From the ancient sludge of lakebeds in Asia's Tibetan Plateau, scientists can decipher a vision of Earth's future. That future, it turns out, will look very similar to the mid-Pliocene warm period—an epoch 3.3 million to 3 million years ago when the average air temperature at mid-latitudes rarely dropped below freezing. It was a time when permanent ice was just beginning to cling to the northern polar regions, and mid-latitude alpine permafrost—or perpetually frozen soil—was much more limited than today.