There are many other indicators of global temperature which have been used to make assertions going back anywhere from 500-100000 years depending on what method

There are many other indicators of global temperature which have been used to make assertions going back anywhere from 500-100000 years depending on what methodology you use: http://grist.org/climate-energy/one-hundred-years-is-not-enough/ http://grist.org/climate-energy/one-hundred-years-is-not-eno...