Thursday, November 15, 2018

The art of the possible


I support the left
Though I'm leaning to the right
I'm just not there
 when it comes to a fight
     - Cream (Political Man)


Come Senators Congressmen
Please head the call
     - Bob Dylan

Greetings



       Well, the election returns are in, and the results are not that good for the environment.  Citizens of several states, unhappy with the pace of legislative action attempted to appeal directly  to the people.   The fossil fuel companies joined the fight, and the people were persuaded by their arguments.  However some environmentally minded representatives were elected.  See here and here

         The current political situation means that the only movement in the next two years will be with states and cities.   In the meantime it is encouraging to see young people getting organized and putting pressure on the democratic establishment to put together a climate program for 2020.  See here


Protesters have a simple question for Nancy Pelosi. Nelson Klein, Sunrise
On Tuesday, close to 200 climate activists crowded into the Capitol Building offices of House Minority Leader Nancy Pelosi, who will re-assume the position of House speaker when the new Congress is sworn in come January.


Meanwhile carbon emissions continue to rise.   And the effects of 1 degree continue to be felt in places liked California.   So, where does that leave us?  Here is one way to describe it.   In short, keeping below two degrees is very unlikely if not impossible.  Bellow three is the new target.  Two is a long-term disaster, three is a short-term one.  see here


The odds of succeeding, according to a recent study based on current emissions trends, are one in 20. If by some miracle we are able to limit warming to two degrees, we will only have to negotiate the extinction of the world’s tropical reefs, a sea -level rise of several meters and the abandonment of the Persian Gulf. The climate scientist James Hansen has called two-degree warming “a prescription for long-term disaster.” Long-term disaster is now the best-case scenario. Three-degree warming is a prescription for short-term disaster: forests in the Arctic and the loss of most coastal cities. Robert Watson, a former director of the United Nations Intergovernmental Panel on Climate Change, has argued that three-degree warming is the realistic minimum. Four degrees: Europe in permanent drought; vast areas of China, Indi, a Bangladesh claimed by desert; Polynesia swallowed by the sea; the Colorado River thinned to a trickle; the American Southwest largely uninhabitable. The prospect of a five-degree warming has prompted some of the world’s leading climate scientists to warn of the end of human civilization
Caldeira and a colleague recently published a paper in Nature finding that the world is warming more quickly than most climate models predict. The toughest emissions reductions now being proposed, even by the most committed nations, will probably fail to achieve “any given global temperature stabilization target.”
More carbon has been released into the atmosphere since the final day of the Noordwijk conference, Nov. 7, 1989, than in the entire history of civilization preceding it. In 1990, humankind emitted more than 20 billion metric tons of carbon dioxide. By 2017, the figure had risen to 32.5 billion metric tons, a record. Despite every action taken since the Charney report — the billions of dollars invested in research, the nonbinding treaties, the investments in renewable energy — the only number that counts, the total quantity of global greenhouse gas emitted per year, has continued its inexorable rise.
The timetable for this approaching disaster is always changing, as new studies find that things are moving "faster than expected".  One recent study suggests that the best guidance is  the one described by the IPPC as the worst case. RCP8.5 

One reason is that the climate is changing faster than expected, leaving the models behind.  As Ken Caldeira, one of the authors explained here and here


But an emerging challenge is that the climate is changing faster than the models are improving, as real-world events occur that the models didn’t predict. Notably, Arctic sea ice is melting more rapidly than the models can explain, suggesting that the simulations aren’t fully capturing certain processes. 

“We’re increasingly shifting from a mode of predicting what’s going to happen to a mode of trying to explain what happened,” Caldeira says.



See here for a detailed explanation of that study.

Here is the key graph:

Brown Caldeira 2017 Nature
Figure 2d
This would suggest that unless things significantly change, the following temperatures can be expected in 2020: 1.25,  2030: 1.75, 2040: 2.0,  2050: 2.5 2060: 3,  et cetera 
But, hopefully, that prognosis is too pessimistic.   After all, RCP8.5 assumes that the world will continue in its fossil-fueled ways for the rest of the century.  It doesn't address the possibility of a peak in fossil fuel use, either because of supply or demand.

