Greenland And Antarctica Tipping Points Near Or Just Above The 1.5-2.0 C Threshold

[bluewave]

https://www.nature.com/articles/s41558-018-0305-8.epdf?shared_access_token=zooxRw-On3fgULlmEI7hDNRgN0jAjWel9jnR3ZoTv0P_tXi6EBxQ8p_EcCElhVk0mzj-1VRC3iQllL4RNWUFGvmCZygJ3nW44MDllPI04_p-Z1CDbnGTRkJn-_V-QsSXqjYYE03eFD83L-W5qR6LL7vkdR7Nk8yjrduy42MuVc8%3D

Even if anthropogenic warming were constrained to less than 2 °C above pre-industrial, the Greenland and Antarctic ice sheets will continue to lose mass this century, with rates similar to those observed over the past decade. However, nonlinear responses cannot be excluded, which may lead to larger rates of mass loss. Furthermore, large uncertainties in future projections still remain, pertaining to knowledge gaps in atmospheric (Greenland) and oceanic (Antarctica) forcing. On millennial timescales, both ice sheets have tipping points at or slightly above the 1.5–2.0 °C threshold; for Greenland, this may lead to irreversible mass loss due to the surface mass balance–elevation feedback, whereas for Antarctica, this could result in a collapse of major drainage basins due to ice-shelf weakening.

 

Other recent papers indicate that the Arctic will become ice free during the summer at the same temperature range.

https://mashable.com/2018/04/02/arctic-sea-ice-temperature-targets/#z7LXBG.Irgq9

Using different climate model simulations and techniques, the studies both show that adhering to the aspirational target of 1.5 degrees Celsius under the Paris Agreement would have a far better chance of keeping the Arctic Ocean ice-covered year-round. Sure, there might be a year or two where natural variability would push sea ice cover low enough to be considered ice-free, but this wouldn't happen year after year. 

Specifically, holding global warming to 1.5 degrees Celsius, as opposed to 2 degrees, would cut the probability of an ice-free summer occurring by the year 2100 from 100 percent to 30 percent, according to one of the studies, by Alexandra Jahn, a climate researcher at the University of Colorado at Boulder. 

Under a 2-degree scenario, though, that ice-free summer would be far more likely to happen, putting Arctic wildlife like polar bears, walrus, as well as human settlements at risk. Considering that the world is currently on course for at least 3 degrees Celsius, or 5.4 degrees Fahrenheit, of warming by 2100, when compared to preindustrial levels, a 1.5-degree target might seem quaint, or even pointless to study. After all, 3 degrees of warming could yield a permanently ice-free Arctic Ocean in the summer, with all the cascading repercussions throughout ecosystems and weather patterns that would entail.

 

 

[etudiant]

I'd thought that NASA had concluded, on the basis of satellite measurement, that Antarctica was still gaining mass,

More broadly though, the climate record laid down in the ice sheets suggests that abrupt changes are more likely than gradual shifts. 

This is a system with many contributing elements, some alive, some just physical. Humility seems a useful attribute when trying to understand its functioning.

[chubbs]

13 hours ago, etudiant said:

I'd thought that NASA had concluded, on the basis of satellite measurement, that Antarctica was still gaining mass,

More broadly though, the climate record laid down in the ice sheets suggests that abrupt changes are more likely than gradual shifts. 

This is a system with many contributing elements, some alive, some just physical. Humility seems a useful attribute when trying to understand its functioning.

There was one NASA study a couple of years ago with that result, but all the other studies have concluded the opposite.  Even the NASA study, indicated that the vulnerable W Antarctic ice sheet was starting to go. Below is a chart from the best current reference, a comprehensive review published earlier this year. You are right, the climate record is clear, we are headed for abrupt changes, that is exactly what the thread article is describing.

https://www.nature.com/articles/s41586-018-0179-y

 

[BillT]

studies show the DATA, they make no "conclusions"   people make the conclusions........

[skierinvermont]

37 minutes ago, BillT said:

studies show the DATA, they make no "conclusions"   people make the conclusions........

