Model-based evidence of deep-ocean heat uptake during surface-temperature hiatus periods

Journal name:
Nature Climate Change
Volume:
1,
Pages:
360–364
Year published:
DOI:
doi:10.1038/nclimate1229
Received
Accepted
Published online

There have been decades, such as 2000–2009, when the observed globally averaged surface-temperature time series shows little increase or even a slightly negative trend1 (a hiatus period). However, the observed energy imbalance at the top-of-atmosphere for this recent decade indicates that a net energy flux into the climate system of about 1Wm−2 (refs 2, 3) should be producing warming somewhere in the system4, 5. Here we analyse twenty-first-century climate-model simulations that maintain a consistent radiative imbalance at the top-of-atmosphere of about 1Wm−2 as observed for the past decade. Eight decades with a slightly negative global mean surface-temperature trend show that the ocean above 300m takes up significantly less heat whereas the ocean below 300m takes up significantly more, compared with non-hiatus decades. The model provides a plausible depiction of processes in the climate system causing the hiatus periods, and indicates that a hiatus period is a relatively common climate phenomenon and may be linked to La Niña-like conditions.

At a glance

Figures

  1. Surface temperatures and ocean heat content.
    Figure 1: Surface temperatures and ocean heat content.

    a, Annual mean globally averaged surface temperature for the five climate-model ensemble members (coloured lines) and ensemble mean (black line), highlighting two ten-year negative-temperature-trend periods and ten-year running trends from this ensemble member (inset). b, Left: composite global linear trends for hiatus decades (red bars) and all other decades (green bars) for TOA net radiation (positive values denote net energy entering the system). Right: global ocean heat-content (HC) decadal trends (1023J per decade) for the upper ocean (surface to 300m) and two deeper ocean layers (300–750m and 750m–bottom), with error bars defined as ± one standard error ×1.86 to be consistent with a 5% significance level from a one-sided Student t-test. c, Composite average SST linear trends for hiatus decades; stippling denotes 5% significance.

  2. Ocean circulation and subsurface temperature.
    Figure 2: Ocean circulation and subsurface temperature.

    a, Zonal-mean global long-term-average ocean meridional overturning stream function from the model; positive stream-function contours indicate clockwise flow, negative anticlockwise. b, Composite decadal trends of meridional overturning stream function for the upper Pacific Ocean for hiatus periods (note the different vertical scale from a; there are no values plotted south of about 35°S owing to the open Pacific basin at those latitudes). c The same as b except for zonal-mean temperature trends for the Pacific Ocean. d The same as b except for meridional overturning stream function for the Atlantic Ocean. e The same as b except for zonal-mean temperature trends for the Atlantic Ocean. Stippling denotes 5% significance.

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Author information

Affiliations

  1. National Center for Atmospheric Research, Boulder, Colorado 80307, USA

    • Gerald A. Meehl,
    • Julie M. Arblaster,
    • John T. Fasullo,
    • Aixue Hu &
    • Kevin E. Trenberth
  2. Centre for Australian Weather and Climate Research (CAWCR), Bureau of Meteorology, Melbourne 3001, Australia

    • Julie M. Arblaster

Contributions

G.A.M., J.M.A., J.T.F., A.H. and K.E.T. contributed to model data analysis. G.A.M., J.M.A., J.T.F., A.H. and K.E.T. contributed to writing the paper. All authors discussed the results and commented on the manuscript.

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The authors declare no competing financial interests.

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