It's been much hotter on earth than it is now. Here's a recent study describing one such period. The warming then was NOT human-caused we can be sure.
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Another study just released shows that climate belts and ecosystems are migrating. Former lowland or low lattitude ecosystems are now expanding: upward in elevation or toward the poles. This will put heavy pressure on species that are specialists in survival in tundra, taiga and alpine habitats. That affects animals from the polar bear to the marmot to various ptarmigan. I've blogged before about animals and plants altering their location and behavior in concert with the changing climate. They don't bother to belabor data points or wait for some conference to tell them what to do. Wildlife plays the survival game very day and they must shift with the change or lose out.
The study found that in flat areas species may be moving toward the polar regions at a rate of one kilometer per year. The study estimates that only 10% of today's parks and wildlife reserves will maintain their current ecosystems over the next century. That means many plants and animals seeking survival will inevitably clash with man's use of much of the planet.