page_title: Milankovitch cycles
section_title: Predicted effects mystery
hierarchical_section_title: Milankovitch cycles / Theory constraints / Predicted effects mystery
context_page_description: Milankovitch cycles describe the collective effects of changes in the Earth's movements on its climate over thousands of years. The term is named for Serbian geophysicist and astronomer Milutin Milanković. In the 1920s, he hypothesized that variations in eccentricity, axial tilt, and precession resulted in cyclical variation in the solar radiation reaching the Earth, and that this orbital forcing strongly influenced climatic patterns on Earth.
  Similar astronomical hypotheses had been advanced in the 19th century by Joseph Adhemar, James Croll and others, but verification was difficult because there was no reliably dated evidence, and because it was unclear which periods were important.
  Now, materials on Earth that have been unchanged for millennia are being studied to indicate the history of Earth's climate. Though they are consistent with the Milankovitch hypothesis, there are still several observations that the hypothesis does not explain.
context_section_description: Physical evidence shows that the variation in Earth's climate is much more extreme than the variation in the intensity of solar radiation calculated as the Earth's orbit evolves. If orbital forcing causes climate change, science needs to explain why the observed effect is amplified out of linear proportion to the theoretical cause.
  Some climate systems exhibit amplification (positive feedback) and others exhibit damping responses (negative feedback). As an illustration, if during an ice age the northern land masses were covered in year-round ice, solar energy would be reflected away, counteracting the eventual warming effect from orbital forcing and extending the ice age.
  The Earth's current orbital inclination is 1.57° (see above). Earth presently moves through the invariable plane around January 9 and July 9. At these times, there is an increase in meteors and noctilucent clouds. If this is because there is a disk of dust and debris in the invariable plane, then when the Earth's orbital inclination is near 0° and it is orbiting through this dust, materials could be accreted into the atmosphere. This process could explain the narrowness of the 100,000-year climate cycle.
caption: 420,000 years of ice core data from Vostok, Antarctica research station, with more recent times on the left
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