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To make better land-use decisions, we must consider air quality too

Natural Capital Project researchers at the University of Minnesota demonstrate importance of an often-overlooked ecosystem service
Expansion of agricultural land can have significant air quality effects. Image by Mateusz Mikulski from Pixabay.

A new study from Natural Capital Project researchers based at the University of Minnesota’s Department of Applied Economics finds that land-use decisions can greatly affect human health through changes in air quality.

The research, published in Environmental Science & Technology, offers an integrated model that evaluates the environmental and economic consequences of land-use, including the effects on air quality. The analysis includes both how changes in land use affect surrounding vegetation’s ability to remove pollutants from the air, and emission of pollutants, such as from agricultural nitrogen release, dust plumes, and biogenic pollutants from soils and trees.

“It's well-known that the land and the atmosphere interact in complex ways,” said Sumil Thakrar, postdoctoral research associate at the University of Minnesota. “But the question is: how much do these effects actually matter for people and the planet? To answer that, we estimated how land-use decisions affect air quality, and how this in turn affects human health. We valued the health effects in dollar terms, and compared them to the other changes we care about, such as the value of agricultural crop production. When we do this, it turns out that air quality matters a lot.”

The researchers found that the effect of land use on air quality often dominates the effects of other, more conventionally assessed social costs and benefits, such as the value of growing crops or the value of carbon sequestration. In fact, incorporating air quality effects can make land-use changes that looked beneficial turn out to be detrimental, and vice versa. This is true in particular for expansion of agricultural land, which greatly increases crop returns. When we appropriately value changes in air quality, we find that expansions of cropland often result in costs exceeding benefits, resulting in net losses for society.

“Ecosystem service assessments often leave out some services that are harder to assess, even though we know that they are large,” said Steve Polasky, Regents Professor and the Fesler-Lampert Professor of Ecological and Environmental Economics at the University of Minnesota. “Air quality regulation is a great example. It’s the most important environmental health risk we know about, and even pollution from non-intuitive sources, like dust or soil emissions, can have very large impacts.”

The study finds that, under incentives for increased afforestation, the effects on air quality can be mixed. Biogenic pollution emitted by trees can worsen air quality, but the effect is offset by the capacity for the trees to remove pollution. Also, it matters what alternative land use is being compared to forests. Cropland is usually worse for air quality than forest, so if more forest means less cropland, the result can be an improvement in air quality. This study finds that increased afforestation worsens air quality on net, but the effect is smaller than the increases in carbon sequestration and timber returns. So, when we consider a wider set of ecosystem services, not just air quality in isolation, incentives for afforestation appear beneficial overall.

The researchers hope that this is not the final word on land use and air quality. “Now that the importance of air quality in land-use decision-making has been demonstrated, we hope to encourage efforts to include more of the impacts, and to better constrain the uncertainties,” said Thakrar. For example, this study does not include how changes in land use can affect wildfire risk, or biomass burning—not to mention whether people move to more or less polluted places. “This is all part of a bigger project: to develop tools that guide us towards decisions that actually benefit human wellbeing and the environment, rather than being guided by narrower objectives.”

The University of Minnesota’s Department of Applied Economics is a core partner of the Natural Capital Project, whose global hub is at Stanford University, within the Doerr School of Sustainability and the School of Humanities & Sciences. 

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