Increasing temperature is likely to be accompanied by increasingly unpredictable weather, water shortages and less productive and less secure agriculture and political and economic instability. One immediate impact is rising sea-level. Some project that perhaps a billion people will be displaced. Many of the small island nations in the Pacific and Indian Oceans are likely to disappear within a few decades. What can/will we do about it?
Our activities have radically altered the Earth’s surface and the chemistry and behaviour of its atmosphere. The major culprit, the burning of fossil fuels, has increased the concentration of greenhouse gasses, notably carbon and methane. Although we focus on rising temperature, the package is complex and may include increasing climatic variability, increased storminess, higher intensity ENSO events and rising sea-levels.
The time since the last ice retreat, the Holocene, is marked by a series of climatic shifts that lasted for decades to centuries. Some appear to be global, while others are largely regional phenomena. One of these was the Medieval Warm Epoch, between 950 and 1350 AD. It’s marked by an expansion of agriculture into higher latitudes and altitudes, but is best remembered for its coincidence with Norse expansion across Europe and the North Atlantic.The period of cooling after the Medieval Warm Epoch known as the Little Ice Age lasted from about 1350 AD to 1850 AD. It was marked
Climate Change and the Rise and Fall of Civilizations: El Nino (ENSO) and its Effects on the Asian Monsoon and the Early Civilizations of the Americas
El Nino is a periodic climatic phenomenon initiated by the reversal of oceanic and atmospheric circulations in the equatorial Pacific, but its effects are global. Severe ENSO events may have catastrophic consequences. Several major famines in India and China have been attributed to ENSO. It is likely that multiple ENSO events were responsible for the demise of the Maya in Central America, the Moche, Chimu and Nazca in South America and the Anasazi in the Chaco Canyon area of the US southwest
From about twenty five million years ago Earth’s climate cooled and became more seasonal. This culminated in the series of pulse-like ice advances and retreats that have marked the last two million years. Cooling climate constrained the evolution of hominids and their spread around the world. Plant and animal domestication appears to be a feature of the present interglacial, the Holocene. Did people develop agriculture as a response to the pronounced climate change at the end of the Pleistocene or were other influences involved? What were the consequences?
Over the last half billion years, life has become more diverse and complex. Although there seems to have been an increase in diversity through that time, the record is marked by several episodes of mass extinction. Five major events are recognized. The largest, at the end of the Permian, may have eliminated 70-90% of species. Each extinction provides opportunities for survivors. The biological modernization of our world comes after the extinction event at the Cretaceous-Tertiary boundary, about sixty five million years ago. Climate change appears to have been heavily involved in all of these events.
The Earth is located in our solar system’s Goldilocks Zone (not too hot, not too cold, etc.). That suggests that the critical control on our climate is distance from the sun, but the internal processes of our planet (plate tectonics) also play a major role. They control the carbon cycle and atmospheric chemistry and thus the processing of solar radiation.
What is climate and how do we measure it? Information on past climate spans nearly four billion years, but it’s plentiful only for the last half billion. What is the nature of the record? What does it tell us? How do past climates compare to what we have today?