Both [thermometer and proxy] records also show that the global warming in the last 15 years of the record (1980–1995) is significantly faster than that of the long-term trend (1880–1995).
— NOAA (2013): Independent Evidence Confirms Global Warming in Instrument Record.
To figure out what the weather and climate were like in the past, before things like thermometers were invented, scientists use proxies such as: the change in tree ring thickness; differences in the isotopic composition of shells and rocks; records of species change in the oceans; gases in bubbles trapped in glacial ice (as well as the character of the ice itself). Paleoclimatologists at NOAA have analyzed 173 different proxy records to provide a lot more evidence that the increase in temperature we’ve been measuring for the last 150 years (with thermometers) is real.
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