When I was young, driving a car through a warm night on a country road would produce a windshield thick with smashed bugs. This doesn’t happen anymore. I can drive for miles at night and have only a few insect remains to scrape off. When I was a kid, at the ballpark for a night game, I’d always see nighthawks wheeling in the sky around the light stanchions, diving and swerving as they snapped up insects attracted to the lights. I haven’t seen a nighthawk in years. Not too long ago, at my farm in northern Pennsylvania, tree swallows routinely nested nearby and were often seen soaring over the fields. I haven’t seen a tree swallow for a few years now.
These experiences, of bugs no longer thick in your headlights, of insect-eating birds no longer commonly seen, are confirmed by many reports in the literature of insect declines and declines in bird populations. For example, Sanchez-Bayo and Wychhuys (2019) reviewed studies reporting trends in insect populations. They demonstrated that a decline of massive proportions in insect populations is underway, and that this decline presents grave problems for ecosystems. It stands to reason that a decline in insects would lead to a decline in numbers of other creatures that eat insects, such as birds. Cornwall (2026), for example, reports on numerous findings of bird declines.
These well-chronicled declines in insect and bird populations are typically attributed to insecticide pollution, loss of habitat, light pollution, and global warming or to combinations of any or all of these. The entomologist Douglas Tallamy adds another culprit, the wide-scale planting of non-native plants that do not support plant-eating insects to the same degree as native plants. All of these causes could be important.
But a puzzle, as noted by Cornwall (2026) and by Lister and Garcia (2018) is that insect and bird declines are being observed not just in human-dominated landscapes, but in remote forests that are presumably unaffected by any of the above causes except for the on-going disruption of the climate due to global warming.
I think there is a bigger and more widespread cause that is staring us in the face. It’s carbon dioxide. It is clear that the physics of CO2 – its ability to absorb infrared radiation and augment the greenhouse effect – has a profound effect on the climate. But what about the chemistry of CO2? It should not be a surprise that the chemical impacts of enriched CO2 could also be huge.
The CO2 concentration of Earth’s atmosphere, now over 425 ppm, is 50% higher than it has been for millions of years, and the increase to this level has been extremely rapid compared to nature’s ability to adapt.
One impact of this increase could be that plants now have a major advantage in their eons-long “arms race” with insects. Plants produce a variety of chemicals to ward off insect predation. Producing these chemicals is metabolically costly. CO2 is a plant food. Give an organism access to 50% more food, and you empower that organism to produce metabolically costly chemicals at a greater rate. Because of this boost, plants may now be exceptionally successful at limiting insects. If and when CO2 levels are stabilized, a new balance between plants’ deterrent chemicals and insects' counter measures will likely develop, but for now, plants could be way ahead in the game.
Another chemical effect could be operating as well. Plants are intimately connected to the atmosphere and their input of carbon, now enriched due to the 50% higher CO2 concentration, may be leading to a changed ratio of nitrogen to carbon in products such as pollen and seeds. A striking example of this effect was reported by Ziska, et al. (2016). These authors found that the protein concentration of Solidago canadensis (Canada goldenrod) pollen, a vital nutrient for North American bees, has declined in inverse proportion to the rise in atmospheric CO2, dropping from a concentration of approximately 18% in the mid-1800s to approximately 12% today. They noted that pollen is the sole source of protein for bees, and also fulfills dietary requirements for lipids, sterols, vitamins, and minerals needed for larval development.
There are other studies that support the idea that enriched carbon dioxide is having profound effects on insects and other biota such as birds. I referenced some relevant work in letters I wrote to entomology journals: https://academic.oup.com/ee/article-abstract/48/2/274/5372493 and https://www.sciencedirect.com/science/article/abs/pii/S0006320720302822?via%3DihubI also discussed this issue here: https://www.nivemnic.us/?p=3924 . There is much information in Lewis Ziska's book: https://cup.columbia.edu/book/greenhouse-planet/9780231556613/
It is well known that chemical effect of enriched CO2 is taking place in the oceans. CO2 dissolves in the ocean and forms carbonic acid. Due to this input, the ocean’s average pH has dropped from 8.2 to 8.1 within the last 200 years. Because pH is a logarithmic scale, this decrease represents an increase in hydrogen ion concentration of over 25%, a change that is already threatening some marine creatures. More on this is available from many sources; e.g., Kolbert (2014).
If pollution of Earth’s atmosphere by the rising concentration of carbon dioxide is having a profound chemistry-related impact on Earth’s biota, we have another pressing reason besides climate change to move away from fossil fuel combustion and to push for more clean sources of power such as nuclear, geothermal, solar, and wind.
References
Cornwall, Warren, 2026, Fading Melodies, Science 391 (6788), DOI: 10.1126/science.aeg6834
Kolbert, E., 2014, The Sixth Extinction, Henry Holt & Co., NY
Lister, Bradford and Andres Garcia (2018). Climate-driven declines in arthropod abundance restructure a rainforest food web. PNAS. 115:E10397–E10406
Sanchez-Bayo, Francisco, and Kris A. G. Wyckhuys, 2019. Worldwide decline of the entomofauna: A review of its drivers. Biological Conservation. 232, 8-27.
Ziska, L.H., J.S. Pettis, J. Edwards, J.E. Hancock, M.B. Tomecek, A. Clark, J.S. Dukes, I. Loladze, and H.W. Polley. 2016. Rising atmospheric CO2 is reducing the protein concentration of a floral pollen source essential for North American bees. Proc. R. Soc. B, 283(1828): 20160414.
No comments:
Post a Comment