How Hot is That Ice?
Ancient snow—now in the form of ice—reveals a lot about past temperatures: the chemical makeup of snow depends on the air temperature at which it formed. Scientists examining ice cores from Greenland have determined that for much of the past 108,000 years, the climate fluctuated between long cold periods and short warmer periods, as can be seen in a graph in the exhibition. Over the past 11,600 years, however, the climate has been stable and warm.
Trees from a wide geographic area provide some of the best evidence for climate of the past 1,200 years. Scientists examined the annual growth rings in many trees to create a graph in the exhibition of Northern Hemisphere temperature.
Earth's climate continually changes: centuries-long temperature swings, such as those during the so-called "Medieval Warm Period" and "Little Ice Age," are evident in the climate record of the past 1,200 years. But those changes were slower and apparently less severe than the warming of the past 100 years.