El Nino as a mediator of the solar influence on climate

Publication Type  Journal Article
Year of Publication  2007
Authors  Emile-Geay, J.; Cane, M.; Seager, R.; Kaplan, A.; Almasi, P.
Journal Title  Paleoceanography
Volume  22
Issue  3
Pages  -
Journal Date  Aug 8
ISBN Number  0883-8305
Accession Number  ISI:000248876300001
Key Words  north-atlantic climate; radiocarbon age calibration; sea-surface temperature; past 1000 years; southern-oscillation; nino/southern-oscillation; tropical pacific; thermohaline circulation; equatorial pacific; american droughts

Using a climate model of intermediate complexity, we simulate the response of the El Ni (n) over tildeo-Southern Oscillation (ENSO) system to solar and orbital forcing over the Holocene. Solar forcing is reconstructed from radiocarbon production rate data, using various scaling factors to account for the conflicting estimates of solar irradiance variability. As estimates of the difference since the Maunder Minimum range from 0.05% to 0.5% of the solar "constant,'' we consider these two extreme scenarios, along with the intermediate case of 0.2%. We show that for large or moderate forcings, the low-pass-filtered east-west sea surface temperature gradient along the equator responds almost linearly to irradiance forcing, with a short phase lag (about a decade). Wavelet analysis shows a statistically significant enhancement of the century-to-millennial-scale ENSO variability for even a moderate irradiance forcing. In contrast, the 0.05% case displays no such enhancement. Orbitally driven insolation forcing is found to produce a long-term increase of ENSO variability from the early Holocene onward, in accordance with previous findings. When both forcings are combined, the superposition is approximately linear in the strong scaling case. Overall, the sea surface temperature response is of the magnitude required, and is persistent enough, to induce important climatic perturbations worldwide. The results suggest that ENSO may plausibly have acted as a mediator between the Sun and the Earth's climate. A comparison to key Holocene climate records, from the Northern Hemisphere subtropics and midlatitudes, shows support for this hypothesis.


202BKTimes Cited:2Cited References Count:86

URL  <Go to ISI>://000248876300001
DOI  Doi 10.1029/2006pa001304