Count weeds and insect pests among the beneficiaries of climate change. Meanwhile, the crops we need will have fewer nutrients that make them beneficial, scientists revealed this week.

At the root of the problem: Rising carbon dioxide levels, warming temperatures and more frequent extreme weather events do not treat all plants, insects and soil nutrients equally, according to a new federal climate report and a Harvard University study.

"Weeds are going to be winners under any climate change scenario that we anticipate," said Lewis Ziska, a plant physiologist at the U.S. Department of Agriculture's crop systems and global change program, and co-author of the National Climate Assessment released Tuesday.

Crop-devouring insects, too, are predicted to win. Ultimately, the biggest losers may be us.

April was the first month in human history when carbon dioxide levels averaged greater than 400 parts per million in the atmosphere. It's an arbitrary but ominous milestone, according to experts, who forecast concentrations of the greenhouse gas will surpass 550 parts per million within the next 40 years.

Both food crops and their weedy nemeses thrive on carbon dioxide. It's the core ingredient of photosynthesis, the process by which a plant coverts energy from the sun into sugar to grow. Yet some plants turn the gas into a competitive edge more efficiently than others.

"A lot of our worst weeds benefit the most from high carbon dioxide," said David Wolfe, an expert in climate change and plant physiology at Cornell University in Ithaca, New York.

What's more, many weeds are incredibly adaptive to environmental changes -- warmer temperatures, or extreme events such as droughts or floods -- which may help them further choke out critical crops, experts noted.

Still, Ziska said he sees a "silver lining" in weeds' resiliency. "Many of these adaptive weeds are cousins to crops," he said. "So, we're trying to identify their beneficial characteristics and then transfer them into crops such as wheat, oats, barley or rice."

Insect pests, even more than weeds, thrive in warmer temperatures, which can increase the speed at which the menaces grow and reproduce, and the chances that their progeny will survive to continue feeding on and infecting crops with harmful bacteria, viruses and fungi.

Some of the pests are already expanding into territories -- such as the Northeast -- that were once too cold to host them, Wolfe said.

'KILLING THE PESTS'

Dealing with these weeds and bugs creates a two-fold threat to public health: The increased use of herbicides and insecticides. More chemical dousing means higher costs to farmers -- the U.S. already spends more than $11 billion a year to control weeds -- and greater contamination of soil, food and water.

The National Climate Assessment adds that there may be toxic effects for farmers, farmworkers and consumers exposed to these chemicals.

The report also notes that "the most widely used herbicide in the United States, glyphosate (also known as Roundup and other brand names), loses its efficacy on weeds grown at CO2 levels projected to occur in the coming decades."

Tom Helscher, a spokesman for Monsanto, the manufacturer of Roundup, criticized the statement. "The phrasing 'loses its efficacy' seems to exaggerate what the referenced study described as 'slightly increased' in tolerance to glyphosate," Helscher told The Huffington Post.



Ziska authored a 1999 paper on glyphosate and carbon dioxide that was referenced in this week's climate assessment. He has published a handful of other studies since on the same subject, nearly all reaching the same conclusion: Glyphosate is less effective at higher concentrations of carbon dioxide.

"It takes more chemicals to kill the weeds," Ziska said.

Further, noted Ziska, that escalating need for more chemicals comes on top of already growing use of glyphosate and other herbicides in the U.S.

Much of the increase has been linked to evolving resistance among weeds to the widely used chemicals. Many farmers are then driven to apply greater quantities of glyphosate, or supplement with other -- often more toxic -- herbicides such as 2,4-D.

A DROP IN QUALITY

A study published in the journal Nature on Wednesday warns of yet another public health threat from rising carbon dioxide: Fewer nutrients in important food crops, including wheat, rice and soybeans.

In other words, it's not just quantity, but also quality that is at stake. Researchers simulated conditions expected by mid-century and found significant reductions in zinc, iron and protein.

"The nutritional impacts of these large environmental perturbations is one of the biggest public health challenges we face," said Dr. Samuel Myers, an environmental health expert at the Harvard School of Public Health and lead author on the paper.

Nearly 2 billion of the world's people receive the majority of their zinc and iron from food crops. The minerals are critical for a healthy, functioning body -- everything from the immune system to the brain. A lack of protein is also dangerous, and can lead to stunted growth and losses in muscle mass, including a weakened heart.

"We can now produce more calories than we need to feed every person on the planet, but what we really have a problem with is malnutrition," added Cornell's Wolfe. "A higher carbon dioxide world is going to work against us."

Carbon dioxide may help a plant produce more sugars, starches and other high-energy carbohydrates. A resulting low-level swap of protein for carbohydrates may increase risks of obesity, diabetes, heart disease and other chronic diseases in both the developed and developing worlds, Myers said.

Diana Liverman, a professor of geography and development at the University of Arizona, suggested that the "poorest in society are the most vulnerable." Higher prices for food may preclude the poor from obtaining expensive meat and seafood that could supplement the lower nutrient content found in staple foods.

"We're taking some very complicated risks in a warming climate," said Liverman, noting a host of other climate change impacts on the food system, including high temperatures during the transportation of goods and potential effects on valuable insects such as bees and other pollinators.

Liverman and other experts further emphasized the need for agriculture to adapt to the changing environment, whether that's diversifying the types of crops that fill farmers' fields or employing technological tools.

Robert Fraley, executive vice president and chief technology officer at Monsanto, noted important roles for plant breeding and biotechnology in "the fight against these mounting threats."

"We need both to adapt agriculture to climate change and to mitigate climate change itself," Fraley wrote in a recent HuffPost blog post. "All agricultural practices -- from GMO to organic to conventional -- have roles to play."