Scientific American: Global average temperatures are now higher than they have been for about 75% of the past 11,300 years, a study suggests. And if climate models are any indication, by the end of this century they will be the highest ever since the end of the most recent ice age.
Instrumental records of climate extend back to only the late nineteenth century. Beyond that, scientists depend on analyses of natural chronicles such as tree rings and isotope ratios in cave formations.
But even these archives have...