There is often an assumption that the more aggressive climate targets means more BECCS.

This is only weakly true, many 2°C scenarios use as much BECCS as 1.5°C scenarios, & even >2.5°C scenarios use BECCS at scale!

IAMs just love BECCS 😍🥰😘

1/
These are scenarios that go over 2°C. Yes, some scenarios use over 20GtCO₂/yr in 2100 (we currently emit 40GtCO₂/yr). These are not aggressive mitigation scenarios, these are >2°C, & where we could end up with only weak climate policies like we have today.

2/
It is not that 1.5°C or 2°C (or even 3°C) needs large-scale BECCS, this is just the cost-effective pathway that most IAMs find. This could be for a variety of structural reasons.

Since BECCS is so prolific in scenarios, we obsess over it. It may just be a model artifact!

3/
The black crosses in the figure are the four Illustrative Pathways used in IPCC SR15.

There is one scenario with extreme BECCS (P4), which everyone discards as ridiculous, but it is an outlier in the high overshoot scenarios! Some high overshoot have very little BECCS!

4/
These are the four Illustrative Scenarios. It is worth remembering that P1 and P4 are the absolute extremes in one characteristic (BECCS). There is a whole spectrum of scenarios in between that may be more desirable in characteristics other than BECCS!

5/
All the data is from the IPCC SR15 database data.ene.iiasa.ac.at/iamc-1.5c-expl…, the figure are from me though...

/end my morning rant on BECCS is not a 1.5°C thing, it is a IAM thing, that no one seems to understand!

6/6

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More from @Peters_Glen

8 Oct
THREAD: N₂O

We have a new paper in @nature on nitrous oxide (N₂O), five years in the making!

Like many GHGs, N₂O concentrations have been stable for thousands of years, but that balance between sources & sinks has been dramatically changed by humans.

rdcu.be/b8cgZ Image
2. N₂O is a potent GHG, 300 times worse than CO₂ over 100 years (GWP). It destroys the ozone layer & contributes to water pollution.

N₂O is ~7% of current radiative forcing, but because of its long lifetime & difficulty to mitigate, this will increase even in 1.5°C scenarios. Image
3. N₂O comes almost equally from natural (60%) & anthropogenic sources (40%).

Natural sources are dominated by microbial processes that break down nitrogen-containing compounds in the soil & oceans. These sources have previously balanced with the atmospheric chemical sinks. Image
Read 11 tweets
6 Oct
Even though N₂O’s Ozone Depletion Potential is only 0.017, roughly one-sixtieth of CFC-11s, the large anthropogenic N₂O emissions make N₂O the single most important source of ozone depletion (that was in 2009!)

1/

science.sciencemag.org/content/326/59…
For the emission metric nerds out there, there is a close historical link between the Global Warming Potential (GWP) and the Ozone Depletion Potential (ODP).

The paper uses GWP & ODP, to contrast climate & ozone impacts.

2/
If you want to understand the GWP, read up on the ODP...

In this paper on the integrated Global Temperature change Potential (iGTP) I dug into some of the history, & it made me understand the GWP much better...

3/

iopscience.iop.org/article/10.108…
Read 4 tweets
6 Oct
The results of yesterdays poll on EU climate ambition.

There was some ambiguity with the question, essentially to what degree the EU should adjust to the ambition of others.

There was a reason for the way I posed the question, around net-zero, linking to the ">2°C" option

1/
Scenarios with 50% chance of staying below 2°C rarely reach net-zero GHG by the end of the century (from IPCC SR15). The EU is aiming for net-zero GHG in 2050. The EU, in this case, would be more than 50 years ahead of the global average.

2/
This is the temperature response from those scenarios, still below 2°C (median in 2100 is 1.8°C).

So, to pick the option that the EU is consistent with over 2°C (>2°C in the poll) is rather extreme, & I would say inconsistent with the science (sorry).

3/
Read 7 tweets
5 Oct
How is a 1.5°C scenario defined?

It should be simple to define? No? These are the definitions used in IPCC SR15, which has three types of 1.5°C scenarios depending on "overshoot".

This has implications...

1/ Image
The Paris agreement has "well below 2°C ... pursing ... 1.5°C". A broad interpretation would be somewhere between 1.5°C-2°C (closer to 1.5°C).

This is where the SR15 scenarios go. The 1.5°C scenarios are generally below 1.5°C except for a period of over 1.5°C.

And so?

2/ Image
This 'overshoot' has big implications for Carbon Dioxide Removal (CDR). Here is CDR just from BECCS... Add on top of this CDR from afforestation!

Choosing aggressive definitions of 1.5°C generally requires assuming more CDR. Which is fine, as long as this trade-off is clear.

3/ Image
Read 4 tweets
25 Sep
"We estimate that 30 years of natural forest regrowth across 349 Mha & 678 Mha could [lead to uptake of 5.9 to 8.9 GtCO₂/yr]". This includes some below ground carbon.

Plenty to unpack, but how does it compare to emission scenarios?

1/

nature.com/articles/s4158…
1.5°C scenarios with no or low overshoot from #SR15 have afforestation in 2050 (30 years from now) consistent with those numbers (some even higher).

Worth noting, the CO₂ uptake will not continue at that high rate...

2/
IAMs that provide data on land use for afforestation use similar areas, of ~350-650Mha in 2050.

The carbon uptake rates seem broadly in the same ranges (though harder to check given the data reported in IAMs).

At least, no glaring inconsistencies...

3/
Read 5 tweets
24 Sep
Come on Tweeps, surely afforestation is a Negative Emission Technology (NET)?

This pole really surprised me, 50% think afforestation is not a NET. Wow. I mean WOW. When did this happen?

1/

Image
Many said they use process, or mechanism, or similar, & prefer Carbon Dioxide Removal (CDR). This is really coming down to what is a "technology".

Others basically said it is a question of efficacy. Does it work? If not, it is not a NET. I didn't think of that issue.

3/
I could go through numerous articles where afforestation is a NET. IPCC says afforestation is a NET depending on report, more commonly CDR.

Here is one article, just as an example
iopscience.iop.org/article/10.108…

CDR is a much better term, but afforestation is still a NET... (IMHO)

4/
Read 8 tweets

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