Montana Climate Assessment: Warmer temps, lower snowpack, longer growing seasons

Montana’s average annual temperatures have increased 2-3 degrees since 1950, and are projected to warm 5.6-9.8 degrees by the end of the century, 32 scientists from the public and private sectors said in the first Montana Climate Assessment, released Wednesday.

The joint UM-MSU Montana Institute on Ecosystems organized the report, which said the state “is projected to continue to warm in all geographic locations, seasons, and under all emission scenarios throughout the 21^st century.”

The impacts will be significant.

By mid-century, statewide temperatures are expected to increase by 4.5-6 degrees, depending on the rate at which greenhouse gas emissions continue. Slowing those emissions will slow the rate of temperature increase.

The state-level temperature changes are larger than the average changes projected globally and nationally, the scientists said, adding that they are in “high agreement” and have “robust evidence” of that projection.

Precipitation likely will continue to decrease during the summer months, the assessment notes.

But an increase in precipitation is projected for Montana’s future winters, springs and falls, with the largest increases expected during spring in the southern part of the state.

Along with central Montana, the state’s southern counties are also those with the largest anticipated decreases in summertime precipitation.

The Montana Climate Assessment, by its own definition, 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 intent is not political, but rather informational in the interest of recognizing and planning for the changes – all of which are already occurring, the scientists said.

This first assessment is only the start, they said. The effort will be sustained. “We plan to regularly incorporate new scientific information, cover other topics important to the state.”

Included in the first assessment are projected key impacts of climate change on Montana agriculture, forests and water.

Since 1950, winter and spring months have experienced the most warming, the report concludes, with average temperatures rising 3.9 degrees through 2015.

Overall, “rising temperatures will reduce snowpack, shift historical patterns of streamflow, and likely result in additional stress on Montana’s water supply, particularly during the summer and early fall,” the assessment notes.

Montana’s snowpack has declined in the mountains both east and west of the Continental Divide. While the report includes records since the 1930s, the snowpack’s decline has been most pronounced since the 1980s.

In addition, the report says:

Warming temperatures over the next century, especially during spring, are likely to reduce snowpack at mid and low elevations.

• 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.

• Earlier onset of snowmelt and spring runoff will reduce late-summer water availability in snowmelt-dominated watersheds.
• 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.

“Rising temperatures will exacerbate persistent drought periods that are a natural part of Montana’s climate,” the assessment says. Key messages associated with these findings include:

• Multi-year and decadal-scale droughts have been, and will continue to be, a natural feature of Montana’s climate;
• rising temperatures will likely exacerbate drought when and where it occurs.
• Changes in snowpack and runoff timing will likely increase the frequency and duration of drought during late summer and early fall.

In their analysis of climate change’s impacts on Montana forests, the scientists emphasized that “the impacts from increased extreme heat will be negative.”

“In the face of changing climate, forest managers can best maintain forest health and stable product yield by understanding past trends and planning for a range of climate scenarios,” they wrote.

In addition:

• An increase in fire risk (i.e., probability of occurrence)—including an increase in size and possible frequency and/or severity (i.e., tree mortality)—is expected in the coming century as a result of a) prolonged fire seasons due to increased temperatures, and b) increased fuel loads from past fire suppression.
• Rising temperatures are likely to increase bark beetle survival [high agreement, strong evidence], but climate-induced changes to other insects and forest pathogens are more varied and less certain.

The assessment adds: “It is important to note that current forest conditions will largely determine the potential impacts from current and future climate change. Forest conditions vary across land ownership types, and many Montana forests are under stress due to past forest management practices.”

Montana’s $5.2 billion agriculture industry has always been tied to weather events, many of which are extreme, and is similarly tied to climate change, the assessment notes.

Since 1951, the state’s growing season already has increased by 12 days. The average number of warm days has increased by 2 percent, while the number of cool nights has decreased by 4.6 percent.

“Montana agriculture has always faced volatility, extreme events, and variability across the state and these conditions will continue to be the case with projected climate changes in Montana,” the report says. “Climate model projections show a warmer Montana in the future, with mixed changes in precipitation, more extreme events, and mixed certainty about upcoming drought.”

Among the assessment’s key findings:

• Every component of agriculture — from prices to plant pollinators and crop pests — exhibits complex relationships to climate, depending on the location, weather variability, and agricultural and economic practices and policies. Social and economic resilience to withstand and adapt to variable conditions has always been a hallmark of Montana farmers’ and livestock producers’ strategies for coping with climate variability.
• Decreasing mountain snowpack will continue to lead to decreased streamflow and less reliable irrigation capacity during the late growing season. Reduced irrigation capacity will have the greatest impact on hay, sugar beet, malt barley, market garden, and potato production across the state.
• Increases in temperature will allow winter annual weeds, such as cheatgrass, to increase in distribution and frequency in winter wheat cropland and rangeland. Their spread will result in decreased crop yields and forage productivity as well as increased rangeland wildfire frequency.
• Climate change affects global-price-determined commodity agriculture differently than it affects non-commodity agriculture. Commodity crops, such as small grains, are more directly driven by global markets and agricultural subsidies, whereas non-commodity crops tend to be more directly tied to local or specialized non-local markets and local micro-climates.
• Diversified cropping systems, including rotation with pulse crops and innovations in tillage and cover-cropping, along with other measures to improve soil health, will continue to allow adaptation to climate change.

“Understanding current climate change and projecting future climate trends is of vital importance, both for our economy and our well-being,” the scientists emphasized.

“The motivation for the MCA arose from citizens and organizations in Montana who have 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,” they said.

Here is a link to the full report and to the full list of contributors.

Watch Missoula Current in the days to come with additional reports on and analysis of the Montana Climate Assessment.