New maps of ancient warming show strong response to carbon dioxide

New maps of ancient warming show strong response to carbon dioxide
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Global map of precipitation changes due to warming 56 million years ago: green = wetter, brown = drier.  Circles show where geologic data shows it got drier or wetter to verify the new results.
Enlarge / Global map of precipitation changes due to warming 56 million years ago: green = wetter, brown = drier. Circles show where geologic data shows it got drier or wetter to verify the new results.

Tierneyet. Al.

And a Study published in PNASUniversity of Arizona Professor Jessica Tierney and colleagues have created complete global maps of the carbon-driven warming that occurred 56 million years ago during the Paleocene Eocene Thermal Maximum (PETM).

While the PETM shows some parallels with current warming, the new work contains some unexpected findings – the climate’s response to CO2 was about twice the current best estimate by the Intergovernmental Panel on Climate Change (IPCC). But changes in precipitation patterns and the increase in warming at the poles were remarkably consistent with modern trends, even though it was a very different world then.

Another world

The warming of the PETM was triggered by a geologically rapid release of CO2mainly from a spasm of magma in the earth’s mantle at the place where Iceland is today. The magma invaded oil-rich sediments in the North Atlantic and evaporated CO2 and methane. It took an already warm, high CO2 climate and made it hotter for tens of thousands of years, some of them drifting creatures of the deep sea and some tropical plants to extinction. Mammals evolved smallerand there were big ones migrations across continents; Crocodiles, hippopotamus-like creatures and Palm trees all thrived just 500 miles from the North Pole, and Antarctic was ice free.

As our climate warms, scientists will increasingly consider past climate for insights, but they are hampered by uncertainties related to temperature, CO2 Levels and the exact timing of the changes — previous work on the PETM, for example, had temperature uncertainties on the order of 8° to 10°C. Now, Tierney’s team has narrowed that range of uncertainty down to just 2.4°C, showing that the PETM has changed by 5 .6 °C, a refinement of the previous estimate of about 5 °C.

“We’ve really been able to narrow this estimate down from previous work,” said Tierney.

The researchers also calculated the CO2 Concentrations before and during PETM derived from isotopes of boron measured in fossil plankton shells. They found CO2 was around 1,120 ppm just before the PETM and rose to 2,020 ppm at its peak. For comparison: pre-industrial CO2 was 280 ppmand we are currently at approx 418 ppm. The team was able to take advantage of these new temperatures and CO2 Values ​​to calculate how much the planet has warmed in response to a doubling of CO2 Values ​​or the “Equilibrium Climate Sensitivity” for the PETM.

Highly sensitive

The IPCC’s best estimate for climate sensitivity in our time is 3°C, but that comes with a lot of uncertainty – it could be anything in between 2° to 5° C– due to our imperfect knowledge of feedback in the earth system. If the sensitivity turns out to be on the higher end, we’ll be heating up more for a given amount of emissions. Tierney’s study found that the PETM climate sensitivity was 6.5°C — more than double the IPCC’s best estimate.

A higher number is “not too surprising,” Tierney told me, because previous research had indicated the Earth’s reaction to CO2 is stronger at higher CO2 Planes of Earth’s past. Our climate sensitivity won’t be that high: “We don’t expect to see a climate sensitivity of 6.5°C tomorrow,” explained Tierney.

However, your paper suggests that if we continue to increase CO2 levels, it will trigger the temperature response to that CO2 higher. “We could expect some level of heightened climate sensitivity in the near future, particularly if we emit more greenhouse gases,” Tierney said.

Climate mapping by “data assimilation”

The new, sharper picture comes from the way Tierney’s team dealt with geologists’ perennial problem: We don’t have data for every place on Earth. Geological data for the PETM is limited to locations where sediments from this period are preserved and accessible – usually either via a borehole or outcrop on land. Any conclusions about global Climate needs to be scaled up from these sparse data points.

“It’s actually a tough problem,” Tierney noted. “If you want to understand what’s happening spatially, it’s really difficult to do that just from geological data alone.” So Tierney and colleagues borrowed a technique from weather forecasting. “What weather people do is they run a weather model, and throughout the day they measure wind and temperature, and then they assimilate it into their model … and then run the model again to improve the forecast, Tierney said.” .

Instead of thermometers, her team used temperature measurements of microbial and plankton debris preserved in 56-million-year-old sediments. Instead of a weather model, they used a climate model with Eocene geography and no ice sheets to simulate the climate just before and at the peak of PETM warmth. They ran the model a few times and varied the CO2 planes and the configuration of the Earth’s orbit because of the uncertainties in these. Then they used the microbial and plankton data to select the simulation that best matched the data.

“The idea is really to exploit the fact that model simulations are spatially complete. But they’re models, so we don’t know if they’re right. The data knows what happened, but it’s not spatially complete,” Tierney said. “So by mixing them, we get the best of both worlds.”

To see how well their blended product matched reality, they checked it against independent data obtained from pollen and leaves and from locations not involved in the blending process. “They were really, really a good match, which is a bit reassuring,” Tierney said.

“The novelty of this study is to use a climate model to rigorously work out which climate state best fits the data, both before and during the PETM, reflecting patterns of climate change around the world and a better estimate of global mean temperature change.” delivers.” said dr. Tom Dunkley Jones from the University of Birmingham, who did not take part in the study.

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