People write their conclusions into studies so that other people can read and debate whether the data in the study supports the conclusions of the study. Otherwise there would be no means of communicating and debating conclusions through the written word.

Almost all peer-reviewed studies will be formatted with Intro, Method, Data, and then Conclusion/Discussion sections or something similar. Formats similar to this for scientific work are taught at a young age to middle school school and high school students (I was a middle school science teacher for a couple of years, I also paid attention in middle school and high school).

[WidreMann]

21 minutes ago, skierinvermont said:

People write their conclusions into studies so that other people can read and debate whether the data in the study supports the conclusions of the study. Otherwise there would be no means of communicating and debating conclusions through the written word.

Almost all peer-reviewed studies will be formatted with Intro, Method, Data, and then Conclusion/Discussion sections or something similar. Formats similar to this for scientific work are taught at a young age to middle school school and high school students (I was a middle school science teacher for a couple of years, I also paid attention in middle school and high school).

I can't believe you are having to explain this on a science board.

[BillT]

3 minutes ago, WidreMann said:

I can't believe you are having to explain this on a science board.

"but all the other studies have concluded the opposite. "     i merely pointed out the ERROR in claiming the study made conclusions..........nothing needed to be explained to me.....

[donsutherland1]

5 hours ago, BillT said:

"but all the other studies have concluded the opposite. "     i merely pointed out the ERROR in claiming the study made conclusions..........nothing needed to be explained to me.....

The studies are published with the conclusions. Hence, it’s not unreasonable to state that the studies (more specifically those who were responsible) concluded what they did.

[Vice-Regent]

12 hours ago, donsutherland1 said:

The studies are published with the conclusions. Hence, it’s not unreasonable to state that the studies (more specifically those who were responsible) concluded what they did.

All of the above data is solidly backed by sea level rise trends. However the recent increase in sea level cannot be attributed directly but it's likely the lions share of recent SLR has derived from Antarctica. Locally, the high tides and sunny day flooding has ticked up substantially since 2015.

[donsutherland1]

5 minutes ago, Vice-Regent said:

All of the above data is solidly backed by sea level rise trends. However the recent increase in sea level cannot be attributed directly but it's likely the lions share of recent SLR has derived from Antarctica. Locally, the high tides and sunny day flooding has ticked up substantially since 2015.

Yes. That’s correct.

[bluewave]

https://agu.confex.com/agu/fm18/meetingapp.cgi/Paper/458431

• GC13D-1046:  Climatic Thresholds for Widespread Ice Shelf Hydrofracturing and Ice Cliff Calving In Antarctica: Implications for Future Sea Level Rise

Monday, 10 December 2018 

 

13:40 - 18:00

• Walter E Washington Convention Center
•  
  • - Hall A-C (Poster Hall)
   

The loss or thinning of buttressing ice shelves and accompanying changes in grounding-zone stress balance are commonly implicated as the primary trigger for grounding-line retreat, such as that observed in Amundsen Sea outlet glaciers today. Ice-shelf thinning is mostly attributed to the presence of warm ocean waters beneath the shelves. However, climate model projections show that summer air temperatures could soon exceed the threshold for widespread meltwater production on ice-shelf surfaces. This has serious implications for their future stability, because they are vulnerable to water-induced flexural stresses and water-aided crevasse penetration, termed ‘hydrofracturing’. Once initiated, the rate of shelf loss through hydrofracturing can far exceed that caused by sub-surface melting, and could result in the complete loss of some buttressing ice shelves, with marine grounding lines suddenly becoming calving ice fronts. In places where those exposed ice fronts are thick (>900m) and crevassed, deviatoric stresses can exceed the strength of the ice and the cliff face will fail mechanically, leading to rapid calving like that seen in analogous settings such as Jakobshavn on Greenland.

