A new study presents a new curve for global average surface temperature, showing that Earth’s temperature varied more than previously thought during most of the Phanerozoic Era, a period marked by the diversification of life, land colonization, and multiple mass extinctions. The curve also confirms that Earth’s temperature is strongly related to the amount of carbon dioxide in the atmosphere.
Examining the temperature of the world’s past
The Phanerozoic Era began about 540 million years ago with the Cambrian explosion, when complex, hard-shelled organisms first appeared in the fossil record. Although researchers can create simulations starting from this period, the study’s temperature curve focuses on the last 485 million years because of the limited geological record of temperatures from earlier periods.
“It’s hard to find rocks that old that preserve temperature indicators; we don’t have many of them even from 485 million years ago,” said study co-author Jessica Tierney, a paleoclimatologist at the University of Arizona.
Development of temperature curve
The researchers developed the temperature curve using an approach called data assimilation, which allowed them to combine data from the geological record and climate models to create a more consistent understanding of ancient climates.
“This method was originally developed for weather forecasting,” said Emily Judd, lead author of the paper and a former postdoctoral researcher at the Smithsonian National Museum of Natural History and the University of Arizona. “Instead of using it to predict future weather, we’re using it to predict ancient climates.”
Improving scientists’ understanding of how Earth’s temperature has fluctuated over time provides important context for understanding modern climate change.
Looking back to predict the future
Scott Wing, co-author of the paper and curator of paleobotany at the Smithsonian National Museum of Natural History, is the study’s co-author.
“If you look at the last few million years, you’re not going to find anything like what we expect in 2100 or 2500,” Wing said. “You have to go back even further to the periods when the Earth was really warm, because that’s the only way we can better understand how the climate might change in the future.”
CO2 makes the largest contribution to temperature
The new curve shows that temperatures have changed much more than previously thought over the past 485 million years. During that period, global temperatures ranged from 52 to 97 degrees Fahrenheit. Periods of extreme heat were mostly associated with increasing levels of the greenhouse gas carbon dioxide in the atmosphere.
“This study clearly shows that carbon dioxide has been the dominant control on global temperature throughout geologic time,” Tierney said. “When CO₂ is low, temperature is low; when CO₂ is high, temperature is high.”
Rapid increase in temperature on Earth
The findings also suggest that Earth’s current global temperature of 59 degrees Fahrenheit is colder than it was during most of the Phanerozoic.
But researchers say greenhouse gas emissions from human-caused climate change are currently warming the planet much faster than even the fastest events of that time. This rapid warming poses risks to species and ecosystems worldwide and is causing sea levels to rise rapidly. Several other rapid climate change events in the Phanerozoic have triggered mass extinctions.
Humans evolved in colder climates
A rapid transition to warmer climates could endanger humans, who mostly live within a global temperature range of 10 degrees Fahrenheit, compared with a global temperature range of 45 degrees over the past 485 million years.
“Our entire species has evolved into an ‘icehouse’ climate that doesn’t reflect much of geologic history,” Tierney said. “We’re really decontextualizing the climate for humans. The planet has been warmer and could be warmer, but humans and animals can’t adapt as quickly.”
Earth’s global temperature during the Phanerozoic
The collaboration between Tierney and researchers from the Smithsonian began in 2018. The team aimed to present museum visitors with a curve showing Earth’s global temperature throughout the Phanerozoic, which began about 540 million years ago and continues to the present day.
The researchers compiled more than 150,000 estimates of ancient temperatures, calculated from five different chemical indicators preserved in fossilised shells and other types of ancient organic matter. Their colleagues at the University of Bristol created more than 850 simulation models of what the Earth’s climate might have looked like at various times in the distant past, based on the location of the continents and the composition of the atmosphere.
The complete curve of the world’s temperature change
By combining these two lines of evidence, the team created the most accurate curve yet showing how the Earth’s temperature has changed over the past 485 million years. Another key finding from the study relates to climate sensitivity, a measure of how much the climate warms as a result of a doubling of carbon dioxide levels.
“We found that carbon dioxide and temperature are not only very closely related, but equally related over 485 million years. We do not see that climate is more sensitive to hot or cold,” Tierney said. The study was published in the journal Science.
Source: Port Altele
