Sciencescience

Mon Jul 22, 2019, 11:43 AM

The point of no return for climate action: effects of climate uncertainty and risk tolerance

Abstract
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If the Paris Agreement targets are to be met, there may be very few years left for policy makers to start cutting emissions. Here we calculate by what year, at the latest, one has to take action to keep global warming below the 2 K target (relative to pre-industrial levels) at the year 2100 with a 67 % probability; we call this the point of no return (PNR). Using a novel, stochastic model of CO2 concentration and global mean surface temperature derived from the CMIP5 ensemble simulations, we find that cumulative CO2 emissions from 2015 onwards may not exceed 424 GtC and that the PNR is 2035 for the policy scenario where the share of renewable energy rises by 2 % year−1. Pushing this increase to 5 % year−1 delays the PNR until 2045. For the 1.5 K target, the carbon budget is only 198 GtC and there is no time left before starting to increase the renewable share by 2 % year−1. If the risk tolerance is tightened to 5 %, the PNR is brought forward to 2022 for the 2 K target and has been passed already for the 1.5 K target. Including substantial negative emissions towards the end of the century delays the PNR from 2035 to 2042 for the 2 K target and to 2026 for the 1.5 K target. We thus show how the PNR is impacted not only by the temperature target and the speed by which emissions are cut but also by risk tolerance, climate uncertainties and the potential for negative emissions. Sensitivity studies show that the PNR is robust with uncertainties of at most a few years.

How to cite.
Aengenheyster, M., Feng, Q. Y., van der Ploeg, F., and Dijkstra, H. A.: The point of no return for climate action: effects of climate uncertainty and risk tolerance, Earth Syst. Dynam., 9, 1085-1095, https://doi.org/10.5194/esd-9-1085-2018, 2018.
1 Introduction
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The Earth system is currently in a state of rapid warming that is unprecedented even in geological records (Pachauri et al., 2014). This change is primarily driven by the rapid increase in atmospheric concentrations of greenhouse gases (GHGs) due to anthropogenic emissions since the industrial revolution (Myhre et al., 2013). Changes in natural physical and biological systems are already being observed (Rosenzweig et al., 2008), and efforts are made to determine the “anthropogenic impact” on particular (extreme weather) events (Haustein et al., 2016). Nowadays, the question is not so much if but by how much and how quickly the climate will change as a result of human interference, whether this change will be smooth or bumpy (Lenton et al., 2008) and whether it will lead to dangerous anthropogenic interference with the climate (Mann, 2009).

The climate system is characterized by positive feedbacks causing instabilities, chaos and stochastic dynamics (Dijkstra, 2013) and many details of the processes determining the future behavior of the climate state are unknown. The debate on action on climate change is therefore focused on the question of risk and how the probability of dangerous climate change can be reduced. In scientific and political discussions, targets on “allowable” warming (in terms of change in global mean surface temperature, GMST, relative to pre-industrial conditions1) have turned out to be salient. The 2 K warming threshold is commonly seen – while gauging considerable uncertainties – as a safe threshold to avoid the worst effects that might occur when positive feedbacks are unleashed (Pachauri et al., 2014). Indeed, in the Paris COP21 conference it was agreed to attempt to limit warming below 1.5 K (United Nations, 2015). It is, however, questionable whether the commitments made by countries (the so-called nationally determined contributions, NDCs) are sufficient to keep temperatures below the 1.5 K and possibly even the 2.0 K target (Rogelj et al., 2016a).

