Colorado and Oregon will vote on GMO labeling Tuesday. Here's what's at stake.

(Update: Both Oregon and Colorado voted against GMO-labeling initiatives on November 4. Below is original rundown of the issue and the arguments for and against.)

It's time to debate GMO labeling — again. On Tuesday, residents in Colorado and Oregon will vote on whether packaged foods that contain genetically modified ingredients should be labeled as such in stores.

GMO Labeling bills have been introduced in 28 states

Here's the text of Oregon's Proposition 92, which would require packaged foods with GM ingredients to include the words "genetically engineered" on the front or back of the product "clearly and conspicuously." Here's the text of Colorado's Proposition 105, which is similar. Both have exemptions for animals fed with GMO crops and for food served in restaurants.

Those in favor of labeling, including organic food companies and food activists, argue that consumers have a right to know what's in their food. Even though there's no good evidence that GMOs are unsafe for human health, they've become a contentious topic for a variety of reasons. (The vast majority of corn, soy, and sugar beets in the US are genetically modified, which means that roughly 60 to 70 percent of processed foods at the grocery store include some GM ingredients.)

Those opposed to labeling, including food and biotechnology companies, say the laws could lead to higher prices at the grocery store or frivolous lawsuits. A number of scientists, meanwhile, argue that genetic engineering could be a useful tool for addressing global hunger or climate change — and these labels put an unwarranted stigma on the technique. The "no" campaigns have raised millions of dollars, from large companies like Monsanto, Dupont Pioneer, Pepsi, Coca-Cola, and Kellogg.

This is just the latest in what's becoming a contentious fight at the state level. Earlier this year, Vermont enacted the nation's first GMO-labeling law, set to take effect in 2016. California and Washington have both previously rejected labeling initiatives by narrow votes. And labeling bills have been introduced in 28 state legislatures.

At the moment, polls suggest that Oregon's initiative might pass but Colorado's will fail. Here's a primer on the broader debate:

What is genetically modify food?

(BSIP/Universal Images Group/Getty Images)

Farmers have been selectively breeding crops for tens of thousands of years in order to produce desirable genetic traits. But that's not what people usually mean by "genetically modified food."

Genetic engineering isn't any one thing — it's a technique that can be used for all sorts of purposes

Since the 1990s, scientists have been able to manipulate the genomes of crops and animals directly. That might involve things like taking a few well-characterized genes from one species (say, bacteria) and transplanting them into a crop (say, corn) to produce certain desired traits. This is different from traditional plant breeding, and it's what is causing all the controversy.

Scientists might genetically modify crops for a number of reasons. Some crops are genetically modified to be resistant to herbicides — such as Monsanto's Roundup Ready soybeans — so that it's easier for farmers to spray fields with weed-killer. By contrast, Bt corn is modified with a bacterial gene in order to secrete a poison that kills pests like rootworm. That can reduce the need for chemical pesticides.

There are other potential uses, too: golden rice has been artificially fortified with beta carotene, to help alleviate vitamin deficiencies in countries like the Philippines. (So far, however, golden rice is still in the testing phase and has met opposition from protesters.) And many researchers are looking for ways to engineer crops that are resistant to drought.

Genetic engineering isn't any one thing — it can be used for a variety of purposes. In practice, large biotech companies like Monsanto tend to focus much of their research efforts on traits like herbicide resistance and pest tolerance for major cash crops like corn, soy, cotton, and canola. At the same time, academic researchers, such as UC Davis's Pamela Ronald, are interested in harnessing genetic techniques to boost sustainable agriculture or address world hunger.

How prevalent are GM foods?

(US Department of Agriculture)

More than 93 percent of corn, soy, and cotton planted in the United States is genetically modified in some way. Most of that ends up as animal feed or ethanol or corn syrup, which in turn gets into lots of foods.

60 to 70% of processed foods in grocery stores contain GMO ingredients

Meanwhile, more than 95 percent of sugar beets in the United States are genetically modified to be herbicide tolerant — and those beets are responsible for roughly half of all sugar production.

