As a result of decades of work and a large international collaboration, climate scientists have finally compiled a continuous, high-fidelity record of variations in Earth’s climate extending 66 million years ago.
Earth’s 4 Main Climate States
The record reveals four main climate states dubbed as:
Within each major climate states, the climate shows rhythmic variations corresponding to changes in Earth’s orbit around the sun.
“We’ve known for a long time that the glacial-interglacial cycles are paced by changes in Earth’s orbit, which alter the amount of solar energy reaching Earth’s surface, and astronomers have been computing these orbital variations back in time.”
– James Zachos, coauthor, distinguished professor of Earth and planetary sciences and Ida Benson Lynn Professor of Ocean Health at UC Santa Cruz
Since the researchers have compiled a continuous, astronomically dated climate record of the past 66 million years, they now see that the climate’s response to orbital variations depends on the following factors: greenhouse gas levels and the extent of polar ice sheets, with most of the major climate transitions associated with changes in greenhouse gas levels.
Earth’s climate has been in an Icehouse state for the past 3 million years. Due to greenhouse gas emissions and other human activities, the planet is now driving toward the Warmhouse and Hothouse climate states.
The said climate states have not been seen since the Eocene epoch, which ended about 34 million years ago. The average global temperatures during the early Eocene were 9 to 14 degrees Celsius higher than today.
“The IPCC projections for 2300 in the ‘business-as-usual’ scenario will potentially bring global temperature to a level the planet has not seen in 50 million years,” said the co-author and professor at UC Santa Cruz.
The study is called “An astronomically dated record of Earth’s climate and its predictability over the last 66 million years” and it was published in the journal Science on September 10, 2020.