Making sense of the early-2000s warming slowdown

Journal name:
Nature Climate Change
Volume:
6,
Pages:
224–228
Year published:
DOI:
doi:10.1038/nclimate2938
Published online

It has been claimed that the early-2000s global warming slowdown or hiatus, characterized by a reduced rate of global surface warming, has been overstated, lacks sound scientific basis, or is unsupported by observations. The evidence presented here contradicts these claims.

At a glance

Figures

  1. Annual mean and global mean surface temperature anomalies.
    Figure 1: Annual mean and global mean surface temperature anomalies.

    Anomalies are from three updated observational datasets3, 4, 5 and the ensemble mean (black curve) and 10–90% range (darker grey shading) GMST of 124 simulations from 41 CMIP-5 models using RCP4.5 extensions from 200528. Anomalies are relative to 1961–1990 climatology. We obtain 1972 as the end year of the big hiatus (the period of near-zero trend in the mid-twentieth century) by constructing an optimal piece-wise bilinear fit to the NOAA-Karl data over the period 1950 to 2001. We hence use 1972–2001 as a baseline period, a period similar to the WMO climate normal period 1971–2000, against which the early-twenty-first-century records can be compared. Using the 1971–2000 period rather than the baseline determined by a bilinear fit to the data (yielding a 1972 start date) does not materially change the result. Choice of the 2001 start year of the warming slowdown avoids possible end-point effects associated with large El Niño or La Niña events in 1998 and 2000 (respectively).

  2. Overlapping trend in annual mean temperature.
    Figure 2: Overlapping trend in annual mean temperature.

    a–c, Overlapping trend in global mean surface temperature (GMST) in three updated observational datasets3, 4, 5. d, Ensemble mean GMST from 124 simulations from 41 CMIP-5 models using RCP4.5 extensions from 200528. The shading in a–e is plus to minus one standard deviation of the 15-year overlapping trends from the CMIP-5 simulations. e, Overlapping trend in so-called pacemaker12 experiments where a CMIP-5 climate model was forced with observed eastern tropical Pacific sea surface temperature variability and RCP4.5 extensions from 200528. f, Overlapping trend in the temperature of the lower troposphere (TLT), spatially averaged over the near-global (82.5° N–70° S) coverage of two satellite-based datasets21, 22; model results are from 41 simulations of historical climate change performed with 28 CMIP-5 models, with RCP8.5 extensions from 200528. Peaks in the running 15-year trends centred around 2000 reflect recovery from the Pinatubo eruption in 1991.

  3. Anomalies in the ratio of trends in annual mean and global mean surface temperature, to trends in anthropogenic radiative forcing.
    Figure 3: Anomalies in the ratio of trends in annual mean and global mean surface temperature, to trends in anthropogenic radiative forcing.

    The ratio of trends over each period shown in this figure (that is, 1950–1972, 1972–2001 and 2001–2014) is expressed as an anomaly relative to the trend computed over the full period from 1950 to 2014. The caption to Fig. 1 explains the rationale for the end date and start date for the big hiatus and warming slowdown periods respectively.

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Author information

Affiliations

  1. Canadian Centre for Climate Modelling and Analysis, Environment and Climate Change Canada, University of Victoria, Victoria, British Columbia, V8W 2Y2, Canada

    • John C. Fyfe,
    • Gregory M. Flato,
    • Nathan P. Gillett &
    • Neil C. Swart
  2. National Center for Atmospheric Research, Boulder, Colorado 80307, USA

    • Gerald A. Meehl
  3. ARC Centre of Excellence for Climate System Science, University of New South Wales, New South Wales 2052, Australia

    • Matthew H. England
  4. Department of Meteorology and Earth and Environmental Systems Institute, Pennsylvania State University, University Park, Pennsylvania, USA

    • Michael E. Mann
  5. Program for Climate Model Diagnosis and Intercomparison (PCMDI), Lawrence Livermore National Laboratory, Livermore, California 94550, USA

    • Benjamin D. Santer
  6. National Centre for Atmospheric Science, Department of Meteorology, University of Reading, Reading RG6 6BB, UK

    • Ed Hawkins
  7. Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Drive, MC 0206, La Jolla, California 92093, USA

    • Shang-Ping Xie
  8. Research Center for Advanced Science and Technology, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan

    • Yu Kosaka

Contributions

J.C.F. and G.A.M. conceived the study. J.C.F. undertook the calculations and wrote the initial draft of the paper. All the authors helped with the analysis and edited the manuscript.

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