Ice age how fast

In addition, the more northerly position of the ITCZ during interstadials results in enhanced freshwater precipitation in the tropical North Atlantic, further reducing surface salinity.

Eventually, surface salinity is reduced enough to weaken AMOC, shifting the climate into a cold stadial b. During stadials, cooler conditions in the North Atlantic reduce meltwater input from the ice sheets, allowing surface salinity to increase. In addition, the ITCZ shifts southward during stadials, reducing the amount of freshwater input to the tropical North Atlantic. Both mechanisms result in an increase in North Atlantic salinity that eventually causes AMOC to strengthen, returning the climate system to an interstadial.

An alternative hypothesis to explain the D-O cycles of the last glacial period has to do with large-scale changes in wind patterns over the North Atlantic Romanova et al. Mountain ranges are responsible for forming special atmospheric circulation features, known as stationary waves, which form as wind is pushed up and over topographic highs. Seager et al. The jet stream is a fast flowing current of wind in the upper atmosphere responsible for steering storm systems in the mid-latitudes around the globe.

As the jet stream flows over the Rocky Mountains, it is forced to dip southward over the central US and then turns sharply to the northeast to flow over the open North Atlantic and then northern Europe. Therefore, the presence of the Rocky Mountains in North America forces the jet stream flow to be less zonal east-west oriented and more meridional north-south oriented over the North Atlantic.

Because the jet stream tends to separate colder, sub-polar air masses to the north from warmer, tropical air masses to the south, climate over northern Europe is warmer compared to climate at the same latitude on the western side of the Atlantic e. During the last ice age, massive continental ice sheets up to five km high covered much of North America and northern Europe the Laurentide and Fennoscandian ice sheets, respectively.

Like mountain ranges, the ice sheets were tall enough to influence stationary waves and change the path of the jet stream. Indeed, computer modeling results suggest that regional elevation changes in the Laurentide ice sheet could have had a large effect on the position of the jet stream during the last glacial period Figure 4 Jackson Studies have suggested large changes in sea level up to 35 m across D-O cycles Siddall et al.

Therefore, abrupt topographic changes in Northern Hemisphere ice sheets could have forced large-scale atmospheric circulation reorganizations as continental glaciers constantly waxed and waned.

According to this hypothesis, the path of the jet stream over the Northern Hemisphere oscillated between more meridional Figure 4a versus zonal flow Figure 4b as it interacted with changes in the elevation and overall size of the continental ice sheets, resulting in the saw-tooth pattern of D-O cycle temperature changes recorded in the Greenland ice core records Wunsch Figure 4: Mechanism of the wind field oscillation hypothesis.

The hypothesized position of the jet stream during warm interstadials a compared to cold stadials b during the last ice age. The presence of larger and thicker ice sheets during cold stadials forced the jet stream to shift farther south, resulting in a more zonal flow across the Atlantic Ocean. Note that the jet stream separates warm subtropical air to the south from cooler polar air masses to the north.

Therefore, the more zonal flow of the stadial jet stream allowed cold, glacial conditions to extend farther south, resulting in a much colder climate in the North Atlantic and Europe. Although climate scientists have worked hard to determine the ultimate trigger of abrupt climate change during the last ice age, it is likely that a combination of ocean and atmospheric circulation changes were involved.

For example, a subtle shift in atmospheric circulation to a more meridional jet stream flow would encourage the transport of warm, salty water into the sub-polar North Atlantic, which in turn could lead to the reestablishment of strong AMOC and enhanced oceanic heat transport to the high-latitude North Atlantic. In this case, ocean circulation changes associated with AMOC may have amplified small changes initiated in the atmosphere on the transition into warm interstadials. Conversely, a sudden reduction in AMOC due to an influx of freshwater into the high-latitude North Atlantic region has the potential to trigger a regional cooling that can significantly alter tropical atmospheric circulation around the globe.

Although we still do not know which happened first, interactions between both the ocean and the atmosphere must have played an important role in driving the dramatic climate oscillations of the last ice age. This paper only discusses two hypotheses to explain the abrupt climate shifts of the last ice age.

Isotope: Any of the forms of a chemical element with the same atomic number but differing atomic mass. Interstadial: A period of abrupt warming during an otherwise cold climate characteristic of the last Ice Age. Dansgaard-Oeschger Cycles: Periods of rapid climate variability that occurred throughout the last Ice Age, during which time climate alternated between cold stadial conditions and relatively mild interstadial periods.

Proxy: A preserved natural recorder of climate variability that scientists can use to estimate climate conditions of the past e. Trade Winds: Strong surface winds found in the tropics that blow from east to west and converge near the Equator. Gulf Stream: A strong, fast moving ocean current that originates in the subtropical Atlantic and flows northward along the eastern coast of North America, transporting warm tropical waters to the high-latutudes.

Atlantic Meridional Overturning Circulation AMOC : The combined processes of the northward movement of warm waters via the Gulf Stream to the sub-polar regions of the North Atlantic, and subsequent sinking of these waters as they cool and become denser, forming North Atlantic Deep Water.

Intertropical Convergence Zone ITCZ : Area of low atmospheric pressure formed by the convergence of the Northeast and Southeast trade winds, often characterized by a band of clouds and rain near the Equator. Stationary waves: A feature of atmospheric circulation formed by wind that is pushed up and over topographic highs e.

Subtropical Jet stream: Fast flowing, narrow air current that flows from west to east, often having a meandering shape, caused by a combination of Earth's rotation and heating of the atmosphere by the Sun.

