The study essentially argued that based on the AR5 carbon budgets, viewed from 2014, there was seven years (2021) until the 1.5°C carbon budget was used, & therefore 1.5°C was essentially a "geophysical impossibility".
They had a new method with a more realistic budget.
2/
The @CarbonBrief post was titled: "Why the 1.5°C warming limit is not yet a geophysical impossibility"
The authors wrote: "[A]lthough 1.5°C is not yet a geophysical impossibility, it remains a very difficult policy challenge."
I distinctly remember trying to understand why that language was used. It seems like "1.5°C was impossible, now it is possible, & so now it makes sense to mitigate".
This was all around the time of Paris, SR15 preparation, etc
5/
Right wing media loved the language, & the article was a hit, the study "concedes that it is now almost impossible that the doomsday predictions made in the last IPCC assessment report ... will come true"
I wrote a blog post, "Did 1.5°C suddenly get easier?", which made me very unpopular as the right-wing media picked it up.
My main point? Drop uncertain carbon budgets & go for net-zero instead...
7/
I claimed that carbon budget have been published ranging from -200 to 1000 GtCO₂... I felt that was quite risky to write, but was confident it was correct.
It turns out I was way too conservative according to this study (see left panel).
In any case, the Millar et al budgets turned out to be much larger than used in the IPCC SR15 (below), but many aspects of their method are used in recent carbon budget estimates (making sure estimates align with historical warming).
9/
I am surprised I forgot that language & debate back in 2017. I felt I became very unpopular amongst colleagues for my blog.
I had many paper ideas for carbon budgets, but put them in the bin. I wrote a commentary in the /end.
Despite China building more coal capacity (net), coal use has been flat in the decade (green). This means the coal power utilisation rate is declining.
Coal is going down in Europe & the US, but up in most other places.
1/
And here is the same figure as a line chart, which makes it easier to compare countries and see the trends...
There are much more ups & downs in coal production. Most of the differences (to consumption) are likely to relate to stock piles (& statistical differences).
'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)
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...