Perhaps the most difficult question in climate science. That is, how much global warming does carbon dioxide cause? A new analysis of 66 million years of Earth’s climate history suggests that the Earth is far more sensitive to greenhouse gases than current climate models predict, which could lead to even warmer temperatures in the long term. This means that there is a possibility of further development.

A key factor determining the impact of our emissions on the planet is how much the planet warms in response to the extra CO2 we pump into the atmosphere. This sensitivity is affected by various feedback loops related to clouds, melting ice sheets, and other influences.

One way to measure this sensitivity is to look at how the climate has changed in the past. Gases trapped in ice cores can only take us back about 800,000 years, so to go even further back in time to look at temperatures and CO2 levels in the atmosphere, researchers used proxies. Masu. For example, the density of pores in plant leaves and the isotope levels in the fossil shells of marine organisms change in response to CO2 levels.

However, discrepancies between different proxies have led to an uncertain view of Earth’s ancient climate. Now, an extensive review by a team of over 80 researchers provides a clearer picture. More accurate representation of ancient CO2 levels. “We now have a much clearer picture of what carbon dioxide levels have been in the past,” he says. Berber Henisch He coordinated the project at Columbia University in New York.

This allows us to understand current CO2 levels in the atmosphere alongside the deep past. This indicates that the last time CO2 levels were as consistently high as they are now was about 14 million years ago, and much earlier than that. previous estimate.

By comparing this new CO2 data with temperature records, “we can learn how sensitive the climate has been to changes in carbon dioxide,” Hoenisch says. Current climate models estimate that doubling his CO2 levels in the atmosphere would result in a warming of 1.5°C to 4.5°C. However, the results suggest that the temperature increase is even larger, between 5°C and 8°C.

However, there is a big caveat. This new insight into the history of Earth’s deep climate covers trends over hundreds of thousands of years, rather than the short timescales of decades or centuries that are relevant to humanity today, and therefore It doesn’t tell you what the temperature is likely to be. “It’s a slow cascading effect that slowly kicks in,” Hoenisch says.

The vast time scales covered in this study also mean that details of climate sensitivity cannot be detected. michael man Researchers at the University of Pennsylvania say climate sensitivities may have been different at other times in Earth’s history compared to today, which is likely why the study yielded higher estimates than those based on more recent periods. I think this explains why I got there.

“The bottom line is that the climate sensitivity estimates from this study probably don’t apply to current anthropogenic warming,” Mann says. “Nonetheless, this study confirms a very close relationship between CO2 and global temperatures, highlighting the continuing threat of fossil fuel combustion.”