It feels as if global warming campaigners are breaking open the champagne and raising a toast to record temperatures, together with that wagging finger: “I told you so!” BBC News has reported that global temperatures breached the 1.5°C threshold for the first time between February 2023 and January 2024. That is to say, average global temperatures were 1.5°C higher in that 12 months than they were in the 1850-1900 period, according to the EU Copernicus Climate Change Service (C3S). This followed an earlier EU C3S claim of 1.48°C for the calendar year 2023.
We have indeed seen some record temperatures in Europe in the last couple of years. On January 25th, a temperature of 30.7°C was reported at Calles in Spain. And in the U.K., a record maximum value of 40.3°C was measured at Coningsby on July 19th 2022. It’s possible that this peak reading was affected by aircraft movements – as discussed in the Daily Sceptic – but the hourly reported value of 39.6°C at 1400 and 1500 UTC, in a moderate southeasterly wind, was almost a degree above the previous U.K. maximum (38.7°C on July 25th 2019 in Cambridge Botanic Garden). These appear to be real records above the long-term values. But we ought to ask: what might have caused such high values, alongside the claimed record global temperatures in 2022 and 2023? A small part of the rise may be due to the urban heat island effect, or changes to instruments or screens, but that is far from the whole story. Upon closer inspection, much of this additional atmospheric heat is due to changes to oceanic sea surface temperatures (SST), which then warms the lower atmosphere. BBC News shows a rise to 21.05°C in global SST by February 3rd 2024.
El Niño
One major factor is the onset of a strong El Niño event, although this only had an impact in late 2023 as the Pacific Ocean warmed. The Oceanic Niño Index (ONI) rose to 1.6 in the Autumn (August to October 2023) and was 1.9 by the end of the year (October to December). Previous occasions when the ONI has gone above 1.5 in the last 70 years are the events in 2015-16, 2009-10, 1997-98, 1991-92, 1987, 1982-83, 1972-73 and 1965. The later events correspond with spikes in the satellite temperature data of the global lower atmosphere. El Niño events normally last 12 to 18 months – the strongest events occurred in 2015-16 and 1997-98, which peaked at 2.4 and 2.6 respectively.
Atlantic Multidecadal Oscillation
A longer trend in the ocean temperature is the Atlantic Multidecadal Oscillation (AMO), with sea surface temperatures varying by a degree or so over many years (as measured between the equator and 70°N). The AMO is itself coupled with changes in the troposphere and stratosphere, while the stratospheric wind regime may also be affected by changes in solar activity. A declining AMO trend in the 1960s and 1970s led to fears of the return of an Ice Age, but with an increase in the 1990s and 2000s there was a recovery in northern hemisphere temperatures. The AMO index has been positive since that time and it varies by about a degree and a half (°C) over these long periods.
It is interesting to compare the AMO index with the UAH V6.0 satellite temperature dataset, which began in 1979, while the AMO index has been reconstructed back to the mid-19th century. The satellite data of the lower atmosphere have the benefit of overcoming changes to such things as the urban heat island effect. When the two datasets are plotted alongside each other, from 1979 to 2022, they show a close correlation – in fact, the trend line is close to one-to-one (see chart below). Of course, correlation doesn’t equal causation, and one would not expect a change in the North Atlantic sea surface temperature to have an equally measurable change upon the global atmospheric temperatures. The close correlation may be due to the way the index is constructed. However, it is not unreasonable to expect that there would be some physical connection between the Atlantic sea surface temperature and the temperature of the lower troposphere, particularly in Europe, which may partly explain the record high European temperatures of recent years.
Cleaner air
Since 2000, good progress has been made in cleaning the global atmosphere of industrial pollutants, first in North America and Europe, but increasingly in Asia. Pollutants include particulate matter, sulphur dioxide and nitrates. Using NASA satellite data, the estimated climatic influence of this pollution is thought to have reduced the global temperature by 0.5°C, while removing the pollution may have brought forward the time when it is forecast to rise 1.5°C above the pre-industrial levels. Pollutants have a direct effect in modulating the amount of energy that enters and leaves the Earth’s system, but there is also a secondary effect through physical changes to clouds. Atmospheric pollutants act as cloud condensation nuclei. So, more numerous particles and sulphur aerosols in the lower atmosphere lead to an increase in the number of cloud droplets, but they are smaller in size. Overall, the cloud liquid water content rises in the presence of such pollution. This makes clouds more reflective to incoming solar energy.
Further regulation that came into force in 2020 through the International Maritime Organisation (IMO) has also led to a decrease in the amount of sulphur that can be released from a ship’s exhaust – down to 0.5% from 3.5%. Overall, with a cleaner atmosphere and less reflection from clouds, there is likely to be a corresponding rise in the amount of solar radiation absorbed in the oceans; hence the ocean temperature may rise. This may partly explain the rise in global ocean sea surface temperature, which feeds into a rise in the lower troposphere temperatures.
Hunga Tonga – Hunga Ha’apai
On January 15th 2022, a massive volcanic eruption in the Pacific Ocean sent a plume of ash, water vapour and other gases into the atmosphere, reaching as high as 55 km – that is through the stratosphere and into mesosphere. It is estimated that 146 mega-tonnes of water vapour were added to the thin stratospheric atmosphere as a result. Pressure shock waves were observed around the world and measured on barometers at ground level. When sulphur dioxide is pumped into the stratosphere it can cool the planet, as occurred with Pinatubo from 1992, but such an excessive amount of water vapour released so high may trap additional heat below. One paper, published in Nature Climate Change, suggested that this could lead to a temporary warming of surface temperatures to 1.5°C above the long-term average within the following decade.
Summary
Many politicians, climate scientists and the mainstream media are pushing the world towards Net Zero carbon emissions because of rises in greenhouse gases and global temperatures. But, as has been widely noted, this is a policy goal that does not fully consider the economic impact upon ordinary people. Closer inspection of recent changes to the global atmosphere and ocean sea surface temperatures suggests that increased greenhouse gases is only one factor in the recent rise in temperatures. Natural variability in terms of the short-lived El Niño event, the longer-term rise in the AMO index, a move towards cleaner air and less pollution, and volcanic activity from the Hunga Tonga – Hunga Ha’apai volcano may all have had a significant impact upon recent rises in global temperatures. Consequently, the long-term climate sensitivity to increases in greenhouse gas emissions, which is somewhat uncertain, may in fact still be at the lower end of expectations, as argued for by Lewis and Curry for example. If that is so, then the rush to meet Net Zero targets is misguided.
Andrew Sibley is a semi-retired Chartered Meteorologist with an MSc in Environmental Decision-Making and an MPhil in Theology.
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