The earliest measurements of the Earth’s climate using thermometers and other tools started in the 1850s, but when scientists want to look further back in time to study the Earth’s climate and temperatures, they have to rely on the Earth itself.
We can look back almost a million years by studying the air bubbles trapped in ice cores, but to investigate climate much further back in time, scientists examine the biological and chemical signatures of deep-sea sediments. The information gleaned from core samples of deep-sea sediment is like a tape recording of the past.
Geoscientist Richard Zeebe of the University of Hawai’i at Manoa, along with his colleagues, looked at changes in the Earth’s temperature and atmospheric carbon dioxide levels dating back to the end of the age of dinosaurs. The sediment cores they used were obtained by geologists working aboard the ocean drillship JOIDES Resolution, reports Science News Online.
“In studying one of the most dramatic episodes of global change since the dinosaurs, the researchers show that we are currently in uncharted territory in the rate carbon is being released into the atmosphere and oceans,” said Candace Major, program director in the National Science Foundation (NSF) Division of Ocean Sciences, which funded the research.
“The findings suggest that humans are responsible for releasing carbon 10 times faster than during anytime in the past 66 million years,” says the NSF.
Understanding the Paleocene-Eocene Thermal Maximum
Using a new approach, the scientists were able to determine the duration of the onset of the Paleocene-Eocene Thermal Maximum (PETM), an important climate event that took place 56 million years ago, The PETM is also called the Initial Eocene Thermal Maximum (IETM), and is a relatively short period of time, about 100,000 years, characterized by the highest global temperatures of the Cenozoic Era.
It is believed that the sudden rise in temperature was caused by the sudden release of methane gas, caused by a massive volcanic eruption. The onset of PETM was sudden, occurring within a few thousand years. This resulted in widespread extinctions in both marine and terrestrial ecosystems.
Sea surface and land air temperatures increased by more than 5 °C (9 °F) during the transition into the PETM. Sea surface temperatures in the higher reaches of the Arctic rose as high as 23 °C (73 °F). The temperatures gradually dropped back to pre-PETM levels, but slowly rose again over a few million years to near-PETM temperature levels during a period called the Eocene Optimum.
Again, there followed a slow decline in global temperatures to about 34 million years ago. Scientists have been able to documents these changes in global temperature from marine sediments and in paleontological records from the continents, showing where vegetation zones moved toward the Equator
The past and today’s carbon release rates
“As far as we know, the PETM had the largest carbon release during the past 66 million years,” Zeebe said. Zeebe and his team combined analyses of chemical properties of sediment cores with numerical simulations of the Earth’s climate and carbon cycles. Using the new approach, they were able to study the rates of change from the sediment record.
Basically, what the scientists found was that the amount of carbon released during the PETM, about 66 million years ago was much smaller than the amount of carbon released into the atmosphere from human activities. Carbon release rates from human activity in 2014 amounted to 37 billion metric tons of CO2.
However, the carbon release rate during the PETM were calculated to be no more than than four billion metric tons of CO2 per year, or about 10 times less than today. The PETM suggests that the “consequences of our massive burning of fossil fuels will have much longer-lasting effects,” said Zeebe.
“Because our carbon release rate is unprecedented over such a long time period in Earth’s history, it also means that we have effectively entered a ‘no-analogue’ state,” said Zeebe. “This represents a big challenge for projecting future climate change because we have no good comparison from the past.”
The researchers point out that everyone is focusing today on what will happen by 2100, but that is only about two generations. What the earth will be like past that time is something none of us can foresee.
