Nearly 50 years ago President Richard Nixon signed the National Environmental Policy Act declaring environmental sustainability as national policy. This policy’s goals were “to create and maintain conditions under which humans and nature can exist in productive harmony, and fulfill the social, economic and other requirements of present and future generations.” This month President Donald Trump pulled the U.S. out of the international Paris climate accord, potentially reversing decades of progress. This could affect Hawaii more than many other states due to projected increased temperatures and rising sea levels.

The concept of sustainability extends far beyond economic concerns or meeting energy needs for our cars and homes. At the most basic level, sustainability means an adequate supply of essential nutrients and calories to promote human health and vitality without squandering future resources.

There are many reasons why the U.S. should have stayed with the 2015 Paris climate accord. In addition to the obvious issues of increasing temperatures and unpredictable weather, projected climate change will clearly affect the United States’ and world’s ability to produce both adequate food and adequate essential nutrients to maintain health.

QUESTION: What effects do projected climate changes have on food production?

ANSWER: For many decades it has been known that cycles of drought can cause population hunger and starvation. From satellite data it has been shown that in some areas an increase of only 1 degree Celsius in average temperature can cause a decrease in crop yield, substantially decrease potential crop area and reduce the ability to grow two crops on the same land within a single growing season. Clearly, this decreases food production while the world’s population continues to increase. The obvious result: increased global food insecurity.

Q: How does climate change affect the nutrient content of staple crops?

A: The known effects of increasing greenhouse gases on the nutrient content of staple crops is reason for major concern. In 2015 carbon dioxide (CO2), primarily produced through burning fossil fuels (coal, natural gas, oil and gasoline), solid waste and wood products, contributed 82 percent of the accumulating greenhouse gases.

In addition to raising global temperatures, elevated atmospheric CO2 now has been shown to decrease essential nutrients in our staple crops (wheat, rice, field peas, soybeans, corn and sorghum). In a three-country study (Australia, Japan and the U.S.) at seven locations, it was shown that three essential nutrients — iron, zinc and nitrogen (the critical component of protein) — are all lower when these crops are grown in a higher-CO2 environment.

Q: How do these nutrient changes affect people and their children?

A: Iron and zinc deficiencies seriously harm normal growth and brain development in children and impair multiple physical and mental functions in adults. An estimated 2 billion people currently are deficient in iron and zinc. Increased CO2 makes meeting these essential nutrient needs even more difficult, especially with plant-based diets.

Many governors, including Gov. David Ige, have vowed to continue adhering to the Paris climate accord criteria in spite of Trump’s position.

Alan Titchenal, Ph.D., C.N.S., and Joannie Dobbs, Ph.D., C.N.S., are nutritionists in the Department of Human Nutrition, Food and Animal Sciences, College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa. Dobbs also works with University Health Services.