When could we reasonably expect such a peak?  Well, here is a study from Carbon Tracker and Grantham that shows a scenario of peak carbon emissions by 2020.   On the other hand, the International Energy Agency suggests that fossil fuels will continue to dominate energy use and that CO2 emissions will not peak before 2040.  see here.  See also. Renewable energy is surging but not fast enough to stop warming

So, for now, lets split the difference and assume that CO2 peaks in 2030 and drops after that.    Based on the Caldeira study, by 2030 we would be at 1.75 degrees above pre-industrial.  What then?   Do we get off the RCP 8.5 curve?

I'd suggest that we may actually stay on the curve for another 10-20 years for two reasons.   First, after the peak we will continue to emit CO2, just at a lower level.  The difference will be small for a while.  I addition, as Dirk has pointed out, shutting down coal plants will reduce aerosols which are currently cooling the planet.   See here  (NASA) The removal of aerosols from the atmosphere will cause the temperature to rise by .5 to 1 degree.   These factors may offset each other in the short term resulting in continued warming..  

But those temperature predictions are not the important point.  What is important is what happens when we reach those temperatures.  And once again the story keeps changing.

Here is what experts currently expect at various temperatures   From here. 

"At two degrees, the melting of ice sheets will pass a tipping point of collapse, flooding dozens of the world’s major cities this century. At that amount of warming, it is estimated, global GDP, per capita, will be cut by 13 percent. Four hundred million more people will suffer from water scarcity, and even in the northern latitudes heat waves will kill thousands each summer. It will be worse in the planet’s equatorial band. In India, where many cities now numbering in the many millions would become unbelievably hot, there would be 32 times as many extreme heat waves, each lasting five times as long and exposing, in total, 93 times more people. This is two degrees — practically speaking, our absolute best-case climate scenario.
At three degrees, southern Europe will be in permanent drought. The average drought in Central America would last 19 months and in the Caribbean 21 months. In northern Africa, the figure is 60 months — five years. The areas burned each year by wildfires would double in the Mediterranean and sextuple in the United States. Beyond the sea-level rise, which will already be swallowing cities from Miami Beach to Jakarta, damages just from river flooding will grow 30-fold in Bangladesh, 20-fold in India, and as much as 60-fold in the U.K. This is three degrees — better than we’d do it all the nations of the world honored their Paris commitments, which none of them are. Practically speaking, barring those dramatic tech deus ex machinas, this seems to me about as positive a realistic outcome as it is rational to expect.
At four degrees, there would be eight million cases of dengue fever each year in Latin America alone. Global grain yields could fall by as much as 50 percent, producing annual or close-to-annual food crises. The global economy would be more than 30 percent smaller than it would be without climate change, and we would see at least half again as much conflict and warfare as we do today. Possibly more. Our current trajectory, remember, takes us higher still, and while there are many reasons to think we will bend that curve soon — the plummeting cost of renewable energy, the growing global consensus about phasing out coal — it is worth remembering that, whatever you may have heard about the green revolution and the price of solar, at present, global carbon emissions are still growing.
None of the above is news — most of that data is drawn from this single, conventional-wisdom fact sheet

But these expectations may be optimistic. Other studies are noting that more significant impacts can occur at lower temperatures.


