Bitterrooters got a chance recently to hear the latest update from one of the leading authors of the 2017 Montana Climate Assessment, not only about how climate change is affecting Montana, but how it is affecting the Bitterroot valley and Hamilton in particular. According to some parameters such as average annual temperature and precipitation, Hamilton is trending at a different rate or even in a different direction than a lot of other places in the state.
The Montana Climate Assessment (MCA) is an effort to synthesize, evaluate, and share credible and relevant scientific information about climate change in Montana with the citizens of the state. The motivation for the MCA arose from citizens and organizations across the state who expressed interest in receiving timely and pertinent information about climate change, including information about historical variability, past trends, and projections of future impacts as they relate to topics of economic concern.
Apparently, that initial public interest remains high as more Bitterrooters showed up for the latest climate update than the venue at the Forest Supervisor’s Office in Hamilton could hold. The update was being provided by Bruce Maxwell, Director of the Montana Institute on Ecosystems at Montana State University. As all the chairs quickly filled, people began lining up along the walls. While some sat on the floor up front surrounding the speaker, the standing crowd spilled into the adjoining hallways to the point that some simply couldn’t hear and left.
It was the Montana Institute on Ecosystems, a statewide center based at both Montana State University and University of Montana, that took on the responsibility of organizing the MCA. It involved two years of work by university faculty and students, state and federal agency researchers, non-profit organizations, resource managers, and citizens from across Montana. Maxwell said that he participated in over 4,000 interviews over that period.
The assessment begins with an analysis of Montana’s recent climate trends and how climate is projected to change in the future. This information is used throughout the assessment to explain the key impacts of climate change observed in recent decades and projected in the future. Discussion of climate change impacts on Montana’s water, forests, and agriculture are presented next. The assessment concludes with an analysis of major knowledge gaps—and thus areas for future research—related to climate change and its impacts on the three sectors covered.
Some key messages from the report include:
• Annual average temperatures, including daily minimums, maximums, and averages, have risen across the state between 1950 and 2015. The increases range between 2.0-3.0°F (1.1-1.7°C) during this period (see Figure II). [high agreement, robust evidence]1
• Despite no historical changes in average annual precipitation between 1950 and 2015, there have been changes in average seasonal precipitation over the same period. Average winter precipitation decreased by 0.9 inches (2.3 cm), which can largely be attributed to natural variability and an increase in El Niño events, especially in the western and central parts of the state. A significant increase in spring precipitation (1.3-2.0 inches [3.3-5.1 cm]) also occurred during this period for the eastern part of the state. [moderate agreement, robust evidence]
• Montana is projected to continue to warm in all geographic locations, seasons, and under all emission scenarios throughout the 21st century. By mid century, Montana temperatures are projected to increase by approximately 4.5-6.0°F (2.5-3.3°C) depending on the emission scenario. By the end-of-century, Montana temperatures are projected to increase 5.6-9.8°F (3.1-5.4°C) depending on the emission scenario. These state-level changes are larger than the average changes projected globally and nationally (Figure III). [high agreement, robust evidence]
• Across the state, precipitation is projected to increase in winter, spring, and fall; precipitation is projected to decrease in summer. The largest increases are expected to occur during spring in the southern part of the state. The largest decreases are expected to occur during summer in the central and southern parts of the state. [moderate agreement, moderate evidence]
Other trends and future scenarios include:
Atmospheric CO2 concentrations
Global atmospheric carbon dioxide concentrations have increased over 100 ppm since Montana statehood and are projected to increase under both future scenarios considered here.
Since 1950, average statewide temperatures have increased by 0.5°F/decade (0.3°C/decade), with greatest warming in spring; projected to increase by 3-7°F (1.7-3.9°C) by mid-century, with greatest warming in summer and winter and in the southeast.
Maximum temperatures have increased most in spring and are projected to increase 3-8°F (1.7-4.4°C) by mid-century, with greatest increases in August and in the southeast.
Days above 90°F (32°C)
Extreme heat days are projected to increase by 5-35 additional days by mid century, with greatest increases in the northeast and south.
Minimum temperatures have increased most in winter and spring and are projected to increase 3-7°F (1.7-3.9°C) by mid-century, with greatest increases in January and in the southeast.
Frost-free days are projected to increase by 24-44 days by mid-century, particularly in the west.
Statewide precipitation has decreased in winter ( 0.14 inches/ decade [-0.36 cm/decade]) since 1950, but no significant change has occurred in annual mean precipitation, probably because of very slight increases in spring and fall precipitation. Precipitation is projected to increase, primarily in spring (0.2-0.7 inches [0.5-1.8 cm]) in the northwest; a slight statewide decrease in summer precipitation and increased year-to-year variability of precipitation are projected, as well.
