Paleoclimate archives including tree rings, ice cores, and coral records can be used to reconstruct the long-term behavior of variability in the climate system, for example, phenomena such as the Pacific Decadal Oscillation (PDO) and the El Niño Southern Oscillation (ENSO; Verdon et al. 2006; Cobb et al. 2003 & 2013). Both of these processes are complex patterns of ocean-atmosphere variability in the Pacific Ocean. However, each varies in frequency, duration, and intensity of effects. These climate patterns are of particular interest to both scientists and policy makers because of their effects on weather patterns, and management of marine resources.
Corals are tremendously valuable for these reconstructions and can help scientists investigate how ENSO has changed over time. Corals live from decades to centuries, grow annual bands (like tree rings), and store detailed environmental information on timescales that humans think about. Using corals, we have been able to reconstruct El Niño throughout the Holocene, and it appears to be a persistent feature of our ‘modern’ climate system. There is some evidence that ENSO has changed through time, with variations in both the frequency and magnitude of these events. From modern climate studies, we know that ENSO interacts with other interannual and interdecadal scale ocean-climate patterns, such as with the Pacific Decadal Oscillation (PDO). For our class, we focused on a paper by Dr. Kim Cobb and colleagues. This study uses information recorded in ancient corals from the Northern Line Islands in the Pacific to reconstruct past changes in seawater temperature and link them to ENSO-like oscillations. Uranium-thorium dating (similar to carbon dating) tells us how old these corals are, and differences in oxygen isotopes - a sort of chemical fingerprint - in the coral’s annual bands can be used as a proxy for ocean temperature during individual years. The paper shows that there is unusually high variability in ENSO in the 20th century, but we cannot yet ascertain whether or not this variability stands out from past oscillations. Right now, it is hard to predict based upon these records how climate patterns such as ENSO and PDO will react to anthropogenic climate change. We can also reconstruct ENSO like conditions in older geologic intervals. One reconstruction by Dr. Michael Wara and colleagues demonstrates a period of permanent El Niño like conditions during the Pliocene Warm Period (over 3 million years ago). Analysis of foraminifera from Ocean Drilling Program sites show an absence of the typical west-east asymmetric sea surface temperature of the modern Pacific. This deeper or warmer thermocline reduces winds and weakens Walker circulation, resulting in major disruptions to the Pacific ocean-atmosphere system. Understanding records like these is essential for building future models that forecast effects of ENSO events in a changing climate. One interesting question we were left with was: If higher ENSO variability occurs in the future, what does this mean for people along the coast? We contacted Christina Toms, Senior Environmental Scientist with the SF Bay Regional Water Quality Control Board for her thoughts on this. She reminded us that a recent paper by USGS scientists documents coastal erosion in CA during the record El Nino of winter 2015-2016. Christina added, “If higher ENSO variability leads to more frequent severe El Nino events, it’s likely that the CA Coast will experience more frequent episodes of severe erosion. But from a planning/management standpoint, ENSO/PDO is one of the relatively lesser-understood forcing mechanisms, so it generally takes a back-seat to mechanisms about which we have more confidence, such as sea level rise, tectonics, littoral processes, etc.” Which is a perfect place to stop, because up next on our blog, we’ll be discussing sea level rise and other processes, such as ocean acidification and oxygenation change. Stay tuned! Videos we like about ENSO: https://www.youtube.com/watch?v=_KBgIe_-3QM https://www.youtube.com/watch?v=dzat16LMtQk https://vimeo.com/92968230 Written by the members of UC Davis GEL 232: K. Barclay, R. Banker, P. Edwards, C. Fish, K. Hewett, T. Hill, G. Hollyday, C. Livsey, H. Palmer, P. Shukla, D. Vasey. A blog written by the students of UC Davis GEL 232 (Oceans & Climate Change) Class
This quarter, we’ll be taking a deep dive into the paleoclimate literature - scientific studies about how the Earth’s climate and environment have changed in the past - in order to understand how this knowledge can inform policy decisions. We’ll consider topics such as:
Each week, we’ll read and discuss 2-3 excellent papers on these topics, and update you on what we are learning here. We’ll post relevant papers, links, and interesting articles as we find them so that you can join in the fun. Are you a policymaker, manager, or other individual who would like to learn more about how to use these studies in your work? We’d love to hear from you - please send an email to Professor Tessa Hill (tmhill at ucdavis dot edu) so we can incorporate your ideas into future blogs and discussions. As a starting point, please enjoy these resources that we find useful: NASA Paleoclimatology IPCC Chapter on Paleoclimate Written by the members of UC Davis GEL 232: K. Barclay, R. Banker, P. Edwards, C. Fish, K. Hewett, T. Hill, G. Hollyday, C. Livsey, H. Palmer, P. Shukla, D. Vasey. |
ArchiveSea Levels: Past, Present and Future
How has El Niño changed in the past? Lessons from paleoclimate archives Paleoclimate into Policy: is there a bright future for learning from the past AuthorsWritten by the members of UC Davis GEL 232: K. Barclay, R. Banker, P. Edwards, C. Fish, K. Hewett, T. Hill, G. Hollyday, C. Livsey, H. Palmer, P. Shukla, D. Vasey. Categories
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