Climate variability

Climate variability and dynamics during the warm period of the Lower to Middle Pliocene provide clues for future climate change


Field photograph of the Shilou red clay sequence of the eastern Chinese loess plateau. Credit: Ao Hong

A recent study by an international research group led by Professor Ao Hong of the Institute of the Earth’s Environment of the Chinese Academy of Sciences revealed the variability and dynamics of the Asian climate during the warm period of the Pliocene lower than medium, thus providing clues for future climate. cash.

The joint research team included scientists from China, Australia, Germany, France, the Netherlands and the United States. The group’s findings were published in Nature Communication November 26.

The warm period of the early to mid-Pliocene, about 5 to 3 million years ago (Ma), which preceded the glaciation of the northern hemisphere, was the most recent period of persistent warmer conditions than today. ‘hui. During this warm interval, the average annual air temperatures at the Earth’s surface were about 2-4 ° C higher than today, the northern hemisphere was largely ice-free, global sea level was about 20 to 25 m higher than today and atmospheric CO2 concentrations were comparable to current levels.

The sixth assessment report of the Intergovernmental Panel on Climate Change (IPCC) predicts that current CO emissions2, the warm conditions will continue for a long time and are likely to intensify, which could cause the Earth’s future climate to shift to a warm state similar to the warm period of the early to mid-Pliocene.

“Understanding the variability and dynamics of climate during the warm period of the early to mid-Pliocene is important to better project future climate responses to sustained global warming,” said Professor Ao, principal investigator of the study.

The loess / red clay aeolian sequences on the Chinese Loess Plateau (CLP) provide a unique high-resolution archive of terrestrial climatic variations spanning continuously over the past 25 million years (Myr). The researchers established summer monsoon records of about 4.7 Myr (Al / Na, Rb / Sr and luminosity) continuously covering the period from about 8.1 to about 3.4 Ma at a resolution about 1 to 2 thousand years (kyr) from the Shilou Aeolian Red Clay Succession on the eastern CLP. These recordings reveal the details and forcing mechanisms of Asian climate variability on an orbital timescale as well as longer trends from the late Miocene to mid-Pliocene.

High resolution records of Al / Na, Rb / Sr and luminosity show that the Asian summer monsoon had significant periodicities of 405 kyr and ~ 100 kyr between 8.1 and 3.4 Ma, which corresponds to a dynamic response to the modulation of the eccentricity of solar insolation, a forcing at low latitudes.

Surprisingly, the cyclicity of the obliquity is only weakly expressed in these monsoon records, although it dominated the Antarctic ice cycles throughout the late Miocene-Pliocene. Thus, it appears that orbital-scale Asian summer monsoon variability responded more dynamically to sunstroke forcing than to ice cap forcing during the Late Miocene to mid-Pliocene, when the he northern hemisphere was largely ice free and continental scale. ice caps only developed in Antarctica.

By integrating their new CLP records on red clay and the summer monsoon with existing terrestrial records, land-sea correlations and climate model simulations, the research group found that CO2-Global warming induced across the Miocene-Pliocene boundary (MPB) at ~ 5.3 Ma both increased summer monsoon moisture transport over East Asia and improved the aridification over large parts of Central Asia by increasing evaporation.

This finding offers paleoclimate-based support for the “wet- gets wetter and drier- gets drier” projections of future regional hydroclimatic responses to sustained anthropogenic forcing.

Observing the intensification of the hydrological gradient at continental scale over Asia linked to global warming through the DPP has important implications for future Asian climate responses to high and sustained anthropogenic emissions.

“This implies that with long-term sustainable global warming, most of the monsoon regions of East Asia could become even wetter than they are now, with increasing flood risks, while Central Asia could become even drier, with more persistent droughts and desertification going forward, ”said Professor Jin Zhangdong, study co-author and director of the State Key Laboratory of Loess and Quaternary Geology.

Bridging the knowledge gap on the evolution of the Asian monsoons

More information:
Hong Ao et al, Global warming-induced Asian hydrological climate transition across the Miocene-Pliocene boundary, Nature Communication (2021). DOI: 10.1038 / s41467-021-27054-5

Provided by Chinese Academy of Sciences

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