THREAD (without figures)

Four principles for thinking about CO₂ removal:
1. Don't forget the long game
2. It's not all about CO₂
3. Split, don't lump
4. Don't bet it all on being right…
2. First: Don't forget the long game

Cutting GHG emissions must remain at the center of that strategy: CDR would be too slow, expensive, and technically uncertain to replace the need for rapid emissions reductions.
3. Different roles for CDR:
* Mop up to compensate for hard-to-abate (or expensive-to-abate) sectors
* Mop up after agricultural sectors (net-zero GHG emissions)
* Draw down "legacy carbon" remaining in the atmosphere from past emissions
4. Can start deploying CDR now (e.g., ecosystem restoration or afforestation), but if gigatonne scale CDR is needed later this century, then now is the time to get started on developing and adopting appropriate policies for CDR research, development, & rollout.
5. Second, it is not all about the carbon

Different approaches to CDR have different resource requirements & different social & environmental impacts.

Are we talking about an individual farmer adopting cover-crops or a multinational cooperation doing Direct Air Capture?
6. Is BECCS all bad?

Compare a small BECCS facility fueled by local municipal waste with a BECCS system in which huge swathes of commercially farmed land provide switchgrass to fuel large power plants that pipe carbon dioxide long distances for sequestration.
7. Evaluating CDR at the level of broad technologies or practices obscures these differences. A complete assessment of CDR requires assessing not only cost and sequestration potential but also environmental and social impacts.
8. Third, split don't lump

Not all CDR is created equal in terms of social, economic, & environmental impacts, & nuanced positions are needed to distinguish better technologies, practices, projects, and policies from worse ones.

E.g, not all BECCS is created equal...
9. Fourth, Don't bet it all on being right

Large-scale CDR might fail, but rapid short-term emission reductions might not emerge either.

Don't put all your cookies in one basket whether CDR or rapid reductions, both are needed.
10. We agree that precaution precludes us from betting it all on CDR’s panning out as the models project. We also worry about making the opposite mistake by counting only on rapid emissions abatement.

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More from @Peters_Glen

20 Aug
I just came across some great EV explainers from @AukeHoekstra. They are only short (<15 minutes), but effectively get across key messages.

The first two are great for anyone that wants to learn about different types of EVs, the next two get a little more technical...

How do EVs & ICEs differ?

Two main issues:
* Motor: EVs win, much simpler & lighter
* Energy storage: ICEs win, gasoline / diesel very energy dense

On balance, EVs are starting to win (gains in motor more than offsets weaknesses in storage)


What are the pros & cons of different types of electric vehicles?
- hybrids (HEVs)
- plug-in hybrids (PHEVs)
- full electric vehicles (FEVs, also BEVs)
- fuel cell electric vehicles (FCEVs)
(also comparisons with ICE & biofuels)


Read 6 tweets
28 Jul
One of the biggest problems with Border Carbon Adjustments (BCAs) is also the problem that is least discussed.


@arvindpawan1 explains (plus many other issues)…
Whether it is the intention or not, BCAs have the effect of reducing output in developing countries.

That is, when rich countries apply a BCA, poor countries get lower GDP & rich countries get higher GDP. Typical! All BCA studies show this.

BCAs are also against the spirit of the Paris Agreement.

The unique aspect of the PA was that countries would put forward NDCs, & other countries would accept them as sufficient. It is not a top-down Kyoto style agreement, it is a bottom-up style agreement.

Read 11 tweets
11 Jun
1. Will energy technologies grow exponentially until they reach "materiality" & then have linear growth?

A common perception, but what does history say?

[Short answer: Old technologies are growing exponentially (not nuclear), just slower due to crowding out effects!]

2. There was a paper in @nature in 2009 that used a "materiality" concept to say there will be a slow switch to low carbon sources.

I have been wanting to update their figure for some time, & see if their "laws" were correct.
3. They came up with two laws, essentially that technologies grow exponentially until they become 'material', then growth changes to linear.

This is used to argue that there are 'physical limits' to the growth of new (low carbon) technologies.

But what does the data say?
Read 14 tweets
28 May
THREAD on Carbon Budgets

The 'Carbon Budget' is the cumulative CO₂ emissions from one point in time to another given a temperature limit, such as exceeding 1.5°C, reaching net-zero (~peak temperature), or to (say) 2100 for a 1.5°C scenario.…
2. The #IPCC #SR15 had different categories of scenarios.

The 'Below 1.5°C' scenarios never exceeded 1.5°C (no 'exceed' budget), but they all reach net-zero CO₂ emissions leading to a 'net-zero' or 'peak' budget (as peak cumulative CO₂ occurs at net-zero CO₂ emissions).
3. Most 1.5°C scenarios exceed 1.5°C, reach a peak temperature (over 1.5°C), & then decline back below 1.5°C (peak & decline scenarios).

How to define the budget? A net-zero budget is a clear definition, but corresponds to ~peak temperature (eg 1.7°C) & varies a factor of two!
Read 9 tweets
22 May
"The result remains the gold standard for policy: global warming potential (GWP), which compares the impact of different greenhouse gases on climate." @KHayhoe @Wuebbles


That statement pulled me up...

I have no doubt about the statement before "When they argued that it was too difficult [to compare GHGs in a single metric], Houghton insisted that they must, because they were the best people in the world to do this."

Don Wuebbles was instrumental in the Ozone Depletion Potential (ODP) & the GWP uses essentially the same concepts.

Houghton pushed as there was a need to compare GHGs for policy, though, I am not sure scientists were so keen on the GWP at the time, nor the years later.

Read 6 tweets
22 May
Ooops. Only out by a factor of two... A short 60 billion bucks!

This is quite amazing...

Surely, they had someone that did a quick back of the envelope check? "Hey guys, that number looks a tad high"... 🤔

Not sure why the ABC is blaming businesses here for making a mistake. You would think there would be a variety of checks & balances in place...

I would put blame on the government for not running the numbers more carefully. Perhaps they should employee a few data scientists?
When I heard the 6.5 million people on JobKeeper, I even did a quick scratch of the head. It must imply a pretty devastating unemployment rate, but move on, I have emissions to estimate.

Doesn't the government have an idea on how many people are employed & might need help?
Read 4 tweets

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