Alexandra Clark is a sustainable-food campaigner at Humane Society International. She recently presented HSI's meat reduction work at the COP21 in Paris. Prior to joining HSI, Clark worked for the vice president of the European Parliament and was responsible for a number of high-profile parliamentary initiatives on sustainable food systems. She contributed this article to Live Science's Expert Voices: Op-Ed & Insights.

Global leaders in Paris accomplished much with the climate change agreement they reached late last year, but it had its shortcomings — including a failure to specifically mitigate the emissions of climate-changing gases from animal agriculture.

However, outside of the Paris talks, policymakers in the European Union (EU) are beginning to advance that discussion, pushing for a shift away from diets heavy in meat, egg and dairy products, in an effort to clear the air.

Meat, math and emissions

There is extensive research showing the outsize impacts of animal agriculture on the environment. The Food and Agriculture Organization of the United Nations (FAO) has concluded that "the livestock sector emerges as one of the top two or three most significant contributors to the most serious environmental problems, at every scale from local to global."

It's not hard to see why. The process of converting energy and protein in animal feed into meat calories and protein for humans is highly inefficient:

Land. Animal agriculture already constitutes the largest human use of land worldwide. More than 60 percent of corn and barley, and more than 97 percent of soymeal, becomes farm animal feed, according to the FAO report Livestock's Long Shadow. Animal feed. According to a study in Ambio, in research led by environmental scientist Vaclav Smil, it takes 9.3 pounds (4.2 kilograms) of feed to produce 2 lbs (1 kg) of edible chicken, 23.6 lbs (10.7 kg) of feed to produce 2 lbs (1 kg) of pork and 69.9 lbs (31.7 kg) of feed to produce 2 lbs (1 kg) of beef. Water. The farm-animal sector is also a major consumer of scarce water resources. Animal products generally have larger water footprints than non-animal products, according to a study published in 2012 in the journal Ecosystems by Mesfin Mekonnen and Arjen Hoekstra, professors at the University of Twente.Greenhouse gas emissions. Animal agriculture is responsible for approximately 14.5 percent of human-induced greenhouse gas emissions, according to the FAO. Studies from the United States, India, the U.K. and Italy, among others, have shown plant-based agriculture has a lower carbon footprint. For example, a 2014 study led by Henk Westhoek for the PBL Netherlands Environmental Assessment Agency, and appearing in Global Environmental Change, found a 50 percent reduction in all EU consumption of meat, dairy and eggs would cut agricultural greenhouse gas emissions by 19 to 42 percent.

Similar research that year in the journal Climatic Change found that, in the U.K., vegetarian and vegan diets had 32 percent and 49 percent lower greenhouse gas emissions , respectively, than medium-meat diets. Compared to high-meat diets, the difference was even starker, with vegan diets emitting 60 percent less greenhouse gasses.

Yet, reductions aren't the projected future we face. One 2010 study by Nathan Pelletier and Peter Tyedmers at Dalhousie University, published in the Proceedings of the National Academy of Sciences, projected a 39 percent rise in emissions from animal agriculture by 2050 over year-2000 levels, accounting for more than two-thirds of the amount of greenhouse gases considered safe by 2050.

Given the threats that climate change and other environmental impacts from farm animal production pose to long-term food security, there is a need for a global shift away from meat-heavy diets.

Less meat for the wealthy, food security for the poor

Eggs, meat and milk can continue to serve as sources of nutrition — particularly in rural areas of developing countries, which sometimes exhibit higher rates of undernutrition.

Farm animals can provide a variety of supports to pastoralists, mixed farmers and landless peoples in rural areas. In rural communities around the world, people use farm animals as a means of acquiring cash income, a way to save and accumulate assets, as a food source, and as insurance against health or other financial crises. Integrated into a broader rural landscape of small farms, animals provide inputs and services for crop production.

However, most farm animal production (and growth in production) is taking place in polluting and inhumane industrial farm animal production systems. These industrial systems are feeding middle- and higher-income consumers who could benefit from more plant-based diets.

According to the World Health Organization (WHO), approximately 40 percent of adults across the globe are overweight, and noncommunicable diseases linked to the overconsumption of fats and energy-dense foods (such as meat, eggs and milk) are now a leading cause of illness and death worldwide. The WHO has called for an increase in the consumption of plant-based foods — specifically fruits, vegetables, legumes, whole grains and nuts — as part of the solution.

Developed countries like the United States still have the highest per-capita meat consumption. However, according to the FAO, developing and emerging economies already account for the majority of meat production overall, and are projected to account for the majority of growth in animal consumption in the coming years.

