It has been a long time since anyone was able to say that the past year was the warmest ever solely due to global warming.
Dr David Whitehouse, Science editor
Last week the UK Met Office released its measurement of the global temperature of 2021, a year described by the Guardian as one of climate crisis.
The continent of Africa had its warmest January on record. There was torrential rains in Malaysia and Turkey was in the tenth year of drought. In February vicious winter weather hit Texas resulting in ten million people being without power. In March Australia was hit by severe flooding forcing thousands to flee in New South Wales. Come April there were huge sandstorms in China and a hurricane brought record rainfall to some parts of Western Australia. In May the governor of California declared a drought.
June saw a remarkable heatwave in North America, Europe and Asia had their second warmest Junes on record. New Zealand temperatures broke records. The next month Death Valley in California recorded 54.4 C. Torrential rain in India killed over a hundred. In August wildfires broke out in the Mediterranean as well as swathes of Siberia. Floods hit Japan, Turkey and South America. In December floods hit Australia again. Kentucky experienced a devastating tornado.
Despite all this the data for 2021 showed it to be the seventh warmest year on record. Announcing the global temperature the Met Office emphasised that global temperatures were temporarily cooled by successive La Niña events at either end of the year.
Global temperature change in the 21st century. Source: UK Met Office
There was a little reticence in proclaiming the news that 2021 was far from being a record breaking year. The explanation is that 2021 was very warm but it came after a few years whose temperatures were boosted by a super El Nino event. 2021, it is claimed, continues a long-term trend, super El Nino notwithstanding.
Dr Colin Morice, of the Met Office, said: “2021 is one of the warmest years on record, continuing a series of measurements of a world that is warming under the effects of greenhouse gas emissions. This extends a streak of notably warm years from 2015 to 2021 – the warmest seven years in over 170 years of measurements.”
Emphasising the long-term trend Prof Tim Osborn, of the University of East Anglia, added: “Each year tends to be a little below or a little above the underlying long-term global warming. Global temperature data analysed by the Met Office and UEA’s Climatic Research Unit show 2021 was a little below, while 2020 had been a little above, the underlying warming trend. All years, including 2021, are consistent with long-standing predictions of warming due to human activities.”
“WMO Secretary-General, Prof. Petteri Taalas commented, “Back-to-back La Niña events mean that 2021 warming was relatively less pronounced compared to recent years. Even so, it was still warmer than previous years influenced by La Niña. The overall long-term warming as a result of greenhouse gases is now far larger than the year-to-year variability caused by naturally occurring climate drivers.”
Consider though that in these climate conscious times it has been a long time since anyone was able to say that the past year was the warmest ever solely due to global warming. What’s more, new research by a group of Chinese scientists from the Ministry of Natural Resources to be published in the Journal of Climate suggest that the above or below the long-term trend line argument might be too simplistic.
By looking at all available global temperature datasets and a comprehensive span of durations and start and end times they find that the so-called global warming hiatus of the 2000s and beyond was real. Moreover, they find that the rapid warming of the late 1900s and the hiatus of the 2000s are statistically incompatible.
The ending of the hiatus is also interesting. It ended with a (record) El Nino since which global temperatures have not increased. Some see this as significant, others as we have seen there has been a resumption of the long-term linear increase despite, as the Chinese scientists point out there has been 30 years of non-linear increases in global temperature. Bear in mind that 30 years is frequently used as the definition of climate.
What I take from this is that sometimes it is very useful to draw a straight line through noisy data as it often shows the fundamental factors of a data set. Sometimes though it might not be what it seems.