Scientists extend and straighten iconic climate “hockey stick” 24,000 years of climate history
Ars Technica: “The climate “hockey stick” refers to a reconstruction of temperatures over the past 1,000 years. The data shows flattish temperatures over the last millennium, like the handle of a Hockey stick, ending in a “blade” of rapidly rising temperatures since the industrial revolution. The idea first appeared in a paper by Michael Mann and Raymond Bradley of the University of Massachusetts and Malcolm Hughes of the University of Arizona. The work became famous after appearing in a UN climate report, after which it was the focus of climate denial, hacking, defamation, and disinformation, all of which was dramatized in a recent BBC TV drama called “The Trick.” Today, in a paper published by Nature, scientists show that the “handle” of the “hockey stick” extends back 9,500 years, while its “blade” is taller—the last decade was 1.5° C hotter than the average temperature over the last 11,700 years. “Human-caused global temperature change during the last century was likely faster than any changes during the last 24,000 years,” said lead author Dr. Matt Osman of the University of Arizona…The researchers’ work allowed them to produce maps and graphs of global temperatures as Earth emerged from the last ice age, providing 200-year time slices going back 24,000 years.
- Source: Osman, M.B., Tierney, J.E., Zhu, J. et al. Globally resolved surface temperatures since the Last Glacial Maximum. Nature 599, 239–244 (2021). “Globally resolved surface temperatures since the Last Glacial Maximum: “Climate changes across the past 24,000 years provide key insights into Earth system responses to external forcing. Climate model simulations and proxy data have independently allowed for study of this crucial interval; however, they have at times yielded disparate conclusions. Here, we leverage both types of information using paleoclimate data assimilation to produce the first proxy-constrained, full-field reanalysis of surface temperature change spanning the Last Glacial Maximum to present at 200-year resolution. We demonstrate that temperature variability across the past 24 thousand years was linked to two primary climatic mechanisms: radiative forcing from ice sheets and greenhouse gases; and a superposition of changes in the ocean overturning circulation and seasonal insolation. In contrast with previous proxy-based reconstructions our results show that global mean temperature has slightly but steadily warmed, by ~0.5 °C, since the early Holocene (around 9 thousand years ago). When compared with recent temperature changes, our reanalysis indicates that both the rate and magnitude of modern warming are unusual relative to the changes of the past 24 thousand years.”