Here's an example.  Recently biologists study a wildlife preserve in Puerto Rico.  This is an area which is far from the effects of humans.  No poisons, no hunting.  But no reserve can be far from climate change.  Robert Hunziker reports on their findings here



Biologists Brad Lister and Andres Garcia of the Universidad Nacional Autónoma de México returned to Puerto Rico’s Luquillo Rainforest after 40 years, and what they found blew them away. The abundance of insects, and arthropods in general, declined by as much as 60-fold and average temps had risen by 2°C over the past four decades. According to the scientists, global warming is impacting the rainforest with distinctive gusto.
According to Lister: “It was just a collapse in the insect community. A really dramatic change… The insect populations in the Luquillo forest are crashing.” (Source: Climate-Driven Crash in a Rainforest Food Web, Every Day Matters, Oct. 22, 2018).
It doesn’t get much worse than “crashing” of ecosystem support systems, i.e., insects and arthropods in general, which are in the phylum Euarthropoda, inclusive of insects, arachnids, myriapods, and crustaceans. This equates to a loss of basic structures of biosphere life forces.
The research team believes they are already seeing today what the recent IPCC report predicted for climate change in 2040. In their words: “It’s a harbinger of a global unraveling of natural systems.”
“The central question addressed by our research is why simultaneous, long-term declines in arthropods, lizards, frogs, and birds have occurred over the past four decades in the relatively undisturbed rainforests of northeastern Puerto Rico. Our analyses provide strong support for the hypothesis that climate warming has been a major factor driving reductions in arthropod abundance and that these declines have in turn precipitated decreases in forest insectivores in a classic bottom-up cascade.” (Lister)


The reference to "what the recent IPCC report predicted for climate change in 2040", refers to the IPCC report that came out last month.  It describes some of the impacts which are predicted if we reach 1.5 degrees above pre-industrial, and it suggests that this could happen as soon as 2040.  See here from the New York Times


The report, issued on Monday by the Intergovernmental Panel on Climate Change, a group of scientists convened by the United Nations to guide world leaders, describes a world of worsening food shortages and wildfires, and a mass die-off of coral reefs as soon as 2040 — a period well within the lifetime of much of the global population.
The report “is quite a shock, and quite concerning,” said Bill Hare, an author of previous I.P.C.C. reports and a physicist with Climate Analytics, a nonprofit organization. “We were not aware of this just a few years ago.” The report was the first to be commissioned by world leaders under
The scientists in Puerto Rico are suggesting that the impacts predicted for 2040 are already occurring,  20 years early,  and that the impacts are occurring at 1-degree c,  not 1.5 degrees. 

And of course, it's not just insects that are in trouble

From 1970 to 2014, 60 percent of all animals with a backbone – fish, birds, amphibians, reptiles, and mammals – were wiped out by human activity, according to WWF’s Living Planet report, based on an ongoing survey of more than 4,000 species spread over 16,700 populations scattered across the globe.  see here

Fish, in particular, are on the edge

The world’s ocean fish stocks are “on the verge of collapse,” according to a special report from IRIN. Already small fishers in poor countries are reeling, turning to ever-more destructive techniques and suffering from poor health and dwindling livelihoods.
.....
The main trend of the world marine fisheries catches is not one of ‘stability’ as cautiously suggested early by FAO,” they write, “but one of decline.”
An estimated 70 percent of fish populations are fully used, overused, or in crisis as a result of overfishing and warmer waters. If the world continues at its current rate of fishing, there will be no fish left by 2050, according to a study cited in a short video produced by IRIN for the special report.  see here


It's kind of amazing is that although this information is available, most people's response is to completely ignore it.    But some folks have a different response.  As Joe Hill says " Don't mourn, organize"  Here's what George Monbiot says.  The Earth is in a Death Spiral, It will take Radical Action to Save Us




Those to whom we look for solutions trundle on as if nothing has changed. As if the accumulating evidence has no purchase on their minds. Decades of institutional failure ensures that only “unrealistic” proposals – the repurposing of economic life, with immediate effect – now have a realistic chance of stopping the planetary death spiral. And only those who stand outside the failed institutions can lead this effort.
Two tasks need to be performed simultaneously: throwing ourselves at the possibility of averting collapse, as Extinction Rebellion is doing, slight though this possibility may appear; and preparing ourselves for the likely failure of these efforts, terrifying as this prospect is. Both tasks require a complete revision of our relationship with the living planet.
Because we cannot save ourselves without contesting oligarchic control, the fight for democracy and justice and the fight against environmental breakdown are one and the same. Do not allow those who have caused this crisis to define the limits of political action. Do not allow those whose magical thinking got us into this mess to tell us what can and cannot be done.

