Bibliographic record
Abstract
Recent work has shown that a rapid rise in the emission of ozone depleting substances resulted in substantial Arctic warming and accelerated Arctic sea ice loss over the second half of the twentieth century. However, ozone depleting substances have been heavily regulated since the Montreal Protocol entered into effect in 1989, and their atmospheric concentrations have been stabilized and are now decreasing. This raises the obvious and important questions of the impact of the Montreal Protocol on climate change in the Arctic. More specifically we are here interested in quantifying the impact of the Montreal Protocol on the date of the first ice-free Arctic summer (defined as the first occurrence of Arctic sea ice extent below 1 million km2). The timing of the ice-free Arctic is of great interest both to stakeholders in the Arctic and to the scientific community. To address this question, we have performed and analyzed ten-member ‘World Avoided’ companion ensembles to the CESM Large Ensemble (using RCP8.5 forcings) and to the CESM Medium Ensemble (using RCP4.5 forcings). The companion ensembles are identical to their CESM-LE and CESM-ME counterparts, respectively, except for the levels of ozone depleting substances which do not decrease following the Montreal Protocol, but instead increase at a rate of 3.5% a year. This allows us to isolate the effect of the Montreal Protocol on Arctic sea ice trends by simulating what would have happened if it had never been enacted (hence the name, ‘World Avoided’). We examine both RCP8.5 and RCP4.5 forcings, to quantify the uncertainty related to emissions scenarios over the coming decades. We find that without the Montreal Protocol the mean date of the first ice-free Arctic advances from 2041 to 2033 for the RCP8.5 forcings, and from 2050 to 2035 for the RCP4.5 forcings. Thus, enacting the Montreal Protocol has delayed the onset of an ice-free Arctic by approximately one decade. This signal is robust when accounting for the high levels of internal variability in Arctic sea ice trends. Our results are also robust to different definitions of ‘ice-free Arctic’. Overall our results highlight the importance of the Montreal Protocol as a major climate mitigation treaty, even for the Arctic, where no ozone-hole has formed.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.004 | 0.009 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.002 | 0.003 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.229 | 0.061 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".