Researchers Sequence Genome of Photosynthetic Bacterium That Uses Near-Infrared Light
Alstom Unveils Prototype 224 MPH AGV Train and Its First Customer

Researchers Describe “Tipping Elements” for Earth’s Climate System

Anthropogenic forcing could push the Earth’s climate system past critical thresholds, so that important components may “tip” into qualitatively different modes of operation. An international team of researchers has devised a new term—“tipping elements”—to describe those components of the climate system that are at risk of passing a tipping point.

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 researchers 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.

Their work is described in a paper in the current edition of the Proceedings of the National Academy of Sciences.

Society must not be lulled into a false sense of security by smooth projections of global change. Our findings suggest that a variety of tipping elements could reach their critical point within this century under human-induced climate change. The greatest threats are tipping of the Arctic sea-ice and the Greenland ice sheet, and at least five other elements could surprise us by exhibiting a nearby tipping point.

—Tim Lenton of the University of East Anglia (UEA), lead author

The nine tipping elements and their possible timeframes are:

  • Melting of Arctic sea-ice (approx 10+ years, small uncertainty). 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.

  • Decay of the Greenland ice sheet (more than 300 years, small uncertainty). 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.

  • Collapse of the West Antarctic ice sheet (more than 300 years, large uncertainty). 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.

  • Collapse of the Atlantic thermohaline circulation (approx 100 years, intermediate uncertainty). 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.

  • Increase in the El Niño Southern Oscillation (approx 100 years, large uncertainty). 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.

  • Collapse of the Indian summer monsoon (approx 1+ year, large uncertainty). 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.

  • Greening of the Sahara/Sahel and disruption of the West African monsoon (approx 10 years, large uncertainty). 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.

  • Dieback of the Amazon rainforest (approx 50 years, large uncertainty). 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.

  • Dieback of the Boreal Forest (approx 50 years, large uncertainty). 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.

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.

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.


  • 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


Lou Grinzo

The paper is available (in final proof form) here:

Rafael Seidl

Note that the complete disappearance of Arctic ice cover in summer would have no direct impact on mean sea level as the ice is already floating anyhow. However, it would represent severe habitat loss for arctic fauna and also yield a certain amount of positive global warming feedback. After all, the Arctic ocean is only so large and only receives so much of the world's total solar irradiation. However, it is a integral part of the atmospheric circulation patterns in the Northern hemisphere, so we could see significant changes in weather patterns, especially in Europe and the West Coast of North America.

More prosaically, both the North-West and the North-East passage could become seasonally significant freight shipping routes in coming decades. Along with that could come increased efforts to develop the natural resources of the Arctic ocean, incl. especially oil & gas reserves. Both of these changes could lead to serious international tensions; Russia has already seen fit to stake its claim early.

Al Fin

Logically, they should be more concerned about "tipping points" toward runaway cooling. Cooling has always been the larger threat to human civilisation and large ecosystems.


And logically you would respond to something that is actually happening!!!

Al Fin

Logically, one could say the same for CO2 hysterics.


And to make matters more troublesome there is this new push for tipping 20:

Who can really afford this?


I would add methane release from melting permafrost to the list as well. Methane is 22 times more potent as a GHG than CO2 and if the permafrost melts, enough methane will be released to greatly accelerate the process. As more warming occurs, more permafrost melts. This is a run away effect that we should not risk starting in the first place.


With this discussion group sitting in Oct 2005 and their report embargoed till Feb 2008, we should be asking how do these tipping projections relate to current observations.
Plainly reports where available are supportive of the more general "Tipping" future scenario.
With the luxury of hindsight results or "outcomes" based on observation verification. This is a very persuasive tool if you know what you are looking at (for).
The problem for naysayers is not the short 2 year embargo as in his case, but the much longer history of the verification of predictive analysis tools.

Sulleny , you should have left that tip for the barman.

Stan Peterson

The collapse of the smooth Global Warming science theses, in the face of 21st century's factual Science findings, has created a problem. The Cassandras must invoke calamities like "tipping points" to create new semi-credible hystericsand keep the cash flowing.

The Earth has been warmer and colder in the recent past by as much as several degrees and displayed no 'tipping points' But don't let that mere historical truth and fact, interfere with a good hysteria-inducing proposal.