Developing countries where farm animal production is expanding may no longer require an overall increase in the consumption of animal source foods among all segments of their populations, as a significant proportion of their populations are already meeting or exceeding their energy requirements.

Ironically, many developing countries with high levels of hunger and malnutrition now simultaneously bear the burden of an obesity-related public health crisis, with the number of overweight women already exceeding the number of underweight women in most developing countriesby 2005, according to research published in the American Journal of Clinical Nutrition.

To allow for a more equitable distribution of agricultural resources and to ensure long-term food security and health for all communities around the world, society should place greater emphasis on small-scale, multipurpose, more animal-welfare-friendly and environmentally sustainable farm animal production led by small farmers. Middle- and higher-income populations should also reduce their consumption of animal products.

A global solution

A side event held within the U.N. climate conference — entitled "Meat: The Big Omission from the Talks on Emissions," hosted by leading international organizations such as the Royal Institute of International Affairs (Chatham House) and Humane Society International — brought together policymakers, scientists and civil society groups, and emphasized the need to reduce the number of animals raised for food. The event highlighted successful efforts around the world to achieve this goal by encouraging people to consume more plants and less meat.

Jo Leinen, a German member of the European Parliament, spoke at the event, emphasizing nations' inability to mitigate climate change without shifting away from meat-centric diets. His comments came on the heels of a recently published report by Chatham House, "Changing Climate, Changing Diets: Pathways to Lower Meat Consumption," which specifically addresses potential government interventions to encourage meat and dairy reduction, ranging from public-awareness-raising campaigns to a carbon tax.

Even Arnold Schwarzenegger agreed with the event premise — the former California governor, actor and bodybuilder made waves during the climate conference by calling on people to keep meat off their plates one or two days a week to address climate change, according to the BBC. And, a growing number of food service providers, educational institutions, environmental groups and other stakeholders are embracing meat-reduction initiatives such as Meatless Monday.

In October, HSI launched Green Monday South Africa and a Meatless Monday campaign in Mexico with events attended by media, celebrities and other stakeholders. There are also thriving humane eating campaigns in India, China and other emerging economies where meat consumption is rapidly rising, along with problems relating obesity and chronic disease.

The growing middle- and upper-class consumers in these countries are becoming increasingly sensitive to animal welfare, health and environmental issues, as exhibited by the increasing number of food companies in these regions adopting animal welfare policies, and the growth in the market for organic and other sustainable products.

The emerging response

HSI advocates what it calls compassionate eating, or the three R's: "reducing" or "replacing" consumption of animal products, and "refining" diets by choosing products from sources that adhere to higher animal welfare standards. In the EU, those goals are gaining popularity, and there is growing public support for meeting the target of a 30 percent reduction in animal product consumption by 2030 through a variety of policy mechanisms.

HSI launched this formal call in September 2015 at The Free Lunch, one of the largest food events ever held outside the European Parliament, where approximately 1,000 people, including politicians, attended in support of reducing the consumption of animal-based foods in the EU. The event featured cross-party members of the European Parliament, including the Parliament's vice president, civil society representatives and a representative of the EU Health and Food Safety Commission.

Pathways to the 30 percent goal include incorporating sustainable food consumption into the EU and its member states' climate action plan; revising the European Commission's Green Public Procurement guidelines; and developing guidelines for healthy and sustainable diets.

If you're a topical expert — researcher, business leader, author or innovator — and would like to contribute an op-ed piece, email us here. In early 2015, more than 60 cross-party members of the European Parliament wrote to European Commission President Jean-Claude Juncker and others to demand the publication of the blocked Communication on Building a Sustainable System, as well as EU sustainable dietary guidelines including a reduction in consumption of animal-based foods. The communication has been held up by a "principle of political discontinuity," practically ensuring that this important document never sees the light of day.

Follow the science

Yet science demands more work to move this issue forward. With its overall goal and its recognition of the importance of people's consumption choices, the Paris Agreement provides a signal at the global level.

The preamble of the document states that "sustainable lifestyles and sustainable patterns of consumption and production, with developed country Parties taking the lead, play an important role in addressing climate change." The parties should elaborate this at the national and subnational level.

Research increasingly shows the benefits of moving toward more plant-based diets — to improve the welfare of farm animals, promote environmental sustainability and protect human health. It is time to really get to the meat of the matter and stop avoiding the elephant — or chicken or pig — in the room.

Follow all of the Expert Voices issues and debates — and become part of the discussion — on Facebook, Twitter and Google+. The views expressed are those of the author and do not necessarily reflect the views of the publisher. This version of the article was originally published on Live Science.