But for many people, especially those folks on the front lines in California, mourning may be appropriate.  Eric Holthaus at Grist offers this


An organization called Good Grief is trying to take on the challenge of helping to guide people like me who sometimes struggle with the loss and uncertainty that comes with being immersed in stories of climate disaster. They’ve developed a 10-step path to resiliency that I think everyone could benefit from. (Here’s some background on how they developed these steps.)
Of course, for people close enough to experience the smoke of the fire, the grief is even more intense. There’s a national disaster distress hotline that was set up specifically for times like this. Studies show that PTSD in survivors of previous disasters is often triggered during national crises. Survivor’s guilt is real.
Feeling like this is expected, at least some of the time. We feel this way because we love each other and we love the world. The changes we’re seeing are happening at a geological scale, faster than at any time in our planet’s history. We humans just aren’t built to process that kind of change.
It’s also worth remembering — every damn day — that a burned and broken world is not our destiny. We aren’t fated to any particular future, and the choices each of us make every day mean a lot, especially at this important moment in history. The best thing that each of us can do going forward is to talk about how important climate change is with everyone you can. It’s only by building up a groundswell of support that our leaders will notice and take bold action in the time we have left.

There's another group of people, including those with young children,  who are hoping -hoping that people will try to fix things, and to the extent its too late, will try to help each other.    Here is a perceptive piece from environmental reporter Brian Merchant,  from here

My second son was born last week, right before two historic wildfires hit his new home state and burned whole cities to the ground. One burned about thirty miles west of the hospital he was born in, thickening the air with smoke, turning the sun deep red—we marked his first week anniversary by watching ash fall from the sky into our front yard. The other burned an hour and a half's drive north of where I grew up, of where my parents live, and reduced a town of thirty thousand people to embers so fast that the highway was left littered with abandoned and charred cars attempting escape, and dozens dead.  
...
My sons are going to live in cities on fire, in nations led by men who don't care, and they are going to have to learn to help tackle the problem, as we are. If I can in any way help them tap into that capacity that I felt last night, if they can help me, and if others can—and if that relation can help topple power in denial—then maybe we can sustain this pre-apocalypse, whether it takes another blue wave or nine, a political revolution, mass psilocybin hallucinations, or something else. If we can relate that goodness where applicable and confront power whenever possible, my sons may not have to live their adult lives in omnipresent fear of fires.
People are basically good, power corrupts but is not de-corruptible, and there is a lot of work to do.
At least, that's what gave me hope that week as I watched the world burn, literally and figuratively, but mostly literally, as my beautiful new ward eked out his being amongst the smoke.

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Thursday, October 25, 2018

Slow Down, you move too fast


The train it won't stop going 
But it could slow down  
    -Jethro Tull

I ride the mail train, baby
Can't buy a thrill
    Bob Dylan


Good news:

The whole country is on grid parity for rooftop solar. See here


Public Service Announcements

Joint Interim Committee on Carbon Reduction.  Next meeting November 8



Greetings


     Well the new IPCC report has got people stirred up. Perhaps it could be the spark that gets things moving.  Let's hope so.

     They set some ambitious timetables- reducing emissions by 45% by 2030,  and by 100% by 2100.  See here

     So,  one way to look at the future is two phases.  First, the time between now and when we hit between 1.5 -2 degrees above pre-industrial.  This is the opportunity to stop the warming before the "positive " reinforcing system, the "tipping points", start to kick in.   Second is what I call  the 'autopilot date".    At some point between 1.5 and 2,  no one knows when, its a lock, the tipping points take over and the system goes on autopilot.  Once that happens it will take centuries to millennia to stop.

