A few months ago I discussed the possible long-run impact of climate change on Montana in light of some recent research estimating the economic and agricultural effects across the country. Now the Montana Institute on Ecosystems, a program of Montana University System studying ecosystem sciences, has recently released a major report on the likely environmental impacts of climate change on Montana. You can read the executive summary or, if you have a free weekend, the entire report here.
The report is divided into chapters on the likely effect of climate change on Montana’s climate, water, forests and agriculture. Montana’s average temperatures are likely to increase by 4.5-6.0°F, higher than average nationally (mostly due to climate impacts being more severe as you go further from the equator). This will have an adverse effect on Montana’s snowpack and thus its water supply, particularly in the late summer. Groundwater tables will be depleted faster. These trends will be exacerbated by more frequent droughts like the one seen this past summer.
The impacts on Montana’s forests are much more ambiguous. Higher CO2 concentrations are actually beneficial for plant and tree growth, but reduced water flow will have an adverse effect on tree growth and higher temperatures will increase the tree mortality rate. There are also several indirect effects that could have a large impact. Higher temperatures will lead to more bark beetles that eat away at trees, but will also reduce the prevalence of some harmful pathogen species. Whether the overall net effect is positive or negative for a given forest will depend on several local, forest-specific conditions, along with how severe the temperature rise and frequency of droughts turns out to be.
The final chapter of the report evaluates the impact on agriculture. Because agriculture depends to a great extent on complex interactions between market, government and environmental factors, predictions about the overall impact of climate change are deeply uncertain. In addition to uncertainty about climate modeling and in agricultural yield modeling, how well farmers will adapt and how commodity markets will adjust adds an additional layer of difficulty to forecasting. But the report does make some broad claims with high confidence. The increased temperature and rainfall may well be beneficial in the short term, but the negative effects will grow as warming accelerates. Decreased streamflow will harm irrigation capabilities. Further, winter annual weeds will spread significantly more in warmer temperatures, leading to decreased yields. Farmers will face considerably higher volatility in both yields and market prices, particularly those exposed to globally priced commodities since extreme weather events around the world can wreak havoc on these markets.
The report paints a somewhat bleaker picture for Montana agriculture than the paper I discussed in my earlier post. That paper attempts to make concrete numerical predictions by estimating the effects of a humidity index and a measure of heat waves, and extrapolating those estimates to predictions about future climate change. The Montana Climate Assessment foregoes exact predictions but considers a much wider range of direct and indirect effects that cannot be accounted for in a numerical exercise. Both approaches are valid and useful, but the Montana Climate Assessment suggests that the simpler approach may produce an overly optimistic forecast for Montana.