Does ENSO regularity increase in a warming climate?
The impact of a warming climate on El Nino-Southern Oscillation (ENSO) is investigated in large ensemble simulations of the Community Earth System Model (CESM1). These simulations are forced by historical emissions for the past and the RCP8.5-scenario emissions for future projections. The simulated...
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| Format: | Journal article |
| Language: | English |
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American Meteorological Society
2019
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| _version_ | 1826302388702543872 |
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| author | Berner, J Christensen, H Sardeshmukh, P |
| author_facet | Berner, J Christensen, H Sardeshmukh, P |
| author_sort | Berner, J |
| collection | OXFORD |
| description | The impact of a warming climate on El Nino-Southern Oscillation (ENSO) is investigated in large ensemble simulations of the Community Earth System Model (CESM1). These simulations are forced by historical emissions for the past and the RCP8.5-scenario emissions for future projections. The simulated variance of the Nino-3.4 ENSO index increases from 1.4<jats:sup>◦</jats:sup>C<jats:sup>2</jats:sup> in 1921-1980 to 1.9<jats:sup>◦</jats:sup>C<jats:sup>2</jats:sup> in 1981-2040 and 2.2<jats:sup>◦</jats:sup>C<jats:sup>2</jats:sup> in 2041-2100. The autocorrelation timescale of the index also increases, consistent with a narrowing of its spectral peak in the 3- to 7-yr ENSO band, raising the possibility of greater seasonal to interannual predictability in the future. Low-order linear inverse models (LIMs) fitted separately to the three 60-yr periods capture the CESM1 increase in ENSO variance and regularity. Remarkably, most of the increase can be attributed to the increase in the 23-month damping timescale of a single damped oscillatoryENSO eigenmode of these LIMs by 5 months in 1981-2040 and 6 months in 2041-2100. These apparently robust projected increases may however be compromised by CESM1 biases in ENSO amplitude and damping timescale. A LIM fitted to the 1921-1980 observations has an ENSO eigenmode with a much shorter 8-month damping timescale, similar to that of several other eigenmodes. When the mode’s damping timescale is increased by 5 and 6 months in this observational LIM, a much smaller increase of ENSO variance is obtained than in the CESM1 projections. This may be because ENSO is not as dominated by a single ENSO eigenmode in reality as it is in the CESM1. |
| first_indexed | 2024-03-07T05:46:48Z |
| format | Journal article |
| id | oxford-uuid:e77d42e9-a633-45b4-8e58-3faa6cbb2688 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-07T05:46:48Z |
| publishDate | 2019 |
| publisher | American Meteorological Society |
| record_format | dspace |
| spelling | oxford-uuid:e77d42e9-a633-45b4-8e58-3faa6cbb26882022-03-27T10:39:09ZDoes ENSO regularity increase in a warming climate?Journal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:e77d42e9-a633-45b4-8e58-3faa6cbb2688EnglishSymplectic Elements at OxfordAmerican Meteorological Society2019Berner, JChristensen, HSardeshmukh, PThe impact of a warming climate on El Nino-Southern Oscillation (ENSO) is investigated in large ensemble simulations of the Community Earth System Model (CESM1). These simulations are forced by historical emissions for the past and the RCP8.5-scenario emissions for future projections. The simulated variance of the Nino-3.4 ENSO index increases from 1.4<jats:sup>◦</jats:sup>C<jats:sup>2</jats:sup> in 1921-1980 to 1.9<jats:sup>◦</jats:sup>C<jats:sup>2</jats:sup> in 1981-2040 and 2.2<jats:sup>◦</jats:sup>C<jats:sup>2</jats:sup> in 2041-2100. The autocorrelation timescale of the index also increases, consistent with a narrowing of its spectral peak in the 3- to 7-yr ENSO band, raising the possibility of greater seasonal to interannual predictability in the future. Low-order linear inverse models (LIMs) fitted separately to the three 60-yr periods capture the CESM1 increase in ENSO variance and regularity. Remarkably, most of the increase can be attributed to the increase in the 23-month damping timescale of a single damped oscillatoryENSO eigenmode of these LIMs by 5 months in 1981-2040 and 6 months in 2041-2100. These apparently robust projected increases may however be compromised by CESM1 biases in ENSO amplitude and damping timescale. A LIM fitted to the 1921-1980 observations has an ENSO eigenmode with a much shorter 8-month damping timescale, similar to that of several other eigenmodes. When the mode’s damping timescale is increased by 5 and 6 months in this observational LIM, a much smaller increase of ENSO variance is obtained than in the CESM1 projections. This may be because ENSO is not as dominated by a single ENSO eigenmode in reality as it is in the CESM1. |
| spellingShingle | Berner, J Christensen, H Sardeshmukh, P Does ENSO regularity increase in a warming climate? |
| title | Does ENSO regularity increase in a warming climate? |
| title_full | Does ENSO regularity increase in a warming climate? |
| title_fullStr | Does ENSO regularity increase in a warming climate? |
| title_full_unstemmed | Does ENSO regularity increase in a warming climate? |
| title_short | Does ENSO regularity increase in a warming climate? |
| title_sort | does enso regularity increase in a warming climate |
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