The claim by Justin Gillis in the Jan. 8, 2012, New York Times — “Not Even Close: 2012 Was Hottest Ever in U.S.” — is so egregiously untrue, that I have to assume he and the editors are simply arrantly ignorant of Earth’s natural history. Nobody would intentionally tell such a blatant untruth.
All of the “records” referred to are for the past 150 years for which we have thermometer records. In precise usage, this is what “on record” means. Scientists agree that Earth has been much warmer many times in the past.
The Intergovernmental Panel on Climate Change Fourth Assessment Report indicates that over the last 150 years “warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global mean sea level.” True enough for the last 150 years, but Earth is 4.6 billion years old.
The increase over the last 150 years does nothing more than return Earth from the Little Ice Age to temperatures almost as warm as those that prevailed during the Medieval warm period.
The current interglacial (warm period) began 10,000 years ago with an increase of nearly 10 degrees centigrade in about 10 years. This interglacial does not appear to be as warm as at least three of the previous four that have occurred on an approximately 100,000-year cycle. About 18,000 years ago, during the last Ice Age, the Mediterranean Sea level was 300 feet lower than it is today. Three million years ago Earth was 2 to 3 degrees centigrade warmer than today, and sea level was 100 feet higher. About 35 million years ago Earth was 5 to 8 degrees centigrade warmer than today, sea level was 200 feet higher, and Earth was ice free.
What is unusual is how stable and clement temperatures have been for the last 10,000 years. The epiphenomena (species migrations, melting ice, storm intensities, droughts, etc.) associated with the current interglacial are just that (i.e. they are not etiological). For example, during the middle Cretaceous warm climate, organisms did well in both Polar Regions, although this warming was manifestly not anthropogenic.