A range of studies has appeared to provide insight into the safe level of cumulative emissions to stay below either the 1.5 or 2.0 K target at a certain time in the future with a specified probability, usually taken as the year 2100. The choice of a particular year is necessarily arbitrary and neglects the possibility of additional future warming. Early studies made use of Earth System Models of Intermediate Complexity (EMICs; Huntingford et al., 2012; Steinacher et al., 2013; Zickfeld et al., 2009) to obtain such estimates. Because it was found that peak warming depends on cumulative carbon emissions, EΣ, but is independent of the emission pathway (Allen et al., 2009; Zickfeld et al., 2012), focus has been on the specification of a safe level of EΣ values corresponding to a certain temperature target. In more recent papers, also emulators derived from either C4MIP models (Sanderson et al., 2016) or CMIP5 (Coupled Model Intercomparison Project 5) models (Millar et al., 2017b), with specified emission scenarios, were used for this purpose. Such a methodology was recently used in Millar et al. (2017a) to argue that a post-2015 value of EΣ≈200 GtC would limit post-2015 warming to less than 0.6 ∘C (so meeting the 1.5 K target) with a probability of 66 %.

In this paper we pose the following question: assume one wants to limit warming to a specific threshold in the year 2100, while accepting a certain risk tolerance of exceeding it, then when, at the latest, does one have to start to ambitiously reduce fossil fuel emissions? The point in time when it is “too late” to act in order to stay below the prescribed threshold is called the point of no return (PNR; van Zalinge et al., 2017). The value of the PNR will depend on a number of quantities, such as the climate sensitivity and the means available to reduce emissions. To determine estimates of the PNR, a model is required of global climate development that (a) is accurate enough to give a realistic picture of the behavior of GMST under a wide range of climate change scenarios, (b) is forced by fossil fuel emissions, (c) is simple enough to be evaluated for a very large number of different emission and mitigation scenarios and (d) provides information about risk, i.e., it cannot be purely deterministic.
(more)

https://www.earth-syst-dynam.net/9/1085/2018/


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Arrow 21 replies Author Time Post
Reply The point of no return for climate action: effects of climate uncertainty and risk tolerance (Original post)
orson Jul 2019 OP
Solesurvivor Jul 2019 #1
quad489 Jul 2019 #2
Grebbid Jul 2019 #3
foia Jul 2019 #4
SatansSon666 Jul 2019 #5
orson Jul 2019 #7
foia Jul 2019 #8
adozenpirates Jul 2019 #9
oflguy Jul 2019 #11
adozenpirates Jul 2019 #12
oflguy Jul 2019 #13
adozenpirates Aug 2019 #14
oflguy Aug 2019 #15
adozenpirates Aug 2019 #16
oflguy Aug 2019 #17
adozenpirates Aug 2019 #18
oflguy Aug 2019 #19
adozenpirates Aug 2019 #20
oflguy Aug 2019 #21
Carl Jul 2019 #6
oflguy Jul 2019 #10

Response to orson (Original post)

Mon Jul 22, 2019, 12:09 PM

1. And all you have to do to stem global warming is pay

More taxes and cede more of you liberties

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Response to orson (Original post)

Mon Jul 22, 2019, 12:17 PM

2. Well, if you're already past the ''point of no return for climate action'', might as well fire up...

...the charcoal grill and live it up before the Earth's surface burns up.

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Response to orson (Original post)

Mon Jul 22, 2019, 12:53 PM

3. We probably just need more diversity and my $$ to fix everything

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Response to orson (Original post)

Mon Jul 22, 2019, 03:05 PM

4. How many "tipping points" have we already been through in the last 30 years?

June 1989 - A senior U.N. environmental official says entire nations could be wiped off the face of the Earth by rising sea levels if the global warming trend is not reversed by the year 2000.

https://www.apnews.com/bd45c372caf118ec99964ea547880cd0

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Response to foia (Reply #4)

Mon Jul 22, 2019, 04:27 PM

5. Don't get your science from officials.

It happens every time.
They say something false and everyone runs with that while the scientists can't believe how their research has been misused.

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Response to foia (Reply #4)

Mon Jul 22, 2019, 08:38 PM

7. Yep. They predicted climate change 40 years ago

but no one paid a goddamned bit of attention. We could have done something back then, but no. Reagan took the solar panels off the White House and it was morning in America. Having a senile dunce as president has always been a bad idea.

