Darrell Kaufman, Northern Arizona University – Is It Really the Hottest in 100,000 Years?

This summer has been a hot one…but was it as unprecedented as it seemed?

Darrell Kaufman, Regents’ professor of earth and environmental sciences at Northern Arizona University, determines the answer using history.

Dr. Darrell Kaufman is a Professor in the School of Earth and Sustainability at Northern Arizona University. He was a lead author on the 2021 climate report of the Intergovernmental Panel on Climate Change. As a paleoclimate scientist, he studies the geological evidence of past climate changes in Alaska and globally.

Is It Really the Hottest in 100,000 Years?

When was it ever this hot before? Some news outlets reported that daily temperatures in July hit a hundred-thousand-year high. That claim may well be correct but the geologic record extending back millennia is blurred. Paleoclimate scientists like me are reluctant to compare the long-term record of past temperature with today’s short-term extremes.

Nonetheless, even before this year’s heatwaves, we could see that Earth had entered a new climate state, one characterized by a global warming level that exceeds 1 degree Celsius warmer than pre-industrial times. This level of global warming or warmer will very likely persist for centuries, even under the most optimistic scenarios in which humans stop burning fossil fuels. This multi-century period of ongoing global warming can be reliability compared to the burry temperature records of the past.

The youngest candidate for a multi-century interval with temperatures higher than the 1 degree warming level was roughly 125 thousand years ago, prior to the last major ice age. At that time, average temperature was probably no more than 1.5 degrees above preindustrial levels – not much higher than now.

Without rapid and sustained reductions in greenhouse gas emissions, the Earth is currently on course to reach a warming level of roughly 3 degrees by the end of the century, and possibly quite a bit higher. From there, we would need to look back millions of years to find a climate state with temperatures as high. That would take us back to the previous geologic epoch, the Pliocene, when the Earth’s climate was a distant relative of the one that sustained the rise of human civilization.

Read More:
More information about global temperatures on multi-century time scales, including the underlaying datasets are at: https://doi.org/10.5194/cp-18-911-2022

A story about a recent review article focusing on whether global temperatures were warming up or cooling down prior to industrialization is at: https://news.nau.edu/holocene-temperature-conundrum/