Atlantic-induced pan-tropical climate change over the past three decades

TLDR: In this paper, the authors investigated the role of the Atlantic Ocean in tropical sea surface temperature (SST) teleconnection and found that the Atlantic plays a key role in initiating the tropical wide teleconnection, and the Atlantic-induced anomalies contribute ∼55-75% of the tropical SST and circulation changes during the satellite era.

Abstract: The dipole-like trend of tropical sea surface temperature is investigated and this study finds it to be initiated in the Atlantic Ocean. Atlantic warming drives wind and circulation changes and influences Pacific Ocean surface temperatures. During the past three decades, tropical sea surface temperature (SST) has shown dipole-like trends, with warming over the tropical Atlantic and Indo-western Pacific but cooling over the eastern Pacific. Competing hypotheses relate this cooling, identified as a driver of the global warming hiatus1,2, to the warming trends in either the Atlantic3,4 or Indian Ocean5. However, the mechanisms, the relative importance and the interactions between these teleconnections remain unclear. Using a state-of-the-art climate model, we show that the Atlantic plays a key role in initiating the tropical-wide teleconnection, and the Atlantic-induced anomalies contribute ∼55–75% of the tropical SST and circulation changes during the satellite era. The Atlantic warming drives easterly wind anomalies over the Indo-western Pacific as Kelvin waves and westerly anomalies over the eastern Pacific as Rossby waves. The wind changes induce an Indo-western Pacific warming through the wind–evaporation–SST effect6,7, and this warming intensifies the La Nina-type response in the tropical Pacific by enhancing the easterly trade winds and through the Bjerknes ocean dynamical processes8. The teleconnection develops into a tropical-wide SST dipole pattern. This mechanism, supported by observations and a hierarchy of climate models, reveals that the tropical ocean basins are more tightly connected than previously thought.

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UC San Diego Previously Published Works
Title
Atlantic-induced pan-tropical climate change over the past three decades
Permalink
https://escholarship.org/uc/item/59m9g10g
Journal
Nature Climate Change, 6(3)
ISSN
1758-678X
Authors
Li, X
Xie, SP
Gille, ST
et al.
Publication Date
2016-03-01
DOI
10.1038/nclimate2840
Peer reviewed
eScholarship.org Powered by the California Digital Library
University of California

!
"!
Title: "!
Atlantic Induced Pan-tropical Climate Change over the Past Three Decades #!
$!
Author information: %!
Author &!
Xichen Li
1*
, Shang-Ping Xie
1*
, Sarah T. Gille
1
& Changhyun Yoo
2
. '!
(!
Affiliations: )!
1
Scripps Institution of Oceanography, University of California, San Diego, USA. *!
2
Department of Atmospheric Science and Engineering, Ewha Womans University, Seoul, "+!
Republic of Korea. ""!
*
Corresponding author "#!
"$!
Contact Information: "%!
Xichen Li: xichenslc@gmail.com "&!
Shang-Ping Xie: sxie@ucsd.edu "'!
Sarah Gille: sgille@ucsd.edu "(!
Changhyun Yoo: cyoo@ewha.ac.kr ")!
"*!

!
#!
Summary "*!
During the last three decades, tropical sea surface temperature (SST) has shown dipole-#+!
like trends, with warming over the tropical Atlantic and Indo-Western Pacific but cooling #"!
over the Eastern Pacific. Competing hypotheses relate this cooling, identified as a driver ##!
of the global warming hiatus
1,2
, to the warming trends in either the Atlantic
3,4
or Indian #$!
Ocean
5
. However, the mechanisms, the relative importance, and the interactions between #%!
these teleconnections remain unclear. Using a state-of-the-art climate model, we show #&!
that the Atlantic plays a key role in initiating the tropical-wide teleconnection, and the #'!
Atlantic-induced anomalies contribute ~55%-75% of the tropical SST and circulation #(!
changes during the satellite era. The Atlantic warming drives easterly wind anomalies #)!
over the Indo-Western Pacific through the Kelvin wave, and westerly anomalies over the #*!
eastern Pacific as Rossby waves. The wind changes induce an Indo-Western Pacific $+!
warming via the wind-evaporation-SST effect
6,7
, and this warming intensifies the La $"!
Niña-type response in the tropical Pacific by enhancing the easterly trade winds and $#!
through the Bjerknes ocean-dynamical processes
8
. The teleconnection develops into a $$!
tropical-wide SST dipole pattern. This mechanism, supported by observations and a $%!
hierarchy of climate models, reveals that the tropical ocean basins are more tightly $&!
connected than previously thought. $'!
$(!