 From then on humans can no longer stop climate change by reducing emissions, they can merely slow it down.

The window on the first phase is getting smaller and smaller. The IPCC says we have about 10 years.   Depending on how you measure it, we may have already passed 1.5.  And we are beginning to see some of the self-reinforcing systems already.

Unfortunately these self-reinforcing system or "tipping points". are not well enough understood for the IPPC to include them in the models they use to project temperatures.

This creates some problems.  see e.g  here
 
For instance, the following editorial by Mario Molina. Nobel prizewinner in Chemistry appearing in the Bulletin of the Atomic Scientists.  Here is a snip:

These cascading feedbacks include self-reinforcing Arctic’s sea ice, which could disappear entirely in summer in the next 15 years. The ice serves as a shield, reflecting heat back into the atmosphere, but is increasingly being melted into water that absorbs heat instead. Losing the ice would tremendously increase the Arctic’s warming, which is already at least twice the global average rate. This, in turn, would accelerate the collapse of permafrost, releasing its ancient stores of methane, a super climate pollutant 30 times more potent in causing warming than carbon dioxide.
By largely ignoring such feedbacks, the IPCC report fails to adequately warn leaders about the cluster of six similar climate tipping points that could be crossed between today’s temperature and an increase to 1.5 degrees—let alone nearly another dozen tipping points between 1.5 and 2 degrees. These wildcards could very likely push the climate system beyond human ability to control. As the UN Secretary-General reminded world leaders last month, “We face an existential threat. Climate change is moving faster than we are. If we do not change course by 2020, we risk missing the point where we can avoid runaway climate change, with disastrous consequences….”

Unfortunately recent studies indicate  that some of these tipping points are already being triggered.  Abrupt permafrost melting.  ,  Mineral weathering of permanfrost  Permafrost will melt faster than thought

So the question is, how big and how fast are these feedbacks?    The good news is that they are relatively slow, so in the short term ( out to 2100) they are not expected to be too large.  The bad news is that in the long term they just keep growing.   This is explained pretty well in the so called " Hothouse Earth" paper..  You probably should read it.

Here's what it looks like

 Agricultural production and water supplies are especially vulnerable to changes in the hydroclimate, leading to hot/dry or cool/wet extremes. Societal declines, collapses, migrations/resettlements, reorganizations, and cultural changes were often associated with severe regional droughts and with the global megadrought at 4.2–3.9 thousand years before present, all occurring within the relative stability of the narrow global Holocene temperature range of approximately ±1 °C (56).
SI Appendix, Table S4 summarizes biomes and regional biosphere–physical climate subsystems critical for human wellbeing and the resultant risks if the Earth System follows a Hothouse Earth pathway. While most of these biomes or regional systems may be retained in a Stabilized Earth pathway, most or all of them would likely be substantially changed or degraded in a Hothouse Earth pathway, with serious challenges for the viability of human societies.
For example, agricultural systems are particularly vulnerable, because they are spatially organized around the relatively stable Holocene patterns of terrestrial primary productivity, which depend on a well-established and predictable spatial distribution of temperature and precipitation in relation to the location of fertile soils as well as on a particular atmospheric CO2 concentration. 

The authors of that paper explain what would needed to avoid the hothouse earth, and take path to a  "new normal"as follows

The Stabilized Earth trajectory requires deliberate manage-
ment of humanity’s relationship with the rest of the Earth System if
the world is to avoid crossing a planetary threshold. We suggest
that a deep transformation based on a fundamental reorienation of human values, equity, behavior, institutions, economies, and
technologies is required. Even so, the pathway toward Stabilized
Earth will involve considerable changes to the structure and func-
turning of the Earth System, suggesting that resilience-building
strategies are given much higher priority than at present in decision
making. 


