polarocean.bsky.social
Father of 3, ocean biogeochemical modeller at the University of Bern, interested in high-latitude oceans, carbon cycle, ocean-climate interaction & ecosystem stressors such as ocean acidification and primary production.
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However, this does not mean that it is unexpected fast on the long term. It is an expected acceleration with added variability in my opinion. And every gram of reduced emissions s will reduce the warming rate
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... for a long time. Once the sea ice disappears, warming will even more accelerate. In brief, I believe we come out of one or two decades with slower warming due to decadal variability and turn to a phase of faster warming now, we basically catch up to the long term trend as sea ice melts
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... so much variability in the system. In the end, it is not surprising that warming is accelerating because emissions have continously risen. It was more surprising that warming was linear for such a long time. My take on that is that relatively robust sea ice has halted the acceleration...
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I'd not take it out, the years 2023/24 were also exceptional because they years before were unusual cold compared to the long-term trend. So, it does not make much sense to remove it, I believe. However, statistical analyses 9f significance are important to be able to determine trends with...
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It can also not be excluded at the moment that there is no unexpected accelerated warming in addition to the expected and observed acceleration of warming. But at the moment SSTs are consistent with climate models and can well be within expected accelerated warming based on emission increases
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We adress the question by showing that SSTs as 2023/24 exist also in climate models, meaning that 2023/24 is not necessarily a sign of unexpected warming but can also be variability. @tguinaldo.bsky.social show that the Atlantic SSTs can also be explained by internal variability.
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The question that remains is if there is an additional unexpected warming. There are different possibilities, such as the Antarctic sea ice feedback that likely means that warming was lower over the last two decades and that warming will increase much more soon and ECS is larger than expected 😢👇
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Temperatures would still have accelerated more in the last decade than in any decade before. Simply because emissions habe never been that high. It expected to see an accelerated warming if emission increase as they did over the last decades, with or without the jump in 2023/24
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We explained what caused the unusual winds (persistence of NAO- conditions and blocking syste over the British Isles) and showed also that the key factor that boosted this event is the long-term stratification which is linked to anthropogenic activities.
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If I can add something. Here we demonstrate that NATL warming was due to natural variability. The event was excepted and in line with climate projections (return period around 10 years). The processes are well known and we can explain it.
www.nature.com/articles/s43...
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And if SSTs do not return to pre-jump levels, this event is another indicator for a higher ECS/TCRE than previously estimated. There is really not much good news here.
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It is really unfortunate that this is mis-used. The event has been extreme and it had extreme effects. And it would not have been possible without the strong underlying warming trend. So there is really not much good news here.
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They are, however, not "expected" that often. Given that it is a 1-in-512 years event under current warming, the likelihood is higher that it had not occurred than that it occurred (assuming that we will reduce emissions and hence the warming trend in the next 100 years)
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The title has different aspects, that is right. We came more from the modelers perspective and were also trying to rectify this statement: www.nature.com/articles/d41.... It was important to us that models can simulate such events. They are hence "expected"
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That is unfortunate, everyone should know by now that warming scales with cumulative emissions. If emissions are higher, warming is faster, emissions have increased, hence warming has accelerated. In the scientific community, there is no disagreement, I believe or better I hope
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I believe warming has accelerated, it is not a belief, it is measured. But has it accelerated more than expected based on emissions, I don't think so yet
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I think it is a false security to rely on past warming as unknown feedbacks like this sea ice feedback will kick in with a high likelihood. At least that's what I believe
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It is in brief a large decadal variability that kept warming low. Once we get out of this negative phase, temperatures will rise faster. This will not be an acceleration, just a back to normal. It will look like an acceleration though
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We argue exactly this in this preprint:
egusphere.copernicus.org/preprints/20...
We believe that the Antarctic sea ice has kept global warming relatively low. Once it melts, warming will be much faster. Thus, past warming dies not inform well about future warming or ECS
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If SSTs don't come back soon, I think it is reason to panic even more about climate change as we already should do. Not because warming would have accelerated but because climate sensitivity is probably higher than expected.
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It might be cloud-driven and it would be exciting to look if climate models show similar cloud patterns as observed during the global heatwaves.
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Is that for the North Atlantic only as in your plot? The reason why I have doubts about the aerosol argument is that almost all global heatwaves were exceptionally warm im the North Atlantic and North Pacific even without aerosols.
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I guess my pas exchanges with other people have made me somewhat sensitive towards not always well meant humorous comments 🥺 I see that this was not at all the case here and that it was a very balanced presentation. Thanks a lot for the clarification
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Fully agree :)
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Thanks for explaining. That helps a lot
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Unfortunately, I could not attend this talk. Do you know how this was presented. I feel it very disrespectful towards our author team to present us basically as ignorant, stupid idiots. But maybe it was presented orally in a different way? 🤔
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If you show the graph with the change in radiation, it would be better to also show the same lines from models to compare it accurately
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A global heatwave can happen in many ways, almost always with a very warm North Atlantic. Once we talk about jumps, we also have to ask what the year before looked like. A large number of cold years can also lead to a large jump. In general, the NA is not colder than was expected from models.
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The North Atlantic is certainly much more unusual than the global heatwave, however it is mainly due to unusual winds in that year (meetingorganizer.copernicus.org/EGU25/EGU25-...). This paper will come out soon in Nature and was presented at EGU by Matthew England, also highlighting the variability
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If we use another 12-month window, the results remain almost unchanged (see Methods of the paper). So using Aug 23 to July 24 gives the same results
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If we make the time longer than 12 months, the different numbers are not independent anymore because they would overlap. Hence, only 12 months. We started in April because that is when the jump happened and when El Nino is somehow to be expected.
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So if we do not see monthly mean SSTs going once below the values before 23 until this October, it could mean that we underestimated ECS.
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Pre-jump temperatures are any monthly mean temperatures before April 2023. In the models the monthly mean SSTs for one month are before Oct 25 at least once smaller than the monthly mean SSTs in that month before April 23. It is not a running mean. Only in high ECS models, that is not the case.
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And these SSTs stopped to be record-breaking in July 2024
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Exactly, they are both atmospheric datasets averaged over the whole globe. BUT, we look at SSTs from 60S to 60N. So that explains the differences. In our paper, we only say how we believe SSTs are going to develop based on model simulations
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I am afraid that is not as simple as it sounds. I believe what you are showing are atmospheric temperatures and not SSTs from 60S to 60N. Is that possible?
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This looks very different compared to the NOAA data: climatereanalyzer.org/clim/sst_dai....
Do you have an idea why the two are different? DId you compare your averages to NOAA satellite data?
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It is improbable but not necessary a blind spot. It can happen rarely as far as we know
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However, there is one important exception. In fast warming models (high ECS/TCRE), the models do not return to pre-jump levels but continue to warm as expected from the long-term trend.
So if SSTs do not return by September, we might have underestimated the ECS/TCRE
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Until September in the 2nd year after the jump, the monthly SSTs in the models are at least once smaller than the maximum SST in that month before the jump.
For the observed jump, we thus expect the SSTs to be back to monthly SSTs before the jump once before September this year.
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Let's use bgcArgo floats to evaluat ocean biogeochemistry models!
Simone Le Chevere:
Evaluation of the interior ocean ventilation of biogeochemical tracers in a global ocean model using observation-based metrics
Thursday, 16:48–16:58, Room 1.34
#EGU25
@awi.de @erc.europa.eu #OceanPeak
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Please do not hesitate to ask me more about our study if you are interested
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At the same time, I want to thank the large majority of colleagues in the field, who congratulated us for this important study in the field of AMOC research! Thank you all for this important support.