The daily change in temperature from noon to midnight anywhere in the world save the deeps of the ocean, are several times if not ten times the postulated worst conceivable temperature change by the most fanatic of the hysteria peddlers.

Yet the world doesn't achieve "tip" daily. If that is not assurance, than consider the difference in temperature over any point in the world between a mid-summer noon and a midwinter Mid-night temeperature. If that is not a difference of 75 degreees F than no "tipping point exsits in that range.

These people are no different, in concept, to the guy on the street corner carrying a pair of sandwich boards exhorting you to "Repent. The End is Near!"

And just about as valid.

The only validity is the genuine Albedo effects of altering that global reflectivity from an average of 30% with snow and ice increasing it to about 60%over the Arctic.

Widespread adoption of supposedly "clean" Solar Energy would alter the Albedo drastically to some negative 10% or so over the solar grids. If you want to actively create global warming, then build lots of solar energy, that is the only way that I can conceive of it ever being achieved.

Trojan Man

The thing about "Cassandra" is...she was correct wasn't she? And the Trojans paid for it...with their lives...


For over 20 years the evidence has pointed to anthropogenic climate change as valid. For 20 years, deniers have had the time to peer review it and put up valid reasonable objections. They have had time to put forth their own version of climate theory and how observations fit it. They have tried and failed. The observations support the view that recent climate change is caused by human activity.

That said. Some of these tipping points are obvious physical signs of massive change. They are not a sign that the warming was caused by human activity (which I and the majority of scientific thought think it is) but a sign that if they happen, some will cause massive feedback effects, some are the easily seen side of GW effects, some of which will have large wide standing effects on land and peoples. Once these things happen, they will have a tendency to keep happening.

Loss of artic ice, will decrease the amount of solar energy reflected back into space. This will tend to keep the water in liquid form. It would also tend to raise the temperature in the area. Raising the temperature in the land would lower the permafrost layer increasing methane which would be a positive feedback. Counting on the ground cover replacement, we could have a positive or negative feedback. Boreal forest for instance may be a net positive feedback because although they take up CO2, they also absorb light in northern latitudes.


The reason why Methane is not a part of this discussion, although it is several times more potent to cause global warming (if indeed it is a monotonosly rising phenomenon over hundreds of thousands of years), is because very little of it is 'anthropogenic'!!! Can't regulate cows, can we, now?

As to the 'believers', can someone explain why the temperature rise has always PRECEDED (i.e., occured before, for the science or language-illiterates) the rise in atmospheric CO2 concentrations? If A follows B, then, the most logical conclusion that can be drawn is that A is caused by B (again, this is misapplying 'correlation = causality' principle, but even then).

I believe in conservation as it will keep non-renewables available long-enough to find alternative viable forms of energy resources. On the other hand, anthropogenic Global Warming is 100% politics and 0% 'science', especially when you consider that (a) many of the so-called researchers are sociologists who know nothing about climate science (b) Every time, the 'believer' community is up in arms both shouting out anyone trying to have a logical discussion on the topic, as well as crowding the 'contrarian' researchers out of their careers and funding and (c) on the IPCC report, even the serious folks interested in really investigating the causality of mean surface temperature variations, who happened to disagree on the general hypothesis, were included as the consenting parties.

General rule - global warming research follows the $$, and $$ follow political agendas.

1970s brought global cooling to the agenda, and 10 years from now, the 'global warming' researchers will find some other sources of funding (and topics for research). This is opportunism at its best.


If CO2 follows temp rise and we are seeing temp rise on the back of anthropological CO2, Given that this is a first case study, the expected outcome from this "cocktail" must surely be toward a spring boarding from the high greenhouse base. This being the result of anthropological releases of millions of years of sequestered carbon.
Cows and sheep should be able to be considered as anthropogenic factor as they are domesticated.
I am sure that he moose or reindeer with their car equivalent emissions will do quite nicely without human herders so really this is an area of contention.
The much larger methane emissions from biological sources are a very big concern as the CO2 equivalent is around 22*. Large releases Of both Methane and CO2 are being documented from soils (England's farmland carbon banks data 50's -on, Permafrost methane releases current and projected, being the most well recognised.) .
The absorbed CO2 status of oceans is reported as "High" with diminishing ability to sequester.
The effect on calcium formation in such living organisms as shellfish, coral reefs is that as the ocean becomes more acid - CO2 + H2O = fizzy drink, I is harder to form the hard calcium required for survival.
The naysayers have a captive audience like creation "scientists", like kids who I'm told some believe in Santa Claus have a vested interest.
Are prepared to accept the comfort and assurance from which makes doing nothing or facing reality just too hard.
As is thinking for oneself, accepting ones own part, these mindsets find it much easier to deny,
There have throughout history always been those willing to lead the ignorant. They have no special talent other than to recognise a power base amongst the most intellectually impoverished. Known for their inability to answer any rational argument. Any dissention is seen as a threat and so they make the clear distinction. ie Greenies, Towel heads, anti American, Socialists Do- gooders Liberals Infidels, Heathens etc etc .


