Several years ago I was coaching a high school debate team in Boston and my students were asked to debate increasing alternative energy incentives in the United States. As one would expect, the debate became one about the effects of climate change. Some students used the tactic of arguing that climate change was a positive phenomenon. They mainly cited an author who wrote that CO2 emissions increase plant growth – in fact this became such a popular point that I heard it argued about five times a tournament, and never well. After digging around a bit more, what I found was that most of the students making this argument were basing their conclusions on one-sided evidence: literature that examined only one aspect of climatic effects on agriculture that negated the net result of increased global emissions (such as melting ice caps and rising sea level that destroy coastal vegetation).
With that in mind, for this week’s Reading Old Magazines I decided to look at a 1994 Nature study by Cynthia Rosenzweig, a senior research at NASA’s Goddard Institute, and Martin L. Parry, currently at the Grantham Institute, but previously a co-chair of Working Group II at the IPCC, called “Potential Impact of Climate Change on World Food Supply.” (pdf) Parry and Rosenzweig used the latest climate change models to determine the impacts of increasing CO2 emissions on agriculture, although they only looked at the atmospheric effects and not water acidification. They then applied the results to a trade model that examined how shifts in growing patterns would affect worldwide food distribution models.
Reading the paper, I was struck by how far the science and modeling of climate change has come. I’m not an expert on scientific models, but the data publicly available now seems to be way beyond what these researchers had access to. Climate modeling in particular has dramatically improved. In this paper, however, the authors were forced to make some strong assumptions about other greenhouse gas emissions and the linearity of climate change effects that we account for more thoroughly now.
Being a bit of a data-modeling geek, I was excited to see a paper that applied the agricultural impacts of climate change to world trade. Unfortunately the paper did not do a very thorough job of it. The authors took a model of global trade that was static and assumed no changes in per capita income across the globe or other industries that rely on agricultural outputs (the construction industry’s use of lumber or the energy industry’s use of palm oil and corn, for example), while only manipulating the quantities of food available in different regions (which subsequently allowed the price of food to change). Because climate change will impact all systems, the Rosenzweig-Parry model is, at best, of very limited utility. Add to this that they assumed only limited trade liberalization in the post-Soviet bloc area and did not account for changes in the price of anything other than basic grains. Nor did they include the impact that China would have on the world market. While it was a very innovative idea and one I would like to see repeated, future iterations would benefit from a more thorough examination of the basic assumptions supporting the model.
The really interesting part of this article, though, is that it attempts to look at whole system effects of climate change. During the 1990s, most research examined the regional and national effects of climate change in isolation. (Rosenzweig and Parry provide ample references and summaries of these research projects in their endnotes but, unfortunately, they are not available online.) The Rosenzweig and Parry model broke this trend, however. According to the authors, agriculture outputs may increase in some countries that are mainly located in the Northern hemisphere, but climate change will result in lowered agricultural outputs in Africa and South America. They also note that while the developing world will be harder hit by these changes, it will be the least able to afford the increase in the price of food. Consequently, the number of people in the world experiencing famine will dramatically increase if subsistence farming fails in developing nations.
While none of the conclusions are groundbreaking, it is important to look back at the early models that examined the interaction of food supply and climate change. While the negative impacts of climate change on agriculture are generally agreed upon now, the study’s reliance on data and global impacts was new in the 1990s. It was followed by several worthwhile reads on complementary topics and certainly provides an interesting way to examine the net effects of climate change. Indeed, Rosenzweig and Parry provide a great data-based analysis of systematic effects of climate change. And while their assumptions may have been somewhat flawed, their study was a worthy attempt to understand that impacts of climate change on food. Now if only I could have had my high school debate students to read it.