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Friday, June 24, 2016

Models Miss Another Factor Impacting Climate?

Hardly a month or even a week goes by without a new study
Colored stalactites and stalagmites in the cave.
coming out examining another natural factor scientists have found that provably affects temperature or climate — a factor neither the climate models, nor the Intergovernmental Panel on Climate Change have or, perhaps even can, account for.
The most recent of these climate drivers brought to my attention was brought to light in a study in Nature Communications.
In it, researchers at the Australian National University Research School of Earth Sciences measured trace elements and stable isotopes in stalagmites from the Indonesian island of Flores, comparing ancient rainfall patterns to records from East Asia and the central-eastern equatorial Pacific. They found alternating multi-century-long El Niño/La Niña-like patterns have affected global climate for at least the past 2,000 years. Climate models do not reproduce those patterns.
Note these are not the familiar El Niño/La Niña patterns that occur off the coasts of North and South America in the Eastern Pacific (which are also not reproduced in climate models) but rather periodic, repeated ocean oscillations in the tropical, South Central and Western portion of the Pacific
Alena Kimbrough, a member of the research team, said, “We’ve shown [Pacific El Niño/La Niña oscillations are] an important part of the climate system that has influenced global temperatures and rainfall over the past millennium.”
The paper states:
Our results highlight significant discrepancies between the proxy records and model simulations for the past millennium. … We cannot rule out the possibility that some of the low-frequency Pacific variability was a forced response to variable solar intensity and changing teleconnections to higher latitudes that are not simulated by the models, … or that unforced, low-frequency internal climate variability (that is difficult for models to simulate) was responsible for at least some of the global temperature change of the past millennium.
According to the researchers the tropical Pacific La Niña -like pattern is thought to be a contributing factor to the recent hiatus in warming temperatures and also affected temperature shifts earlier in the twentieth century. Their analysis suggests projections of tropical rainfall patterns, global temperature extremes, and other climate phenomena will remain uncertain until paleoclimate records and models consistently capture the climate impact of natural El Nino/La Niña-type patterns in the tropical Pacific.
To quote the lead author of the study, Michael Griffiths, Ph.D. from William Paterson University in the United States, “Until we can model this lower-frequency behavior in the tropical Pacific, one can only speculate on how the warming will play out over the next few decades.”
With the addition each new factor discovered to impact climate change, or a better understanding of natural factors already understood, though not well, to affect the climate, the role human greenhouse gas can have played in the recent modest warming of the latter 20th century diminishes. There is only so much warming to account for and if natural factors have played a larger role than climate models project, then the impact of human greenhouse gas emissions must necessarily play a smaller role.

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