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Tipping elements in the Earth's climate system
Posted on Monday, February 04, 2008 @ 23:29:27 UTC by vlad
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 Anthropogenic forcing could push the Earth’s climate system past
critical thresholds, so that important components may “tip” into
qualitatively different modes of operation. In the renowned magazine Proceedings of the National Academy of Sciences
(PNAS) an international team of researchers describes, where small
changes can have large long-term consequences on human and ecological
systems.
“Society may be lulled into a
false sense of security by smooth projections of global change,“ the
researchers around Timothy Lenton from the British University of East
Anglia in Norwich and Hans Joachim Schellnhuber from the Potsdam
Institute for Climate Impact Research report. Global change may appear
to be a slow and gradual process on human scales. However, in some
regions anthropogenic forcing on the climate system could kick start
abrupt and potentially irreversible changes. For these sub-systems of
the Earth system the researchers introduce the term “tipping element”.
Drawing on a workshop of 36
leading climate scientists in October 2005 at the British Embassy,
Berlin, Germany, a further elicitation of 52 experts in the field, and
a review of the pertinent literature, the authors compiled a short-list
of nine potential tipping elements. These tipping elements are ranked
as the most policy-relevant and require consideration in international
climate politics.
Arctic sea-ice and the Greenland Ice Sheet are regarded as the most
sensitive tipping elements with the smallest uncertainty. Scientists
expect ice cover to dwindle due to global warming. The West Antarctic
Ice Sheet is probably less sensitive as a tipping element, but
projections of its future behavior have large uncertainty. This also
applies to the Amazon rainforest and Boreal forests, the El Niño
phenomenon, and the West African monsoon. “These tipping elements are
candidates for surprising society by exhibiting a nearby tipping
point,” the authors state in the article that is published in PNAS
Online Early Edition. The archetypal example of a tipping element, the
Atlantic thermohaline circulation, could undergo a large abrupt
transition with up to ten percent probability within this century,
according to the UN climate report from 2007.
Given the scale of potentially dramatic impacts from tipping
elements the researchers anticipate stronger mitigation. Concepts for
adaptation that go beyond current incremental approaches are also
necessary. In addition, “a rigorous study of potential tipping elements
in human socio-economic systems would also be welcome,” the researchers
write. Some models suggest there are tipping points to be passed for
the transition to a low carbon society.
Highly sensitive tipping elements, smallest uncertainty
Greenland Ice Sheet - Warming over the ice sheet accelerates ice
loss from outlet glaciers and lowers ice altitude at the periphery,
which further increases surface temperature and ablation. The exact
tipping point for disintegration of the ice sheet is unknown, since
current models cannot capture the observed dynamic deglaciation
processes accurately. But in a worst case scenario local warming of
more than three degrees Celsius could cause the ice sheet to disappear
within 300 years. This would result in a rise of sea level of up to
seven meters.
Arctic sea-ice - As sea-ice melts, it exposes a much darker ocean
surface, which absorbs more radiation than white sea-ice so that the
warming is amplified. This causes more rapid melting in summer and
decreases ice formation in winter. Over the last 16 years ice cover
during summer declined markedly. The critical threshold global mean
warming may be between 0.5 to 2 degrees Celsius, but could already have
been passed. One model shows a nonlinear transition to a potential new
stable state with no arctic sea-ice during summer within a few decades.
Intermediately sensitive tipping elements, large uncertainty West Antarctic Ice Sheet -
Recent gravity measurements suggest that the ice sheet is losing mass.
Since most of the ice sheet is grounded below sea level the intrusion
of ocean water could destabilize it. The tipping point could be reached
with a local warming of five to eight degrees Celsius in summer. A
worst case scenario shows the ice sheet could collapse within 300
years, possibly raising sea level by as much as five meters.
Boreal forest - The northern forests exhibit a complex interplay
between tree physiology, permafrost and fire. A global mean warming of
three to five degrees Celsius could lead to large-scale dieback of the
boreal forests within 50 years. Under climate change the trees would be
exposed to increasing water stress and peak summer heat and would be
more vulnerable to diseases. Temperate tree species will remain
excluded due to frost damage in still very cold winters.
Amazon rainforest - Global warming and deforestation will probably
reduce rainfall in the region by up to 30 percent. Lengthening of the
dry season, and increases in summer temperatures would make it
difficult for the forest to re-establish. Models project dieback of the
Amazon rainforest to occur under three to four degrees Celsius global
warming within fifty years. Even land-use change alone could
potentially bring forest cover to a critical threshold.
El Niño Southern Oscillation (ENSO) – The variability of this
ocean-atmosphere mode is controlled by the layering of water of
different temperatures in the Pacific Ocean and the temperature
gradient across the equator. During the globally three degrees Celsius
warmer early Pliocene ENSO may have been suppressed in favor of
persistent El Niño or La Niña conditions. In response to a warmer
stabilized climate, the most realistic models simulate increased El
Niño amplitude with no clear change in frequency.
