- 4068 - EARTH'S ORBIT - and salty seas? Nearly 10,000 years ago, Earth came out of its most recent ice age. Vast, icy swaths of land around the poles thawed, melting the glaciers that had covered them for nearly 100,000 years. Why, after such a long period of cold, did the ice age finally come to an end?
------------------
4068 - EARTH'S
ORBIT - and salty seas?
- The traditional explanation for why ice ages begin and end is a series of eccentricities and wobbles in the planet's orbit known as the “Milankovitch cycles”. Named after Serbian scientist Milutin Milankovitch, these cycles describe patterns in Earth's orbit and axial tilt. Over time, our planet's orbit around the sun alternates from being more circular to more egg-shaped. At the same time, our planet's axis tends to both tilt and wobble.
-
- Milankovitch found
that these factors combine at regular intervals to cause land at 65 degrees
north latitude (a parallel that runs through Canada, Alaska and parts of
Eurasia) to become warmer than normal and theorized that this warming and then
subsequent cooling of the Northern Hemisphere explained the planet's cycle of
ice ages , or glacials, and warmer periods, or interglacials.
-
- However, while
there is evidence that Milankovitch cycles drive the ebb and flow of ice ages,
many modern glaciologists don't think the cycles' reported ties to ice ages
completely checks out. One issue is that when the glaciers in the Northern
Hemisphere melted, glaciers in the Southern Hemisphere melted too.
-
- But with the
traditional explanation, it's unclear how warming in one hemisphere would melt
glaciers in the other, when the
Milankovich-driven changes in sunlight intensity that would produce warmer
temperatures in the north would cause temperature drops in the south,
counterbalancing any net warming.
-
- Glaciologists have
attempted to fill in the gaps between what we know about Milankovitch cycles
and Earth's ice ages. The missing link needs to explain how these cycles cool
and warm the entire planet at once, not just one hemisphere at a time.
-
- One possible
explanation is that when the Northern Hemisphere began to warm around 13,000
years ago, meltwater and icebergs flooded the North Atlantic Ocean, causing a
temporary cooling of the Northern Hemisphere known as the Younger Dryas period
(12,900 to 11,700 years ago).
-
- There is some
evidence that the Younger Dryas affected ocean currents in a way that caused
the Southern Atlantic to warm up, stirring up the ocean in the process and
releasing tons of stored carbon dioxide into the atmosphere, which in turn
caused glaciers in the Southern Hemisphere to melt over the next 1,500 years.
The end result was likely a more carbon-rich atmosphere that continued to warm
both hemispheres, lifting the planet out of the glacial period.
-
- Another
hypothesis, published in 2021, suggests that the length and intensity of the
Southern Hemisphere's winters could dictate when ice ages end. On the surface,
it sounds like the polar opposite of the Milankovitch theory, which suggests
that Northern Hemispheric summers drive the climatic changes.
-
- However, long
winters in the Southern Hemisphere alter wind patterns near the tropics, which
can create frequent storms over an area of the Pacific Ocean known as the
Tropical Warm Pool, region of ocean that stores and releases great amounts of
heat. Altered winds can create storms in this area, which in turn releases
massive amounts of water vapor that can act as a greenhouse gas.
-
- Another idea is
that salty water pouring from the Indian Ocean into the Atlantic Ocean helped
end the last ice age. The Indian Ocean had become super salty because a drop in
sea level had cut off a critical current that flows from the Pacific to the
Indian Ocean; normally, this current diluted the Indian's very salty tropical
waters.
-
- A change in wind
patterns and currents in the Indian Ocean could have caused the Indian Ocean to
dump tons of dense, salty water into the Atlantic Ocean, altering its currents
and temperatures in both the Northern and Southern hemispheres.
-
- More evidence is
needed to know for sure if any of these hypotheses can actually explain why the
last ice age ended. But glaciologists are continuing to look into this cold
case.
-
- Nearly 10,000
years ago vast, icy swaths of land around the poles thawed, melting the
glaciers that had covered them for nearly 100,000 years. Why, after such a long period of cold, did
the ice age finally come to an end?
-
- Another
hypothesis, published in 2021, suggests that the length and intensity of the
Southern Hemisphere's winters could dictate when ice ages end. It sounds like the polar opposite of the
Milankovitch theory, which suggests that Northern Hemispheric summers drive the
climatic changes.
- However, long
winters in the Southern Hemisphere alter wind patterns near the tropics, which
can create frequent storms over an area of the Pacific Ocean known as the
“Tropical Warm Pool”, a region of ocean that stores and releases great amounts
of heat. Altered winds can create storms in this area, which in turn releases
massive amounts of water vapor that can act as a greenhouse gas.
-
- Another idea is
that salty water pouring from the Indian Ocean into the Atlantic Ocean helped
end the last ice age. The Indian Ocean had become super salty because a drop in
sea level had cut off a critical current that flows from the Pacific to the
Indian Ocean; normally, this current diluted the Indian's very salty tropical
waters.
-
- A change in wind
patterns and currents in the Indian Ocean could have caused the Indian Ocean to
dump tons of dense, salty water into the Atlantic Ocean, altering its currents
and temperatures in both the Northern and Southern hemispheres.
-
- More evidence is
needed to know for sure if any of these hypotheses can actually explain why the
last ice age ended. But glaciologists are continuing to look into this cold
case.
-
-
June 26, 2023 EARTH'S ORBIT
- and salty seas? 4068
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