Comparing CMIP5 & observations

[Given recent interest in previous comparisons of CMIP5 simulations and observations of global mean surface air temperature, this is now a permanent page which will be incrementally updated as more data accumulates]

The figure below shows a comparison of CMIP5 simulations & observations of global mean surface air temperature, using a 1986-2005 reference period, and is an updated version of Figure 11.25 from IPCC AR5. The HadCRUT4 observations are shown in black with their 5-95% uncertainty. Several other observational datasets are shown in blue.

The grey shading shows the CMIP5 5-95% range for historical (pre-2005) & all future forcing pathways (RCPs, post-2005); the grey lines show the min-max range. The red hatching indicates the IPCC AR5 assessed likely (>66%) range for the 2016-2035 period. The UK Met Office forecast for 2015 is shown by the green error bar.

There are several possible explanations for why the observations are at the lower end of the CMIP5 range. First, there is internal climate variability, which can cause temperatures to temporarily rise faster or slower than expected. Second, the radiative forcings used after 2005 are from the RCPs, rather than as observed. Given that there have been some small volcanic eruptions and a dip in solar activity, this has likely caused some of the apparent discrepancy. Third, the real world may have a climate sensitivity towards the lower end of the CMIP5 range. Last, the exact position of the observations within the CMIP5 range depends slightly on the reference period chosen. A combination of some of these factors is likely responsible.

Note also that as the HadCRUT4 dataset has gaps over the Arctic it is likely to be a slight underestimate of the true recent global temperature anomaly. And, in this version of the figure, the CMIP5 simulations are NOT masked to the HadCRUT4 observational coverage, unlike some previous examples on this blog.

Update of Fig. 11.25
Updated version of IPCC AR5 Figure 11.25 with HadCRUT4 (black) global temperature time-series. The CMIP5 model projections are shown relative to 1986-2005 (light grey). The red hatching is the IPCC AR5 assessed likely range for global temperatures in the 2016-2035 period. The blue lines represent other observational datasets (Cowtan & Way, NASA GISTEMP, NOAA NCDC, ERA-Interim, BEST). [Click for larger version]

UPDATES:
26th January 2015: Entire page updated for 2014 temperatures
27th January 2014: Page created.

10 thoughts on “Comparing CMIP5 & observations”

  1. Your update of Fig 11.25 should use the Cowtan and Way uncertainty envelope as this data series is now widely preferred to HadCrut4 for the evaluation of recent temperature trends, for obvious reasons. HadCrut4 should be shown as a dotted line without the uncertainty envelope, to emphasize its deprecation.

      1. Would downloading the global mean from KNMI also give the uncertainty envelopes? I did download KNMI and calculated mean and envelope for RCP4.5. But I had to download all model series to do that. Or am I missing something here?

        Perhaps you could post the consolidated CMIP5 data as you provided to Schmidt et al. Or better yet just post the data as charted (i.e. CMIP5 model mean with uncertainty envelopes, assessed likely range).

        Also, AR4 has a very good feature where data to reproduce each chart was made available. Is that available for AR5?

  2. Hi Deep Climate,

    The plotted 5-95% future ranges are here.

    The red hatched box corners are:
    [2016: 0.133 0.503]
    [2035: 0.267 1.097]

    I don’t think there is such a data feature for AR5. Where is the AR4 one?

    cheers,
    Ed.

    1. I misremembered a bit – it’s not for all figures.

      However AR4 WG1 Fig 10.5 (scenario projections) can be reproduced from GCM model means found here:

      http://www.ipcc-data.org/sim/gcm_global/index.html

      I found these easier to work with than KNMI, because they are exactly as used in AR4 (can’t get KNMI to match up exactly for various reasons), and also are already merged with 20th century hindcasts.

      I don’t think a similar page for AR5 GCM mean output exists yet.

    2. Oh and many thanks for that – I’ll use it to replace the RCP4.5 I have.

      I would like the historical envelope too please (at least from say 1980 so as to cover the 1986-2005 baseline period).

      Nice to have would be min-max and an ensemble mean or median, but don’t bother if you don’t have these easily at hand. Thanks again!

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