Small variations in the Sun's brightness over past centuries may have impacted certain modes of the Earth's ocean-atmosphere circulation, such as the El Niño - Southern Oscillation (ENSO). Some climate model simulations suggest that a persistently brighter sun leads to a colder or more "La Niña-like" state in the tropical Pacific. This response is dubbed the "ocean dynamical thermostat" because the ENSO response tends to counteract the direct warming effect of solar heating. However, paleoclimatic evidence in support of a thermostat response to solar forcing is thus far equivocal and limited to the past 1000 years. Initial results from an ocean sediment core collected off of Baja California appear to support centennial-to-millennial-scale solar forcing of the ENSO system over the past 14,000 years, as well as a slower response related to changes in the Earth's orbit around the Sun. This new study, led by a researcher at the University of Colorado, Boulder, will use additional cores from the same location to further elucidate the response of ENSO to both solar and orbital changes over the past 12,000 years.
This work will test the hypothesis that a major mode of the climate system is more sensitive to solar forcing than is currently simulated by most climate models. If the data generated here support that assertion, they will provide a crucial target for IPCC-class models. This type of data-model intercomparison could ultimately lead to more robust predictions of future climate change, particularly for a system that results in economically and societally important impacts on agriculture, fisheries, and natural disasters. This project will also provide research and training experiences for a PhD student and an undergraduate geology student.
