84 Glaciations and Deglaciations: scientific evidence

Glaciations:  increase in continental ice

Deglaciations: decrease in continental ice

 

  • Refer to multiple advances (glaciations) and retreats (deglaciations) of glaciers.

  • Rare during the earth’s 4.6 billion year history (or we just did not find any records).

  • Several in the last 1 billion years.

Pleistocene Epoch: lasted from about 2,580,000 to 11,700 years ago

 

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Multiple ice ages:

  • Glaciers covered 30% of Earth (today 10%)

  • Last Glacial Maximum (LGM) extent 21,000 years ago

  • Global sea level was >100 m (330 ft) lower than today

 

Causes of Glaciations/Deglaciations:

  • Mostly unknown

  • Related to position of continents

  • Changes in amount of solar radiation influence advance and retreat:

  • Milankovitch cycles: changes in Earth’s orbit around Sun, tilt and wobble of Earth’s axis of rotation

  • Correlate well with change in global temperatures

Solar Forcing? Are we getting it right?

  • Solar light, heat, and particle streams drive weather and atmospheric chemistry

  • scientists have been making direct measurements (from space) of the total solar radiative input into Earth’s atmosphere only since 1978

  • Solar variability affects Earth’s climate in many intricate and nonlinear ways. Most effects are ultimately driven and modulated by the solar magnetic field and its conspicuous solar cycle, which repeats approximately every 11 years.

  • The effect of solar variability on climate is mostly hidden in the natural variability of the climate system; thus, careful statistical analysis is required to extract it from a noisy background.

  • For many years, a single quantity, total solar irradiance (TSI), which describes the total solar radiated power incident on Earth’s upper atmosphere, was used to summarize the solar contribution into climate models, neglecting other contributions. The discovery of the effects of radiation in the ultraviolet (UV) wavelength band shattered this simple picture.

  • Although the TSI is a key ingredient in Earth’s global energy budget, the spectrally resolved solar irradiance (SSI) provides much deeper insight into the impact of solar variability on the atmosphere. Unlike TSI, which integrates the contribution from all spectral bands (UV, visible, infrared) into one single quantity, SSI reveals variations at specific wavelengths, each of which affects Earth’s environment in a different way.

  • Making accurate SSI observations is a real challenge: SSI measurements must be carried out from space.

Source: Dudok de Wit, T., B. Funke, M. Haberreiter, and K. Matthes (2018), Better data for modeling the Sun’s influence on climate, Eos, 99. Published on 04 September 2018. https://doi.org/10.1029/2018EO104403

 

 

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Geology 101 for Lehman College (CUNY) Copyright © by Yuri Gorokhovich and Lumen Learning is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

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