So, it seems we are between a rock and a hard place.  If the recommendations made above were followed we might be able to avoid the tipping points. And avoid the hothouse earth.   But we would still have whatever warming we have caused.   That would be our " new normal ".    This would last for a long time as the CO2 slowly washed out of the atmosphere.    We would still have made significant changes to the earth's climate.


so, here we are.

This is all pretty hard to take.   Eric Holthaus wrote a good piece in Grist called:  If you are suffering from climate grief, you are not alone.  You may want to read it.  Here is part of it.


Last week’s U.N. climate report gave a terrifyingly clear picture of a world on the brink of locking in catastrophe. It told us what was needed and the horrors that awaited if we failed to mobilize. As a scientific report, it was dazzling. But it didn’t tell us how to process, cope, and adapt our lives to the grief of that overwhelming knowledge.
In 1969, after interviewing hundreds of terminally ill patients, psychiatrist Elisabeth Kübler-Ross wrote On Death and Dying, a milestone text on how humans process permanent loss. Kübler-Ross’ description of those reactions — denial, anger, bargaining, depression, acceptance — are now famous, but they were never meant to be an orderly progression of “stages.” There is no “correct,” linear way to grieve. Our reactions are complicated because people are complicated.
There’s no one-size-fits-all approach for taking in something like the looming existential threat of climate change. I’ve been listening to a lot of ’90s country music. One of my colleagues has substantially upped her sleep, while one of our Grist editors “stress bakes.” What we feel is what we feel, and it determines our reality — and importantly, our response, to the news.
And then

What we need now is a major mobilization on climate change. That would require, in the words of the IPCC, “rapid and far-reaching transitions” in “all aspects of society.” We’re taking much more than just solar panels and reusable shopping bags here. After decades of delay, the scale of changes that are necessary will force us to rethink everything. To put in the changes necessary, we have to be able to connect our emotions to our actions. We have to process our grief. We have to somehow move through it, and we have to do all that together.  
   







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Sunday, October 7, 2018

Growing Pains


Eat a lot of peaches
     -John Prine
     
Eat a Peach
    - Allman Brothers


PSA:   Watch Anote's Ark, a film, and hear Professor Dickerson on climate refugees, Oct 16

Quick preview 

"The report will be released on October 8. From leaked drafts, we know the basics of scientists’ findings: World greenhouse gas emissions must peak by 2020 — just 15 months from now. The scientists also show the difference in impacts between 1.5 and 2 degrees would not be minor — it could be make-or-break for the West Antarctic Ice Sheet, for example, which would flood every coastal city on Earth should it collapse.
"After only one degree of warming, the world has seen deadly storms engorged by rising seas and a crescendo of heatwaves, drought, flooding and wild fires made more intense by climate change.
Without a radical course change, we are headed for an unliveable 3C or 4C hike. And yet, humanity has avoided action for so long that any pathway to a climate-safe world involves wrenching economic and social change "unprecedented in terms of scale," the report said.
Greetings

I recently read a nice piece by George Monbiot, noting that the current strategy of replacing fossil fuels with renewable energy isnt really working.   

Despite the growth of wind and solar,  fossil fuel use just isn't dropping.  So far renewables are not a substitute, but a way of having more energy.
This, of course, has been our history.   Each time we have added a new energy resource, we have asks continued to use the old one, merely increasing the total amount of energy used.
Monbiot notes that a growing economy makes this task of substitution more difficult if not impossible. 

See also this article Why Growth Can't Be Green. summarizing recent studies.

 We are essentially trying to go on a healthy diet, we are willing to eat more vegetables but we can't seem to give up the cake!   And as long as we won't give up the cake, we continue to spew CO2.

Hopefully, this state of affairs won't last much longer.   And hopefully, the transition will occur "in time". 

