THREAD "Limiting climate change to 1.5°C is now virtually impossible"

Therefore, a report that focuses on 3°C temperature rise by 2100 (2.7–3.1°C based on current climate policies).

While noting "acting early & urgently reduces the scale of the impacts"

science.org.au/supporting-sci…
2. I am not sure what the fuss is about "virtually impossible"? Has anyone read the 'consensus' #IPCC #SR15?

The SPM writes 1.5°C pathways "require rapid & far-reaching transitions in energy, land, urban & infrastructure and industrial systems (𝒉𝒊𝒈𝒉 𝒄𝒐𝒏𝒇𝒊𝒅𝒆𝒏𝒄𝒆)"
3. Current "ambitions would not limit global warming to 1.5°C (𝒉𝒊𝒈𝒉 𝒄𝒐𝒏𝒇𝒊𝒅𝒆𝒏𝒄𝒆)"

Not even 'virtually', just "not" possible!

Noting, that even updated pledges so far lead to a 1% decrease in global emissions, not the required 45% reduction!
4. Even if the world follows the oft-cited 50% by 2030, net-zero CO₂ by 2050, then CDR on massive scale in scenarios (100–1000 GtCO₂).

"CDR deployment of several hundreds of GtCO₂ is subject to multiple feasibility & sustainability constraints (𝒉𝒊𝒈𝒉 𝒄𝒐𝒏𝒇𝒊𝒅𝒆𝒏𝒄𝒆)"
5. Yes, the 'carbon budget' is uncertain. Yet, everyone uses the smaller 66% budget for 1.5°C, not the 33% the-budget-is-uncertain bigger budget.

(Deduct 3*40=120GtCO₂ from these budgets to be relevant from today).

Of course, IPCC AR6 will update these budgets. Maybe bigger?
6. This paper really shows the uncertainty in a 1.5°C remaining carbon budget. It could be negative or it could be large.

An uncertain carbon budget could change 1.5°C from "virtually impossible" to anything from "impossible" to just "challenging".

nature.com/articles/s4324…
7. I am going to get @'ed this thread from @JoeriRogelj a billion times today.

I understand Joeri thinks "virtually impossible" is overplaying, but saying 1.5°C is "challenging" is underplaying (IMHO).

Note: "virtually impossible" ≠ "impossible"

8. With "virtually impossible", it is important to note there is still a huge role for deep mitigation.

The IPCC did a good job at trying to reframe from a 1.5°C 'deadline'.

“Every bit of warming matters, every year matters, every choice matters”

9. It seems 1.5°C has come down to semantics, "virtually impossible" versus "challenging"?

I see my job as a scientist to be frank on the challenges, but to doomsdayers, noting the challenges is not the same as giving up. Still plenty to fight for.
cicero.oslo.no/no/posts/klima…

/end
Bonus tweet 1: I think the scientific community has done itself a disservice with framing carbon budgets as single numbers with a probability (eg 475 GtCO₂ for a 66% chance).

Better to use ranges (eg 760 GtCO₂ with 33–66% range 475–930 GtCO₂). rdcu.be/bHT2C
Bonus tweet 2: Using a single number gives a false precision, & leads to the "12 years to..." framing.

A range explicitly brings in the uncertainty, & allows more nuance to be given on the feasibility of 1.5°C. This would avoid much of this thread...
Bonus tweet 3: Here is the 5-95% temperature uncertainty for 1.5°C scenarios from two simple climate models (FAIR, MAGICC) used in SR15. The peak temperature ranges from 1.1°C to >2°C.

If FAIR is correct, 1.5°C is not 'virtually impossible'...

• • •

Missing some Tweet in this thread? You can try to force a refresh
 

Keep Current with Glen Peters

Glen Peters Profile picture

Stay in touch and get notified when new unrolls are available from this author!

Read all threads

This Thread may be Removed Anytime!

PDF

Twitter may remove this content at anytime! Save it as PDF for later use!

Try unrolling a thread yourself!

how to unroll video
  1. Follow @ThreadReaderApp to mention us!

  2. From a Twitter thread mention us with a keyword "unroll"
@threadreaderapp unroll

Practice here first or read more on our help page!

More from @Peters_Glen

26 Mar
'Net' emissions are a slippery slope, but we already deal with net emissions. It is not so scary...

In most Annex I countries LULUCF emissions are a net-sink. The sink is mainly forest regrowth & recovery.

Net emissions have been here since 1990, at least...

1/
In the EU, most of the sink is increased uptake in existing forests, there is a small part of afforestation (dark green). There are also emission sources, such as from grasslands & new settlements.

Maintaining the sink over time (with climate impacts) could be hard.

2/
The EU27 now includes the land sink (LULUCF) in its climate targets.

