Now we can add another spate of potential victims to climate change: arthropods, a hyper-diverse group of species that includes insects, spiders, centipedes, and the like.
A recent study has linked climate change to dramatic declines in arthropod populations. If broadly valid, the study could have chilling implications for a rapidly warming world.
In the mid-1970s, researchers measured the total biomass (living mass) of insects and other arthropods in intact rainforests on the Caribbean island of Puerto Rico.
Other researchers returned to the island recently and repeated the study using the exact same methods. To their surprise, they found that arthropod biomass was just one-eighth to one-sixtieth of that in the 1970s — a shocking collapse overall.
And the carnage didn’t end there. A bevy of lizards, birds, and frogs that feed on arthropods had fallen sharply in abundance as well.
For the Earth’s ecosystems, a collapse of arthropods could be downright apocalyptic. Arthropods pollinate plants, disperse seeds, recycle nutrients, and form the basis of food chains that sustain entire webs of life and agricultural production.
This is partly because arthropods are so abundant and diverse, comprising 70 percent of all known species on Earth. Humans think we rule the world, but the planet really belongs to arthropods.
Killer Heat Waves
The researchers who documented the arthropod collapse in Puerto Rico considered a variety of possible causes — but the evidence kept pointing to one likely driver: rising temperatures.
Temperatures in the rainforest have risen progressively in recent decades — by 2 degrees C (3.6 degrees Fahrenheit) on average.
But far scarier than a gradual rise in the thermometer is periodic heat waves. In Puerto Rico, the frequency of hot-weather events has risen sharply in recent years.
Heat waves are critical because nearly all living species have finite thresholds of temperature tolerance.
Consider, for example, the giant bats known as flying foxes. At 41 degrees C (106 degrees Fahrenheit), flying foxes become badly heat-stressed, struggling to find shade and flapping their wings desperately to stay cool.
But nudge the thermometer up just one more degree, to 42 C (108 degrees Fahrenheit), and the bats suddenly die.
Earlier this week, heat waves that peaked at 42 degrees C in tropical Queensland killed off almost a third of the region’s Spectacled Flying Foxes. The ground beneath bat colonies was littered with tens of thousands of dead and dying animals.
Global Warming and El Niño
And just as researchers were discovering the surprising vulnerability of arthropods, new research appears to be resolving a longstanding uncertainty about global warming.
The question was whether global warming will affect El Niño events — the vast fluctuations in Pacific sea-surface temperatures that drive multi-year variations in weather across large swaths of the Earth.
Crucially, in strong El Niño years, droughts and heat waves ravage many parts of the world, leading to intense wildfires and drought-related deaths of many plants and animals.
And this ties back to arthropods, because the researchers in Puerto Rico are convinced that an increase in El Niño heatwaves is the main driver of the arthropod Armageddon there.
Climate change is clearly involved in some of these declines. But habitat disruption, intensive agriculture, insecticides, and introduced parasites and pathogens are also taking a toll.
At a planetary scale, it’s apparent that arthropods are suffering from a variety of environmental insults. There is no single reason why their populations are collapsing.
We are changing our world in many ways at once. And the closer we look, the more we’re finding that the myriad little creatures that play vital roles in the fabric of life are struggling to survive the onslaught.