It behooves us to note how kind the weather has been world-wide over the past century and how politically and economically disruptive severe weather changes can be.
The four great asian droughts noted in the tree ring records starkly parallel political collapses.
ScienceDaily (July 24, 2010) —
By sampling the wood of thousands of ancient trees across Asia, scientists at Columbia University's Lamont-Doherty Earth Observatory assembled an atlas of past droughts, gauging their relative severity across vast expanses of time and space.
The tree-ring records in the study reveal at least four great droughts that are linked to catastrophic events in history. For starters, the study suggests that climate may have played a powerful role in the 1644 fall of China's Ming dynasty. The tree rings provide additional evidence of a severe drought in China referenced in some historical texts as the worst in five centuries. This study narrows it down to a three-year period, 1638-1641. The drought was most sharply expressed in northeastern China, near Beijing, and is thought to have influenced peasant rebellions that hastened the demise of the Ming.
Another severe monsoon failure came in 1756-1768, coinciding with the collapse of kingdoms in what are now Vietnam, Myanmar and Thailand. The drought roiled political structures all the way to Siberia, and the tree rings also indicate that western India was severely affected. ...The study appears to provide an explanation for the so-called "strange parallels" that Victor Lieberman, an historian at the University of Michigan, has spent his career studying. "It provides confirmation that there are very strong climate links between monsoon regimes in India, Southeast Asia and southern China," said Lieberman in an interview.
Then, the so-called East India drought hit in 1790-1796. This one appears to have been felt worldwide, spreading civil unrest and socioeconomic turmoil. For instance, in Mexico, water levels at Lake Pátzcuaro fell so much they gave rise to ownership disputes over the land that emerged. In Europe, drought led to crop failures that preceded the French Revolution. Famines hit India.
Perhaps the worst drought, the scientists found, was the Victorian-era "Great Drought" of 1876-1878. The effects were felt across the tropics; by some estimates, resulting famines killed up to 30 million people. According to the tree-ring evidence, the effects were especially acute in India, but extended as far away as China and present-day Indonesia. Colonial-era policies left regional societies ill-equipped to deal with the drought's consequences, as historian Mike Davis details in his book Late Victorian Holocausts. Famine and cholera outbreaks at this time in colonial Vietnam fueled a peasant revolt against the French.
Asia's Most Devastating Droughts Reconstructed