Here we explore the implications of hydrofacturing and subsequent ice-cliff collapse in a warming climate, by parameterizing these processes in a hybrid ice sheet-shelf model. Model sensitivities to meltwater production and to ice-cliff calving rate (a function of cliff height above the stress balance threshold triggering brittle failure) are calibrated to match modern observations of calving and thinning. We find the potential for major ice-sheet retreat if global mean temperature rises more than ~2ºC above preindustrial. In the model, Antarctic calving rates at thick ice fronts are not allowed to exceed those observed in Greenland today. This may be a conservative assumption, considering the very different spatial scales of Antarctic outlets, such as Thwaites. Nonetheless, simulations following a ‘worst case’ RCP8.5 scenario produce rates of sea-level rise measured in cm per year by the end of this century. Clearly, the potential for brittle processes to deliver ice to the ocean, in addition to viscous and basal processes, needs to be better constrained through more complete, physically based representations of calving.

Authors

• Robert M Deconto
  • University of Massachusetts Amherst
• David Pollard
  • Pennsylvania State University
• Knut A Christianson
  • University of Washington
• Richard B Alley
  • Pennsylvania State University

[chubbs]

Here is an article summarizing the Deconto presentation, flagged above, and others at the recent AGU session on ice sheet stability. Sounds like relatively good news, I guess.

https://www.theatlantic.com/science/archive/2019/01/sea-level-rise-may-not-become-catastrophic-until-after-2100/579478/

 

 

 

[Vice-Regent]

It's not good news. It reduces the urgency for change and action. Keep in mind that the immediate effects of fossil fuel emissions are not matured for at least 30-50 years after the initial release. However the rate of emissions alone will function to diminish the lag time function.

https://skepticalscience.com/Climate-Change-The-40-Year-Delay-Between-Cause-and-Effect.html

Guest post by Alan Marshall from climatechangeanswers.org

Following the failure to reach a strong agreement at the Copenhagen conference, climate skeptics have had a good run in the Australian media, continuing their campaigns of disinformation. In such an atmosphere it is vital that we articulate the basic science of climate change, the principles of physics and chemistry which the skeptics ignore.

The purpose of this article is to clearly explain, in everyday language, the two key principles which together determine the rate at which temperatures rise. The first principle is the greenhouse effect of carbon dioxide and other gases. The second principle is the thermal inertia of the oceans, sometimes referred to as climate lag. Few people have any feel for the numbers involved with the latter, so I will deal with it in more depth.

The Greenhouse Effect

The greenhouse effect takes its name from the glass greenhouse, which farmers have used for centuries, trapping heat to grow tomatoes and other plants that could not otherwise be grown in the colder regions of the world. Like glass greenhouses, greenhouse gases allow sunlight to pass through unhindered, but trap heat radiation on its way out. The molecular structure of CO₂ is such that it is “tuned” to the wavelengths of infrared (heat) radiation emitted by the Earth’s surface back into space, in particular to the 15 micrometer band. The molecules resonate, their vibrations absorbing the energy of the infra-red radiation. It is vibrating molecules that give us the sensation of heat, and it is by this mechanism that heat energy is trapped by the atmosphere and re-radiated to the surface. The extent to which temperatures will rise due to a given change in the concentration of greenhouse gases is known as the “climate sensitivity,” and you may find it useful to search for this term when doing your own research.

Most principles of physics are beyond question because both cause and effect are well understood. A relationship between cause and effect is proved by repeatable experiments. This is the essence of the scientific method, and the source of knowledge on which we have built our technological civilization. We do not question Newton’s laws of motion because we can demonstrate them in the laboratory. We no longer question that light and infrared radiation are electromagnetic waves because we can measure their wavelengths and other properties in the laboratory. Likewise, there should be no dissent that CO2 absorbs infrared radiation, because that too has been demonstrated in the laboratory. In fact, it was first measured 150 years ago by John Tyndall using a spectrophotometer. In line with the scientific method, his results have been confirmed and more precisely quantified by Herzberg in 1953, Burch in 1962 and 1970, and others since then.

