Scientists

The graph below shows the temperature over Greenland going back over 15,000 years. The minor ice age called the Younger Dryas, around 10,000 BC, might have induced us to invent agriculture. 8,200 years ago there was another abrupt cooling of the Northern Hemisphere. The “Little Ice Age” around 1730 might have been enough to wipe out the Greenland Norse.

It is important to know that some of these temperature drops were very abrupt, perhaps five degrees Fahrenheit in a decade. A five degree change in average temperature is a big deal, more than it sounds like. The length of growing seasons and the local viability of particular crops change. They were sufficient to cause a great deal of turmoil. What if this century experience such an abrupt change?

If the scientists’ consensus is right, global warming is accelerating and will manifest itself in hurricanes, wildfires, famines, ice ages, wars, and even revolutions. For example, events in sub-Saharan Africa are partly attributable to climate change there.

First, let us review the scientific. The International Panel on Climate Change (IPCC), the agency of the UN recently awarded part of the Nobel Peace Prize, says greenhouse gases began rising in 1800 probably causing warming beginning in 1900. Here are the graphs.

Naturally, there is less agreement about the future. For example, several climate experts guessed the chance of the Gulf Stream stopping for different increases in global temperature. Their median guesses were 20% for a five degree increase, 25% for a seven degree increase, and 30% for an eight degree increase. Without the Gulf Stream, Northern Europe would be as cold as Canada. If enough ice melts fast enough, the change could happen in a decade. Thus global warming could precipitate significant cooling of the Northern Hemisphere, causing a minor ice age like those of 1730 or even 6200 BC.

Peter Novig has done a good meta-analysis of the scientific papers along with indications of how you can do it yourself.