Perhaps this is good? It forces the EU to maintain & expand its sink.

Perhaps this is bad? The EU can now have 'net-zero' emissions in 2050 (though, studies suggest this is mainly agricultural)

3/
Read 7 tweets
22 Mar
Historically, the land & ocean sink have removed about one-half of the anthropogenic CO₂ emissions.

If we mitigate successfully in the future, the sinks will take up less CO₂ since emissions are lower, but they will be replaced by 'engineered sinks'.

1/n
This is a more detailed figure showing the anthropogenic CO₂ emission sources (top), & the land and ocean sinks (with the balance remaining in the atmosphere). Bread & butter carbon cycle...

2/
globalcarbonproject.org/carbonbudget/i…
As we mitigate, the land & ocean sinks take up less, but engineered sinks (eg BECCS) & afforestation increase.

If the land sink is included as an emissions source, then emissions still need to go to zero about the same time (dashed line).

Fig based on science.sciencemag.org/content/355/63…
3/
Read 9 tweets
19 Mar
IPCC: "In model pathways with no or limited overshoot of 1.5°C, global net anthropogenic CO₂ emissions [reach] net zero ~2050 (2045–2055)"

There are likely equally plausible scenarios (shown here) that reach net-zero CO₂ emissions in 2100 with the same 'carbon budget'.

1/
You don't believe me?

These are the scenarios used for net-zero ~2050 (2045-2055). They basically all cross zero around 2050. This is because they focus on 2100 targets & allow 'overshoot'.

This is a design feature of the scenarios, & are not the only way to get to 1.5°C!

2/
The temperature response to those scenarios all have a 'peak & decline' shape. Some of the 'peak & decline' is due to CO₂ emissions & some to non-CO₂ emissions (GWP100 confuses this point).

Most modelling uses a 2100 target, allowing overshoot (a cost-effective 'feature').

3/
Read 4 tweets
18 Mar
THREAD: Net-zero emissions

What is the the different between zero & net-zero? CO₂ or GHG?

Does net-zero mean emissions continue but are offset by Carbon Dioxide Removal (CDR)? (no)

Based on a presentation: slideshare.net/GlenPeters_CIC…
2. First, why is "net-zero" needed in the first place?

Science shows that the temperature stops rising when CO₂ emissions reach (net-)zero.

There are non-CO₂ emissions, but they have a smaller (secondary) effect & declining emissions may be sufficient

cicero.oslo.no/no/posts/klima…
3. Zero emissions:

If we take a remaining carbon budget consistent with 1.5°C, then emissions need to drop rapidly. This curve converges to zero, there is no physical reason to have a straight line to zero.

(I took 580GtCO₂ from SR15 Table 2.2, not adjusted for time past)
Read 14 tweets
17 Mar
What is net-zero? Is it carbon neutral? CO₂ or GHG?

Did you know that 1.5°C scenarios reach net-zero CO₂ emissions around 2050, but net-zero GHG emissions around 2070?

1/
For a likely below 2°C scenario, the net-zero years are shifted back about 20 years.

In fact, many likely below 2°C scenarios don't require net-zero GHG emissions until after 2100.

2/
And why "net" and not just zero?

That is because it is hard to get all emissions completely to zero, & so some carbon dioxide removal is needed to clean up any remaining emissions.

The scale is important. How much CDR is possible?

3/
Read 6 tweets
16 Mar
IPCC AR5 WG3 (2014) had a figure showing the impact on mitigation costs of various technology restrictions (eg, no CCS).

It also compared lower energy demand (20–30% below baseline by 2050 & 35–45 % by 2100), first set of bars.

This 𝑟𝑒𝑑𝑢𝑐𝑒𝑑 mitigation costs by half.

1/
The 'low energy demand' analysis enforced a reduction on demand, but did not evaluate the costs (ie, mitigation costs of reduced demand are assumed zero).

This is the same as in newer studies
* LED: nature.com/articles/s4156…
* Alternative pathways: nature.com/articles/s4155…

2/
The (infamous) 'Low Energy Demand' scenario essentially combines two components, 'low energy demand' & 'no CCS'.

It also does really detailed analysis on the demand side, not just an arbitrary reduction (which is good).

nature.com/articles/s4156…

3/
Read 10 tweets

Did Thread Reader help you today?

Support us! We are indie developers!


This site is made by just two indie developers on a laptop doing marketing, support and development! Read more about the story.

Become a Premium Member ($3/month or $30/year) and get exclusive features!

Become Premium

Too expensive? Make a small donation by buying us coffee ($5) or help with server cost ($10)

Donate via Paypal Become our Patreon

Thank you for your support!

Follow Us on Twitter!