Why are so many forests on fire?

Wildfires have been reported in Spain, Sri Lanka, Greece and Bosnia this summer – is the extreme weather to blame?

They may be an annual occurrence in California but "wildfires" seem particularly ubiquitous this summer, with big blazes everywhere from Spain to Sri Lanka, Bosnia and Greece.

"Wild" may be a misnomer. The malicious starting of fires is as old as the human fascination with flame and many of the fires may be directly or indirectly caused by humans.

In the dry west of the US, where forest fires are routine in late summer, a winter drought is the trigger for current outbreaks after several cooler, wetter years. Idaho is reporting its worst "fire season" on record, while in California, wild fires, including one on the border of Nevada, have burned more than 500,000 acres this summer, compared with 73,868 acres by the middle of August last year.

America's extreme summer weather has led to fresh debate about whether these fires are linked to the violent weather that climatologists warn of. Scientists are always cautious about making claims about specific events but some think this is what global warming looks like.

In Europe, soaring temperatures are the obvious cause but social, psychological and historical factors are also at play. In Bosnia, the fires are complicated by the fact they have swept through minefields from the Bosnian war, causing explosions in forest areas.

Is it a coincidence that some of the fires are in countries badly hit by the financial crisis? In Greece, wildfires are a regular occurrence but the secret service has been called in to investigate the latest blazes; in the era of austerity arsonists have targeted banks, official buildings and even Microsoft's headquarters. London, of course, was ablaze a year ago.

In Spain, the worst fires for a decade have been exacerbated by cuts to rural firefighting teams, it is claimed, as well as long-term rural depopulation and a decline in grazing animals. With fewer sheep and goats, the undergrowth has sprouted, providing plenty of fuel for the fires.

Studies link arson to social deprivation as well as psychological factors such as physical and sexual abuse. In Britain, a Home Office report found around half of all arsonists are men under 18, and classified about 80% of cases as being motivated by vandalism, boredom and thrill-seeking. Researchers studying wild fires in South Wales found that impoverished areas were more likely to suffer wild fires: the 20% most deprived areas in South Wales are nine times more likely to experience wild fires than the least deprived areas.