How come the experts never look at controlling population growth?

Global consumption of meat needs to fall - to ensure future demand for food can be met and to help protect the environment - a study says.

Research from Cambridge and Aberdeen universities estimates greenhouse gases from food production will go up 80% if meat and dairy consumption continues to rise at its current rate.

That will make it harder to meet global targets on limiting emissions.

The study urges eating two portions of red meat and seven of poultry per week.

However that call comes as the world's cities are seeing a boom in burger restaurants.

The research highlights that more and more people from around the world are adopting American-style diets, leading to a sizeable increase in meat and dairy consumption.

It says if this continues, more and more forest land or fields currently used for arable crops will be converted for use by livestock as the world's farmers battle to keep up with demand.

"Agricultural practices are not necessarily at fault here - but our choice of food is” Lead researcher, Bojana Bajzelj

Deforestation will increase carbon emissions, and increased livestock production will raise methane levels and wider fertiliser use will further accelerate climate change.

The lead researcher, Bojana Bajzelj from the University of Cambridge, said: "There are basic laws of biophysics that we cannot evade."

"The average efficiency of livestock converting plant feed to meat is less than 3%, and as we eat more meat, more arable cultivation is turned over to producing feedstock for animals that provide meat for humans.

"The losses at each stage are large, and as humans globally eat more and more meat, conversion from plants to food becomes less and less efficient, driving agricultural expansion and releasing more greenhouse gases. Agricultural practices are not necessarily at fault here - but our choice of food is."

The report says the situation can be radically improved if farmers in developing countries are helped to achieve the best possible yields from their land.

Another big improvement will come if the world's population learns to stop wasting food.

The researchers say if people could also be persuaded to eat healthier diets, those three measures alone could halve agricultural greenhouse gas levels from their 2009 level.

The study is the latest to warn of the planetary risks of eating intensively-produced meat and dairy produce. Scientists worried about climate change are increasingly making common cause with health experts concerned about the obesity pandemic.

But many people are voting with their wallets and their bellies - as burger bars expand, mushroom burgers are not yet top-selling items.