Let’s summarize what we know about the connection between the world’s climate and the rise and fall of human civilizations so far.
When the Last Ice Age of the Pleistocene ended around 10,000 BC, the world’s average temperature rose slowly, then between 6000 and 3000 BC average temperature increased at a slightly faster rate. By 3000 BC, global temperature was about 2 degrees C above the temperature of 6000 BC. Then from 3000 BC to around 1000 BC, the global climate began to cool. By 1000 BC, the global average temperature was about the same as it had been in 6000 BC. After 1000 BC, the average global temperature began to become warmer again.
It appears that the warming climate after the last ice age and an increasing human population precipitated a change from food gathering to food production in many regions of the world. By 3000 BC, people all over the world had domesticated plants and many began to settle in permanent farming villages. The cooling temperatures after 3000 BC, however, had different effects depending on where these farmers were located.
The cooling weather weakened the jet stream and in some places that meant the rainfall became more inconsistent. In the Near East, state governments formed to conserve water and grow more food to feed their growing population. During this time, the changing climate had little effect on the social organization in China. Society remained one of small villages and chiefdoms. By 2200 BC however, the wanderings of the weakened jet stream brought increased droughts, fewer monsoons, and the “east wind” to the Near East. It also brought increasing rains to Northern China.
Around 2200 BC a state society evolved in China to control the flooding caused by the increased rain. As we learned earlier, while agriculture failed in the Near East, it grew in China. As the influence of the Zhou increased southward, rice became important to the Chinese economy along with millet and their carrying capacity rose. In the Americas, the changing weather must have allowed for the growing of surplus food and farming villages of the Olmec and the Chavín grew into state societies. While in the Mediterranean, civilizations fell apart during the time period between 1200 and 700 BCE.
Then around 750 BCE, the global temperature began to rise again. As the global climate warmed, the path of the jet stream and its patterns of rainfall would have changed again. During this same time period China, the Chavín and the Olmec fell into crisis and by 200 BC the civilizations of the Chavín and the Olmec were a memory. Between 700 and 200 BC the state government of China could no longer maintain control and the country became segmented and ruled by warlords.
Civilization along the Mediterranean however, began to recover. Around 200 BC Rome emerged as the “greatest power the West had ever known” but by 450AD, the glory of Rome was over. Between 200 and 600 AD the global climate was cooling. This means that the paths of the Jet Stream were unstable yet again.
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