Agriculture is the foundation of human civilization. Before domesticated plants and animals ensured a stable and secure food supply, humans lived as hunters and gatherers, moving from place to place in search of food. Life was difficult and tenuous, and evidence suggests that humans almost went extinct around 74,000 years ago because of extreme changes in climate. Settling down in fertile regions allowed towns, cities, and eventually nations to develop. The agriculture that supported this development relied on rich soil, clean water, and a predictable, relatively mild climate.

A geological timeline of the Earth’s temperature shows how remarkably stable the climate has been for the past 10,000 years, during which human civilization has flourished. The Holocene era, which we live in now, began around 12,000 years ago as the Ice Age ended. With the exception of two later periods of cooling—the Late Antique Little Ice Age from 536 to 660 AD and the Little Ice Age from roughly 1300 to 1850 AD, which led to areas of crop failure, famine, and death—humans have experienced a climate conducive to food production.

We can no longer take our stable climate for granted.

Atmospheric carbon dioxide is at a level never previously seen by humanity. Between 1900 and 2000, it surged from 290 to 369 parts per million (ppm)—an increase of approximately 27 percent, largely from burning fossil fuels. In 2013, the level passed 400 ppm for the first time in human history, and it is projected to increase to as high as 1500 ppm if fossil fuel consumption continues at present rates over the next few centuries. There is a time lag of around 30 to 40 years between when carbon dioxide is pumped into the atmosphere and when its effects are felt, because the planet’s massive oceans take longer to warm than the atmosphere. So the climate we are experiencing now is due to greenhouse gas emissions from 30 to 40 years ago. Widespread coral bleaching from ocean acidification is one sign of on-going deleterious change. Coastal flooding is another. We should anticipate climactic conditions getting worse in the future.

In the United States, it’s easy to be complacent about food security. As defined by the World Food Summit in 1996, food security is “when all people, at all times, have physical and economic access to sufficient, safe, and nutritious food that meets their dietary needs and food preferences for an active and healthy life.” Most US-born Americans have never experienced food rationing, shortages, or sky-high food prices. Immigrants from war-torn nations or developing countries often have. According to US Department of Agriculture data, since the end of World War II, the percentage of disposable income Americans spend on food (for consumption both at home and away from home, such as at restaurants, schools, and work) decreased from 21 percent in 1946 to 9.7 percent in 2014. In 2015, US consumers used only around 6.4 percent of their total expenditures to pay for food for consumption at home. Singapore spent the next-lowest fraction at 6.7 percent, and in other developed countries, such as the United Kingdom (8.2 percent), Canada (9.1 percent), Australia (9.8 percent), Germany (10.3 percent), and France (13.2 percent), people spent more. In poor, developing countries, people spend a considerably higher fraction of their money on food for home consumption—35.2 percent in Egypt, for example, and 56.4 percent in Nigeria.

The United States has, in general, enjoyed bountiful food since its founding. Today, its entire consumer economy depends on food security, because inexpensive, safe, accessible food makes it possible for people to spend the rest of their incomes on stuff like cars, cell phones, personal computers, books, and clothing. We take food security for granted.

Local food production, access to global food markets, technology, and climate all impact food security. The United Nation’s Food and Agriculture Organization issued a 2015 Hunger Map highlighting food insecure regions, showing that despite some global progress in reducing hunger, poor countries in sub-Saharan Africa, the Middle East, Asia, and Central and South America remain food insecure. Grid Arendal, an organization affiliated with the UN Environment Programme, has proposed strategies to improve food security: food commodity price regulations, funding to boost small-scale farmer productivity, recycling of post-harvest losses and waste with new technologies, and increasing trade and market access through infrastructure improvements and trade barrier reductions. As longer-term strategies, the organization recommends raising awareness of the pressures of population growth, as well as limiting global climate change.

The question is: Can we sustainably feed ourselves without destroying the natural world as climate change worsens? In September 2015, the United Nations adopted the 2030 Agenda for Sustainable Development, with food security one of its top goals. The UN Secretary-General launched a Zero Hunger Challenge at the 2012 Conference on Sustainable Development with the aim of eliminating malnutrition and ending hunger by making all food systems sustainable, with zero food loss or waste and 100 percent accessibility year-round. These are laudable goals, but it’s not clear whether they are achievable.

In December 2015, the US Department of Agriculture issued a technical report finding that climate change will likely affect local, regional, and global food security, resulting in frequent food production disruptions and increased prices. The global food system will be adversely affected, particularly in tropical regions inhabited by poor populations.

The United States plays a key role in global food security, according to the USDA report. With 16 percent of global agricultural exports, it is the world’s largest food exporter. It has 11 percent of the world’s arable land, and with advanced technologies including genetically modified crops, is able to maximize agricultural yields. It is the world’s largest producer of corn and soybeans and one of the world’s largest producers of wheat and rice. Global food prices are affected by US agricultural production, which is affected by the weather. In 2012, a severe drought affected 80 percent of US farmland resulting in corn and soybean shortages. The shortfall lead to international corn and soybean price increases of 25 and 17 percent, respectively. In the decades ahead, the entire United States is expected to warm considerably.

The adverse impact of rising greenhouse gas emissions on agriculture could even extend beyond decreased yields to include reduced nutrient levels. A study published in Nature in 2014 found that grasses and legumes such as wheat, rice, maize, and soybeans grown in elevated carbon dioxide environments had significantly lower zinc and iron concentrations.

We need political leaders who recognize that human-caused greenhouse-gas-induced climate change poses a threat to food security, and are committed to developing and implementing policies to reduce and mitigate the effects. I’ve written about the need for a new Green Revolution to prepare for a changing climate, one that brings technology to bear on increasing food yields. But much more needs to be done. Lowering global carbon dioxide emissions would also lower the cost of adaptation, which should provide additional incentive to reduce emissions and adhere to the Paris Climate Agreement signed in December 2015.

The Department of Agriculture report determined that about one-sixth of global agricultural production (by mass) is internationally traded, which is good news for places where local or regional food production falls. Building up and strengthening food trade agreements would help support global food security and ultimately international security generally. Technology also has a role to play in supporting global food security, as supply chains that are too long run the risk of jeopardizing safety through contamination and spoilage. Innovative packaging and expanded cold storage can help prolong shelf life and reduce waste.

President Obama’s proposed budget for fiscal year 2017 allocates $138 billion of the total federal budget—about 3 percent—for food and agriculture, focusing on food security. Under the auspices of the Department of Agriculture, the Agricultural Research Service and National Institute for Food and Agriculture conduct in-house and extramural peer-reviewed research, respectively, on issues including crop and livestock production, climate change, and water resources. Their combined proposed budgets for fiscal year 2017 constitute just 1.9 percent of the USDA’s total budget, though. Support for research and development under worsening climactic and environmental conditions will need to increase given the importance of food security.

Beyond traditional agriculture in rural areas, urban populations are becoming increasingly interested in food production, as evidenced by urban, backyard, rooftop, and balcony agriculture. With the global population becoming increasingly urban, this is a good development. In Western countries, community gardens are popular, and there are proposals to develop vertical gardens in skyscrapers. In Africa, urban agriculture might help contribute to local food security.

Food security is too important an issue to wait until climate change worsens before doing something about it. We need to figure out how to sustainably feed ourselves as our environment degrades. Those who deny the reality of climate change and refuse to do anything about it threaten the future of human civilization.