Carnut...You & others make the 'global warming research-$$-political agenda' connection in an era dominated by a business-Bush administration controlling such funds. You disprove this possible connection.

But your NAME shows WHY you wish to disprove the 'car/1.5 pounds carbon dioxide per mile/global warming' connection. Or is your carnuttiness producing more than 1.5 pounds of carbon dioxide per mile?


litesong- it's a classic way the protagonists of the anthropogenic global warming hypothesis change the subject. Rather than providing proof for some of the anomalies I mentioned earlier, they'd feel better if they just attacked the person bringing it to their attention. That way, one does not have to deal with facts. This is unscientific and unconscionable - especially because this kind of misguided activism is going to cost everyone a pretty penny and the world may see global cooling, if the latest news on the sun spot activity are any indication



General rule - global warming research follows the $$, and $$ follow political agendas.

You introduced the point that scientists are not being scientific and then saying that the deniers are attacked just for bringing something to attention. Where's the "proof" that there is money to had. Do they get paid, yes but it isn't huge amounts.

You're attacking the pro scientists, not on the merits of the evidence of the climate record but on the hypothesis that the money is the motivator.

The fact is the climatologists want money to be spent on things like electric cars not on more continuing research. There are far more easily had funds in supporting the present milita/industrial complex, then there is in supporting the AGW theory.

To the point.
Basically is no scientific body of national or international standing that rejects the basic finding of human influence on recent climate change. They are not sociologists or whatever you want to believe they are.

Peer review of the data over the last 20 years has led to AGW becoming mainstream and accepted as part of the way climate works. Peer review has a tendency over time to remove the personal bias of the contributors.

As for funding, what model of how climate works, do the deniers believe in. It doesn't tell me about how climate works or anything. Do people who don't produce tangible results get funding? No. Ask someone looking for a grant for intelligent design if they get money from credible sources.

Lastly, the IPCC is a conservative group composed mostly of scientists. The fact that some didn't totally agree with the final draft means what? That it was a large group of people. That's it. That larger the group, the more unlikely it is that total agreement will be made on anything. I went out with a bunch of people informally to discuss a project and we argued about lunch. The result was a mostly peer produced paper from the IPCC despite political pressure applied by China, the US, and Saudi Arabia (according to the Associated Press). Gee I wonder why they would?

The 70's didn't really bring global cooling to the agenda. It was a story to try to jar the public and that all it was. No scientist really thought it was credible. What it did do was to bring attention to how much we knew on how climate works. That's when we looked at what drove climate.

AGW is the leading theory on how climate works that fits the data. With the theory, we can make guesses on outcomes and scenarios based on how much it matches the observed data. Without it, what planning can be done?

So far the observed data supports AGW. That's why it gets recognition from recognized scientific instituitions and why it gets the money.

You mentioned anomalies? There's only one that I see and that for the CO2 temperature link. Try for an explanation from a climatologist.

As for the methane. My expectation is that if the temperature increases enough to cause a reduction in boreal forest, the methane is a given. Also we are in a solar low (11 year Schwabe cycle)with these recent high temperature years, not as you state a high.

Theories are not mathematically precise. They are working explanations on how something works but not necesarily the specific mechanisms or rules. Evolution was put forth before genetics and before the fossil records were discovered that supported it. AGW is about how climate works. Observed data supports it and seems to support it more strongly as time passes. These tipping points are consequences of the theory and some like the arctic ice are highly probable. Attributing them to "the theory of random climate" is no better than attributing them to a supernatural cause. That is unscientific.


The National Geographic had a good program called Six Degrees Could Change the World. I did not know that in 2005, the Amazon river dried up. That seemed pretty significant to me.

The comments to this entry are closed.