Global warming threatens pollinators and people by Holly Holt, PhD

Humans have emerged as Earth's dominant species because we are able to drastically modify our surroundings to suit our needs. Unprecedented human growth and material culture have led to unparalleled levels of resource consumption, escalating the demands on our planet's remaining natural resources. These human activities have generated excess greenhouse gases, sparking rapid and global changes in climate with deadly consequences. Many species are struggling to adjust to unfavorable environmental conditions that they did not co-evolve with. Some species, however, are able to exploit newly opened ecological niches. The relationships between pollinators and their habitats, and the terms of their survival, are being reshaped by climate change.

Climate change disrupts the links between pollinators and their habitats in several ways. Global warming subjects habitats to extreme weather events, both acute and chronic. Intense storms, droughts, extended periods of precipitation, hotter summers and warmer winters all have cascading effects on ecosystems. For example, new weather patterns can alter when plants bloom and the length of the flowering period. Stressful conditions can also reduce the quantity and quality of nectar and pollen provided by plants. For example, experimentally increasing temperatures to mimic projected climatic conditions decreased nectar production by 90% in key flowering plants on the Tibetan plateau.1 Likewise, elevated carbon dioxide levels decrease the protein concentration in goldenrod, an important fall food source for wild and managed bees in North America.2 Inclement flight weather (too hot, too cold, too windy, too rainy) also restricts bee foraging activity, reducing the quantity of offspring that can be successfully nurtured. Notably, bees have specific adaptations that enable them to survive cold winters and hot summers (including entering a state of suspended activity or quiescence called diapause). However, the duration and intensity of negative environmental conditions can still overwhelm bees' protective adaptations. For example, warmer winters are linked to lower survival of bee species that overwinter as adults. Unseasonably warm winters raise bees' metabolisms. As a result, bees burn more calories and deplete their energy stores at a faster pace. Indeed, bees may emerge earlier in the spring with lower body weight. Altered weather may also signal bees to emerge from quiescent phases when important plant species are not in bloom. Such temporal mismatches between flowers and bees are particularly damaging for specialist species (as summarized in Kammerer et al, 2020).3

As global temperatures rise, the optimal climatic conditions for some species will shift geographically. Humans, however, have fragmented the landscape into a patchwork of developed and natural lands, and everything in-between. Some species are able to disperse more easily than others across human-modified landscapes, which may lack floral resources or be treated with pesticides. Furthermore, shifts in pollinator range will alter the dynamics between pollinators and their pathogens, parasites, parasitoids and other pests. Stressful environmental or nutritional conditions, as well as pesticide exposure also immunosuppress pollinators, making them more susceptible to disease and infestations.

Whether a pollinator species is ecologically disenfranchised by climate change depends on its unique life history and the climatic vulnerability of the blooming plant species it relies on. At a regional scale, some pollinator species may emerge as “winners or losers" as their immediate habitat is redefined by climate change and land use. For example, the range of the arid-adapted Certina australensis bee is expected to expand as regions of Australia become increasingly arid. In contrast, the projected wetter springs, longer and hotter summers and warmer winters in the Northeastern US are expected to decrease wild bee abundance.3 At a global scale, however, pollinator abundance and diversity are in decline. As individual pollinator species fall victim to disruptions caused by climate change and other stressors, ecosystems become more susceptible to further perturbations as they increasingly rely on the services provided by the remaining pollinator species. This lack of system redundancy or “pollinator insurance" creates a precarious situation for the pollinators that anchor natural food webs as well as the many species, including humans, that depend on the fruits of pollinators' labor.

How can you protect the planet and pollinators from climate change?

  1. Estimate your carbon footprint. Learn about your impact on the environment by estimating your carbon footprint.
  2. Make environmentally friendly lifestyle changes. Read about actions you can take to reduce your carbon footprint.
  3. Create pollinator habitat. Help replenish pollinator habitat lost to climate change and other pollinator stressors. Whether you are planting a pollinator garden in your yard or enrolling farmland in the NRCS Conservation Reserve Program, you can take action to support pollinators by creating habitat for them today! The Xerces Society for Invertebrate Conservation provides guidance for creating or enhancing pollinator habitat in natural lands; cities and towns; roadsides and other rights-of way; yards and gardens; and working lands. Information about regionally appropriate native plants is also available through the Xerces Pollinator Conservation Resource Center. The P4 Plan also offers guidance. If you're not sure how best to get involved, reach out to your local university's extension program for ideas and help.
  4. Speak up for pollinators and the planet! Tell your representatives that climate change threatens pollinators and our food security. Advocate for environmentally sustainable action.
  5. Participate in citizen science. Monitor pollinators and their habitat! For example, consider participating in Budburst, which tracks how plant blooming periods are responding to climate change. The data you contribute will support research efforts to conserve pollinators and the resources they need. You can read about and select other programs that matches your interests and availability here.

References

  1. Mu, J. et al. Artificial asymmetric warming reduces nectar yield in a Tibetan alpine species of Asteraceae. Ann. Bot. 116, 899–906 (2015).

  2. Ziska, L. H. et al. Rising atmospheric CO2 is reducing the protein concentration of a floral pollen source essential for North American bees. Proc. R. Soc. B Biol. Sci. 283, 20160414 (2016).

  3. Kammerer, M., Goslee, S. C., Douglas, M. R., Tooker, J. F. & Grozinger, C. M. Shifting norms: wild bees as winners and losers of land use and climate change. In Review. (2020).