In 1958, Charles David Keeling began measuring carbon dioxide emissions at the Mauna Loa Observatory. Decades later, he compiled his findings to create one of the most important graphs in environmental science: The Keeling Curve. This steep, upward curve shows the relationship between humans’ burning of fossil fuels and increased levels of carbon dioxide in the atmosphere. The curve increases steadily on the whole, but closer examination reveals regular vertical increases and decreases that make up the sloping line.
Scholars were immediately struck by the overall trend from year-to-year, which matched the annual burning of fossil fuels. But the less-discussed feature of the curve is the seasonal increase and decrease of carbon dioxide in the atmosphere that is not explained by fossil fuel burning.
Keeling was the first to find that the lifecycles of plants influenced the amount of carbon dioxide in the atmosphere. In the summer, plants withdraw more carbon dioxide for growth and reproduction, whereas in the winter, plants release carbon dioxide as they decompose.
This pattern is described by phenology, a branch of environmental science that studies cycles and seasonal phenomena in the natural world. The Keeling Curve shows how plants influence carbon dioxide levels; but the relationship works in both directions. The timing of seasonal events is integral to the function of the natural world, but has also become inexorably linked to human activity.
Plants help take up some of the carbon we burn off, but the amount of fossil fuels we burn also alters organisms’ lifecycle patterns. Tracking these changes shows us how life in different parts of the world responds to environmental triggers.
Phenology encompasses everything from the blooming of the saguaro flower in Tucson to the annual great wildebeest migration in east Africa. The external environment triggers most of these events, however.
Events such as Japan’s iconic cherry tree blossoming or the famous sardine run up the coast of southern Africa are triggered by changes in temperature. As climate patterns change, so does the timing of such events. That could delay blooming in the desert, confusing pollinators that depend on the flower’s nectar, or it might mean that fish migrate earlier, with potential repercussions for local fisheries if they have predetermined fishing seasons.
Naturalists such as Aldo Leopold began tracking spring “green up” and when leaves lose their colors long before the start of organized phenology databases. History is scattered with individuals recording the timing of different phenophases, but it wasn’t until 2007 that the United States Geological Survey and the UA created the National Coordinating Office for the USA National Phenology Network on the UA campus.
The USA-NPN standardized methods for data collection. Eight years later, the USA-NPN is now the center of national phenology efforts and has created an innovative citizen science phenology network that spans the country, called Nature’s Notebook.
Through Nature’s Notebook, the USA-NPN is able to use observations everyday people make about local organisms and compile an extensive database that is available to the public. These observations are then used to understand how the environment is changing in response to external factors. That analysis can help policy makers consider what changes, if any, need to be made to maintain ecosystem integrity.
LoriAnne Barnett, the education coordinator for the USA-NPN, and Erin Posthumus, the outreach coordinator, noted that in 2015 the Nature’s Notebook dataset was used by researchers to predict that future springs could be as much as three weeks earlier than what we are experiencing today and that warmer winters in California are delaying the timing of plant phenophases. They added that within the next few years, it may be possible to use Nature’s Notebook to determine large-scale trends, such as range shifts and altered migration patterns.
Since Keeling’s discovery, the scientific community has been striving to understand the extent to which climate change will affect the world we live in. Informed decisions about the future require long-term datasets that show changes in the natural world over time.
The USA-NPN is special not only because it is creating such a database, but also because it is doing so by harnessing the power of citizen scientists.
Each region responds differently to environmental triggers, but there aren’t enough resources to install monitoring stations in every city in the country. It is possible to get civilians to input what they see outside their windows every day to crowd source science.
Barnett and Posthumus said that the benefits of Nature’s Notebook include a widespread dataset that allows scientists to see variations among regions and species, and the unique chance for citizens to become involved in science.
The journey to understanding climate change began with one scientist, but the future of climate adaptation will depend on a world of civilians.

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