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How do people respond to scientific information about GMOs and climate change?

The journal Food Policy just published a paper by Brandon McFadden and me that explores how consumers respond to scientific information about genetically engineered foods and about climate change.  The paper was motivated by some previous work we'd done where we found that people didn't always respond as anticipated to television advertisements encouraging them to vote for or against mandatory labels on GMOs.  

In this study, respondents were shown a collection of statements from authoritative scientific bodies (like the National Academies of Science and United Nations) about the safety of eating approved GMOs or the risk of climate change.  Then we asked respondents whether they were more or less likely to believe GMOs were safe to eat or whether the earth was warming more than it would have otherwise due to human activities.    

We classified people as "conservative" (if they stuck with their prior beliefs regardless of the information), "convergent" (if they changed their beliefs in a way consistent with the scientific information), or "divergent" (if they changed their beliefs in a way inconsistent with the scientific information). 

We then explored the factors that explained how people responded to the information.  As it turns out, one of the most important factors determining how you respond to information is your prior belief.  If your priors were that GMOs were safe to eat and that global warming was occurring, you were more likely to find the information credible and respond in a "rational" (or Bayesian updating) way.  

Here are a couple graphs from the paper illustrating that result (where believers already tended to believe the information contained in the scientific statements and deniers did not).  As the results below show, the "deniers" were more likely to be "divergent" - that is, the provision scientific information caused them to be more likely to believe the opposite of the message conveyed in the scientific information.  

We also explored a host of other psychological factors that influenced how people responded to scientific information.  Here's the abstract:

“The ability of scientific knowledge to contribute to public debate about societal risks depends on how the public assimilates information resulting from the scientific community. Bayesian decision theory assumes that people update a belief by allocating weights to a prior belief and new information to form a posterior belief. The purpose of this study was to determine the effects of prior beliefs on assimilation of scientific information and test several hypotheses about the manner in which people process scientific information on genetically modified food and global warming. Results indicated that assimilation of information is dependent on prior beliefs and that the failure to converge a posterior belief to information is a result of several factors including: misinterpreting information, illusionary correlations, selectively scrutinizing information, information-processing problems, knowledge, political affiliation, and cognitive function.”

An excerpt from the conclusions:

“Participants who misinterpreted the information provided did not converge posterior beliefs to the information. Rabin and Schrag (1999) asserted that people suffering from confirmation bias misinterpret evidence to conform to a prior belief. The results here confirmed that people who misinterpreted information did indeed exhibit confirmation, as well as people who conserved a prior belief. This is more evidence that assuming optimal Bayesian updating may only be appropriate when new information is somewhat aligned with a prior belief.”

Wheat Yields and Temperature Change

I'm quite sure I've never seen an article in the Proceedings of the National Academies of Science written by a former teacher, a former student, and  a friend at a former employer.  Well, that changed yesterday.   Three top notch agricultural economists, Jesse Tack, Andy Barkley, and Lanier Nalley, just released a paper published in PNAS about the effect of hot and cold temperatures on wheat yields.   

The abstract:

“Climate change is expected to increase future temperatures, potentially resulting in reduced crop production in many key production regions. Research quantifying the complex relationship between weather variables and wheat yields is rapidly growing, and recent advances have used a variety of model specifications that differ in how temperature data are included in the statistical yield equation. A unique data set that combines Kansas wheat variety field trial outcomes for 1985–2013 with location-specific weather data is used to analyze the effect of weather on wheat yield using regression analysis. Our results indicate that the effect of temperature exposure varies across the September−May growing season. The largest drivers of yield loss are freezing temperatures in the Fall and extreme heat events in the Spring. We also find that the overall effect of warming on yields is negative, even after accounting for the benefits of reduced exposure to freezing temperatures. Our analysis indicates that there exists a tradeoff between average (mean) yield and ability to resist extreme heat across varieties. More-recently released varieties are less able to resist heat than older lines. Our results also indicate that warming effects would be partially offset by increased rainfall in the Spring. Finally, we find that the method used to construct measures of temperature exposure matters for both the predictive performance of the regression model and the forecasted warming impacts on yields”

There's more discussion about the study in this piece in the Washington Post.

Are more efficient farms also better for the environment?

The answer appears to be "yes" according to this paper in the journal Applied Economic Perspectives and Policy.

Their motivation:

“The productive efficiency literature has paid very little attention to environmental performance issues. Growing social and political concerns for the environmental impacts of agriculture make it necessary to study environmental and technical performance using robust methodologies that enable scientists to derive reliable indicators. ”

They found . . .