In our case, it appears that "in time" means pretty soon.   Otherwise we may experience a "hothouse Earth",  a 4-5 degree increase in temperature, and 20 meter rise in sea levels.
If this grim scenario is to be avoided, emissions would have to peak within two to three years and then decline by 6-7 percent a year, Rockström said. Far from peaking, though, energy-related greenhouse gas emissions hit a new record high last year, as cuts in the U.K., the U.S. and, Japan were offset by continued carbon dioxide pollution, particularly in China.
The question of the timing of an energy transition was recently portrayed in an unusual way.   From the perspective of space.  see How Aliens Solve their Climate Change Problem  .  It is generally believed that life has evolved on many planets and on some of them a species has been able to harness the available energy and create an industrial civilization, as we have.   The fact that we haven't heard from any of them, create the so-called Fermi paradox.  Where are they?    Frank suggests that perhaps alien civilizations have run into the same problem we have - the need to move from one energy source to a less polluting one before the pollution destroys the civilization.  He creates a very simple modern to explore the importance of the timing of the transition.  He then ran the model thousands of times with different transition times.

"So, what did the model tell us? We saw three distinct kinds of civilizational histories. The first—and, alarmingly, most common—was what we called “the die-off.” As the civilization used energy, its numbers grew rapidly, but the use of the resource also pushed the planet away from the conditions the civilization grew up with. As the evolution of the civilization and planet continued, the population skyrocketed, blowing past the planet’s limits. The population, in other words, overshot the planet’s carrying capacity. Then came a big reduction in the civilization’s population until both the planet and the civilization reached a steady state. After that, the population and the planet stopped changing. A sustainable planetary civilization was achieved but at a high cost. In many of the models, we saw as much as 70 percent of the population perish before a steady state was reached. In reality, it’s not clear that a complex technological civilization like ours could survive such a catastrophe.

