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6

Hit a large gypsum, or other sulfurous compound, deposit. The main reason the that Chicxulub impact caused long term climatic chaos wasn't the initial rocky impact ejecta, they were bad but what caused hundreds of years global temperature oscillations was that the impact happened in an area rich in carbon and sulfur bearing rocks, mainly limestone and gypsum,...


6

If you simply want an ice age, you may not even need the nuclear winter. Simply let the Sun enter a 1000 years long period of slightly lower intensity. It could be large enough to counteract anything humanity does to heat up the climate. We have evidence that the Sun's output is not constant over large timescales. It is theorized that such low activity was ...


6

There is some reason to believe that the world was heading into an ice age when the industrial revolution started. The industrial revolution of course added a great deal of carbon dioxide to the air. If you are willing to believe that this prevented the ice age, nuclear winter combined with an end to burning fossil fuels could lead to the previous ice age ...


4

Not much explanation is required. Several islands in that area were home to mammoths long after they became extinct on the mainland: Wrangel Island (7,600 sq km), the one on the top left of your map, had mammoths some 8000 years after the steppes disappeared. St. Paul Island is much smaller (100 sq km) and more southerly, but also hosted mammoths thousands ...


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