One thing that has often puzzled me about climate change, is that while a 2°C rise in global temperature is considered safe, a 5°C rise is thought to be catastrophic. In addition, several books I have read have reported that earth temperature has not risen more than 6°C warmer than it has now for hundreds of millions of years. The last time the climate warmed 6°C warmer than now was at the End-Permian mass extinction event, when 90% of species perished. The only vertebrates that survived were ugly pig-like animals that sheltered in pools. However, I read in another book that at the start of the Eocene era, the average temperature in London was 25°C, and that England was covered in rainforest. I thought maybe that was because England was further south, but apparently we were at the same latitude. In addition, crocodiles were living 100 miles from the North Pole, which meant that the water temperature there could never have fallen below 10°C. That sounds like an average temperature rise of well over 5°C. I know the poles are expected to warm up more equatorial area, and that due to trigonometry the surface area of the planet between 45° and 90° latitude is much less than the between 0° and 45°, but still, it seems like a rise well above 5°C.