Global temperatures are higher than at any time in at least 4,000 years, scientists reported Thursday, and over the coming decades are likely to surpass levels not seen on the planet since before the last ice age.
Previous research had extended back roughly 1,500 years and suggested that the rapid temperature spike of the past century, believed to be a consequence of human activity, exceeded any warming episode during those years. The new work confirms that result while suggesting that the modern warming is unique over a longer period.
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Another way to figure out whether or not there is warming of the planet would be to study the history of Jamaica Pond in Jamaica Plain. In the mid eighteen hundreds or thereabouts, there used to be an ice house there filled with ice blocks cut from the pond. Back in the thirties, we could skate there on thick ice. Now you can never skate there.