According to staff writers from Santa Cruz CA, in their Feb 16, 2006 article "Ancient Climate Studies Suggest Earth On Fast Track To Global Warming",

Prof. James Zachos of Earth sciences at the University of California Santa Cruz, a leading expert on an episode of global warming known as the Paleocene Eocene Thermal Maximum (PETM) which occurred about 55 million years ago, said:

"The emissions that caused this past episode of global warming probably lasted 10,000 years. By burning fossil fuels, we are likely to emit the same amount over the next three centuries,".

The staff writers also said that when global temperatures shot up by 5 degrees Celsius (9 degrees Fahrenheit) at the PETM,

"an abrupt shift in the Earth's climate took place as the result of a massive release of carbon into the atmosphere in the form of two greenhouse gases: methane and carbon dioxide."

The Santa Cruz CA staff writers also said

"The greenhouse emissions that triggered the PETM initially exceeded the ocean's absorption capacity, allowing carbon to accumulate in the atmosphere. Unfortunately, humans appear to be adding carbon dioxide to the air at a much faster rate: about the same amount of carbon (4.5 trillion tons), but within a few centuries instead of 10,000 years. What was emitted 55 million years ago over a period of about 20 ocean mixing cycles is now being emitted over a fraction of a cycle.

The article continued with a quotation by Prof. James Zachos which said: "The rate at which the ocean is absorbing carbon will soon decrease," ...