Which causes more greenhouse gas emissions, rearing cattle or driving cars?

Surprise! According to British physicist Alan Calverd, giving up pork chops, lamb cutlets and chicken burgers would do more for the environment than burning less oil and gas - ?global warming could be controlled if we all became vegetarians and stopped eating meat?, he writes in the monthly Physics World.

Claverd is not the only one who comes up with this surprising conclusion. A couple of scientists from the University of Chicago in the US, Gidon Eshel and Pamela Martin, have found that our personal impact on global warming may be influenced as much by what we eat as by what we drive.

It would have been easy to shrug off these discoveries had it not been for a United Nations Food and Agriculture Organisation (FAO) report published recently. According to this report, Livestock?s long shadow - Environmental Issues and Options, ?the livestock sector generates more greenhouse gas emissions as measured in CO2 equivalent ? 18 percent ? than transport. It is also a major source of land and water degradation?.

Damage worsening

With increased prosperity, people are consuming more meat and dairy products every year. According to the FAO, global meat production is projected to more than double from 229 million tons in 1999-2001 to 465 million tons in 2050, while milk output is set to climb from 580 to 1043 million tons.

The global livestock sector is growing faster than any other agricultural sub-sector. It provides livelihoods to about 1.3 billion people worldwide and contributes about 40 percent to global agricultural output. For many poor farmers in developing countries livestock are also a source of renewable energy and an essential source of fertilizer for their crops.

Swap that kebab

But such rapid growth exacts a steep environmental price, according to the FAO report, which warns: ?The environmental costs per unit of livestock production must be cut by one half, just to avoid the level of damage worsening beyond its present level.?

In the course of their research, scientists Eshel and Martin from Chicago University collected data from a wide range of sources and they examined the amount of fossil-fuel energy ? and thus the level of production of greenhouse gases ? required for five different diets. The vegetarian diet turned out to be the most energy efficient, followed by poultry, and what they called the ?mean American diet?, which consists of a little bit of everything.

But this may be of interest ? there was a surprising tie for the last place (the worse diet). In terms of energy required for harvesting and processing, fish and red meat ended up in a ?virtual tie?. Of course, that?s just in terms of energy consumed. When you toss in all those other factors, such as bovine flatulence and gas released by manure, red meat comes in dead last. Amazingly fish remains in the fourth place at some distance behind poultry because the fish favoured by people in developed countries requires a lot of energy to catch.

But can changing one?s diet really have much of an impact?

The Chicago scientists believe that dietary changes could make more difference than trading in a standard sedan for a more efficient hybrid car which reduces annual CO2 emissions by roughly one ton a year.

EarthSave International spokesperson Noam Mohr says, ?Arguably the best way to reduce global warming in our lifetimes is to reduce or eliminate our consumption of animal products.? He explains why this shift in our diet would make more sense; ?even if cheap, zero-emission fuel sources were available today, they would take many years to build and slowly replace the massive infrastructure our economy depends upon today. Similarly unlike carbon dioxide which can remain in the air for more than a century, methane cycles out of the atmosphere in just eight years, so that lower methane emissions quickly translate to cooling off the earth.?

At the moment, livestock is using 30 percent of the earth?s entire land surface, mostly permanent pasture but also including 33 percent of the global arable land used to producing feed for livestock, the FAO report says. As forests are cleared to create new pastures, it is a major driver for deforestation, especially in Latin America where, for example, some 70 percent of former forests in the Amazon have been turned over to grazing.

At the same time herds cause wide-scale land degradation, with about 20 percent of pastures considered as degraded through over-grazing, compaction and erosion.

So can changing one?s diet really have much of an impact?

?It doesn?t have to be all the way to the extreme end of vegan,? says Dr Eshel from Chicago University, whose family raised cattle in Israel. ?If you simply cut down from two burgers a week to one, you?ve already made a substantial difference.?

Or swap that kebab for a dholl puri.