On forced temperature changes, internal variability, and the AMO

We estimate the low‐frequency internal variability of Northern Hemisphere (NH) mean temperature using observed temperature variations, which include both forced and internal variability components, and several alternative model simulations of the (natural + anthropogenic) forced component alone. We...

Full description

Saved in:
Bibliographic Details
Published in:Geophysical research letters 2014-05, Vol.41 (9), p.3211-3219
Main Authors: Mann, Michael E., Steinman, Byron A., Miller, Sonya K.
Format: Article
Language:English
Subjects:
AMO
Anthropogenic factors
Assessments
Climate
Climate change
climate oscillations
Estimates
Geophysics
internal/forced variability
Marine
Meteorology
Oscillations
stadium waves
Stadiums
Statistics
Temperature
Variability
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:We estimate the low‐frequency internal variability of Northern Hemisphere (NH) mean temperature using observed temperature variations, which include both forced and internal variability components, and several alternative model simulations of the (natural + anthropogenic) forced component alone. We then generate an ensemble of alternative historical temperature histories based on the statistics of the estimated internal variability. Using this ensemble, we show, first, that recent NH mean temperatures fall within the range of expected multidecadal variability. Using the synthetic temperature histories, we also show that certain procedures used in past studies to estimate internal variability, and in particular, an internal multidecadal oscillation termed the “Atlantic Multidecadal Oscillation” or “AMO”, fail to isolate the true internal variability when it is a priori known. Such procedures yield an AMO signal with an inflated amplitude and biased phase, attributing some of the recent NH mean temperature rise to the AMO. The true AMO signal, instead, appears likely to have been in a cooling phase in recent decades, offsetting some of the anthropogenic warming. Claims of multidecadal “stadium wave” patterns of variation across multiple climate indices are also shown to likely be an artifact of this flawed procedure for isolating putative climate oscillations. Key Points Certain common procedures fail to isolate internal variability in climate AMO appears to have been in a cool phase in recent decades ‘Stadium wave’ patterns are likely an artifact of flawed assessment procedures
ISSN:0094-8276
1944-8007
DOI:10.1002/2014GL059233