An increase in Indonesian forest fires – the sharpest rise since 2015 – has infuriated neighbouring Malaysia, where residents are inhaling smoke from peat and trees burned hundreds of miles away.

More than 14 megatonnes of carbon dioxide were discharged from the blazes on 5 September, more than triple the average on this day over the previous 15 years, according to satellite data from the Copernicus Atmosphere Monitoring Service.

Although the dramatic increase is too short to determine a trend, the Malaysian government will reportedly send a letter to Jakarta demanding urgent action to extinguish the blazes.

Residents of Kuala Lumpur say the sky has become increasingly smoggy in recent days as the smoke has spread across the strait of Malacca.

“Today is almost unbearable,” said Thomas Smith, an expert in peat fires from the London School of Economics, who is in the Malaysian capital for a research trip. “The smell is very distinct, like a peaty whisky.”

Smith said most of the fires were set deliberately to clear forest or farms. In recent years, a fall in the price of palm oil has prompted some farmers to burn their plantations and replant them with salad vegetables or dragon fruit.

Part of the problem is that many of the affected areas are on peatland, so the fires burn downwards through carbon that has accumulated over thousands of years. “I’ve seen some fires that have been burning for more than three weeks. They don’t spread wide but they go deep,” Smith said. “It’s a bit depressing.”

The Indonesian blazes follow huge fires in Brazil, Bolivia, the Democratic Republic of the Congo, Siberia, Alaska and Greenland, but experts say the situations in each region are too different to make a connection.

Up to 5 September, global fires this year have released about 4.7 gigatonnes of carbon dioxide, according to Mark Parrington of Copernicus. That is more than the annual emissions of the EU and Japan combined, but it is about average for forest fires over the past 17 years.