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Response to orson (Reply #7)

Mon Jul 22, 2019, 09:08 PM

8. At least he wasn't an economic dunce like Obama.

I'm sure that taking solar panels off of The White House doomed the planet. Maybe if he'd worn a sweater like Carter then we'd all be saved.

All of these past fake news "tipping points" have been eclipsed so I guess we're doomed anyhow, right?

We just need to tax people more, right?

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Response to foia (Reply #8)

Wed Jul 24, 2019, 12:36 PM

9. Obama wasn't an economic dunce - he just wasn't working on behalf of people like you or me. nt

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Response to adozenpirates (Reply #9)

Mon Jul 29, 2019, 10:28 PM

11. Its unfair to call Obama an economic dunce

He is a dunce in many ways. Economics is just one of them.

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Response to oflguy (Reply #11)

Wed Jul 31, 2019, 03:00 PM

12. Nah.

I think it's more along the lines of "it is difficult to get a man to understand something, when his salary depends upon his not understanding it." (I'm guessing you've encountered that quote before.) He isn't a dunce by a long shot, he just saw things differently than you or I do.

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Response to adozenpirates (Reply #12)

Wed Jul 31, 2019, 08:39 PM

13. I guess you are right

I don't subscribe to Marxism at all

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Response to oflguy (Reply #13)

Thu Aug 1, 2019, 12:32 PM

14. "Ce qu'il y a de certain c'est que moi, je ne suis pas Marxiste."

Yeah, neither does Obama. He's a garden variety neoliberal globalist.

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Response to adozenpirates (Reply #14)

Thu Aug 1, 2019, 01:46 PM

15. Really?

When did Obama give up Marxism?

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Response to oflguy (Reply #15)

Thu Aug 1, 2019, 02:30 PM

16. I don't know that he was ever a subscriber.

If so, he certainly gave it up before he assumed the office of President.

Honestly, I'm not sure too many people know - or agree on - what "Marxism" is. That's why I quoted Marx in the subject line of my previous reply. In English, what Marx said was "What is certain is that I am not a Marxist."

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Response to adozenpirates (Reply #16)

Fri Aug 2, 2019, 09:58 PM

17. You do know Obama belonged to a Marxist organization in college, right?

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Response to oflguy (Reply #17)

Sat Aug 3, 2019, 10:32 AM

18. So I've heard.

If true, it's not at all clear what the significance is (students dabble in all kinds of things that aren't reflected in later life). As a friend of mine is fond of saying, behavior is truth. A Marxist president wouldn't appoint people like Rahm Emanuel and Tim Geithner. In the wake of a financial crisis with ample evidence of fraud, a Marxist president would have set their justice department on Wall Street like a pack of wolves, not "foamed the runway" for the banks. Nor would a Marxist president attempt to engineer a "grand bargain" that involved cuts to social security. Not to mention that big donors, who as a group are quite politically savvy and attentive to their interests, wouldn't have provided him with lavish funding if they thought he was a Marxist. Nor would the Democrats have rolled out the red carpet; they would have treated him more like they treat Bernie Sanders. The idea that Obama is a Marxist is totally ridiculous.

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Response to adozenpirates (Reply #18)

Sat Aug 3, 2019, 12:29 PM

19. Not ridiculous at all

There are tons of things Obama would have done if he could have gotten away with it.

Keep in mind, Obama's surrogate father, Frank Marshall Davis, was a card carrying communist and a black supremist

Obama's own writings reveal that he was a Marxist

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Response to oflguy (Reply #19)

Sat Aug 3, 2019, 02:03 PM

20. lol

Leave it to this place to make DU look sane.

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Response to adozenpirates (Reply #20)

Sat Aug 3, 2019, 11:51 PM

21. What a shame you didn't pay more attention when Obama was running for president

For Christ's sakes, read his own words in his book

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Response to orson (Original post)

Mon Jul 22, 2019, 07:59 PM

6. Tell it to China.

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Response to orson (Original post)

Wed Jul 24, 2019, 08:30 PM

10. We only have 11 years left, so may as well enjoy ourselves

No point in wringing our hands, is there?

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