IN THE NEWS: Cooling Down Climate Change, While Heating Up Grocery Bills: ES&T’s Top Policy Analysis Article 2012

Tuesday, April 23, 2013
American Chemical Society   (Browse all news)

By: Janet Pelley                                                                                                                                                                                        March 28, 2013

By 2100, the world population will pass 10 billion people. How can we sustain that population, while throttling back climate change? Some scientists think part of the answer is to plant forests and grow biofuel crops, allowing us to use land to sequester carbon. But those changes in land use also could crowd out food crops, raising the cost of food. In ES&T’s Best Policy Analysis Paper of 2012, researchers model the feedback between the atmosphere, Earth’s ecosystems, and the global economy to show that a fossil fuel tax plus incentives for reforestation and biofuels nearly stabilizes the climate by 2100. Unfortunately, the team reports that the trade-off is a hefty rise in food prices (Environ. Sci. Technol., DOI: 10.1021/es2034729).

John Reilly, an energy economist at Massachusetts Institute of Technology, and his team realized that any analysis of climate policies, such as a carbon tax or incentives for reforestation, is complicated by the fact that land use policy, climate, and the economy are tightly linked. For example, as the climate warms, plant productivity changes, which in turn affects people’s decisions about land use, he says. “Thinking of that complex set of interactions and trying to understand what was going on was the motivation for the study,” Reilly says

Previous studies have narrowly focused on one land use at a time, such as finding the best policies to sequester more carbon in forests but ignoring spillover impacts on cropland. Also these studies did not take into account the interactive and downstream effects of a worldwide carbon tax.Reducing greenhouse gases with a carbon tax will increase energy costs, and energy is a big input in agricultural production,” Reilly says.

His team decided to study a combination of policies—a carbon tax and incentives for reforestation and biofuels—and ask what the effects would be on the climate, food prices, and land use.

To do so, they developed a set of three models that feed data among one another. First, a global economic model, provided by the MIT team, predicts food prices, land use, and greenhouse gas emissions every five years. Next, those emissions estimates drive a climate model that simulates future climate conditions. These climate outputs, such as carbon dioxide and ozone concentrations, then feed into an ecosystem model, developed by Jerry M. Melillo and his team at the Woods Hole Oceanographic Institution. The ecosystem model generates changes in crop and forest productivity. The economic model then uses these productivity changes, along with expected demand for products produced from the land, to reassess land and energy use, which then determines the next set of greenhouse gas emissions estimates. And the cycle continues.

The team members ran their models through the year 2100 under several different policy scenarios. They found that if humanity sticks with the status quo and attempts no change in climate policy, CO2 concentrations reach 900 ppm by 2100, and global mean temperature hits 5.8 °C above preindustrial levels. However, a worldwide tax on fossil fuel emissions limits the CO2 concentration to 520 ppm and holds temperature rise to 2.7 °C. These metrics are still above the targets set by the 2009 Copenhagen Accord, which are a 2 °C temperature increase and CO2 levels around 450 ppm CO2.

When the team added incentives for reforestation and biofuels to a tax on energy, CO2 concentrations reach only 490 ppm and global temperature increases 2.2 °C over preindustrial levels by the end of the century. But Reilly says these better climate statistics come at a price: Competition for agricultural land from reforestation and biofuels boosts food prices by 80%.

Stephen Polasky, an environmental economist at the University of Minnesota, Twin Cities, says that this paper reveals that policy makers cannot think of energy and food policies as independent.

Even though the scenarios in the paper are far more aggressive than any proposed policies suggested right now, fossil fuel use in the models never drops to levels scientists say we need to stabilize the climate, says Steve Running, a terrestrial carbon scientist at the University of Montana. He also says the paper highlights how any solution to the climate problem requires choices and trade-offs when it comes to land use.

Reilly hopes that others will adopt his team’s modeling practices to find sensible polices to improve the climate.

The authors declare no competing financial interest.

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