New maps of ancient warming reveal robust response to carbon dioxide

in A study published in PNASProfessor Jessica Tierney of the University of Arizona and colleagues have produced complete global maps of carbon-induced warming that occurred in the Paleocene-Eocene Thermal Maximum (PETM), 56 million years ago.

Although there are some similarities between the PETM period and current warming, the new work includes some unexpected consequences – the climate response to carbon dioxide.₂ It was then twice stronger than the current best estimate by the Intergovernmental Panel on Climate Change (IPCC). But changes in precipitation patterns and amplification of warming at the poles were remarkably consistent with recent trends, despite it being an entirely different world at the time.

different world

The warming of the Petam period was brought about by the rapid geological release of ko₂primarily from a magma spasm In the mantle of the Earth in the place where Iceland is now located. Magma invaded the oil-rich sediments in the North Atlantic, bringing carbon dioxide to a boil₂ and methane. It required a really high carbon monoxide content to be warm₂ The climate has made it hotter for tens of thousands of years, prompting some deep sea creatures And the Some tropical plants to extinction. Mammals evolved smallestand there was a large number Migrations Across the continents crocodiles and hippopotamus-like creatures and Palm trees They all thrived only 500 miles from the North Pole, and Antarctica It was free of ice.

As our climate warms, scientists are getting better Looking increasingly at past climates For insights, but hampered by uncertainties in temperature, carbon dioxide₂ Levels, and exact timing of changes – Previous work on PETM had an uncertain temperature in the range of 8° to 10°C, for example. Now Tierney’s team has narrowed this uncertainty down to just 2.4 °C, showing that PETM has warmed by 5.6 °C, an improvement over the previous estimate of ~5 °C.

“We were really able to narrow that estimate to previous work,” Tierney said.

The researchers also calculated carbon dioxide₂ Levels before and during the PETM period derived from boron isotopes measured in fossil plankton shells. They found CO₂ It was around 1,120ppm before the PETM period, and it rose to 2020ppm at its peak. For comparison, CO₂ I was 280ppmwe are currently about 418ppm. The team was able to use the new temperatures and carbon dioxide₂ Values ​​to calculate how much the planet is warming in response to the carbon dioxide doubling₂ values, or “equilibrium climate sensitivity” for PETM.

very sensitive

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

Tierney told me that the higher number “isn’t too surprising”, because previous search Describe the Earth’s response to carbon dioxide₂ It is stronger at higher CO2 level₂ Earth’s past levels. Our climate sensitivity wouldn’t be that high: “We don’t expect we’ll have a 6.5°C climate sensitivity tomorrow,” Tierney explained.

However, their paper suggests that if we continue to raise CO₂ levels, it will induce a temperature response to that CO₂ higher. “We may expect some level of climate sensitivity increase in the near future, especially if we release more greenhouse gases,” Tierney said.

Climate Mapping Using Data Intake

The new, clearer picture emerges from the way Tierney’s team has tackled the perennial problem of geologists: we don’t have data for every place on the planet. PETM’s geological data is limited to sites where sediments from that time are preserved and accessible – usually either through a borehole or outcrop on the ground. Any conclusions about worldwide Climate must be scaled up from these scattered data points.

“It’s actually a tough problem,” Tierney said. “If you want to understand what’s going on spatially, it’s really hard to do that with geological data alone.” So Tierney and his colleagues borrowed a technique from weather forecasting. “What the weather experts do is they run a weather model, and as the day goes on, they take wind and temperature measurements, and then they integrate them into their model…and then they run the model again to improve the forecast,” Tierney said.

Instead of thermometers, her team used temperature measurements from microbial and plankton remains preserved in 56-million-year-old sediments. Instead of a weather model, they used a climate model with Eocene geography and no ice layers to simulate the climate prior to, and at, peak warmth PETM. They rotated the model several times, with varying degrees of CO₂ levels and the Earth’s orbital configuration due to uncertainties in those. They then used the microbe and plankton data to choose the simulation that best fit the data.

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

To see how well their blended product matched reality, they checked it against independent data derived from pollen and leaves, and from places not included in the blending process. “They matched up actually, really well, which is rather comforting,” Tierney said.

“The novelty of this study is the use of a climate model to accurately work out the climate condition that best fits the data before and during the PETM period, giving patterns of climate change around the world and a better estimate of average global temperature change,” said Dr. Tom Dunkley-Jones from the University of Birmingham, which was not part of the study.