Number of consecutive dry days
Little projected change, with a maximum increase of 3 days to -3 days under the most severe scenario by end of the century. However, increased variability in precipitation suggests potential for more severe droughts, particularly in connection with climate oscillations.
Number of consecutive wet days
No substantial change projected.
The analysis indicates that rising temperatures will reduce snowpack, shift historical patterns of streamflow in Montana, and likely result in additional stress on Montana’s water supply, particularly during summer and early fall. Key messages associated with these findings follow:
• Montana’s snowpack has declined over the observational record (i.e., since the 1930s) in mountains west and east of the Continental Divide; this decline has been most pronounced since the 1980s. [high agreement, medium evidence]
• Warming temperatures over the next century, especially during spring, are likely to reduce snowpack at mid and low elevations. [high agreement, robust evidence]
• Historical observations show a shift toward earlier snowmelt and an earlier peak in spring runoff in the Mountain West (including Montana). Projections suggest that these patterns are very likely to continue into the future as temperatures increase. [high agreement, robust evidence]
• Earlier onset of snowmelt and spring runoff will reduce late-summer water availability in snowmelt-dominated watersheds. [high agreement, robust evidence]
• Groundwater demand will likely increase as elevated temperatures and changing seasonal availability of traditional surface-water sources (e.g., dry stock water ponds or inability of canal systems to deliver water in a timely manner) force water users to seek alternatives. [high agreement, medium evidence]
Rising temperatures will exacerbate persistent drought periods that are a natural part of Montana’s climate. Key messages associated with these findings follow:
• Multi-year and decadal-scale droughts have been, and will continue to be, a natural feature of Montana’s climate [high agreement, robust evidence]; rising temperatures will likely exacerbate drought when and where it occurs. [high agreement, medium evidence]
• Changes in snowpack and runoff timing will likely increase the frequency and duration of drought during late summer and early fall. [high agreement, medium evidence]
Maxwell, who grew up in Hamilton, also noted that the data from the weather station at Hamilton often shows itself to be the exception to the rule when it comes to statewide trends. For instance, while the average mean temperatures at most weather stations around the state show a warming trend, Hamilton and Big Timber don’t show any trend. They appear to be static.
Maximum temperature trends are increasing across the board in the state.
Another important trend for those involved in agriculture is the summertime minimum temperatures at night. Here, too, we see a statewide trend towards warming temperatures at night. Maxwell said this can be hard on cattle when the days get extremely hot. The cattle need cool nights to recover. Here again, Hamilton is an exception. Hamilton is showing a cooling trend for nighttime temperatures.
Overall, according to Maxwell, there is no statewide trend in summer precipitation. But if you look closer there is a slight increasing trend in eastern Montana and a slight decreasing trend in the mountains. Hamilton shows no trend over the very long term, but looking at a shorter more recent span a slight decreasing trend can be detected.
Maxwell offered a plethora of things that farmers and ranchers in Montana could consider doing to deal with these coming changes. Suggestions included:
– Increase certainty by contracting for crops
– Manage for drought by planting earlier
– Recognize that irrigation cannot continue to be expanded
– Plant multi-species cover crops and finish cattle with forage
– Minimize use of nitrogen fertilizer
– Collect monitoring data and try infield experiments
– Consider switching to a more heat tolerant breed of cattle
– Plant trees
– Create local processing plants
– Market products on their quality and production methods
– Use intensive data to increase water and forage efficiency
One complicating factor to consider is that even though the growing season is getting longer, the summers are getting drier and the water may not be available for late season crops.
Add to that the factor that the chance of having a chilling frost has not changed.
Another trend that Maxwell noted was the trend towards more wildland forest fires. He said the science doesn’t show much direct relationship between forest management and this increasing trend. He said it had more to do with the overall rising temperatures with an increasing number of hotter and drier days. The days of extreme fire danger are on the increase, in part because even though the springs and falls are becoming wetter, the summers are becoming much drier. The vegetation flourishes only to be turned into a tender box in July, August and September.
The projection is that from 2040 to 2060 winter average temperatures will increase from 5 to 7 degrees, mainly during warmer Decembers and Januaries. The summer average temperatures are projected to rise by 6 to 7.5 degrees, mainly warming in July, August and September.
Maxwell said that there is a lot of misinformation out about climate change as some reports cherry pick the data, but they did not do that in this report.
“We tried to give the fullest picture possible including all the data that we could,” said Maxwell.
The 2017 Montana Climate Assessment [Whitlock C, Cross W, Maxwell B, Silverman N, Wade AA. 2017. 2017 Montana Climate Assessment. Bozeman and Missoula MT: Montana State University and University of Montana, Montana Institute on Ecosystems. 318 p. doi:10.15788/m2ww8w] may be viewed online at: montanaclimate.org.