- Dona Paula, Goa, India.
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| Abstract Submission No. | ABS-2022-02-0254 |
| Title of Abstract | Emergence time of regional climate signals in the tropical oceans in CMIP5/6 simulations |
| Authors | S Gopika*, I Suresh, Matthieu Lengaigne, Jérôme Vialard, Takeshi Izumo, Kwatra Sadhvi |
| Organisation | CSIR-National Institute of Oceanography, Goa, India. |
| Address | pallathery house, p.o mattathur kunnu,kodakara,680684,thrissur,kerala Thrissur, kerala, India Pincode: 680684 Mobile: 7012230960 E-mail: gopikasurvay@gmail.com |
| Country | India |
| Presentation | Oral |
| Abstract | Estimating the time at which anthropogenically-forced signals emerge from the ambient natural climate noise is crucial for climate-change detection. Here, we propose a new method for estimating the emergence time of climate signals based on an actual significance estimate rather than the signal to noise ratio threshold which is usually used. For signals that tend to emerge late in the 21st century, this method provides earlier emergence times. Here, it is applied relative SST (RSST, SST minus its tropical mean) changes, which tend to emerge much later than absolute SST signals. RSST is of interest, because it is a proxy of the atmosphere vertical stability changes, and keeps track of tropical cyclones and rainfall changes. We hence focus on CMIP5/6 RSST emergence time and investigate its relationship with tropical rainfall emergence time. By 2100, CMIP projections indicate more warming than the tropical mean (positive RSST signal) in the central and eastern equatorial Pacific, equatorial Atlantic, and the Arabian Sea, and reduced warming in the three subtropical gyres of the southern hemisphere. In broad agreement with observations, the Arabian Sea relative warming and South-Eastern Pacific relative cooling are already detectable in most models (median emergence time < 2020), making those regions suitable for testing a model's ability to predict a regional SST trend. In contrast, RSST signals in other regions only become detectable after 2050. Tropical rainfall projections indicate more (less) rain in positive (negative) RSST change regions, but generally emerge one or two decades later. This absence of currently-detectable regional rainfall trends in CMIP makes it difficult to validate climate models' ability to predict tropical regional rainfall trends. The only region where a rainfall signal emerges before a RSST signal is the central and eastern equatorial Pacific, where increasing rainfall signals emerge around 2050 (CMIP median). |