‘Last Decade Was The Warmest’ – Yes, But…
As predictable as Christmas, every year meteorological agencies issue assessments of annual global temperature data in early December – primarily in order to influence the annual UN climate summits.
The World Meteorological Organisation has done it again with a press release that serves very well the purpose of any climate-related press release – to be reported uncritically. The news media, even those that claim to have ‘analysts’ to look behind the habitual hype, did not disappoint and simply regurgitate the spin.
The WMO said:
Global mean temperature for January to October 2019 was 1.1±0.1°C above pre-industrial levels. 2019 is likely to be the second or third warmest year on record. The past five years are now almost certain to be the five warmest years on record, and the past decade, 2010-2019, to be the warmest decade on record. Since the 1980s, each successive decade has been warmer than any preceding decade since 1850.
The WMO showed a nice graph, which a journalist kindly retweeted.
But venture a little beyond the press release and take a closer look at the data.
It is more instructive to look at the past two decades and see why the most recent one is warmer than the other. It’s then obvious just what a big feature the 2016 El Niño is and how it has dominated the global temperature of the last decade. Its influence cannot, as so many press releases and cursory analysts of recent temperature data maintain, be restricted to 2016 and then treated as though it has no effect on other years.
It is obvious from the temperature data that there is a multi-year effect. This makes stories like “2017 was the warmest year without an El Niño” nonsense. Although there was technically a minor El Niño that year it is clear that the influence of 2016 is still strong.
The WMO adds:
The IPCC Special Report on 1.5°C (IPCC SR15) concluded that “Human-induced warming reached approximately 1°C (likely between 0.8°C and 1.2°C) above pre-industrial levels in 2017, increasing at 0.2°C (likely between 0.1°C and 0.3°C) per decade (high confidence)” . An update of the figures to 2019 is consistent with continued warming in the range 0.1-0.3°C/decade.
So what is the decadal increase in temperature, 0.1° C or 0.3° C? It makes a big difference. In reality, the picture is a little more complex than the claim that ‘global warming continues to record levels….’
Go a little further into the WMO press release and you will find: The ocean absorbs over 90% of the heat trapped in the Earth system by rising concentrations of greenhouse gases. Ocean heat content, which is a measure of this heat accumulation, reached record levels again in 2019. The reference for increasing ocean heart content comes from Cheng et al (2019) who have based their conclusions heavily on the fatally flawed paper by Resplandy et al (2018) . The latter paper has been withdrawn, but the WMO seems unaware of this.
About sea level rise the WMO says:
As the ocean warms, sea levels rise. This rise is further increased by melting of ice on land, which then flows into the sea. Short-term trends in sea level are modulated by transitions between La Niña and El Niño, a cooling and warming, respectively of the central and eastern Pacific Ocean surface temperature. Sea level has increased throughout the altimeter record, but recently sea level rose at a higher rate due partly to melting of ice sheets on Greenland and Antarctica. In autumn 2019, the global mean sea level reached its highest value since the beginning of the high-precision altimetry record (January 1993).
The WMO press release shows sea level measurements from only 1993 onwards. Including previous data would have given a different perspective as the current trend in rising seas can be seen to have begun around 1910. Their press release does not mention that any purported acceleration in sea level change is controversial.
There is a lot of good data in the WMO press release, but also a lot of shallow analysis.