Montana: Trout and Drought
Mountain Snow Melting
Two forecasts for March in Montana, 2009 - 2095
This animated map shows projected average March temperatures in Montana from 2009 through 2095, based on climate model projections under two scenarios: pathways of high or low global greenhouse gas emissions. The color scale is designed to make it easy to tell apart areas where temperatures are above versus below freezing. Changes in the timing of spring snowmelt affect when streams start drying up in the summer, with important consequences for trout, anglers, farmers and others (see the video as shown on PBS NewsHour, and the piece’s specially annotated transcript, for more).
Map controls
- The “Change Scenario” button switches between emissions scenarios.
- “Hide Overlay” removes the color-coded map to reveal towns and cities underneath. (“Hide Overlay” then turns into “Show Overlay” for returning to the original map.)
- Clicking on the triangle plays a movie of projected March temperatures in future years. “Faster” and “Slower” buttons adjust movie speed.
- Regular Google Maps zooming and panning are available to the right.
Climate model projections
The future projections underlying this animation are based on results of 16 different global climate models—essentially, these are computer programs that represent the climate, each based on slightly different methods and assumptions. By taking the median temperature projection of all these models, we get what amounts to a “best-guess” of future temperatures. It’s like getting help from 16 different experts. These models were used by the world’s leading and largest scientific body on climate change, the Intergovernmental Panel on Climate Change (IPCC), in its latest major report.
Because climate models make projections only at a broad regional level, we used established methods (see technical explanation here) to add fine, local detail to these future climate estimates—enough detail to make different projections for places as close as ten miles apart. This is important because people want to know climate forecasts for the specific places they live, work and visit; and we all know that even nearby locations can be quite warmer or cooler, wetter or drier than each other.
We also allowed for the fact that year-to-year changes can go in either direction—that is, even if the trend is toward warmer temperatures in general, a given year might be colder than the one before. So to reveal trends more clearly, the temperature shown for a given year at each map location is actually the average of projected temperatures for ten consecutive Marches around and including the focal year.
It is important to remember that climate model outputs are always projections and never predictions; we can use them to anticipate general trends, but never to foretell the exact temperature or precipitation at a particular place and time.
Emissions scenarios
To make projections about future climate change, we must first make an assumption about the future rate of accumulation of greenhouse gases, like carbon dioxide, in the atmosphere. We cannot know what the exact buildup will be over the next century, because this will depend on many things, including human actions. Therefore, a standard set of “scenarios” is used as input to climate models, covering a range of possibilities from high emissions (continuing expansion of fossil fuel use; high population growth) to low emissions (swift shift toward low- or no-carbon energy sources like nuclear, wind and solar; low population growth).
We compared climate change projections for Montana based on one standard future scenario from the high emissions end of the range, and one from the low end. However, in the seven years since scientists developed the current set of standard scenarios, greenhouse gases in the atmosphere have increased somewhat faster than even the highest emissions pathway considered, so climate change projections depending on them—like the ones illustrated here—may be conservative.
The technical labels for the two emissions scenarios used in the climate projections here are SRES B1 (low) and SRES A2 (high) (see here for original scenario definitions and report, and here for a snapshot contrast).
Changes and consequences
The map animations show that over time, the area where temperatures are above freezing in March are expected to steadily expand, as increasing concentrations of greenhouse gases worldwide trap more and more heat.
With above-freezing temperatures occurring earlier in the year, winter snow melts earlier, and more precipitation falls as rains rather than snow. The result is increased river flows in winter and early spring, but less in late spring and summer, when lingering snow would ordinarily keep the rivers supplied with meltwater. These reduced late-season flows can have negative consequences for trout and other aquatic species and also for water supplies for urban and agricultural use. All of these phenomena have already been observed in recent decades.
See our piece as shown on PBS NewsHour, and the piece’s specially annotated transcript, for more.
Graphics Explained
-
Northern Rockies Forest Wildfires
Number of large wildfires on forested federal lands.
-
Montana's Wind Energy Potential
About equal to the electricity consumed by the states lit.
-
Montana Average March Temperature
Average March air temperatures in Montana from 1950 to the present.
Send Us Feedback
We'd like to hear from you.