The high-fidelity record of Earth’s climate history puts current changes in context

Past and future trends in global average temperature over the last 67 million years. Oxygen isotope values ​​in deep-sea bentic foraminifera from sediment cores are a measure of global temperature and ice volume. Temperature 1961–1990 relative to global mean. Data from ice core records of the last 25,000 years describe the transition from the last glaciers to the current warm period, the Holocene. Historical data from 1850 to the present date show the rise after 1950, marking the beginning of the Anthropocene. Regarding the three representative concentration pathways (RCP) scenarios for global temperature for future projections, which is in accordance with benign deep-sea records, the climate state Miocene by 2100 is better than the climate optimum (~ 16 million years ago). Would be way beyond the limit. To munch continental ice sheets. If emissions remain stable after 2100 and not stable before 2250, then by 2300 the global climate enters the world of early eosin (~ 50 million years ago) with many of its global warming events and no large ice sheets at the poles. Can do. Credit: Westerold et al., Cenogrid

For the first time, climate scientists have compiled a continuous, high-fidelity record of variations in the Earth’s climate. The record reveals four distinct climatic states, which the researchers termed hothouses, warmhouses, coolhouses, and icehouses.

These major climatic states persist for millions and sometimes millions of years, and within each climate there are rhythmic variations corresponding to changes in the Earth’s orbit around the Sun. But each climate state has a specific response to orbital variations, which bring relatively small changes in global temperature compared to dramatic changes between different climate states.

New findings were published on 10 September Science, Are the result of decades of work and a large international collaboration. The challenge was to determine climate change precisely on a time scale to see the variability caused by orbital variations (the eccentricity of the Earth’s orbit around the Sun and the tilt and tilt of its rotational axis).

“We have long known that glacial-interglacial cycles are affected by changes in the Earth’s orbit, changes in the amount of solar energy reaching the Earth’s surface, and astronomers calculated these orbital shifts back in time “Said Zachos, Distinguished Professor of Earth and Planetary Sciences and Ida Benson Lynn Professor of Ocean Health at UC Santa Cruz.

“As we recreate previous seasons, we can well observe long-term rough changes. We also knew that there should be finer-scale rhythmic variability due to orbital variations, but in the long run this signal Was considered impossible to recover, “Zachos said. “Now that we have succeeded in capturing natural climate variability, we can see that the projected anthropogenic warming will be much higher than this.”

For the past 3 million years, the Earth’s climate has been in an iceberg state, characterized by alternating glaciers and interstitials. Modern humans evolved during this time, but greenhouse gas emissions and other human activities are now driving the planet toward warmhouse and hothouse climate states that had not been seen since the Eocene era, which ended about 34 million years ago. happened. During the early Eocene, there were no polar ice caps, and the average global temperature was 9 to 14 ° C higher than today.

“The IPCC estimate for 2300 in a ‘business-as-usual’ scenario would potentially bring down global temperatures that the planet hasn’t seen in 50 million years,” Zakos said.

The sediment of the sea revealed 66 million years of Earth's climate

The new global climate record CENOGRID (lower panel) is the first to continuously and accurately explore how the Earth’s climate has changed since the great extinction of dinosaurs 66 million years ago. The record was made using oxygen (shown) and carbon isotopes from small microfossils found in deep-sea sediment collected by the IODP ship R / V JOIDES resolution (shown in photo). Last 66 Million Year Credit: Thomas Westerhold / Adam Kutz

Getting high-quality sediment cores from deep-sea basins through the International Ocean Drilling Program (ODP, later successful in 2013 by the Integrated Ocean Drilling Program, IODP, International Ocean Discovery Program) to compile new climate records Was. Signs of past climates are recorded in the shells of microscopic plankton (called foraminifera) preserved in seafloor sediments. After analyzing the sediment core, the researchers then had to develop an “astrobiology” (known as the Milankovich cycle) by matching climate variations recorded in the sedimentary layers with variations in the Earth’s orbit.

Zachos, who led a study published in the 1990s, said, “The community figured out how to extend this strategy in the old time gap in the mid-1990s.” Science The climatic response to orbital variations appeared for a period of 5 million years covering the transition from the Oligocene era to the Miocene, about 25 million years ago.

“He changed everything, because if we could do that, we knew that we could probably go all the way back 66 million years ago and that these transient events and major transitions in the Earth’s climate caused orbital-scale variation In terms of, “he said. .

Zachos has for years collaborated with lead author Thomas Westrold at the University of Bremen Center for Marine Environmental Sciences (MARUM) in Germany, which has a large reservoir of sediment cores. Bremen Lab, along with the group of Zachos at UCSC, generated a lot of new data for the older part of the record.

Westerhold observes an important step, piecing together overlapping segments of climate records derived from sediment cores from different parts of the world. Zachac said, “It’s a tedious process to collect this long megasplice of the climate record, and we also wanted to replicate the record with separate sediment cores to validate the signals, so it would work together Wale was a major effort of the international community, ”said Zachi.

Now that they have compiled a consistent, astronomically dated climate record of the last 66 million years, researchers can see that the climate’s response to orbital variations depends on factors such as greenhouse gas levels and polar ice sheets .

“In an extreme greenhouse world with no snow, there will be no reaction involving ice sheets, and this changes the dynamics of the climate,” Zakos explained.

Most major climate changes in the last 66 million years have been associated with changes in greenhouse gas levels. Zachos has done extensive research on the Paleocene-Eocene Thermal Maxim (PETM), for example, showing that this episode of rapid global warming, which plunged the climate into the hothouse state, was associated with a massive release of carbon into the atmosphere . Likewise, in the late Euzean, as atmospheric carbon dioxide levels were falling, ice sheets began to form in Antarctica and the climate changed to a coolhouse state.

“When it is near one of these transitions, the climate can be unstable, and we see less predictable responses to orbital forces, so this is something we would like to understand better,” said Zachos.

The new climate record provides a valuable framework for many fields of research. It is useful not only for testing climate models, but also by geoscientists to study various aspects of Earth’s dynamics and paleontologists on how changing environments drive the evolution of species.

“This is an important advance in earth science, and a major legacy of the International Ocean Drilling Program,” Zachos said.

The study analyzes the impact of carbon dioxide on the Earth’s climate 30 million years ago

more information:
T. Westeröld L. al., “An Astronomical Record Over the Past 66 Million Earth’s Climate and Its Prediction,” Science (2020).… 1126 / science.aba6853

Provided by University of California – Santa Cruz

Quotes: High-Fidelity Record of Earth’s Climate History, Current Changes in Context (2020, 10 September) from 10 September 2020 Has been retrieved. .html

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