Birchfield, G. A salt oscillator in the glacial Atlantic, 2, A "scale analysis" model. Paleoceanography 5 , Bond, G. A pervasive millennial-scale cycle in North Atlantic Holocene and glacial climates. Science , Clark et al. Broecker, W. A salt oscillator in the glacial Atlantic? The concept. Paleoceanography 5 , a. The magnitude of global fresh-water transports of importance to ocean circulation.

Climate Dynamics 4 , b. Clark, P. Northern hemisphere ice-sheet influences on global climate change. Freshwater forcing of abrupt climate change during the last glaciation. Clement, A. Mechanisms of abrupt climate change of the last glacial period. And the physical shape of the continents would look completely different across the whole planet.

A huge drop in sea level of up to metres would close down marine channels - the Mediterranean Sea, Torres Strait, Bass Strait and Bering Strait - and create new areas of land that could be used for habitation or agriculture. Ocean ports would no longer be on the ocean, and anyone wanting water views would need to relocate large distances.

During the last ice age, which ran from about , years ago to 10, years ago, the lower sea levels allowed humans to move out across the entire world. While there was still some water between Asia and Australia it took just a few short canoe trips to bring the first humans to Australasia. There was no Torres Strait so humans could have just walked from New Guinea to the Australian mainland.

And there was no Bass Strait so humans could have walked from the Australian mainland over to Tasmania," he said. The whole dispersal of humans around the world during the last , years was made entirely possible by the fact we were in an ice age at the time. It's a fair question - how can we know so much about these major events in the past? Scientists have a variety of methods they use. Evidence for the more recent ice ages comes from changing sea levels in the past, which can be seen by looking at coral reefs or modern landscapes.

Looking at corals, and coral reefs and evidence of past sea level changes in the tropics, they saw there was a cycle of changing sea levels," Dr Phipps said. Ice core records also provide invaluable information on changes in temperature and greenhouse gases over the last , years. But going back further into the past, evidence for ice ages in the last tens of millions of years is predominantly seen in ocean sediments.

And for the deep time ice ages that occurred tens to hundreds of millions of years ago, scientists use the geological record where the story of sea level and climate can be unravelled by analysing rocks of various ages. We acknowledge Aboriginal and Torres Strait Islander peoples as the First Australians and Traditional Custodians of the lands where we live, learn, and work.

What is an ice age? Springer Berlin Heidelberg. Catling, D. The Archean atmosphere. Science Advances , 6 9 , eaax Cox, G. Continental flood basalt weathering as a trigger for Neoproterozoic Snowball Earth.

Earth and Planetary Science Letters , , 89— Earle, S. Physical Geology — 2nd Edition. Accessed October 24, Eldredge, S. Glad you asked: ice ages — what are they and what causes them? Survey Notes , 42 3. Hayes, J. Evolution of the atmosphere. Hoffman, P. A Neoproterozoic Snowball Earth. Science , , — Joel, L. How life on our planet made it through Snowball Earth.

The New York Times. Accessed January 5, Kopp, R. The Paleoproterozoic snowball Earth: A climate disaster triggered by the evolution of oxygenic photosynthesis. Proceedings of the National Academy of Sciences , 32 , — Lechte, M. Subglacial meltwater supported aerobic marine habitats during Snowball Earth. Proceedings of the National Academy of Sciences, 51 , — Luo, G.

Science Advances , 2 5 , e Macdonald, F. Initiation of Snowball Earth with volcanic sulfur aerosol emissions. Geophysical Research Letters. National Park Service. Glaciers and Past Climates. Renwick, J. The Conversation. Scher, H. Schirber, M. This happens in a multitude of ways. Colder ocean water dissolves more CO2 , absorbing more from the atmosphere, though this is somewhat offset by the effect of higher salinity on ocean CO2 absorption — as fresh water from snow freezes into ice sheets.

In addition, ice-age glaciers grind up rocks into dust that provides nutrients to ocean life, helping boost the amount of carbon in the deep ocean as plants get eaten and sink into the ocean. Expanded sea ice also covers up regions of the ocean where upwelling helps bring deep-ocean CO2 back up to the surface, limiting the amount of CO2 that can be released from the oceans back into the atmosphere. Changes to ocean circulation driven by winds, evaporation and salinity also play a role in the reduction of CO2 associated with the onset of glaciation.

Finally, falling sea levels also impact the growth of coral reefs and other ocean ecosystems which affect the amount of CO2 stored in the ocean. The effect of the orbital features on the total sunlight reaching the Earth is almost zero; the sunshine is just moved between areas and seasons. But, the whole world cools into an ice age, and the whole world warms coming out of an ice age, despite half the world getting less sun when the other half gets more.

And, so far, all the explanations of this require the effects of the CO2, which beautifully explain it. A recent study by Dr Daniel Baggenstos at the University of Bern and colleagues examined the relative contribution of different factors during the transition from the last ice age to the current interglacial period. In some ways, however, this is exactly what we would expect; there were no humans burning fossil fuels during the end of the last ice age, so CO2 served more as a feedback to orbital changes rather than the climate forcing that it is today.

So, CO2 must be a feedback. Because the amount of sunshine — and the amount of ice — have direct and immediate effects on temperature, there should be places on Earth in which any change in CO2 lags rather than leads the orbital cause and the temperature change. This should not bother anyone. The analogy I sometimes use is that, if I overspend my credit card and go into debt, interest will kick in and make my debt bigger.

The interest lags debt — first I go into debt, then I pay interest, then I go further into debt. Pretty much everyone understands that this is a sensible, if unpleasant situation. When the orbits affect ice and temperature, this changes other things that, in turn, affect CO2, which, in turn, affects temperature some more — similarly sensible if the full story is understood.

That said, understanding of the interrelationship between CO2 and temperature at the end of ice ages has advanced in recent years with better reconstructions of both past temperature and CO2 levels in ice cores from Antarctica.