Recently in Climate Changes Category

We are in an ice age. Over the last 2.5 million years we have experienced about twenty periods of glaciation and a similar number of interglacial periods. The current, warm, interglacial period is ending.

Keith Briffa and others have used measurements of tree rings in Siberia to estimate the local variations in temperature over the past 2,000 years, and to support an integrated "Global Warming" view of climate change over the last decades and centuries.

This is apparently ascribed to Napoleon. But suspicion and conspiracy theories are more fun!

The Younger Dryas — also referred to as the Big Freeze— was a 1,300 year-long cold climate period, between approximately 12,700 to 11,500 years BP, i.e. around 10,000 BC. Its end marks the start of a warm, interglacial period, the one we live in.

What was it like during the Younger Dryas? Parts of Greenland were about 15°C colder than today. In the UK, evidence suggests mean annual temperature was below freezing. The Younger Dryas ended under just four to five decades; some data suggests an even more rapid transition, just a few years. No human activity has been blamed for that.

Why does it matter? The last glacial period ended about 10,000 years ago, allowing humans to subsequently develop agriculture, civilization, industry, aviation, and information technology. People who worry about Global Warming, and especially those who claim that it's caused by mankind, need to realize that Earth climate has wildly fluctuated over thousands as well as millions of years, and that a major reason we enjoy immense prosperity, freedom, and progress today is that the climate is relatively warmer!

The last glacial period lasted 100,000 years; the Northern hemisphere was largely covered with heavy, three to four km-thick ice sheets, and sea level was about 120m lower than at present. Always remember that we are enjoying an interglacial period of the present ice age. This ice age began 40 million years ago with the growth of an ice sheet in Antarctica; over the last several million years, cycles of glaciation with ice sheets have advanced and retreated on 40,000- and 100,000-year time scales, within the current ice age. None of these cycles and changes can or should be blamed on mankind.

Trivia: the three “Dryas” periods (younger, older, oldest) are named for Dryas octopetala, a marker species detected in peat bogs and core samples of glacial ice. It's an arctic-alpine evergreen shrub, with large white flowers.