A new study finds broad impacts across most of the planet’s ecosystems.
By Michael White
When we speak about climate change, it’s usually in the future tense. If we don’t dramatically reduce our carbon emissions in the next two decades, the average global temperature is likely to rise by more than 2˚C. If temperatures increase by that much or more, sea levels could rise by four feet or more, coral reefs would disappear, and major staple crops could fail to feed the world by 2100.
When we talk about future climate change, our discussion often stalls at the uncertainties inherent in scientists’ statistical models and forecasts. These uncertainties are exploited by those—such as Myron Ebell, head of Donald Trump’s Environmental Protection Agency transition team—who reject the broad scientific consensus that humans are warming the Earth. Instead of developing plans to move to a greener, zero-emissions economy, we’re still arguing over the pace, causes, and consequences of climate change.
But we should stop treating the major impacts of climate change as if they are something that could happen in the future. As a recent paper in Science describes, climate change has already left a “broad footprint” on our planet. Most life on Earth spawns, hatches, buds, blooms, develops, migrates, or hibernates in a way that is governed by climate. All of these processes have already been broadly altered by climate change, argue the authors, an international group of biologists from various fields who surveyed several decades of biological studies. Nearly every ecosystem on the planet has been modified by global warming, and these changes “point toward an increasingly unpredictable future for humans.”
One of the clearest consequences of warmer temperatures is changes in the timing of critical life cycle events of many organisms. Spring behaviors, such as hatching, budding, flowering, and mating “have advanced 2.3 to 5.1 days per decade” in ocean, fresh water, and land environments. One study reviewed by the researchers found substantial shifts in plant-growing seasons across 54 percent of the Earth’s land area in the past 30 years. Because organisms depend on other organisms for food and habitat, such shifts in the timing of life cycles threaten the survival of some species as they fall out of sync with the organisms they depend on. Butterflies lay their eggs on particular host plants; if those plants bloom and then die early, the butterfly larvae don’t survive. In many lakes, algae, which bloom seasonally, are at the base of the food chain; if algae peak earlier than the species that sit one link up in the food chain, the entire lake ecosystem is affected.
Climate change is not only reshaping ecosystems; it’s also reshaping animals’ bodies. Body size is closely tied to metabolism, meaning that, for many species, warmer conditions often favor smaller, more energetically efficient bodies. Over the past half-century, the body sizes of several Appalachian salamander species have shrunk by nearly 10 percent. The wing lengths of several species of birds in the United States have also decreased measurably. Several species of commercially important fish in the North Sea have shrunk over the past 40 years, resulting in a 23 percent decrease in fishing yields by weight. In other cases, animals living in higher and colder climates, like marmots, have increased their body size in response to a longer growing season. Climate change has also altered the sex ratios of some species, including some species of lizards, fish, and sea turtles — many populations have become more feminized or masculinized in ways that affect their reproductive rates.
Other aspects of global warming’s broad footprint on the world’s ecosystems include changes in the abundance of more than 80 percent of the thousands of species included in population studies; major poleward shifts in living ranges as warm regions become hot, and cold regions become warmer; major increases (in the south) and decreases (in the north) of the abundance of plankton, which forms the critical base of the ocean’s food chain; the transformation of previously innocuous insect species like the Aspen leaf miner into pests that have damaged millions of acres of forest; and an increase in the range and abundance of human pathogens like the cholera-causing bacteria Vibrio, the mosquito-borne dengue virus, and the ticks that carry Lyme disease-causing bacteria.
One can argue over how serious any one of these climate-driven changes are, and whether or not they are harmful. Some might even be beneficial, such as the increased yield of crops that do better with warmer temperatures and more carbon dioxide in the atmosphere. But when we consider just how broad the impact of climate change is already, we should be worried. The authors of the Science paper examined 94 distinct ecological processes across marine, fresh water, and terrestrial environments and found that 82 percent of them have been modified by the mere 1˚C of average global warming we have experienced so far.
The consequences of widespread and rapid changes to something as complex as the world’s ecosystems are difficult to predict. The unpredictability of these consequences has been used as an excuse to dismiss them and paint scientists as alarmists. But unpredictability is exactly what should concern us: Our civilization, including our agriculture, water usage, population geography, and public-health measures, are adapted to fit the global climate that we live in. The prospect of further broad, unpredictable shifts to the world’s ecosystems should spur us to action, not complacency. As the authors of the Science paper write, “humanity depends on intact, functioning ecosystems for a range of goods and services.” For most life in those ecosystems, climate change is not a future event, but a present reality.