Food waste is a bigger cause of climate change than plastics, according to Zero Waste Scotland.

The body is urging people to cut down the amount of unwanted food they put in the bin to help reduce the level of harmful methane gas released into the atmosphere.

When food waste ends up in landfill it rots, producing methane, one of the most damaging greenhouse gases driving climate change.

Read more: The astonishing scale of food waste - and what you can do about it

Research by Zero Waste Scotland, which promotes sustainable use of resources, found that 456,000 tonnes of food waste was collected in Scotland in 2016, compared with 224,000 tonnes of plastic waste.

Only 93,000 tonnes of the food waste collected was sent to dedicated food waste recycling collections, with most of the remainder sent to landfill, while around 150,000 tonnes went to home composting or ended up in sewage works after going down the drain from kitchen sinks.

Zero Waste Scotland calculated that the carbon footprint of food waste collected from Scottish households that year was nearly three times that of plastic waste collected from people's homes.

Read more: New Scotland-wide campaign to curb food waste 

The agency has launched a Food Waste Reduction Action Plan together with the Scottish Government with the aim of reducing food waste across Scotland by a third by 2025.

Iain Gulland, Zero Waste Scotland chief executive, said: "It might seem bizarre but scraping that leftover lasagne, mince or salad from your plate into the bin is seriously damaging the planet, because when those scraps of pasta and lettuce which you never got around to eating end up in landfill, they rot.

"As they break down, they emit methane, which is many times more harmful in the short-term to our climate than carbon dioxide (CO2).

"Food waste is actually a bigger cause of climate change than plastics. It is still vital that we continue to reduce plastic waste, which remains an extremely serious issue.

"But as more people ditch single-use plastics as awareness grows of the wider impact of plastic waste, including pollution, we will send a strong message on the damage caused by binning leftovers and other wasted food."

Read more: Scotland dumps more rubbish in landfill despite record recycling

Zero Waste Scotland estimates that every Scottish household could save an average of £440 a year by reducing the food it wastes through steps such as planning meals, making better use of storage such as freezers and being inventive with using up leftovers.

The Scottish Government has also launched a new advertising campaign, entitled Food Gone Bad, to help raise awareness of the impact food waste has on climate change and how to reduce it.

A Scottish Government spokesman said: "Following the First Minister's declaration of a global climate emergency, we are reviewing a range of policies across government to ensure we do all we can to support the public sector, businesses, communities and individuals to meet our shared climate responsibilities.

"We would encourage everyone to consider what more we can all do to help reduce food waste."