A comprehensive new study of ancient climate data finds that the Earth is warmer today than it has been during most of the past 11,300 years.
Researchers at Oregon State University and Harvard University sampled data from 73 ice and sediment core monitoring sites around the world to reconstruct a planet-wide temperature history dating back to the end of the last Ice Age. OSU paleoclimatologist Shaun Marcott, the lead author on the study, says previous climate histories have mainly focused on changes over the past 2,000 years, but the new data puts today's climate change into a much broader and long-term context.
The study, published in the journal Science, looks at temperature variations over a relatively warm period in Earth's history known as the Holocene, which began after the end of the last major Ice Age and continues through all of human history to the present day.
Scientists believe a shift in the Earth's orbit about 12,000 years ago gradually increased solar radiation in parts of the globe and helped drive a one-degree Celsius warming trend. After about 6,000 years, the planet began to cool -- until about 200 years ago, when temperatures began rising steadily.
The Harvard-OSU study finds that the decade from 2000 to 2009 was one of the warmest since modern record-keeping began. And while current global average temperatures have not yet topped the levels reached during the early Holocene, the reseachers say they are heading in that direction. They forecast that by the end of this century, the Earth's average air temperature will rise between two to five degrees Celsius, the warmest the planet has been in 11,300 years.
Marcott and colleagues stress that what sets today's warming trend apart from historic patterns is its suddenness. They say the rate of temperature change over the past 150 years -- since the advent of industrial-age greenhouse gas emissions -- is greater than any previous shifts during the Holocene period.