Organic food has a bigger climate impact than conventionally farmed food, due to the greater areas of land required, according to a study.

Researchers from the Chalmers University of Technology in Sweden developed a new method for assessing the climate impact from land-use, and used this, along with other methods, to compare organic and conventional food production.

The results, published in the journal Nature, show that organic food can result in much greater emissions.

The reason why organic food is so much worse for the climate is that the yields per hectare are much lower, primarily because fertilisers are not used.

To produce the same amount of organic food, you therefore need a much bigger area of land, researchers said.

Even organic meat and dairy products are - from a climate point of view - worse than their conventionally produced equivalents, researchers said.

Since organic meat and milk production uses organic feed-stock, it also requires more land than conventional production, they said.

The researchers used a new metric, which they call "Carbon Opportunity Cost", to evaluate the effect of greater land-use contributing to higher carbon dioxide emissions from deforestation.

This metric takes into account the amount of carbon that is stored in forests, and thus released as carbon dioxide as an effect of deforestation.

The study is among the first in the world to make use of this metric.

“The fact that more land use leads to greater climate impact has not often been taken into account in earlier comparisons between organic and conventional food,” said Wirsenius.