Add it all up, and an estimated 60 to 70 percent of processed foods in grocery stores contain at least some genetically modified ingredients.

If you want to avoid GMOs at the grocery store, you can always buy organic food. Alternatively, some food companies have begun voluntarily putting "non-GMO" labels on foods since 2008.

Are GM foods safe to eat?

Genetically modified corn plants grow as part of a comparative tests of genetically modified plants and plants with are not altered in a laboratory in the Institute of Biology at the Humboldt University of Berlin on September 04, 2013 in Berlin, Germany. (Michael Gottschalk/Photothek via Getty Images)

So far, there's been no good scientific evidence that they're harmful. At this point, billions of people around the world have been eating GM foods for decades without any noticeable ill effects. And numerous scientific studies have concluded that the GM crops currently on the market pose no more of a health risk than conventional crops.

'the science is quite clear: crop improvement by the modern molecular techniques of biotechnology is safe'

Here's what the American Association for the Advancement of Science (AAAS) said in 2012: "The science is quite clear: crop improvement by the modern molecular techniques of biotechnology is safe." The European Commission agreed, after sifting through 25 years of research.

A minority of scientists still insist, however, that more research is needed before GM foods can be definitively considered safe. After all, genetic engineering isn't exactly like traditional breeding and it may have downstream effects scientists haven't fully studied. For example, in a dissent to that AAAS statement, 21 researchers argued that increased herbicide use — which can occur with crops engineered to be resistant to Roundup — might have health effects we don't yet know about.

Are GM crops good or bad for the environment?

Science

There's no easy answer to this, since it can depend on the crops and how they're used. In some cases, GM crops can help farmers use fewer chemical insecticides. In others, their use can lead to an increase in pest resistance and pesticide use.

Here's what the National Research Council concluded in 2010: "Generally, GE crops have had fewer adverse effects on the environment than non-GE crops produced conventionally." But, the report cautioned, "excessive reliance on a single technology combined with a lack of diverse farming practices could undermine the economic and environmental gains from these GE crops." Some examples:

Fewer insecticides: In some select cases, GM crops can benefit the environment. Cotton that's engineered to be pest-resistant can allow farmers to use fewer chemical pesticides. Similarly, insecticide use in U.S. corn fields has fallen significantly since 1996 as genetically modified Bt corn has become more prevalent.

More herbicides — with a caveat: But that's not always the case. The story is murkier for chemical herbicides used on weeds. Due to the prevalence of Roundup-Ready crops that make it easier for farmers to spray fields with Roundup, overall herbicide use has increased in the United States. That said, many farmers are also now using a milder herbicide — glyphosate — than they used to.

Pest resistance and the risk of overuse: The National Research Council also warned against improper use of GM technology: Farmers who plant herbicide-resistant GM crops often use a limited range of herbicides on their fields, which can give rise to herbicide-resistant "superweeds." Similarly, there's evidence that over-planting of Bt corn has fostered a new breed of resistant insects in some fields.

Other risks: There are other environmental concerns, too. The decline of the monarch butterfly in North America has been linked to the increased use of herbicide spraying on herbicide-tolerant crops. There's also the risk that genetically engineered traits still in the testing phase could escape into nature — as apparently occurred in May 2013, when a never-approved strain of GM wheat made its way to an Oregon field.

That said, there are plenty of environmental risks with conventional crops, too — those "superweeds," for instance, can appear on non-GM crop sites. In the end, the National Research Council wasn't convinced that genetically modified crops were inherently riskier — so long as they were used properly.

So what would Oregon and Colorado's laws do?

A Safeway customer browses in the fruit and vegetable section at Safeway's new 'Lifestyle' store July 18, 2007 in Livermore, California. (Justin Sullivan/Getty Images)

Both Colorado's and Oregon's initiatives would require any food sold for retail that contains genetically-engineered ingredients to be labeled "clearly and conspicuously." In Oregon, those labels could appear on the front or back.