Given that the radiative properties of CO2 have been proven in the laboratory, you would expect them to be same in the atmosphere, given that they are dependent on CO2’s unchanging molecular structure. You would think that the onus would be on the climate skeptics to demonstrate that CO2 behaves differently in the atmosphere than it does in the laboratory. Of course they have not done so. In fact, since 1970 satellites have measured infrared spectra emitted by the Earth and confirmed not only that CO2 traps heat, but that it has trapped more heat as concentrations of CO2 have risen.

The above graph clearly shows that at the major wavelength for absorption by CO2, and also at wavelength for absorption by methane, that less infrared was escaping in to space in 1996 compared to 1970.

After 150 years of scientific investigation, the impact of CO2 on the climate is well understood. Anyone who tells you different is selling snakeoil.

The Thermal Inertia of the Oceans

If we accept that greenhouse gases are warming the planet, the next concept that needs to be grasped is that it takes time, and we have not yet seen the full rise in temperature that will occur as a result of the CO2 we have already emitted. The Earth’s average surface temperature has already risen by 0.8 degrees C since 1900. The concentration of CO2 in the atmosphere is increasing at the rate of 2 ppm per year. Scientists tell us that even if CO2 was stabilized at its current level of 390 ppm, there is at least another 0.6 degrees “in the pipeline”. If findings from a recent study of Antarctic ice cores is confirmed, the last figure will prove to be conservative ^[ii]. The delayed response is known as climate lag.

The reason the planet takes several decades to respond to increased CO2 is the thermal inertia of the oceans. Consider a saucepan of water placed on a gas stove. Although the flame has a temperature measured in hundreds of degrees C, the water takes a few minutes to reach boiling point. This simple analogy explains climate lag. The mass of the oceans is around 500 times that of the atmosphere. The time that it takes to warm up is measured in decades. Because of the difficulty in quantifying the rate at which the warm upper layers of the ocean mix with the cooler deeper waters, there is significant variation in estimates of climate lag. A paper by James Hansen and others ^[iii] estimates the time required for 60% of global warming to take place in response to increased emissions to be in the range of 25 to 50 years. The mid-point of this is 37.5 which I have rounded to 40 years.

In recent times, climate skeptics have been peddling a lot of nonsense about average temperatures actually cooling over the last decade. There was a brief dip around the year 2000 following the extreme El Nino event of 1998, but with greenhouse emissions causing a planetary energy imbalance of 0.85 watts per square metre ^[iv], there is inevitably a continual rising trend in global temperatures. It should then be no surprise to anyone that the 12 month period June 2009 to May 2010 was the hottest on record ^[v].

The graph below from Australia’s CSIRO ^[vi] shows a clear rising trend in temperatures as well as a rising trend in sea-level.

Implications of the 40 Year Delay

The estimate of 40 years for climate lag, the time between the cause (increased greenhouse gas emissions) and the effect (increased temperatures), has profound negative consequences for humanity. However, if governments can find the will to act, there are positive consequences as well.

With 40 years between cause and effect, it means that average temperatures of the last decade are a result of what we were thoughtlessly putting into the air in the 1960’s. It also means that the true impact of our emissions over the last decade will not be felt until the 2040’s. This thought should send a chill down your spine!

Conservative elements in both politics and the media have been playing up uncertainties in some of the more difficult to model effects of climate change, while ignoring the solid scientific understanding of the cause. If past governments had troubled themselves to understand the cause, and acted in a timely way, climate change would have been contained with minimal disruption. By refusing to acknowledge the cause, and demanding to see the effects before action is taken, past governments have brought on the current crisis. By the time they see those effects, it will too late to deal with the cause.

The positive consequence of climate lag is the opportunity for remedial action before the ocean warms to its full extent. We need to not only work towards reducing our carbon emissions to near zero by 2050, but well before then to begin removing excess CO2 from the atmosphere on an industrial scale. Biochar is one promising technology that can have an impact here. Synthetic trees, with carbon capture and storage, is another. If an international agreement can be forged to provide a framework for not only limiting new emissions, but sequestering old emissions, then the full horror of the climate crisis may yet be averted.