The second kind of trajectory held the good news. We called it the “soft landing.” The population grew and the planet changed but together they made a smooth transition to a new, balanced equilibrium. The civilization had changed the planet but without triggering a massive die-off.
The final class of trajectory was the most worrisome: full-blown collapse. As in the die-off histories, the population blew up. But these planets just couldn’t handle the avalanche of the civilization’s impact. The host worlds were too sensitive to change, like a houseplant that withers when it’s moved. Conditions on these planets deteriorated so fast the civilization’s population nose-dived all the way to extinction.
The timing turned out to be an important factor.   In some cases, the transition was made but not " in time"
"You might think switching from the high-impact energy source to the low-impact source would make things better. But for some trajectories, it didn’t matter. If the civilization used only the high-impact resource, the population reached a peak and then quickly dropped to zero. But if we allowed the civilization to switch to the low-impact energy resource, the collapse still happened in certain cases, even if it was delayed. The population would start to fall, then happily stabilize. But then, finally and suddenly, it rushed downward to extinction.
The collapses that occurred even when the civilization did the smart thing demonstrated an essential point about the modeling process. Because the equations capture some of the real world’s complexity, they can surprise you. In some of the “delayed collapse” histories, the planet’s own internal machinery was the culprit. Push a planet too hard, and it won’t return to where it began. We know this can happen, even without a civilization present, because we see it on Venus. That world should be a kind of sister to our own. But long ago Venus’s greenhouse effect slipped into a runaway mode, driving its surface temperatures to a hellish 800 degrees Fahrenheit. Our models were showing, in generic terms, how a civilization could push a planet down the hill into a different kind of runaway through its own activity.
See study here. 
Why?  Tipping points, unfortunately.  Civilizations may stop emissions, but if feed-backs can swamp the effect.  And feed-backs on Earth are not that far off.
"Using a combination of computer models and field measurements, Walter Anthony and an international team of U.S. and German researchers found that abrupt thawing more than doubles previous estimates of permafrost-derived greenhouse warming. They found that the abrupt thaw process increases the release of ancient carbon stored in the soil 125 to 190 percent compared to gradual thawing alone. What's more, they found that in future warming scenarios defined by the Intergovernmental Panel on Climate Change, abrupt thawing was as important under the moderate reduction of emissions scenario as it was under the extreme business-as-usual scenario. This means that even in the scenario where humans reduced their global carbon emissions, large methane releases from abrupt thawing are still likely to occur.
The impact on the climate may mean an influx of permafrost-derived methane into the atmosphere in the mid-21st century, which is not currently accounted for in climate projections.
The Arctic landscape stores one of the largest natural reservoirs of organic carbon in the world in its frozen soils. But once thawed, soil microbes in the permafrost can turn that carbon into the greenhouse gases carbon dioxide and methane, which then enter into the atmosphere and contribute to climate warming.
"The mechanism of abrupt thaw and thermokarst lake formation matters a lot for the permafrost-carbon feedback this century," said first author Katey Walter Anthony at the University of Alaska, Fairbanks, who led the project that was part of NASA’s Arctic-Boreal Vulnerability Experiment (ABoVE), a ten-year program to understand climate change effects on the Arctic. "We don’t have to wait 200 or 300 years to get these large releases of permafrost carbon. Within my lifetime, my children’s lifetime, it should be ramping up. It’s already happening but it’s not happening at a really fast rate right now, but within a few decades, it should peak."
In our situation,  it is not clear exactly when would be "too late".  We need a lot more information.   we generally get that from the IPPC.   A recent report by David Sprat, What Lies Beneath  calls into question the accuracy of the information provided by the IPCC, because its reports are overly optimistic. Risks are understated, and it contains optimistic assumptions.   It's a very through report, so I will merely provide the summary and invite you to read it. 
What Lies Beneath analyses why:
    • Human-induced climate change is an existential risk to human civilization: an adverse outcome that will either annihilate intelligent life or permanently and drastically curtail its potential unless dramatic action is taken.
    • The bulk of climate research has tended to underplay these risks and exhibited a preference for conservative projections and scholarly reticence.
    • IPCC reports tend toward reticence and caution, erring on the side of “least drama”, and downplaying the more extreme and more damaging outcomes, and are now becoming dangerously misleading with the acceleration of climate impacts globally.
    • Why this is a particular concern with potential climatic “tipping points”, the passing of critical thresholds which result in step changes in the climate system. Under-reporting on these issues is contributing to the “failure of imagination” in our understanding of, and response to, climate change.
What's next?  Well "hothouse Earth" might be the next stop.  It looks something like this:



"The last time the Earth saw these kinds of carbon dioxide levels was 3m years ago, well before Homo sapiens appeared, in what is called the “Mid Piacenzian Warm Period” of the Pliocene Epoch. This was warm – but not yet truly hot. The Earth still had a lot of polar ice, especially over Antarctica, but ice on Greenland and West Antarctica was much less extensive, and sea levels were some ten metres or more higher. Global mean temperature was perhaps a couple of degrees warmer than at present, with more warming around the poles than at the equator. If carbon dioxide levels now hold steady, this is the kind of Earth we could be heading towards.
This period in Earth’s history was also Eden-like, with a diversity of life on land and at sea – but getting to that state may be traumatic for crowded humanity as the sea level keeps rising. A true Hothouse Earth emerged when carbon dioxide levels reached something like 800ppm – about double those of today. This was the world of the dinosaurs, 100m years ago. There was little or no ice on Earth and the polar regions had forests and dinosaurs which were adapted to living half the year in darkness.
The biosphere thrived, though equatorial regions tested the thermal limits of life. Much of the low-lying land had been claimed by the sea, which was now a worldwide warm bath in which animals steered a course to avoid the large, oxygen-depleted regions, a result of the sluggish ocean currents typical of an ice-free world. Even this type of Earth is not so unpleasant, though – once you’re there.
But it’s the transition that’s tricky. Some combination of unrestrained carbon emissions and the natural feedbacks of greenhouse gas released from melting permafrost and forest die-back might set us on such a trajectory in little more than a century. Humanity, in such a world, might crowd on to the remaining land and mourn its drowned cities.