climate is changing. Likewise, they acknowledge that scientists and their methods of research are legitimate.

Yet, for some reason, when scientists, using identical scientific methods and peer reviewed protocols, determine that the carbon dioxide emissions from the combustion of fossil fuels are the primary cause of warming, suddenly, scientists are involved in a conspiracy. There is a contradiction in their language to which they appear oblivious.

One climatological event sighted as evidence for natural variability was the Medieval Warm Period, 850 to 1250 AD and the Little Ice Age, 1300 through 1800 AD. The North Atlantic Ocean was unusually free of sea ice during the warm phase, which allowed sailing through the region and settlement in Greenland. This warming was felt in many areas; yet globally, temperatures were slightly cooler than those of today.  Afterwards and extending to 1800 AD there was a substantial cooling in northern Europe known as the "Little Ice Age".  

Taken collectively the Medieval Warm Period, MVP, and the Little Ice Age, LIA, are termed "The Medieval Climate Anomaly." It has been discovered that the MVP had two distinct causes: (1) an increase in solar output and (2) a decrease in volcanic activity.

Volcanoes emit particulates that are suspended in the atmosphere and are circulated by upper level winds in the troposphere for a number of years. These particles, called "aerosols," reflect incoming sunlight back into space. thus reducing the amount of sunlight the planet receives.

Carbon dioxide is also emitted from volcanoes, which as we know, warms the planet. Volcanoes tend to cool the planet in the short term due to aerosols and warm it in the long term from the CO2 that remains in the atmosphere for centuries. It is not an entirely linear arrangement, with numerous variables and feedback mechanisms contributing to the final net result.  

The atmosphere and world climates are influenced by the oceans. The "Thermohaline Circulation" is a massive river within the oceans that circulates globally. As the name indicates, it is driven by heat energy and saline density. This transfers tropical heat to the North Atlantic.

The melting in the North Atlantic during the MVP slowed the oceanic circulation thus contributing to the onset of the LIA. Today Greenland and the Arctic melt at alarming rates.

Does history repeat itself? We shall see.