The WMO State of the Global Climate Report: A note on CO2 concentration and global temperature rise
The WMO State of the Global Climate Report: A note on CO2 concentration and global temperature rise
Edward Forman and Rob Shepherd
In a recent contribution, Simon Maxwell reviewed the latest State of the Global Climate Report from the World Meteorologial Organisation. Among other things, he drew attention to the data on the CO2 concentration in the atmosphere, and observed that
‘The rise in CO2 concentration looks alarming, and it is. . . The long term trend looks like an acceleration (though with a lot of variation).’
We have examined the data, covering the period 1979-2024. Computing the 10-year average increase in CO2 (Figure 1), we find that the annual increment is indeed on an upward trend. Averaging the data in this way reduces the influence of years that fall outside of the background rate, making the trend more representative, even if it is perhaps overly cautious. The smoothed annual increment ranged from 1.43-1.53 ppm in the 1990s; it has not been below 2.0 ppm since 2011; in the 2020s, the figure has exceeded 2.4 ppm.
Figure 1
The WMO report plots other quantifiable factors that add to the temperature rise, like reducing the ice sheets (that reflect some of the sun’s rays back into space) and
changes in land use (reducing how nature removes GHGs), and related effects like the rise in sea levels (due to warmer water and some ice melting) and the change in ocean
chemistry (pH values) that impacts ocean life that is our biggest CO2 “sink” (extractor).
The report considers how various experts, with complicated climate models, would interpret recent data as bringing forward the years when the 1.5°C and 2.0°C rise in
temperatures will be reached, but if we just look at the trend ourselves without that complexity, we get the following picture (Figure 2). Our simple chart is more pessimistic than the experts’ complex models, but experts did not predict that temperatures would rise as much as they have, especially in recent years. Simon Maxwell discusses the basis for judging whether the Paris threshold has been breached.
Figure 2
The WMO report mainly restricts itself to things it can measure and track, not suggesting why things disrupt the climate (such as how temperature rises affect the jet streams and ocean currents that redistribute heat around the world). However, it does list some of the consequences, such as storms, heatwaves, droughts and floods, even though it is not always straightforward to attribute extreme weather events to climate change: the UK Met Office has a useful resource on this topic, here.
Are there lessons for us in Brighton & Hove?
The obvious message is we must try harder to reduce our GHG emissions, particularly in the near future, which reinforces recent messages from the IPCC.
However, is the WMO's foreword defeatist? “The global community, along with the WMO, are intensifying efforts to strengthen early warning systems and climate services to help decision-makers and society at large be more resilient to extreme weather and climate”. If we can’t do much better very soon, should we pay more attention to adaptation?
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Edward Forman is on a PhD programme at the University of Southampton
Rob Shepherd is a retired mathematician who has studied air pollution and carbon emissions.
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