!
$!
The tropics have experienced marked climate change since 1979 when the era of $(!
global satellite observations began. Sea surface temperature (SST)! trends exhibit a pan-$)!
tropical dipole-like pattern (Fig. 1a), with extensive warming from the tropical Atlantic $*!
to the Indo-Western Pacific, and a triangular cooling pattern in the Central-Eastern %+!
Pacific. This tropical-wide gradient in the SST trend interacts with the atmospheric and %"!
oceanic circulation throughout the tropics (Fig. 1c, e), with an enhanced Walker %#!
circulation
9-11
and a La-Niña-like Pacific sub-surface response. These changes further %$!
contribute to global climate change
1,12,13
via multiple atmospheric teleconnections
8,14
. %%!
The tropical ocean basins are connected through atmospheric bridge
15
into an %&!
interactive system. On interannual time scales, El Niño-Southern Oscillation (ENSO) %'!
dominates the tropical inter-basin teleconnections
15,16
, although the Indian
17,18
and %(!
Atlantic
19-21
Oceans experience regional effects that can feedback to the Pacific. In this %)!
inter-basin teleconnection, El-Niño warming heats the Indian and Atlantic basins
13
. Were %*!
the same relationship to hold on multidecadal time scales, the cooling of the Eastern &+!
Pacific would be linked to decreased SSTs in the Indian and Atlantic basins &"!
(Supplementary Fig. 1), contrary to the observed trends. This discrepancy implies that &#!
other mechanisms are required to compensate the Eastern Pacific induced tropical &$!
cooling. &%!
The north and tropical Atlantic has experienced a continuous warming trend, due &&!
to the combined effects of anthropogenic radiative forcing
7,22
and the change in &'!
Meridional Overturning Circulation
23,24
. Pioneering work using slab ocean-atmospheric &(!
models
3
and reduced-gravity ocean-atmospheric models
4
suggest that this observed &)!
Atlantic warming directly contributes to the Eastern Pacific cooling, although the full &*!
range of ocean dynamics and atmospheric-ocean interactions may not be well represented '+!
by these idealized oceanic models. Here we simulate the global impact of the tropical '"!

!
%!
Atlantic warming using a fully coupled earth system model, and further investigate the '#!
mechanisms of these teleconnections using a hierarchy of climate models. The results '$!
from the coupled model show that the Atlantic warming can induce a basin-scale '%!
warming over the Indian Ocean and Western Pacific through atmospheric bridge. This '&!
secondary Indo-Western Pacific warming, together with the original Atlantic warming, ''!
intensifies the easterly wind anomaly over the Pacific, accelerates the Walker circulation, '(!
and contributes to the La-Niña-type response over the Pacific (Fig. 1). Both surface heat ')!
fluxes and ocean dynamics play key roles in this tropical-wide pattern formation. '*!
We first test the hypothesis that the tropical Atlantic warming drives the tropical-(+!
wide change by nudging the tropical Atlantic SST in a state-of-the-art fully coupled ("!
model (Fig. 1b), the Community Earth System Model (CESM1, see Method Section). (#!
The restoring reproduces the bulk of the observed warming trend over the tropical ($!
Atlantic (97%, see gray bars in Supplementary Fig. 2c). Forced by this Atlantic (%!
warming, the model (Fig. 1b) captures the detailed features of the observed tropical-wide (&!
SST changes (Fig. 1a), i.e., a significant warming anomaly over the Indo-Western Pacific ('!
(Supplementary Fig. 2c blue bars), and significant cooling anomalies in the off-((!
equatorial Eastern Pacific (purple and green bars). A Mann-Kendall test indicates that the ()!
observed equatorial Pacific cooling trend from 1979 to 2013 is only marginally (*!
significant (left red bar) due to high internal variability and the short period. With a large )+!
sample size, the Pacific cooling is significant in the ensemble simulation with a Student t-)"!
test. In addition, the 25-year-mean results for each of the 12 ensemble members )#!
(Supplementary Fig. 2c) show a cooled equatorial eastern Pacific in response to the )$!
Atlantic warming, indicating a robust anti-correlated relationship between these two )%!
ocean basins. The coupled simulation captures 55% - 75% of the observed trends over the )&!
Indian and Pacific Oceans, highlighting the association between the Atlantic warming )'!

Frequently asked questions

Q1. What is the CAM4 model used in this study?

The NCAR atmospheric model, the Community Atmosphere 282   Model version 4 (CAM4), was used in this study to identify the tropical atmospheric 283   responses to the Atlantic SST trend from 1979 to 2012. 

Q2. What is the spectral dry-dynamical core of the GFDL?

The spectral dry-dynamical-core of an 290   atmospheric general circulation model41, developed at the Geophysical Fluid Dynamics 291   Laboratory (GFDL), was used to investigate the evolution of the atmospheric response to 292   a tropical Atlantic warming, in a primitive-equation dynamical-system. 

Q3. What was used to estimate the trend in the 244 tropical precipitation for the same period?

The Global 243   Precipitation Climatology Project35 (GPCP) data were used to estimate the trend in the 244   tropical precipitation for the same period. 

Q4. What is the easterly wind induced by the Pacific SST 627 changes?

The easterly wind induced by Pacific SST 627   changes is strong over the Western Pacific and is weaker over the Eastern Pacific. 

Q5. What data sets were used to estimate the trend in the tropical Atlantic?

The Kaplan Extended SST version232, and the National 238   Oceanic and Atmospheric Administration (NOAA) Extended Reconstructed SST version 239   3b33, were also used together with the HadISST to reveal the decadal relationship 240   between the Tropical Atlantic and the Indo-Western Pacific. 

Q6. What was used to calculate the tropical ocean temperature trends from 1979 to 2012?

241  The Ishii Subsurface Ocean Temperature Analysis34 was used to calculate the 242   subsurface ocean temperature trends from 1979 to 2012 (Fig. 1e). 

Q7. What was the effect of the tropical Atlantic SST on the model climatology?

In the perturbed run, the Tropical 272   Atlantic SST was restored to the model climatology plus the observed 1979-2012 SST 273   trend. 

Q8. what is the role of aerosols in the development of the North Atlantic?

373  22. Booth, B. B., Dunstone, N. J., Halloran, P. R., Andrews, T. & Bellouin, N. Aerosols 374   implicated as a prime driver of twentieth-century North Atlantic climate variability.