National Geographic: The oldest ice ever found in North America shows that ancient permafrost withstood periods of warming, a new study says. Scientists fear that modern permafrost–soil that remains frozen in the polar regions–may melt and release potentially huge reservoirs of carbon that would speed global warming, scientists say. (See story.) But the new study suggests that such a thaw could take much longer than previously believed, according to study leader Duane Froese, a geology professor …