Rates of change in global temperatures

The recent WMO press release on the climate of the 2001-2010 period highlighted that global temperature change was accelerating. Although this could be a misleading statement, should we even be expecting global temperature changes to be accelerating at present?

Although the rates of change of global temperatures are generally positive since the 1970s*, one key issue with talking about acceleration is that it is non-trivial to define and observe. Also, we do not expect an acceleration to continue indefinitely. These factors ensure that communication of this issue is especially difficult.

The rates of change of global temperatures in observations (black) and the CMIP5 simulations (colours) are shown below, and indicate a warming since around 1970, which generally accelerates until around 2000, with some variability and also dips around large volcanic eruptions. What is most interesting is the general deceleration from 2000 to 2010 in the simulations, and from around 1995 in the observations.

As for the future, RCP2.6 (low emissions) shows almost continuous deceleration and RCP8.5 (high emissions) resumes an acceleration around 2012 until 2050. The mid-range emissions scenario (RCP4.5) shows a flat rate of change until mid-century, followed by a deceleration.

So, the CMIP5 models simulate a deceleration at present which may continue, depending on our future emissions. This suggests that talking about rates of change is useful, but that discussion of acceleration or deceleration is potentially very confusing in communication efforts.

* Shorter periods for the linear trends show a similar picture which much higher levels of variability, and using the most recent 10-year period actually results in a negative rate of change.

Rates of change

Rates of change of global mean temperature – defined as the gradient of overlapping 20 year linear trends, plotted at the mid-point – for historical and future projections, and the HadCRUT4 observations. The coloured thick lines show the CMIP5 multi-model mean trend and the thin lines the standard deviation around the mean.

About Ed Hawkins

Ed Hawkins (twitter: @ed_hawkins) is a climate scientist in NCAS-Climate at the Department of Meteorology, University of Reading. His research interests are in decadal variability and predictability of climate, especially in the Atlantic region, and in quantifying the different sources of uncertainty in climate predictions and impacts. Ed is a Contributing Author to IPCC AR5 and a member of the CLIVAR Scientific Steering Group.
This entry was posted in GCMs, observations, projections, temperature, uncertainty, variability. Bookmark the permalink.

6 Responses to Rates of change in global temperatures

  1. crikey says:

    In terms of communicating this information to the public about future projections ED
    I find your graph of deceleration for global temps from 2000 -2060 inconsistent with what is written on met office projections linked here

    http://www.metoffice.gov.uk/climate-change/policy-relevant/advance
    quote

    RCP 2.6
    Although the mean temperature RISE??!! under RCP 2.6
    is between 1.5 and 2 °C

    BY THE END OF THE CENTURY,

    many regions will experience much greater? (or lower?) increases in temperature.

    [snip... repeating the same mistakes]

    What have l missed here in my interpretation of Ed’s graph vs the met office interpretation of the same graph?

    Yes there is a communication problem

    • Ed Hawkins says:

      Crikey – I think you are quite confused about what acceleration means. The graph clearly shows the rate of change is generally POSITIVE = a warming climate. The rate of change is slowing, but this does not mean that temperatures are cooling.
      Ed.

  2. R James says:

    All the data sets that I study (RSS, UAH, Hadcrut) don’t seem to support accelerated warming. If anything, they indicate no significant change in temperature over the past decade or so. The 1910 – 1940 increase looks much the same rate as the 1970 – 2000 period, then nothing much since then. What caused the 1910 – 1940 increase? I don’t see anything that would correlate with emissions of CO2. Why does this graph start at 1950?

  3. Ed Hawkins says:

    The 1910-1940 is a very interesting period, and not fully understood. It seems likely to be due to a combination of several factors, including: an increase in solar activity, a recovery from the previous strong volcanic activity, an increase in CO2 and some internal climate variability. Determining the relative weight of these factors is ongoing research.
    cheers,
    Ed.

  4. crikey says:

    Would you agree ED that global temperatures have been declining at a rate of 0.44 degree per century since 2005 to 2012

    That is a deceleration for that short period of 7 yrs

    There was a period from 1943 to1975 ( 32 yrs)when global temperatures declined or decelerated
    at a rate of 0.37 deg c per century

    The AMO follows these steps up and down .

    Based on the past AMO pattern and global temp’ inflection point at 2005 downward one might conclude the AMO peaked at 2005 and is on a step decline for the next approx. 25 yr ish years

    AMO is currently near neutral. I wonder if this downward trend will sustain.

    This is what l meant by deceleration. From 2005 to 2012 . sorry about that misunderstanding

    Here is a graph correlating AMO oscillation and global temp

    https://picasaweb.google.com/104698633266954768357/CYCLESAndCorrelations#5895535698714271410

    Would it be fair to say that based on the past 60 yrs ish oscillation that you would expect a deceleration of global temps’ from 2005 to 2037 based on the AMO alone?

    What is the forcing value of the AMO? Is there one?

  5. Pingback: It is normal models heat and cool the planet too fast/slow | Open Malaria Warning

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