The climate in Arizona is transforming, with the state experiencing a temperature rise of approximately two degrees Fahrenheit over the past century. Across the southwestern United States, heat waves are becoming more frequent across the southwestern United States, and snow is melting earlier in the spring. These climate changes will result in various significant impacts in the forthcoming decades. The flow of water in the Colorado River is likely to decrease. Additionally, the frequency and intensity of wildfires are expected to increase, and certain rangelands may undergo desertification.

The primary cause behind this changing climate is the Earth’s global warming. Human activities have contributed to a 40 percent increase in the concentration of carbon dioxide in the atmosphere since the late 1700s. The levels of other greenhouse gases that trap heat have also been rising. As a result, our planet’s surface and lower atmosphere have experienced a warming of approximately one degree over the past 50 years. The warming atmosphere leads to increased evaporation, which raises humidity, average rainfall, and the occurrence of heavy rainstorms in many regions. However, this also contributes to drought conditions in other areas. The decline in global biodiversity has had a profound impact, resulting in the loss of rare species but also causing a rapid decline in common species across various groups of organisms.

Among the concerning consequences is the loss of pollinating insects, which play crucial ecological and economic roles. The western bumble bee (Bombus occidentalis), once abundant in western North America, has experienced a significant decline across its range. To investigate the factors driving this decline, Janouske et al. (2023) used Bayesian occupancy models, analyzing data from 1998 to 2020 on climate, land cover, pesticide use from 2008 to 2014, and projected future occupancy under three scenarios.

By examining 14,457 surveys conducted across 2.8 million square kilometers in the western United States, Janousek et al. (2023) observed strong negative relationships between increasing temperatures, drought, and occupancy. Notably, the authors found that neonicotinoid pesticides, specifically nitroguanidine neonicotinoids, had the greatest detrimental impact on the bumble bee populations in our study region. The average predicted species occupancy declined by 57% between 1998 and 2020, ranging from 15% to 83% across 16 ecoregions. Even under the most optimistic scenario, nearly half of the ecoregions were projected to experience continued declines by the 2050s. In contrast, the most severe scenario predicted average decline of 93% across all ecoregions.

These findings emphasize the precarious future of B. occidentalis and highlight the various stressors that likely contribute to the rapid loss of pollinator species worldwide. It is crucial to implement expanded international species-monitoring programs and enhance the integration of data from formal surveys and community science to improve our understanding of stressors and trends in bumble bee populations. The decline of this versatile species serves as an indicator of the broader loss occurring among numerous taxa sensitive to environmental changes on a global scale.

Janousek WM, et al.. 2023. Recent and future declines of a historically widespread pollinator linked to climate, land cover, and pesticides. Proceedings of the National Academy of Sciences. 2023 Jan 31;120(5):e2211223120.