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WMO Repeat “Hottest Decade Ever” Mantra

July 4, 2013

By Paul Homewood




I’m not sure why it has taken them two years, but the World Meteorological Organisation have just got round to telling us that 2001-10 was hotter than the previous decade. According to the Age:-


The planet has warmed faster since the turn of the century than ever recorded, almost doubling the pace of sea-level increase and causing a 20-fold jump in heat-related deaths, the United Nations said.
The decade through 2010 was the warmest for both hemispheres and for land and sea, the UN’s World Meteorological Organisation said Wednesday in an e-mailed report examining climate trends for the beginning of the millennium. Almost 94 per cent of countries logged their warmest 10 years on record, it said.
“The decadal rate of increase between 1991-2000 and 2001-2010 was unprecedented,” WMO Secretary-General Michel Jarraud said in a statement. “Rising concentrations of heat-trapping greenhouse gases are changing our climate, with far-reaching implications for our environment and our oceans.”
The report underlines the challenge the globe faces in containing temperature gains since industrialisation to the 2-degree Celsius (3.6 Fahrenheit) ceiling set by UN climate-treaty negotiators. The planet is on course to warm by 4 degrees by 2100 because emissions are still rising, the World Bank says.

The average global temperature for 2001-2010 was 14.47 degrees Celsius, according to the report. That’s 0.21 degree warmer than 1991-2000 and 0.79 degree warmer than 1881-1890.



Of course, they might have mentioned that the eruption of Pinatubo in 1991 meant that temperatures in that decade were depressed. GISS have estimated that global temperatures were lower by as much as 0.25C for up to 5 years as a result. This means that about half of the 0.21C warming was simply the rebound from Pinatubo, and nothing to do with greenhouse gases. One wonders why they did not mention this fact.


Figure 1

Composite global surface temperature change near the time of the five volcanos producing the greatest optical depths since 1880: Krakatau (1883), Santa Maria (1902), Agung (1963), El Chichon (1982) and Pinatubo (1991).

A rise of 0.1C per decade is certainly not unprecedented. Indeed, HADCRUT4 numbers show that the 1901-10 average temperature anomaly of –0.439C had increased to –0.022C by 1941-50. So, over four decades, there was a rise of 0.417C, or 0.104C per decade. This is illustrated in Figure 1.



Figure 1


In any event, using artificial decades is, well, artificial. If they want to use 10-Year averages, let’s see what a rolling average looks like.



Figure 2


Figure 3

The 10-Year running averages have essentially flatlined for the last few years, and have actually started to decline slightly since 2010.

For instance, the current 10-Year average for RSS is 0.24C. The period 1997-2006 was 0.25C. In other words, no increase for seven years.

Since 2003, the 10-Year average for RSS has gone up from 0.20 to 0.24C, a rate of less than half a degree a century.

Meanwhile the World Bank babble on about a “4 degree” increase by 2100. Wherever they get this from, it has no basis in reality.



Ed Hawkins, climate scientist at the National Centre of Atmospheric Science of the  University of Reading, makes similar comments.


A recent press release by the World Meteorological Organisation (WMO) described recent global temperature changes, and highlighted extreme weather in the 2001-2010 period. Much of the press release is good, but here I will examine the accuracy of two statements.

WMO Secretary-General Michel Jarraud: “WMO’s report shows that global warming was significant from 1971 to 2010 and that the decadal rate of increase between 1991-2000 and 2001-2010 was unprecedented.”

“The decadal rate of increase in the global temperature accelerated between 1971 and 2010.”

This first is not a very clear phrase. What does ‘significant’ mean, and what does a ‘decadal rate of increase’ mean? But, it suggests that the increase from the average of 1991-2000 to the average of 2001-2010 was unprecedented, and the second phrase suggests an acceleration in the rate of increase in global temperatures. These statements are misleading.

The figure below shows a similar bar graph to that used by the WMO showing averages of particular 10-year periods using HadCRUT4. The top panel shows the changes using the same definition as the WMO, with decades finishing with years ending in zero (i.e. 2001-2010, 1991-2000 etc). The largest change from decade to decade is indeed the last change, at +0.21K.

The bottom panel repeats the analysis but defining decades to end in a two (i.e. 2003-2012, 1993-2002 etc). Now, the largest change (or even second or third largest) change is not to the most recent decade. And, in fact, the largest observed decadal increase is actually from the average of 1987-1996 to the average of 1997-2006, at +0.24K.

Note firstly that different temperature datasets will give slightly different warming rates. However, 2001-2010 is the warmest 10-year period in the instrumental record. This is evidence enough of a warmer climate, but NOT of an accelerated warming rate.


  1. July 4, 2013 7:27 pm

    “Meanwhile the World Bank babble on about a “4 degree” increase by 2100. Wherever they get this from, it has no basis in reality.”

    Of course, they get it from (some) computer models.
    Even though the increase in temperatures since 2000 lower than the projections based on zero growth in greenhouse gasses, the advocates of warming place their faith mostly in the higher projections.
    Unfortunately we will probably have to wait until the end of this decade to totally disprove the most extreme forecasts.

  2. July 5, 2013 8:31 am

    “I’m not sure why it has taken them two years, but the World Meteorological Organisation have just got round to telling us that 2001-10 was hotter then the previous decade.”

    I also wonder whether they waited until the hottest part of the year in the N.H. to publish this report.
    Maybe they have learned a lesson of not talking about “global warming” during the NH winter.

  3. Paul Matthews permalink
    July 5, 2013 11:36 am

    Climate scientist Ed Hawkins has also criticised the WMO claims about decadal warming.

  4. July 5, 2013 7:45 pm

    The Medieval Warming from 800 AD to 1300 AD Micheal Mann erased to make
    his “hockey stick” was several degrees warmer than anything “global
    warmers” fear. It was 500 years of great abundance for the world.

    The Vostock Ice Core data analysis show CO2 increases follow temperature
    increases by 800 years. That makes temperature change the cause and CO2
    change the effect; it is not the other way around. Finally…

    CO2 is a “trace gas” in air, insignificant by definition. It absorbs 1/7th as much IR, heat energy, from sunlight as water vapor which has 188 times as many molecules capturing 1200 times as much heat making 99.9% of all “global warming.” CO2 does only 0.1% of it. For this we should destroy our economy?

    Carbon combustion generates 80% of our energy. Control and taxing of carbon would give the elected ruling class more power and money than anything since the Magna Carta of 1215 AD.

    See The Two Minute Conservative via Google or: and when you speak ladies will swoon and liberal gentlemen will weep.

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