By most accounts, climate change is the single greatest existential threat, not only to human life but also to all life on Earth. We are already seeing the impact in the form of rising sea levels, catastrophic wildfires and water shortages. Animals and our policies toward them are at the very heart of both the causes of climate change and its devastating effects. Our massive factory farming of animals to feed our enormous appetite for meat is a major cause of climate change. And many species of animals living in the wild will suffer and die out in the near future as a direct result of the effects of global warming.

Animal Use as a Cause of Climate Change

Global appetite for meat is growing with rising populations and increasing affluence. Factory farming is the dominant method of food animal production used to meet that need. Factory farming involves not only crowded, polluted feedlots where animals are kept before slaughter but the process also consumes massive amounts of fossil fuels. Producing billions of animals for us to eat necessitates massive production of corn and soybeans for feed resulting in increased emissions from fertilizing (monoculture depletes the soil and nutrients must be replaced), harvesting, transporting and processing of all of these.

In 2006, the United Nations Food and Agriculture Organization published a study, "Livestock's Long Shadow," which highlighted and quantified the effect of animal agriculture on climate change. The report concluded that livestock produced a staggering 18% of the world's greenhouse gas emissions, more than all modes of transportation combined. The FAO study attempted to consider every factor associated with producing meat, including emissions from fertilizer production, converting land from forests to pastures, growing feed, and direct emissions from animals (belching and manure) from birth to death. Some have called the details of the analysis into question but the fact remains that our increasing population coupled with our enormous appetite for meat contributes mightily to global warming.

Demand for meat is rising in developing and emerging economies, raising the specter of continued acceleration of the global warming process. Given the projected population growth in the developing world, absent a change in diet, the continued farming of animals will increase the pace of global warming.

Animal Victims of Climate Change

Our planet is now in the midst of its sixth mass extinction of plants and animals—the sixth wave of extinctions in the past half-billion years. Species extinction is a natural phenomenon but, historically, it occurs at a natural "background" rate of about one to five species per year. Scientists estimate the current rate of extinction at up to 1,000 times the background rate, with dozens of species going extinct every day. The effects of climate change that will profoundly affect animal species include the most visible, polar bears starving and drowning, and coral reefs suffering massive die-off as the waters become too warm, to less highly publicized effects on coastal wildlife who will fall victim to rising sea levels. Scientists predict that if we keep going along our current greenhouse gas emissions trajectory, climate change will cause more than a third of the Earth's animal and plant species to face extinction by 2050—and up to 70% by the end of the century.

When envisioning the effects of global warming on wild animals, most people immediately think of polar bears and melting ice caps but the range of animals impacted by climate change is almost unlimited as are the ways in which climate will impact their lives and survival. At the other end of the Earth, around the South Pole, the Emperor penguin is also facing enormous threats from global warming, which causes profound changes in the Antarctic ecosystem and hurts penguins in diverse ways, from reducing prey species to causing ice shelves to collapse.

Away from the poles, the effects of climate change are just as real. Rising temperatures will create danger to mammals from proliferation of parasites. Milder winters mean higher numbers of winter ticks. Thousands of ticks can attach to a single moose, weakening his immune system and putting his life in danger. Parasites will also flourish in warmer water and are already beginning to attack salmon in Alaska's Yukon River.

Animals that have evolved to blend into their environment to avoid predators will also be profoundly affected by the changing landscape. To help hide from predators, Snowshoe hares have evolved to turn white in winter to blend in with the snow. With climate change, snow in some areas is melting earlier than usual, leaving stark white hares exposed in snow-less landscapes. Although this might be seen as a benefit to predator species, Snowshoe hares are critical players in forest ecosystems and their disappearance will affect that delicate balance.

As temperatures rise worldwide, many species, like the American pika (an animal about the size and shape of a hamster that lives at high elevations where cool, moist conditions prevail) are forced to flee the warming by moving up in elevation or by moving northward or southward, away from warmer equatorial areas. Species who depend on either snow or forest are watching their habitat disappear. Amphibians and fish are threatened by the drought that accompanies climate change, while reptiles like the loggerhead sea turtle have already had their nesting habits impacted by warmer ocean temperatures. Even insects are affected. Butterflies, for example, are threatened as global warming reduces food availability for larvae.

Much of the human-generated carbon dioxide eventually ends up in our oceans, causing ocean acidification and depleting seawater of the compounds that organisms like corals, crabs and zooplankton require to build the protective shells and skeletons they need to survive. Because plankton form the bedrock of the delicate ocean food chain, ocean acidification could disrupt the entire marine ecosystem. Warmer water temperatures have also been shown to slow the growth of phytoplankton—the microscopic plant counterpart to zooplankton—imperiling all species in the ocean food chain.

Species diversity ensures the resilience of all types of ecosystems, allowing ecological communities to withstand stress. Because the rate of change in our biosphere is increasing, and because every species' extinction potentially leads to the extinction of others that interact with that species in an interconnected ecological web, numbers of extinctions are likely to balloon as ecosystems unravel.

International Agreements and the National Environmental Policy Act

In 2017, the United States withdrew its participation in the 2015 Paris Agreement on Climate Change Mitigation, which requires signatory countries to determine, plan and regularly report on the contribution that they undertake to mitigate global warming. Domestically, the National Environmental Policy Act (NEPA) provides the only real opportunity for citizens to comment and be heard on proposed actions that may harm the environment and contribute to climate change. In the words of the Department of Energy, "NEPA is our basic national charter for protection of the environment." When a federal agency is considering a new project or action, such as approving a pipeline or logging on federal lands, NEPA requires a review of the environmental impact (the preparation of an environmental impact statement (EIS). These reviews were designed to ensure that animals and ecosystems are taken into account and protected to the extent possible in the planning of large-scale projects. In 2016, the Obama administration issued detailed guidance instructing all federal agencies to consider climate change and greenhouse gas emissions in their NEPA reviews. In 2017, the Trump administration withdrew the Obama climate change guidance without providing the opportunity for public comment. In 2018, the current administration proposed weakening protections for air, water and wildlife across-the-board by limiting the situations that would require federal agencies to complete a thorough environmental impact statement. Then, this past June, the administration issued its own proposed guidance restricting when and how federal agencies may consider climate change impacts when they review projects under NEPA. The June guidance arguably encourages federal agencies to do only a cursory review of the impact of a project on greenhouse gas emissions.

In sum, we currently have no international or domestic plan to counter the effects of climate change on animals and the habitats we share with them. How much time we have left to stop these effects can be debated. What is clear is that inaction will inevitably come at a high cost to animals and entire ecosystems.

Penny Conly Ellison is an adjunct professor at the University of Pennsylvania Law School, teaching animal law and ethics, and a member of the board of directors of the Pennsylvania SPCA.