Shetland's industrial emissions of planet-warming methane reached their highest level in a decade last year, driven by broken kit at EnQuest's Sullom Voe terminal.

The company attributed the emissions to a nine-month equipment failure which saw all of the facility's gas burnt into the atmosphere over the period. Despite regulators insisting the issue was resolved last year, EnQuest said it has continued to suffer "further outages".

EnQuest confirmed the figures -- published by the Scottish Environment Protection Agency (Sepa) last last month -- and described them as a "temporary increase", adding the offending equipment would soon be "retired".

One councillor called the pollution an "injustice". The chairman of watchdog Environmental Standards Scotland, Richard Dixon, asked why the equipment took most of the year to fix.

"Any piece of industrial equipment can fail, that's the nature of industry. But how on earth could it have failed for a whole nine months?" said Dr Dixon.

"It's an embarrassment for the whole community, which is a big shame because it's EnQuest who are to blame."

Last year SVT's releases of methane reached their highest levels since 2014.

Methane is a particularly powerful climate-warming gas. Different studies put its heating effect at 25 to 80 times that of CO2, and the Intergovernmental Panel on Climate Change attributes nearly half of global warming to the gas.

As well as seeing methane figures jump more than a third, releases of CO2 increased by almost 30,000 tonnes -- half of the entire previous year's emissions.

The terminal's emissions drove Shetland's total industrial methane pollution to its highest level since 2016, and CO2 the highest since 2020.

Meanwhile, the figures released on Tuesday show that most of Shetland's other industrial sources of air pollution either decreased or kept their emissions consistent.

Shetland Gas Plant saw a significant drop in methane emissions and continued a downward trend for CO2. Shetland Heat Energy and Power's incinerator cut CO2 by almost a fifth. While SSE's Lerwick power plant saw a slight increase in CO2 it cut most other air pollutants.

Methane from the Gremista landfill increased from 2007 to 2013 and has continued creeping up since then.

Sepa said EnQuest informed them of the equipment failure at the time and that it "engaged with the operator to explore options to minimise the impact and seek a resolution to the problems identified".

Sepa added that the issue was "resolved in late 2024". EnQuest said it has continued to experience "further outages".

"There has been increased gas flaring at the terminal site due to extended outages of the HP5 compressor, which saw all SVT gas being flared from January to September 2024,"the company said.

Flaring describes when fossil fuel producers burn off gas they cannot capture.

"This compressor outage was directly responsible for the increase in CO2 and methane emissions," EnQuest continued.

"Following remedial work undertaken in September 2024, the compressor is operational; however, it has experienced some further outages since returning to service.

"This piece of equipment will be retired when the New Stabilisation Facility (NSF) is commissioned."

Dr Dixon has also served on Sepa's board and helped draft the government's air quality strategy. He said EnQuest's explanation raised a number of questions.

"If the compressor is such a vital piece of kit, and if it doesn't work there's a big problem, why aren't there two of them?" he said.

"The fact that they fixed it but it still had some problems suggests that it's clapped-out; it's beyond its usable lifetime," he added. "Have they been running it longer than they should have? Should it have been replaced years ago?"

In response to these questions EnQuest said it "would like to reiterate that they are making material investment in the decarbonisation of the terminal, including the New Stabilisation Facility, which will remove the compressor from service."

EnQuest did not respond to further questions about when the NSF was expected to come online, but said it would reduce the terminal's emissions by roughly 80 per cent.

When the project was first announced contractors said it was due by "the end of 2024 or early 2025". In an investor's report from February, the company said it was expected in the fourth quarter of this year.

The terminal maintained "100 per cent" reliability for customers during 2024, according to that report.

Shetland Greens councillor Alex Armitage said the emissions demonstrated EnQuest's priorities.

"They are obsessed with profit -- if they really wanted to they could invest in preventing fossil fuels from leaking into the environment," he said.

"We're all trying as part of a global effort - and these guys are cheating us," he said. "There's an injustice there."

Broken equipment at Sullom Voe caused decade-long peak in emissions