Temporary exceedance of 1.5°C increasingly likely

Here’s some news about global temperatures from the Met Office that I thought you would like to read

Author: Grahame Madge

01:01 (UTC+1) on Thu 27 May 2021

There is more than a 40% chance that the annual average global temperature in at least one of the next five years will temporarily reach 1.5°C above pre-industrial levels.

And these odds are increasing with time, says a new climate update published today, led by the UK Met Office and issued by the World Meteorological Organization. The Global Annual to Decadal Climate Update spans 2021-2025. 

“Assessing the increase in global temperature in the context of climate change refers to the long-term global average temperature, not to the averages for individual years or months. Nevertheless, a temporary exceedance of the 1.5 degree level may already be seen in the next few years.”

Professor Adam Scaife is the head of seasonal to decadal prediction at the Met Office.

The Paris Agreement seeks to keep global temperature rise this century well below 2.0°C degrees Celsius above pre-industrial levels and to pursue efforts to limit the temperature increase even further to 1.5°C. The update also identifies the 90% likelihood of at least one year in the five-year period becoming the warmest on record, dislodging 2016 from the top ranking. Other highlights from the update include the likelihood of high-latitude regions and the Sahel – the region of Africa immediately south of the Sahara desert – becoming wetter. And there is an increased chance of more tropical cyclones in the Atlantic compared to the recent past (defined as the 1981-2010 average).

“These predictions provide a basis to alert governments and aid agencies to regional climate risks.” 

Dr Leon Hermanson – Met Office

The climate update, which is produced annually, harnesses the expertise of internationally-acclaimed climate scientists and the best prediction systems from leading climate centres around the world to produce actionable information for decision-makers. 

In 2020 – one of the three warmest years on record – the global average temperature was 1.2 °C above the pre-industrial baseline, according to the WMO’s report on the State of the Global Climate 2020, released in April. It highlighted the acceleration in climate change indicators like rising sea levels, melting sea ice, and extreme weather, as well as worsening impacts on socio-economic development.

The Global Annual to Decadal Climate Update confirms that trend. In the coming five years, the annual mean global temperature is likely to be at least 1°C warmer – within the range 0.9°C – 1.8°C – of pre-industrial levels. 

The chance of temporarily reaching 1.5°C has roughly doubled compared to last year’s predictions. This is mainly due to using an improved temperature dataset to estimate the baseline rather than sudden changes in climate indicators. It is very unlikely (10%) that the five-year mean annual global temperature for the entire 2021-2025 period will be 1.5°C warmer than pre industrial levels, according to the climate update.

The Global Annual to Decadal Climate Update takes into account natural variations as well as human influences on climate to provide the best possible forecasts of temperature, rainfall, wind patterns and other variables for the coming five years. 

With the UK’s Met Office acting as lead centre, climate prediction groups from Spain, Germany, Canada, China, USA, Japan, Australia, Sweden, Norway and Denmark contributed new predictions this year. Combining forecasts from climate prediction centres worldwide enables a higher quality product than what can be obtained from any single source. 

The development of near-term prediction capability was driven by the WMO co-sponsored World Climate Research Programme, which declared it as one of its overarching Grand Challenges.

Courtesy of the UKMO

BBC News

David Shukman has also been hard at it down at the BBC with some alarming and emotive headlines helped along by some quotes from Leo Hermanson such as :

  • Climate: World at risk of hitting temperature limit soon
  • “What it means is that we’re approaching 1.5C – we’re not there yet but we’re getting close
  • Time is running out for the strong action which we need now.”

Unlike the Met Office, he has at least included a rather crude graph of global temperature change with his article that shows the changes in global temperatures, presumably on an annual basis, since 1850. This in itself is a bit of an achievement because if 1850 was the true dawn of pre-industrial times like they say it is, only two of the six series plotted in the graph have records that extend that far back, and the ERA5 series didn’t even start until 1979. I’m not sure how they got around that one because that 1850 baseline temperature is so crucial to the calculation.

So what are they expecting?

Well as far as I can see they expect that there’s a 40% chance that the 12 month average global temperature will exceed 1.5°C of pre-industrial times. This is where it gets more than a bit confusing because Professor Adam Scaife says that this 1.5°C is not the same as the one in the Paris agreement, but refers to the long-term global average temperature. I’m getting old and so get easily confused but what is the professor talking about here, it sounds remarkably like gobbledygook to me.

The 1850 baseline temperature

The really crucial bit of data in constructing a graph showing changes since 1850 is what that baseline temperature is and how you calculate it. As far as I can see in this UKMO graph they’ve not used the annual mean anomaly for 1850, because back then the world was still in a cold phase, and that would have produced changes much lower than 1.5°C, my guess is that instead they’ve chosen to use the 1850-1879 long-term average, as I have done.
If you would like a bit more detail here is my graph showing a running average 12 month anomaly from the new HadCRUT version five series data, and because it’s monthly you get much finer detail.

What’s been happening recently?

And just to see what’s been going on in recent years here’s a graph (below) of the the last 30 years, overlaid with all ENSO events, and a projection extrapolated from the 30 year linear trend as to when the 12 month average will reach the dreaded +1.5°C line, which according to my calculations should be by the start of 2034. I can count on the graph four months in which the individual months in the HadCRUT5 series went above 1.5°C. But so far the highest the 12 month average in that series is when it peaked at around 1.32°C in 2016, and 1.29°C in a second peak in early 2020. Since then the 12 month average has fallen and is currently at 1.22°C above the pre-industrial level.

Natural variability and the twin peaks

Natural variability will mean the following few years may be slightly cooler and it could be another decade or two or more before the 1.5C limit is crossed permanently.

David Shukman

It’s nice to see that David Shukman admit that there’s such a thing as ‘natural variability’ and the fact that the following few years may be slightly cooler. He is quite right of course, natural variability seems to be much stronger at the moment than AGW is, helped along no doubt by the recent La Niña event. In fact all global temperatures are in the process of doing a ‘twin peaks’ over the last couple of years and global temperatures have been sliding for over a year now. News items like this from the BBC News are no doubt being released to bolster up the message that minor set backs like this are to be expected, but a graph like the one below that compares all the major global temperature series is bound to provoke some awkward and embarrassing questions at the COP26 summit in November if global temperatures don’t pick up during the coming summer.

3 thoughts on “Temporary exceedance of 1.5°C increasingly likely”

  1. Does the fall of CO2 conc in the atmosphere late in each year mean the *trend* isn’t relentlessly upward? It doesn’t. The *trend* of global temperature is pike staff obvious. Year to year variability of global temperature is about .2C but I’ll be astonished if we see global temperate as low as at the start of this century in the rest of the century – another huge unexpected climate forcing excepted..

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