Sahara/Sahel- and West African monsoon - The amount of rainfall is
closely related to vegetation climate feedback and sea surface
temperatures of the Atlantic Ocean. Greenhouse gas forcing is expected
to increase Sahel rainfall. But a global mean warming of three to five
degrees Celsius could cause a collapse of the West African monsoon.
This could lead either to drying of the Sahel or to wetting due to
increased inflow from the West. A third scenario shows a possible
doubling of anomalously dry years by the end of the century.
Indian summer monsoon - The monsoon circulation is driven by a
land-to-ocean pressure gradient. Greenhouse warming tends to strengthen
the monsoon since warmer air can carry more water. Air pollution and
land-use that increases the reflection of sunlight tend to weaken it.
The Indian summer monsoon could become erratic and in the worst case
start to chaotically change between an active and a weak phase within a
few years.
Lowly sensitive tipping elements, intermediate uncertainty
Atlantic thermohaline circulation - The circulation of sea currents
in the Atlantic Ocean is driven by seawater that flows to the North
Atlantic, cools and sinks at high latitudes. If the inflow of
freshwater increases, e.g. from rivers or melting glaciers, or the
seawater is warmed, its density would decrease. A global mean warming
of three to five degrees Celsius could push the element past the
tipping point so that deep water formation stops. Under these
conditions the North Atlantic current would be disrupted, sea level in
the North Atlantic region would rise and the tropical rain belt would
be shifted.
Citation: Article: Lenton, T. M., Held, H., Kriegler, E., Hall, J.
W., Lucht, W., Rahmstorf, S. and Schellnhuber, H. J. (2008). Tipping
elements in the Earth's climate system. Proceedings of the National
Academy of Sciences, Online Early Edition
Source: Potsdam Institute for Climate Impact Research
Via: http://www.physorg.com/news121366474.html
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Re: Tipping elements in the Earth's climate system (Score: 1)
by ElectroDynaCat on Tuesday, February 12, 2008 @ 09:43:45 UTC
(User Info | Send a Message) | Until a catastrophic event occurs, no one will heed the warnings, prefering the 10 second sound bite and news of Britneys troubles to the real troubles they will all be facing in the near future.
Enter the era of consequences, starting this summer. If the pattern continues, look for the first wake up call to occur this summer in the southeast of the U.S..
Expect atmospheric conditions that will bring business as usual to a halt. Extended periods of inferno like temperatures that will cause system wide failures of the power grid for weeks at a time.
Stay out of large urban areas like Atlanta, where the heat island effect will be be a force multiplier. Expect fatalities amoung the elderly, the sick, and even the healthy that will be in numbers unseen since the Black Death.
Have a nice day!
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Re: Tipping elements in the Earth's climate system (Score: 1)
by Technophile on Tuesday, February 05, 2008 @ 09:51:34 UTC
(User Info | Send a Message) | News Release:
Scientists from the Pothead Institute for Climate change issued a report today noting that from June through December of 2007 the Sun came up later and later each day. They note that if this trend continues we may reach a tipping point where the Sun doesn't come up at all. This would lead to a disastrous outlook for the Earth's climate. The fact that the Sun has started coming up earlier since late December doesn't mean anything, they note as this is most likely a short term anomaly in the longer term trend. Pothead scientists note that the only way to avoid the disastrous trend is for the human race to commit suicide and leave the planet to the birds. "This is the only course of action that will placate the Sun God," stated the scientists.
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Re: Tipping elements in the Earth's climate system (Score: 1)
by malc on Tuesday, February 05, 2008 @ 02:14:48 UTC
(User Info | Send a Message) http://web.ukonline.co.uk/mripley | They forgot to mention the gulf stream which warms northern europe preventing it from having a siberian climate. If it was to shift southwards (or stop) then northern europe would cool dramatically. Global warming could cause northern europe to freeze! Too complicated a scenario for the skeptics to understand is that one!
The worst case greenland scenario is based on melting glaciers. recent studies have shown that the glaciers are sliding on melt water faster than they are melting. This sliding is accelerating and so the loss of glacial ice of greenland could be as short as decades. However nobody really knows ....yet. They just know that with the things as they are (and getting worse) it will definitely happen in some timescale.
One thing is consistent. The causes are better understood and the effects are being better modelled year on year. None of it points to "natural" induced phenomena. |
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Re: Tipping elements in the Earth's climate system (Score: 1)
by plastronneke on Tuesday, February 05, 2008 @ 04:45:38 UTC
(User Info | Send a Message) | They also forget to mention that hot magma is melting greenland on the one side and that there are very low temperatures recorded on the whole other side on greenland. And centuries ago the vikings used greenland for agriculture and hunting on "the white fields in the north" (thus, the south was not icy).
The climate has always been on the move, and it always will be. Greenhouse gas-theory is not right according to me. There have been cold periods and warm periods in the medievel-times. The biggest temperature-rising was before WW2, when there was little CO2-produciont. After WW2 there suddenly was a lot CO2 production and the temperatures dropped. The following years scientist warned there was a new ice age coming ...
The deforestation on the other hand, as mentioned, is a big problem in my opinion. There is a big nature-problem, but please look also at the deforestation, the poisioneous waste, etc. CO2 is a new god, but only good for 0.04% of the atmospere ...
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