So we have made some real progress, even if we cannot claim that all the difference between RCP8.5 (4.5C by 2100) and current policies (2.7C by 2100) is a result of advances in policy and technology.
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This is reflected in the rapid increase in energy transition spending. The world now spends nearly as much on clean energy ($2 trillion in 2024) as global military spending ($2.4 trillion), and spending on clean energy has increased rapidly in recent years:
We should be a bit cautious about over-emphasizing most likely outcomes like 2.7C under current policies, as emissions only represent one of three major climate system uncertainties (the others being climate sensitivity and carbon cycle feedbacks):
This means that challenges remain in constraining high-end warming outcomes, and its hard to rule out 4C warming under current policies by 2100 if we roll 6s on the proverbial climate dice. The world also doesn't end in 2100, even though our models do.
At the same time, I'm hopeful that current policies are more likely to represent an upper bound than a lower bound on warming outcomes this century. The idea that we will not enact any more stringent climate polices for the next 75 years seems unlikely.
Looking at your great paper, I must admit, that I have difficulties finding the amount of emissions / effects of tipping points (like GHG emission from thawing permafrost, change in albedo north polar ocean etc).
Your paper is something I've thought a lot about in the past week, and now I'm wondering - how significant of an impact will the drastic shift in US climate policy have on this modelling?
Exactly. Carbon sinks are increasingly turning into carbon emitters, while the frequency and intensity of wildfires continue to rise. Additionally, global marine algae populations are in decline. The biosphere is reacting to higher temperatures, and these changes are likely to intensify.
This one in general as this trend now becomes apparent - not yet clear, but seems that we get here a robust signal with the most recent years included: "The Impact of Recent Climate Change on the Global Ocean Carbon Sink"; https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023GL107030
Excellent thread. 2.7C is fairly encouraging as we still have 75 years till 2100 to bring emissions and temp down, as the IPCC expects we will have to do in addition to limiting emissions. Geoengineering and C removal technologies clearly needed in addition to emissions reduction.
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What is the assumption for this effect?
..this is just more secular ideology trying to send the world to it's grave
Keep promoting shale!
in the Task Force on Climate-related Financial Disclosures
(TCFD) reporting that show benign, or even positive, economic
outcomes in a hot-house world. " https://actuaries.org.uk/media/qeydewmk/the-emperor-s-new-climate-scenarios.pdf
This publication on the ocean carbon sink in 2023 could be decisive, if correct (complicated topic): "Unexpected decline of the ocean carbon sink under record-high sea surface temperatures in 2023"; https://assets-eu.researchsquare.com/files/rs-5198321/v1_covered_538b07ae-65a0-487d-b6b3-662f7c322ec0.pdf?c=1731428416