Like almost everything else with climate change, the impacts are mostly bad news. Increasing drought severity is already driving pollinator declines in the southwest, and secondary climate change impacts like habitat fragmentation are likely adding on to other stressors. We also know that impacts are going to be regional and that different pollinators will respond in unique ways. There’s lots of nuance here and plenty of unanswered questions. So let’s dive into the full story to understand. 

The Biggest Climate Change Threat to Pollinators

Climate change is a big hurdle, but is it the top threat to pollinators? The general consensus is that habitat loss takes that top position. Losing habitat is tough – it isn’t like encountering sub-par pollen or having to cope with increased disease pressure. With habitat loss, there’s simply nothing to eat and nowhere to stay. It does not mean having a harder life; it means there is nowhere to live a harder life. 

The bad news is that, while climate change doesn’t take the top spot, it is still a major threat to pollinators. Perhaps worse, its impacts could exacerbate the threats that are already pushing pollinators into decline, such as habitat loss, pesticide exposure, pathogens, and invasive species impacts.

Direct vs Indirect Effects of Climate Change

Imagine a group of caterpillars in Oklahoma. It is July, and it hasn’t rained for over a month. The caterpillars keep on eating but are growing weak. They would normally do ok in a drought, but this year’s lack of moisture is extreme. The lack of water is so stressful to their bodies that all but a few succumb to minor infections. Climate change, by increasing the severity of drought, has directly impacted the caterpillar’s survival. 

Now imagine their habitat, a community of native plants growing in a ditch alongside a seldom-used gravel road. The little community is drought-tolerant, but the plants closest to the gravel edge are past the tipping point. They succumb. Though indirect, this is also an impact of climate change on our caterpillars; the drought has diminished the total amount of food available for them to eat. 

Climate change has many direct and indirect impacts on insect pollinators. 

Direct impacts are usually driven by things like air temperature, precipitation, or CO2 levels. Our hypothetical direct impact shows how precipitation drops can stress insects. Temperature changes can be similarly disastrous, causing issues with life-stage development or interfering with insect’s ability to overwinter.

Indirect impacts are more tangential and can be harder to understand. The following three indirect impacts are an illustration of how complex these knock-on climate change impacts can be: 

• Pollen protein levels: Native bees get much of their nutrition from pollen, including the protein they need to grow and thrive. The protein content of goldenrod, a major pollen source in the fall, has been shown to decrease with increasing levels of atmospheric CO2. As CO2 levels climb, pollen protein content will continue to drop, reducing the nutrients bees have available to them at an important time of the year. 
• Decreases in flower biodiversity: Pollinators that specialize in certain kinds of flowers are reliant on high plant biodiversity, as they can only get floral resources from a narrow subset of the overall plant community’s flowers. Climate change lowers plant biodiversity by stressing native habitats and increasing the spread of invasive species. As a result, specialist pollinators will have less and less access to the flowers they need to survive as climate change drives down the diversity of the local plant community.
• Reduced genetic diversity: Pollinator populations need to breed outside their local gene pool to stay healthy. Climate change increases the rate of habitat fragmentation, meaning habitats are less connected than they once were. As habitat connections are broken, pollinators are less able to interbreed and maintain diverse genetics. For colony-forming bees, like our native bumble bees, this can create an “extinction vortex.” These occur when colonies in small populations produce sterile males due to inbreeding. The sterile males effectively remove the colony’s genetic diversity from the already diminished gene pool, reinforcing a cycle of genetic diversity loss that will ultimately drive the population to extinction. 

We are still working to understand the nuances of the many direct and indirect climate change impacts on pollinators, but the outlook so far isn’t particularly great. Luckily, there is a lot you can do locally for pollinators as humanity gets its act together to reduce global emissions.

What Can I Do to Help Pollinators?

Think globally, act locally. Climate change will take decades of worldwide effort to solve. You can give pollinators a fighting chance in the meantime by protecting and improving local pollinator habitat. 

• Removing invasive species is one of the most effective conservation actions out there. Find a conservation district workday and volunteer your time. Learn more about invasive species identification and removal on our website. 
• If you own farmland, follow pollinator-friendly mowing guidance in your grassways and ditches, then look up your local NRCS agent to ask about pollinator-friendly conservation practices and programs. 
• If you have an HOA, review their rules and regulations for pollinator-friendly native plants and then install your own native garden! In 2024, Illinois passed the Native Homeowner's Landscaping Act, which prohibits associations from banning planting or growing Illinois native plants. Be sure to take a look at your municipality's ordinance as well, as it may have buffer areas and height restrictions you'll still need to be compliant with.
• If you live in a city, urban areas are surprisingly good for pollinators, volunteer with the city’s park district, or look for pollinator-focused community science projects that need your help.

Check out our podcast episode on this topic to hear more about the impacts of climate change on pollinators with Brodie Dunn, Extension outreach associate.

Listen to the Podcast

More Resources

• The Solitary Bees by Bryan Danforth: book on solitary bees with a section on climate change impacts. Also available through most library systems.
• Monarch project mowing guidelines

Thank you for reading!

References

• Cameron SA, Sadd BM. 2020. Global Trends in Bumble Bee Health. Annu. Rev. Entomol. 65(1):209–232. https://doi.org/10.1146/annurev-ento-011118-111847.
• Crossley MS, Smith OM, Berry LL, et al. 2021. Recent climate change is creating hotspots of butterfly increase and decline across North America. Global Change Biology. 27(12):2702–2714. https://doi.org/10.1111/gcb.15582.
• Danforth BN, Minckley RL, Neff JL, et al. 2019. The Solitary Bees: Biology, Evolution, Conservation. Princeton University Press. https://doi.org/10.2307/j.ctvd1c929.
• Kuhlmann M, Guo D, Veldtman R, et al. 2012. Consequences of warming up a hotspot: species range shifts within a centre of bee diversity. Diversity and Distributions. 18(9):885–897. https://doi.org/10.1111/j.1472-4642.2011.00877.x.
• Miller-Struttmann NE, Geib JC, Franklin JD, et al. 2015. Functional mismatch in a bumble bee pollination mutualism under climate change. Science. 349(6255):1541–1544. https://doi.org/10.1126/science.aab0868.
• Mullen D. Rusty Patched Bumble Bee (Bombus affinis) Species Status Assessment.
• Zayed A, Packer L. 2005. Complementary sex determination substantially increases extinction proneness of haplodiploid populations. Proc. Natl. Acad. Sci. U.S.A. 102(30):10742–10746. https://doi.org/10.1073/pnas.0502271102.
• Ziska LH, Pettis JS, Edwards J, et al. 2016. Rising atmospheric CO 2 is reducing the protein concentration of a floral pollen source essential for North American bees. Proc. R. Soc. B. 283(1828):20160414. https://doi.org/10.1098/rspb.2016.0414.