Spreading the Word

The clock is ticking. All of us who understand clearly the science of climate change, and its implications for humanity, should do what we can to inform the public debate. I wrote the original version of this article in February 2010 to help inform the Parliament of Australia. The letter was sent to 40 MPs and senators, and has received positive feedback from both members of the three largest parties. To find out more about this information campaign, and for extensive coverage of the science of climate change and its technological, economic and political solutions, please visit my web site at www.climatechangeanswers.org.

https://skepticalscience.com/Climate-Change-The-40-Year-Delay-Between-Cause-and-Effect.html

[LibertyBell]

On 1/16/2019 at 9:43 PM, chubbs said:

Here is an article summarizing the Deconto presentation, flagged above, and others at the recent AGU session on ice sheet stability. Sounds like relatively good news, I guess.

https://www.theatlantic.com/science/archive/2019/01/sea-level-rise-may-not-become-catastrophic-until-after-2100/579478/

 

 

 

hmmm I also saw these on The Atlantic

 

https://www.theatlantic.com/science/archive/2019/01/rcp-85-the-climate-change-disaster-scenario/579700/

https://www.theatlantic.com/science/archive/2018/11/national-climate-assessment-black-friday/576589/

https://www.theatlantic.com/science/archive/2019/01/us-carbon-pollution-rose-2018/577549/

https://www.theatlantic.com/science/archive/2018/11/how-hot-will-climate-change-make-earth/576700/

https://www.theatlantic.com/science/archive/2018/08/a-global-rightward-shift-on-climate-change/568684/

 

 and this (courtesy of RutgersWx):

America's oil boom is terrible for the climate
America's push for oil and gas supremacy could lead to a "climate catastrophe," a new report has warned. 

The report by Oil Change International said that the United States is set to "unleash the world's largest burst" of carbon emissions from new oil and gas development if it goes ahead with its plans to expand drilling.

"At precisely the time in which the world must begin rapidly decarbonizing to avoid runaway climate disaster, the United States is moving further and faster than any other country to expand oil and gas extraction," the report said.

https://www.cnn.com/2019/01/18/business/climate-us-coal-mining/index.html

 

[LibertyBell]

On 12/3/2018 at 7:15 AM, donsutherland1 said:

Yes. That’s correct.

The seas have also been warming much faster than expected based on the above information.

[donsutherland1]

49 minutes ago, LibertyBell said:

The seas have also been warming much faster than expected based on the above information.

I believe a new paper was published on that issue very recently.

[chubbs]

A nice explainer on ice sheet dynamics and WAntarctic instability but not for the climate faint of heart.

https://www.sciencenewsforstudents.org/article/big-melt-earths-ice-sheets-are-under-attack

[Bhs1975]

A nice explainer on ice sheet dynamics and WAntarctic instability but not for the climate faint of heart.
https://www.sciencenewsforstudents.org/article/big-melt-earths-ice-sheets-are-under-attack

Yeap it’s gonna be a disaster of epic proportions.


.

[Gray-Wolf]

I think we all now accept that we are as warm as we were 125,000 yrs ago and at that time Greenland was 2/3rds ice free and West Antarctica was ice free. I know we have a bit of 'catchup' to do due to lag in climate response but I think we need be mindful of GHG's 125,000yrs ago and what became of the carbon cycle that supported those levels?

How much of that Carbon cycle is left in suspended animation beneath the ice cover of West Antarctica/Greenland?

If our messing has placed over 120ppm of CO2 (from very ancient carbon cycles) back into the system ,and so have now driven temps/circulation changes to enable the global ice cover of 125,000 yrs ago surely we will pick up some of that buried carbon cycle as we go?

If we do then we should expect fiercer warming and more of our 'hibernating carbon cycle' to become reanimated and around we go again.....

I think the complete glaciation of Antarctica began as CO2 levels dropped below 600 ppm. Is that where we are headed and how much of that PETM carbon cycle is sat below Antarctica's ice cover awaiting its reanimation?

To me Humanity has only managed to light the blue touch paper.

Mother N. is the main charge that we ought be planning to avoid/deal with?