Climate change is impacting our environment
Globally, temperatures are rising, and temperature and precipitation extremes are becoming more common.1 In the United States, average annual temperatures increased by 1.8°F between 1895 and 2016.2 Human activities in the past 50 years, resulting in an unprecedented accumulation of greenhouse gases, especially carbon dioxide, methane, and nitrous oxide, are the primary cause of this warming.3 For example, atmospheric carbon dioxide has increased by more than 40% since the Industrial Revolution (which lasted from about 1760 to about 1840), primarily due to burning coal, oil, and gas, and forest clearing.4
Looking solely at global or national averages does not give an accurate picture of climate change impacts in north central Montana. Impacts in this area may be greater than national averages would suggest, because the rate and magnitude of climate warming in Montana has been greater. For example, the average annual temperature in Montana increased 2.7°F between 1950 and 2015,5 much higher than the amount of warming the United States has experienced over an even longer time period.
While such change can be difficult to visualize, the disappearing glaciers in Glacier National Park are a local, visible reminder that the climate is warming (Figure 1). Since 1966, 39 glaciers in the Park have shrunk, some by as much as 85%.7 Other climate change impacts may not be as easy to see at first glance, though the accumulating effects on the local environment, air, water, weather, oceans, and ecosystems are significant. This section highlights the major ways climate change is impacting the regional environments of north central Montana.
The Blackfeet Nation is located in Montana’s North Central region (Division 3), a climate division defined by the National Oceanic and Atmospheric Administration (Figure 2). The North Central region has seen an average temperature increase of .51°F each decade from 1950 to 2015, with most warming occurring in winter and spring (Figure 3).8 In the same period, total days exceeding 90°F in Montana has increased by 11 days while the percentage of cool days each year has decreased by 15 days.9 Though Montana’s overall growing season length has increased by 12 days,10 effective season length can be limited by reduced water availability.11 While the North Central region has not seen a significant change in summer, fall, and spring precipitation since 1950, it has had an average precipitation decrease of .09 inches per decade in winter, mostly attributed to natural climate variability.12 Furthermore, the Central Rocky Mountains have been experiencing declining stream discharge over the last half century, with significant declines in the month of August.13
To understand how climate change will impact north central Montana’s environment in the future, it is important to acknowledge several sources of uncertainty when making predictions at the regional scale. Climate modeling, ecological responses, and human adaptive responses all introduce uncertainty when predicting the future.14 While there is consensus that climate change is happening and that its impacts are here and will be experienced far into the future, the degree to which it will impact the globe depends on how people act now and in the future. While precise predictions cannot be made about future conditions, there is evidence that across Montana, average annual temperatures will increase (high agreement, robust evidence), annual precipitation will increase in winter, spring, and fall (moderate agreement, moderate evidence), and precipitation will decrease in the summer across Montana (moderate agreement, moderate evidence).15
Contributing to uncertainty is the degree to which the global community will take action to limit and reduce greenhouse gas emissions. When scientists make climate predictions, they must account for different emissions scenarios, which are referred to as Representative Concentration Pathways, or RCPs. For example, RCP 2.6, at one extreme, assumes “immediate and rapid reductions in emissions,” while RCP 8.5, at the other extreme, assumes a continuation of current global emission increases.16 A more middle-of-the-road scenario is RCP 4.5, known as the stabilization scenario. The United Nations Paris Agreement intends to curb emissions at levels between RCP 2.6 and RCP 4.5.17 Table 1 compares North Central Montana scenarios for RCP 4.5 with RCP 8.5. Note that the overall trends are similar for the two scenarios: hotter average temperatures, longer growing seasons, increased late winter and early spring precipitation, and decreased summer precipitation. However, the magnitude of change is greater for RCP 8.5.
In Montana, state-wide average annual temperature is expected to rise up to 6.6°F (for RCP 4.5) and possibly up to 10.8°F (for RCP 8.5) by the end of this century.19 Climate modeling experts predict there will be 3 – 7 more high temperature days per year by the mid-century in North Central Montana, based on the RCP 4.5 scenario.20 The hotter temperature days are predicted to increase most in the month of August,21 a time when water is in shortest supply. Monthly precipitation will decrease, on average, up to 5 inches in North Central Montana in the months of June, July, and August in the period 2040 to 2069 (for both RCP 4.5 and 8.5 scenarios).22 In contrast, monthly precipitation is expected to increase up to 7.5 inches in March, April, and May in North Central Montana the same period (RCP 4.5), and possibly greater increases are expected under the RCP 8.5 scenario.23 Warmer temperatures are likely to increase the frequency and severity of drought conditions in the late summer and early fall, and exacerbate drought conditions when they do occur throughout the year.24
Though summer precipitation will decline, winter and spring snowmelt and precipitation predictions suggest water availability may concentrate in the relatively cooler parts of the year.25,26 Decreased spring snowpack has been observed and is predicted into the future,27,28,29 as is an earlier onset of spring snowmelt.30,31,32 This means that peak spring stream runoff is occurring earlier in the year,33,34,35 and more runoff in winter is predicted.36 Furthermore, long-term stream monitoring has demonstrated that there are already lower stream baseflows (the portion of the stream not from runoff) in late summer,37,38,39 a trend predicted to continue into the future. These lower baseflows, along with warmer air temperatures, are causing stream temperatures to warm.40,41 The frequency of flooding may increase, especially in spring, due to earlier snowmelt, rain-on-snow events and increased precipitation.42,43
In short, climate change is likely to raise temperatures, increase precipitation and snowmelt in colder parts of the year, and decrease precipitation in hotter parts of the year in North Central Montana. These trends have a variety of implications for humans and the environment. A major implication is that rising temperatures and changes in snowpack and runoff timing will exacerbate drought.44 Living with climate change will require adaptation and increased resilience in Blackfeet Country.