Study links Earth's orbital variations, sea ice and ice ages. Earth is currently in what climatologists call an interglacial period, a warm pulse between long, cold ice ages when glaciers dominate our planet's higher latitudes. For the past million years, these glacial- interglacial cycles have repeated roughly on a 1. Now a team of Brown University researchers has a new explanation for that timing and why the cycle was different before a million years ago. Using a set of computer simulations, the researchers show that two periodic variations in Earth's orbit combine on a 1. Southern Hemisphere. Compared to open ocean waters, that ice reflects more of the sun's rays back into space, substantially reducing the amount of solar energy the planet absorbs.

As a result, global temperature cools. New research shows that the expansion of Southern Hemisphere sea ice during certain periods in Earth's orbital cycles can control the pace of the planet's ice ages. Credit: Jung- Eun Lee / Brown University. Orbit and climate. In the 1. 93. 0s, Serbian scientist Milutin Milankovitch identified three different recurring changes in Earth's orbital pattern.

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Each of these Milankovitch Cycles can influence the amount of sunlight the planet receives, which in turn can influence climate. The changes cycle through every 1. The problem is that the 1.

So why that cycle would be the one that sets the pace of glacial cycle is a mystery. But this new study shows the mechanism through which the 1. Earth's glacial cycle. The 2. 10. 00- year cycle deals with precession - the change in orientation of Earth's tilted rotational axis, which creates Earth's changing seasons. When the Northern Hemisphere is tilted toward the sun, it gets more sunlight and experiences summer.

At the same time, the Southern Hemisphere is tilted away, so it gets less sunlight and experiences winter. But the direction that the axis points slowly changes - or precesses - with respect to Earth's orbit.

As a result, the position in the orbit where the seasons change migrates slightly from year to year. Earth's orbit is elliptical, which means the distance between the planet and the sun changes depending on where we are in the orbital ellipse. So precession basically means that the seasons can occur when the planet is closest or farthest from the sun, or somewhere in between, which alters the seasons' intensity. In other words, precession causes a period during the 2. Northern Hemisphere summer happens around the time when the Earth is closest to the Sun, which would make those summers slightly warmer. Six months later, when the Southern Hemisphere has its summer, the Earth would be at its furthest point from the Sun, making the Southern Hemisphere summers a little cooler.

Every 1. 05. 00 years, the scenario is the opposite. In terms of average global temperature, one might not expect precession to matter much. Whichever hemisphere is closer to the Sun in its summer, the other hemisphere will be farther away during its summer, so the effects would just wash themselves out. However, this study shows that there can indeed be an effect on global temperature if there's a difference in the way the two hemispheres absorb solar energy - which there is. That difference has to do with each hemisphere's capacity to grow sea ice. Because of the arrangement of the continents, there's much more room for sea ice to grow in the Southern Hemisphere.

The oceans of the Northern Hemisphere are interrupted by continents, which limits the extent to which ice can grow. Hd Video 720P Hounds Of Love (2017). So when the precessional cycle causes a series of cooler summers in the Southern Hemisphere, sea ice can expand dramatically because there's less summer melting.

Lee's climate models rely on the simple idea that sea ice reflects a significant amount of solar radiation back into space that would normally be absorbed into the ocean. That reflection of radiation can lower global temperature. The answer is that the 1. The 1. 00. 00. 0- year cycle deals with the eccentricity of Earth's orbit - meaning the extent to which it deviates from a circle. Over a period of 1. It's only when eccentricity is high - meaning the orbit is more elliptical - that there's a significant difference between the Earth's furthest point from the sun and its closest. As a result, there's only a large difference in the intensity of seasons due to precession when eccentricity is large.

That's why we see a stronger 1. Much of the carbon dioxide - a key greenhouse gas - exhaled into the atmosphere from the oceans comes from the southern polar region. If that region is largely covered in ice, it may hold that carbon dioxide in like a cap on a soda bottle.

In addition, energy normally flows from the ocean to warm the atmosphere in winter as well, but sea ice insulates and reduces this exchange. So having less carbon and less energy transferred between the atmosphere and the ocean add to the cooling effect.

Explaining a shift. The findings may also help explain a puzzling shift in the Earth's glacial cycle.

For the past million years or so, the 1. But before a million years ago, paleoclimate data suggest that pace of the glacial cycle was closer to about 4. That suggests that the third Milankovitch Cycle, which repeats every 4. While the precession cycle deals with which direction the Earth's axis is pointing, the 4.

The tilt - or obliquity - changes from a minimum of about 2. The models show that, when the Earth was generally warmer than today, precession- related sea ice expansion in the Southern Hemisphere is less likely to occur. That allows the obliquity cycle to dominate the global temperature signature. After a million years ago, when Earth became a bit cooler on average, the obliquity signal starts to take a back seat to the precession/eccentricity signal. Lee and her colleagues believe their models present a strong new explanation for the history of Earth's glacial cycle - explaining both the more recent pace and the puzzling transition a million years ago.

As for the future of the glacial cycle, that remains unclear, Lee says. It's difficult at this point to predict how human contributions to Earth's greenhouse gas concentrations might alter the future of Earth's ice ages. Source: Brown University.

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