El Nino unusually active in the late 20th century

[OKIsItJustMe]

Last edited Tue Jul 2, 2013, 08:55 AM - Edit history (1)

http://www.eurekalert.org/pub_releases/2013-06/uoha-enu062813.php

[font face=Serif]Public release date: 30-Jun-2013

Contact: Talia S Ogliore
[e-mail]
808-956-4531
University of Hawaii at Manoa

[font size=5]El Nino unusually active in the late 20th century[/font]

This graph shows El Niño variability derived from tree rings (blue) and instrumental measurements (red). The dashed lines indicate boundary for natural variability. Recent El Niño behavior is largely beyond natural variability. — International Pacific Research Center

[font size=3]Spawning droughts, floods, and other weather disturbances world-wide, the El Niño – Southern Oscillation (ENSO) impacts the daily life of millions of people. During El Niño, Atlantic hurricane activity wanes and rainfall in Hawaii decreases while Pacific winter storms shift southward, elevating the risk of floods in California.

The ability to forecast how ENSO will respond to global warming thus matters greatly to society. Providing accurate predictions, though, is challenging because ENSO varies naturally over decades and centuries. Instrumental records are too short to determine whether any changes seen recently are simply natural or attributable to man-made greenhouse gases. Reconstructions of ENSO behavior are usually missing adequate records for the tropics where ENSO develops.

Help is now underway in the form of a tree-ring record reflecting ENSO activity over the past seven centuries. Tree-rings have been shown to be very good proxies for temperature and rainfall measurements. An international team of scientists spearheaded by Jinbao Li and Shang-Ping Xie, while working at the International Pacific Research Center, University of Hawaii at Manoa, has compiled 2,222 tree-ring chronologies of the past seven centuries from both the tropics and mid-latitudes in both hemispheres. Their work is published in the June 30, 2013 online issue of Nature Climate Change.

The inclusion of tropical tree-ring records enabled the team to generate an archive of ENSO activity of unprecedented accuracy, as attested by the close correspondence with records from equatorial Pacific corals and with an independent Northern Hemisphere temperature reconstruction that captures well-known teleconnection climate patterns.

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http://dx.doi.org/10.1038/nclimate1936

[Nihil]

1. "Tree-rings have been shown to be very good proxies"?

Not in the period 1900-1940 they weren't.

Whilst I tend to agree that the tree ring data is probably more accurate
than the instrumental measurements during the above, it's a bit clumsy
to be referring to them as "very good proxies" when the graph clearly
proves that not to be true for half of the time ...

[OKIsItJustMe]

2. I think this may be due (at least in part) to a lack of instruments in the tropics at that time

Emphasis added by me.

http://dx.doi.org/10.1038/nclimate1936

[font face=Serif][font size=5]El Niño modulations over the past seven centuries[/font]

…
Nature Climate Change (2013) | doi:10.1038/nclimate1936
Received 13 November 2012 | Accepted 28 May 2013 | Published online 02 July 2013

[font size=3]Predicting how the El Niño/Southern Oscillation (ENSO) will change with global warming is of enormous importance to society. ENSO exhibits considerable natural variability at interdecadal–centennial timescales. Instrumental records are too short to determine whether ENSO has changed and existing reconstructions are often developed without adequate tropical records. Here we present a seven-century-long ENSO reconstruction based on 2,222 tree-ring chronologies from both the tropics and mid-latitudes in both hemispheres. The inclusion of tropical records enables us to achieve unprecedented accuracy, as attested by high correlations with equatorial Pacific corals and coherent modulation of global teleconnections that are consistent with an independent Northern Hemisphere temperature reconstruction. Our data indicate that ENSO activity in the late twentieth century was anomalously high over the past seven centuries, suggestive of a response to continuing global warming. Climate models disagree on the ENSO response to global warming, suggesting that many models underestimate the sensitivity to radiative perturbations. Illustrating the radiative effect, our reconstruction reveals a robust ENSO response to large tropical eruptions, with anomalous cooling in the east-central tropical Pacific in the year of eruption, followed by anomalous warming one year after. Our observations provide crucial constraints for improving climate models and their future projections.[/font][/font]