“Empirical findings suggest that our sample farms, on average, reach technical efficiency scores of 93%, and thus that they can reduce input use by 7% while leaving output levels unaltered. Environmental efficiency scores differ depending on the methodology used and indicate ample scope for improving environmental performance and reducing pesticide use and pollution.”

The punchline:

“environmentally efficient farms tend to be more allocative and technically efficient. Better agri-environmental performance is associated with good agricultural practices, supporting the notion that an efficient use of chemical inputs improves both environmental and technical performance. As opposed to previous studies that found an adverse effect of environmental regulations on productivity (Färe et al. 2001), the high correlation between TE and EE for our sample farms implies complementarity between economic and environmental sustainability.”

Controversy over the new dietary guidelines

Yesterday I filmed a piece on Fox Business about the new dietary recommendations and the call to reduce meat consumption to improve health and the environment (I couldn't get the video to embed, but you can view it here).  I suppose I had at least a couple good points to make because the clip was featured for most of yesterday on the main web page for Fox News.  

One of the hosts mentioned a Cambridge study showing that vegetarians and vegans have substantially lower environmental impacts than meat-eating diets.  A written piece at foxnews.com about the recommendations also mentions the same study.  I'm not sure how representative that cited study is.  My own analysis suggests that vegetarians spend about the same amount on food as do meat eaters.  To the extent prices reflect resource use, that stat would suggest both diets are "using up" similar levels of "stuff."  I've also written on the argument that the grain fed to livestock is "wasted."

But, perhaps more importantly, what evidence is cited in the new report of the dietary guidelines committee?  The papers they cite seem to suggest small improvements in greenhouse gas (GHG) emissions and improved health outcomes (but more on that in a minute) from a move to vegetarian diet.  Here are some selected quotes of the review in Chapter 5 part D where quantitative impacts on environment were mentioned (note: there are many other cited studies, some of which suggest higher impacts).

“Peters et al. examined 42 different dietary patterns and land use in New York, with patterns ranging from low-fat, lacto-ovo vegetarian diets to high fat, meat-rich omnivorous diets . . . although meat increased land requirements, diets including meat could feed more people than some higher fat vegetarian-style diets”

and

“Aston et al. assessed a pattern that was modeled on a feasible UK population in which the proportion of vegetarians in the survey was doubled, and the remainder adopted a diet pattern consistent with the lowest category of red and processed meat (RPM) consumers. They found . . . the expected reduction in GHG for this diet was ~3 percent of current total carbon dioxide (CO2) emissions for agriculture. De Carvalho et al. also examined a high RPM dietary pattern with diet quality assessed using the Brazilian Healthy Eating Index.They found . . . that excessive meat intake was associated not only with poorer diet quality but also with increased projected GHG emissions (~ 4 percent total CO2 emitted by agriculture). ”

This one is most interesting references:

“a report from Heller and Keoleian suggests that an isocaloric shift from the average U.S. diet (at current U.S. per capita intake of 2,534 kcals/day from Loss-Adjusted Food Availability (LAFA) data) to a pattern that adheres to the 2010 Dietary Guidelines for Americans would result in a 12 percent increase in diet-related GHG emissions. This result was modified, however, by their finding that if Americans consumed the recommended pattern within the recommended calorie intake level of 2,000 kcal/day, there would be a 1 percent decrease in GHG emissions. ”

My take?  Eating too many calories likely has as much an impact on GHG as eating meat.  Reducing meat consumption would lower GHG emissions, but I would characterize the effects as "small" (3 to 4% of the GHG emissions from agriculture, or likely less than 1% of the total of all GHG emissions), particularly if people move toward pork and poultry, which have far fewer GHG emissions than ruminants like cattle.  Moreover, if we want to improve environmental impacts of livestock production, I think we're likely to get a bigger bang for our buck by improving productivity and researching new ways to reduce impacts than we will be cajoling people to eat less meat (see this paper on the reduction in environmental impact of beef production brought about over the past 40 years due to technological advancement).

What about the health impacts of meat consumption?  It is true that many observational, epidemiological studies show a correlation between red meat eating and adverse health outcomes (interestingly there is a fair amount of overlap on the authors of the dietary studies and the environmental studies on meat eating).  But, this is a pretty weak form of evidence, and much of this work reminds of the kinds of regression analyses done in the 1980s and 90s in economics before the so-called "credibility revolution." 

There have been many, many books written on the topic of whether meat eating is good or bad for you, and I won't try to adjudicate them all here.  However, I will point you to this really interesting exchange (see the comments section) on Marion Nestle's website where she mentions the new guidelines and takes a swipe at Nina Teicholz's book, Big Fat Surprise.  Nina responds, as do her critics.