Vegan diet advocates believe that if majority of people in the US became vegan, it will be good for the environment.But a new study found that the truth is more complicated than imagined.According to the US Environmental Protection Agency, about 25 percent of the total greenhouse gas emissions in the country come from agriculture and forestry.And almost half of those agricultural emissions are produced by animals, states a report from Science Magazine.

If Americans shift to the vegan diet, it would cut the greenhouse gases from agriculture by 28 percent, a new study found.However, the radical change of diet will hurt the people's nutrition, according to Robin White of the Virginia Polytechnic Institute and Mary Beth Hall of the US Department of Agriculture.

In the study, a remodeled system that does not involve consuming meat products will increase the total food production by 23 percent while reducing GHGs from agriculture by 28 percent.But it will only reduce the country's overall GHG by 2.6 percentage units.This is because many agricultural byproducts, such as corn stalks and potato waste, will be consumed by livestock.And any leftovers will be burned to remove it that leads to 2 million tons of carbon dioxide a year -- an ineffective way to reduce GHGs.

If livestock is not involved, the lack of livestock-produced manure will require the use of artificial fertilizer to grow crops.Manufacturing artificial fertilizer adds 23 million tons of carbon gas emissions every year.So removing animals out of the agricultural picture does not solve the intense amount of GHGs associated with climate change.

Moreover, removing animal-based diet will affect people because some important nutrients are derived easily from meat.

- Meat products provide at least 24 percent total of energy consumption.

- Meat products provide at least 48 percent total of protein consumption.

- Meat products provide essential fatty acids from 23 to 100 percent in total.

- Meat products provide essential amino acids from 34 to 67 percent in total.

- Other nutrients, such as calcium, vitamin A, vitamin B12, and key fatty acids won't be provided by a plant-only system.

"With carefully balanced rations, you can meet all of your nutrient requirements with a vegetarian diet.But the types of foods that seem to do that, we don't currently produce in sufficient quantities to make it a sustainable diet for the entire population," said White.

Greenhouse Gas Emissions

Most greenhouse gas emissions are the by-products of human activities such as the burning of fossil fuels and are currently linked to global warming caused by climate change.Carbon dioxide, methane, nitrous oxide, and F-gases are the key greenhouse gases that make up global gas emissions, based on 2010 data by EPA.

1.Carbon dioxide makes up 76 percent of the global GHGs, about 65 percent of it from fossil fuel and industry processes, and 11 percent from agriculture and land use.The gas is emitted from human activities, such as manufacturing, deforestation, and degradation of soils.

2.Methane makes up 16 percent of the global GHGs.Agricultural activities, waste management, and energy use are some human activities that emit methane gas.

3.Nitrous oxide makes up 6 percent of the global GHGs.Human activities like fertilizer use and burning of fossil fuel emit nitrous oxide.

4.Fluorinated gases make up 2 percent of the global GHGs.Industrial process and use of many consumer products, such as refrigerators, contribute to a number of F-gases in the atmosphere.

Global GHGs can also be broken down by economic activities.Electricity and heat production amounts to 25 percent of global GHGs, while agriculture and forestry activities contribute about 24 percent.Industrial activities contribute 21 percent, transportation contributes 14 percent, and other energy sources contribute about 10 percent to the global GHGs.From 1970 to 2010, the total carbon dioxide emissions increased by 90 percent.In 2014, China, the United States, the European Union, India, and Russia were the top five contributors to the global greenhouse gas emissions.

Health Effects of Greenhouse Gases

The heavy concentration of greenhouse gases can affect human health.Air pollution degrades the quality of air that leads to respiratory diseases, especially among people with asthma or chronic lung disorders.With climate change, cases of climate-sensitive diseases such as allergies, and food and waterborne diseases are expected to rise.Many populations who already have poor health or who are living in unfavorable environments are more likely to feel the impact of climate change.

Additional Information

- The estimated global emissions from human activities totalled to almost 46 billion metric tons of GHGs in 2012.

- Emissions of carbon dioxide are increasing faster in certain parts of the world.The majority of GHG contributors are from the continents Asia, Europe, and the United States, accounting for 88 percent of total GHGs in 2012, according to EPA.