Jersey's changing climate

THE dramatic change in Jersey’s climate has been laid bare in new data which reveals the Island is seeing a significant rise in temperatures and is coming to the end of its hottest decade since records began.

The figures, provided to the JEP by Jersey Met, show an almost consistent increase in temperatures since the start of the 1900s, with a noticeable escalation in the number of hotter-than-average years since the beginning of the 1990s.

To demonstrate the warming experienced in Jersey, the figures have been processed into a ‘climate-stripe’ chart. The graph’s line shows the average temperature for each decade, while the stripes demonstrate whether the individual years were colder than the 20th-century average (blue), hotter (red) or in line with that average (white).

The masses of blue at the start of the 1900s and the almost unbroken reds at the other side of the chart demonstrate the seemingly runaway rise in temperatures being recorded in the Island.

The chart and other data given to this newspaper shows that:

• Every decade since the start of the 1900s – except for the 1960s – was hotter than the previous.

• Seven of the top ten hottest years on record have occurred since 2000.

• Based on forecasts and data, this decade will be Jersey’s hottest and 2019 will be the Island’s 11th warmest year. The hottest was 2014.

• Jersey’s average temperature has risen by 1.5°C since 1900.

• And sea temperatures are also rising, with nine of the top ten years occurring since 1990.

Separate data issued by the UK Met Office last year – and confirmed by Jersey Met as applicable to the Island – showed that summer temperatures could rise by as much as 5.4°C by 2070, which would see the mercury hitting up to 40°C in Jersey during the summer.

Winter temperatures, meanwhile, could rise by 4.2°C, meaning maximums in January and February could hit 18°C and 20°C respectively.

The change in Jersey’s climate is being mirrored across the British Isles and other parts of the world.

Last week, the UK Met Office said that globally 2019 was expected to be the second or third warmest year since records began in 1850, and 2010 to 2020 was likely to be the hottest-ever decade.

‘The five warmest years for average global surface temperature since records began have all occurred in the past five years. By contrast the five coldest all occurred before 1912. This is climate change and not a coincidence,’ said professor Tim Osborn, the director of research at the University of East Anglia’s Climatic Research Unit.

The local and national figures have been released during a year in which governments around the world – including the States – declared a climate-change emergency and vowed to reduce their carbon emissions.

Commenting on the Island’s figures, John Searson, principal meteorologist at Jersey Met, said: ‘The climate-stripe chart clearly shows that at the beginning of the 20th century we were seeing mostly blue lines and now we are seeing mostly reds.

‘What we are seeing in Jersey is consistent with the global picture. This shows that our Maison St Louis observatory is giving us a good record of climate change and it confirms that the rationale for the government to declare a climate-change emergency was sound.’

Asked if the rise in temperatures was likely to continue, Mr Searson said: ‘In my view yes. We know that the level of carbon dioxide in the atmosphere is increasing every single year and there is no real indication that this process is slowing.

‘Carbon dioxide has a major influence on the global atmosphere and global temperatures and so we expect to see a continued increase.’

The average temperature for the 1960s – the only decade that was colder than the previous – was pegged back by a series of individual ‘normal’ years and the notoriously freezing winter of 1962/63, which was so cold parts of the sea in St Aubin’s Bay iced over.

The decadal line since the early 2000s appears to show a slowing down in temperature rises. However, Jersey Met say this apparent stall has been caused by two average years in a short period of time, and that the figure taken over a 30-year period, rather than a decade, would iron out the two anomalies and show a more consistent increase. The two years in question are shown by white and yellow lines among a sea of red since the start of the new millennium.

The effects of climate change – and the pressures it brings – are already being felt. Climatologists have long warned that rising global temperatures will generate more and heavier rainfall, punctuated by periods of drought.

During 2018 and the first half of this year, Jersey experienced 13 consecutive months with below average rainfall. The long dry spell was broken in June, which was the joint-wettest for seven years.

By the following month, Jersey Water was urging people to conserve supplies as the Island entered an absolute drought – a period of 15 consecutive days with no measurable rain. The dry conditions became such a concern that the desalination plant was turned on at the start of the autumn. Just three months later, Jersey had seen its second-wettest autumn on record.

‘We have found that the period of October to March has seen increasing amounts of rainfall since the start of the 1900s,’ said Mr Searson. ‘But when you look at the summer months you see a noticeable decline in rainfall. This is in line with what you would expect with climate change,’ he added.

Jersey Water has already started planning for shortages caused by major fluctuations in rainfall. Earlier this year it set out several options, including building a new reservoir, raising the dam wall at Val de la Mare and increasing the capacity of the desalination plant.