There are exceptions: Restaurants would be exempt, as would alcoholic beverages, as would any animals that have been feed GM crops but are not genetically modified themselves.

Both bills set out detailed definition of "genetically modified," but note that there may be some gray areas here. Many biotech companies have been experimenting with new techniques, such as engineering specific proteins, that do not meet the traditional definition of "genetically modified." It's unclear how those might be affected by either law.

What have past GM-labeling laws accomplished?

Currently, some 64 countries require labeling of GM foods, including Japan, Malaysia, New Zealand, and Australia:

(Center for Food Safety)

Some studies of labeling laws in Netherlands and China found they did not substantially affect consumer behavior. That said, after the EU required labeling in 1997, many retailers in Europe removed foods containing genetically modified ingredients from their shelves.

Will GM labels increase the cost of food?

Labels could possibly increase the cost of non-GM food, though it's hard to say how much. Everyone in the food chain — from the farmer to the grain processor to the retailer — would, in theory, have to keep detailed tabs on non-GM food to be able to verify that it doesn't contain any GMO ingredients.

But when economists have done estimates on these costs, they vary pretty widely. Some studies suggest that GMO labeling would cost just a few dollars per person per year. Others suggest it could cost as much as 10 percent of the food bill. A lot depends on how much consumers care about the label and how far food companies have to go to prove that they're selling non-GM food.

See this essay in Slate by James McWilliams for a good breakdown of why it's so hard to get a good precise estimate. And this essay by Demos' Michael Lipsky argues that the price increase would be very minimal.

What's the argument against GM labeling laws?

(BSIP/Universal Images Group/Getty Images)

Critics of labeling laws often argued that they stigmatize genetically modified foods in a way that's out of proportion to the risks involved. What's more, the fact that a plant was "genetically engineered" doesn't tell you anything meaningful about the food. So why go out of the way to highlight it?

Some scientists have raised related concerns: Back when California was considering a labeling law (which eventually failed), David Zilberman of the University of California Berkeley worried that labeling laws might "create a stigma effect" that will hinder future research into using GM foods to improve nutrition or help ameliorate the effects of climate change.

There are also fears that labeling laws could lead to a flurry of frivolous lawsuits. Note that California's Prop. 65, which required companies to post warnings about chemicals, led to a slew of costly lawsuits and eventually had to be revised.

What's the best argument for GM labeling laws?

Labels on bags of snack foods indicate they are non-GMO food products, in Los Angeles, California, October 19, 2012. (Robyn Beck/AFP/Getty Images)

It's true there are lots of scientifically unsupported claims about the harms of GM foods. But there are other, more nuanced arguments in favor of labeling, too.

Some critics of GMOs have argued in the past that labeling laws could force transparency on an industry that tends to be dominated by just a few large corporations like Monsanto and Dupont.

Others think labeling could help defuse a polarizing debate. Back in 2013, Nathanael Johnson spent months reporting on the science of genetically modified foods, talking to critics and scientists alike. His conclusion was that "the actual hazard associated with the GM foods is somewhere between negligible and non-existent." But, he pointed out, there's still widespread unease among the public. Labeling might resolve that:

In a famous paper on risk perception, published in Science in 1987, Paul Slovic pointed out that people judge voluntary, controllable actions as much less risky than those that are involuntary and out of their control. Similarly, people see the unknown as much more risky than the known. Genetically engineered foods are, for most people, both unknown and uncontrollable.

There's a simple, almost magical, solution to both these problems: labeling. Labeling makes the unknown known; it puts people in control of what is currently uncontrollable. It removes dread fear from the debate. ... If the rhetoric and emotions surrounding this issue cooled off we could begin a reasoned and overdue discussion about what tools we want to use to meet the agricultural challenges of the future.

In any case, it's unlikely that GMO labeling is going away. If more and more states end up passing their own bills, Congress could eventually be forced to take up the issue — particularly if food companies find that they have to deal with a state-by-state patchwork of conflicting laws.

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