Apparently, according to some scientists and a study, today's temperatures are similar to Earth 81,000 years ago.

Sea levels on Earth change as glaciers grow and shrink, lowering as temperatures cool and more ice forms. According to a release about the study, which appears today in Science:

81,000 years ago, the level of the sea was actually more than a meter above where it stands now, a result seemingly at odds with prevailing ideas about ice sheet growth. Since the sea rises and falls with the melting and forming of large glaciers, respectively, this finding therefore implies that polar ice sheets were smaller and global temperatures were at least as high (or even higher) 81,000 years ago than they are now, even though the concentration of carbon dioxide in the atmosphere was much lower back then. In order to reach these new conclusions, Jeffrey Dorale and colleagues took measurements from a cave formation on the Spanish island of Mallorca which has been intermittently submerged in the Mediterranean Sea over hundreds of thousands of years. Their data suggest that glaciers may grow and shrink faster than experts had believed, and if verified, the results of this study are poised to change the debate over precisely how ice ages come and go.

via Science

 Encrusted stalactites at present sea level, Vallgornera Cave, Spain. Image © Bogdan P. Onac
dorale1hr_01.jpg
Image from the No Name Room, Vallgornera Cave, Spain. Image © Bogdan P. Onac

dorale2hr_01.jpg
  Typical morphology for tidal range-related carbonate encrustation (size 20 cm),

dorale3hr_01.jpg
Vallgornera Cave, Spain. Image © Bogdan P. Onac

dorale4hr_01.jpg
Encrusted stalactites forming at present sea level in Vallgornera Cave, Spain. Image © Bogdan P. Onac

dorale5hr.jpg
Last glacial encrusted stalactite, Vallgornera Cave, Spain. Image © Bogdan P. Onac

dorale1hr_01.jpg
Calcite macrocrystals lining the walls of a fresh water gour, Vallgornera Cave, Spain. Image © Bogdan P. Onac

dorale6hr.jpg