There is little better on a winter's evening than curling up next to a wood fire, or the modern equivalent, a wood-fired boiler – unless it is the green warm glow you get from knowing that the fuel you are using is environmentally friendly and sustainable.

Except that it is not always. And nor is that two-year-old diesel car you bought because its fuel efficiency, compared with petrol models, makes it more green. As a United Nations report has just uncovered, wood burning and diesel vehicles are two of the biggest culprits in the developed world in generating the black carbon – soot – that is a major cause of climate change.

"It's nice to sit in front of a wood fire in the winter, but we should all be feeling pretty guilty," said Joseph Alcamo, chief scientist at the UN Environment Programme.

The most up-to-date, and expensive, models of wood-fired boilers do not produce black carbon. Pellets, for instance, are fine. But Markus Amann, of the International Institute of Applied Systems Analysis, in Austria, warned: "It's the cheap ones." Models that burn logs instead of pellets are particularly bad, as they are near impossible to retrofit with particle-catching technology that would render them harmless. Most diesel cars more than two years old are also likely to emit particulate matter that is big enough to cause air pollution – which causes the premature death of hundreds of thousands of people in Britain – and climate change.

Black carbon is a problem because it is black – it absorbs heat, and in the worst cases it dirties the snow in areas such as the Arctic, Siberia and high mountains. The blackened snow absorbs more heat and instead of reflecting the sun, and helping to cool the planet, it warms the surrounding areas. Repeated on a global scale, this is a major cause of short term climate change.

The good news is that tackling black carbon, and other so-called "short-lived climate forcers" such as methane, could be a quick win in terms of tackling climate change. If the world were to take urgent action on the leading causes of the problem, we could knock about half a degree Celsius off the expected warming in the short term. That means a lot in terms of global warming – world leaders have pledged to try to limit global temperature rises to no more than 2C above pre-industrial levels, because scientists regard that as the limit of safety, beyond which climate change would become catastrophic and irreversible.

Cutting black carbon also saves lives – acting on air pollution would avoid millions of premature deaths around the world each year. The UN advocates a number of measures that would all be either low-cost or would pay for themselves – in terms of lower fuel costs – within a few years. For instance, replacing wood fired cooking in the developing world with low-emissions sources such as solar cookers, petroleum based stoves or other modern technology would cost about $20 (£13) to $60 per stove, but would save millions of lives.

Changing farming practices would also save millions of tonnes of carbon emissions a year – for instance, rice paddy fields generate methane, a greenhouse gas many times more powerful than carbon dioxide. By changing practice so that the paddy fields were dried out once a year and exposed to the air, the amount of methane produced could be drastically reduced, at no cost to farmers and with no reduction in the overall rice yield.

Composting is also a good idea, according to the UN – the methane emitted can be captured and used as a small power source. Although at present it takes a farm to produce enough manure and waste to power an anaerobic digester, smaller scale versions could power a single heating source or cooker.