Dusty rainfall records reveal new understanding of Earth’s long-term climate

Posted: May 25, 2018 by oldbrew in atmosphere, climate, Ice ages, Ocean dynamics, research, wind

Antarctic sea ice [image credit: BBC]

Have scientists been looking through the wrong end of the telescope, so to speak, regarding ice ages theory?

Ancient rainfall records stretching 550,000 years into the past may upend scientists’ understanding of what controls the Asian summer monsoon and other aspects of the Earth’s long-term climate, says EurekAlert.

Milankovitch theory says solar heating of the northernmost part of the globe drives the world’s climate swings between ice ages and warmer periods.

The new work turns Milankovitch on its head by suggesting climate is driven by differential heating of the Earth’s tropical and subtropical regions.

The standard explanation of the Earth’s regular shifts from ice ages to warm periods was developed by Milutin Milankovitch in the 1920s. He suggested the oscillations of the planet’s orbit over tens of thousands of years control the climate by varying the amount of heat from the sun falling above the Arctic Circle in the summer.

“Here’s where we turn Milankovitch on its head,” said first author J. Warren Beck, a UA research scientist in physics and in geosciences. “We suggest that, through the monsoons, low-latitude climate may have as much effect on high-latitude climate as the reverse.”

During the northern summer, the subtropics and tropics north of the equator warm and the tropics and subtropics south of the equator cool.

Modern observations show the difference in heat propels atmospheric changes that drive the intensity of the monsoon. Beck said the monsoon can affect wind and ocean currents as far away as the North Atlantic and Arctic Oceans.

The Asian monsoon season is the biggest annual rainfall system on Earth and brings rainfall to about half the world’s population. The monsoon season occurs approximately April to September.

Beck and his colleagues found that over tens of thousands of years the changes in the intensity of the Asian summer monsoon corresponded to the waxing and waning of the polar ice caps.

The researchers suggest those long-term changes in the monsoon drove global changes in wind and ocean currents in ways that affected whether the polar ice caps grew or shrank.

Beck said this new explanation of the Earth’s past climate cycles will help climate modelers figure out more about the world’s current and future climate.

Continued here.

  1. p.g.sharrow says:

    Icecaps, snow fields, Glaciers all grow or shrink on the AMOUNT of snow fall on them, Not waxing and waning of the average local temperature. Local temperature changes are CAUSED by the amount of snow accumulated.
    Evaporation from the oceans and air flows funnel the moisture into areas that have low enough temperatures to result in snow, Heavy Snow. not extreme cold is the cause of lower average temperatures and ice buildup…pg

  2. E.M.Smith says:

    I don’t buy it.

    It isn’t a question of how the ice forms. The natural state of things is to have a glacial condition. What must be answered is just “why does all the ice melt briefly every 120,000 years or so?

    Ice melts from heating. Simply having less snowfall in a cold place does not cause melting.

  3. p.g.sharrow says:

    Go look into the central Antarctic, super cold, very little snow falls there and what falls sublimates, it very rarely gets warm enough to melt. there is bare ground there.
    In coastal Alaska where there are Glaciers everywhere it rarely gets very cold but it snows heavily, over 100feet in a winter. In the interior, 50 miles away it gets really cold and bare ground, in spite of the winters being 100F colder, because it only gets 2 feet of dry snow in a winter.

    It is not the cold, It is the BTUs of energy that is the key. The volume/amount of energy, temperature is not a measurement of total energy involved, Change of state of the MASS involved is where the majority of the energy is,. not in the the temperature.

    All of that 100,000 years of accumulated Ice warms from bottom up due to geothermal energy accumulation but it can not make the transition until the full measure of energy accumulates in all of the mass. Ice is conductive of energy. The Quads of energy lost to space in freezing all that snow must accumulate before it can melt. I have watched the “breakup” after a long cold winter, It warms and warms and nothing happens for weeks and then it all disappears in a rush. The full measure of energy required to transition from solid at 32F to liquid at 32 F has been accumulated…pg

  4. RobR says:


    The monsoon does not just deliver rainfall. It also delivers heat. Heat delivery melts ice. A lack of heat delivery allows ice to accumulate. The amount of summer sunshine over the Northern Hemisphere ice caps is not a particularly good proxy for the amount of available heat. The insolation gradient from the tropics to the high latitudes is what tends to cause the biggest variation in heat and moisture delivery to the ice caps. The insolation gradient changes in a cyclical manner in time with the waxing and waning of the ice sheets. Direct sunshine, surface albedo variation, changes in ocean circulation etc all play a part. In my opinion the formula for glacial terminations has not been convincingly cracked yet by anyone.

  5. oldmanK says:

    Maybe we are getting there. Milankovitch was correct in principle but based on a wrong assumption. No one AFAIK proved obliquity is eternally fixed to close limits.

    Quote “— intensity of the Asian summer monsoon corresponded to the waxing and waning of the polar ice caps.” But as E M Smith asks “— why does all the ice melt briefly every 120,000 years or so?” It has been said (don’t have ref right now) there cannot be a glaciation at 22-24 deg obliquity. A lesser obliquity (~14.5deg) means more evaporation inter-tropics and no summer melt at the poles. The evidence for that is in the ice-caps. Compare polar to equatorial ice records in proxies; it is evident. Check when that happened during the Holocene Max and that corresponds to markers from a number of studies and proxies.

    A check on the Milankovitch assumption re obliquity is a good starting point. That goes back to Stockwell and Newcomb. Story here: https://malagabay.wordpress.com/2015/04/14/celestial-crystal-balls-and-the-temple-of-amen-ra/

    And here: http://adsabs.harvard.edu/full/1979A%26A….73..129W