Study finds that land cooled by 6 degrees Celsius during the last ice age may have an impact on global warming

The researchers showed that previous studies underestimated the cooling of the last ice age, which underestimated the sensitivity of Earth's climate to greenhouse gases. Higher climate sensitivity is not good news for future global warming, which may be stronger than expected using previous best estimates.

According to a new study published in the journal Nature, during the last end-glacial period (LGM), the low-elevation mid-to-low latitude land surface cooled by an average of 5.8±0.6 Celsius.

The temperature estimates in the study are significantly lower than those of some well-known marine and low-elevation ground-based studies, which relied on various proxies to reconstruct past temperatures during the LGM, a process that dates back about 20,000 years ago and represents the latest update on global stability. expansion period. Much cooler climate than today.

"The real significance of our paper is that previous work has grossly underestimated cooling during the last ice age, and the latter's impact on Earth's climate sensitivity to greenhouse gases," said co-author Jeffrey Severinghouse, professor of geosciences. Underestimated." Scripps Institution of Oceanography, University of California, San Diego. "The main reason the previous work was flawed was that it relied heavily on species richness. But just like humans, species also tend to migrate to places suitable for the climate. For example, imagine snowbirds relocating from Canada to Arizona, where winter ... So species are not very good thermometers."

The paper does broadly support the recent marine proxy research by Tierney et al. The paper published last year found that cooling at lower latitudes was much greater than previous efforts, and in turn, it was more sensitive to climate than previous studies. The earlier paper suggested that the equilibrium response to a doubling of atmospheric carbon dioxide in Earth's global average surface temperature is 3.4 degrees Celsius, which is in line with the range of estimates from the latest climate models, but a bit warmer than the usual best estimate of 3.0 degrees Celsius.

Our findings suggest that high sensitivity to climate is not good news for future global warming, which may be stronger than previous best estimates. In particular, our global assessment results further corroborate the findings of several case studies of noble gases present in the tropics. Commented Werner Esbach, Professor at the Heidelberg Institute for Environmental Physics: University of Heidelberg, Germany.

The paper utilizes a technique that can directly and quantitatively determine past surface temperatures by measuring dissolved noble gases in ancient groundwater. The noble gases in the atmosphere are chemically and biologically inert, with no apparent sinks or sources over the 40,000-year time horizon relevant to this study. They dissolve in groundwater, and their equilibrium concentrations are strongly temperature-dependent. The authors compiled four decades worth of groundwater noble gas data on every continent except Antarctica, as well as previously unpublished measurements in a number of important tropical regions, to produce a global record of noble gas-derived temperatures for the LGM.

"Noble gas paleotemperature records are so strong because they are based on physics and are not greatly affected by life - which always complicates everything - and short-term extreme events," said article co-author Martin Stott. , who is a professor in the Department of Environmental Sciences at Barnard College and an adjunct senior research scientist at the Lamont Doherty Earth Observatory. "They provide average temperatures over hundreds to thousands of years. From studies in the early 1990s to the most recent one, it's amazing to me how well the paleotemperature reconstructions of noble gases at low latitudes are and makes I am happy."

According to the authors, the study supports methods for analyzing noble gases to reconstruct paleotemperatures and provides more confidence in climate models.

"Another major goal of our study was to assess the overall accuracy of so-called 'noble gas paleothermometers' reconstructing land temperatures during the last ice age. Naturally, we are confident in the ability to use this tool to understand the past by combining modern temperature observations with Comparing the results with independent estimates of noble gases in relatively young groundwater, we found that noble gas thermometers are very accurate over a wide temperature range of around 2 to 33 degrees Celsius (36 to 91 degrees Fahrenheit). Cooling estimates during LGM add a lot of confidence," said Alan Seltzer, lead author of the paper and assistant scientist in the Department of Oceanography and Geochemistry at the Woods Hole Oceanographic Institution.

The new analysis is important, Seltzer added, because climate models "provide an important tool that policymakers can use to decide how to prepare for future environmental changes. The study allays concerns that the models may be overdone based on LGM proxy data." Predicting the global mean temperature response to carbon dioxide. Indeed, based on our study and a recent compilation of ocean proxies, it is clear that the proxies and models of the paleoclimate are consistent."