For some, the
culprit was clear. Microscopic algae smothered aquatic life to death in the San
Francisco Bay. Drought killed 512 wildebeests, 430 zebras, 205
elephants, 51 buffaloes, and 12 giraffes in Kenya. Starvation wasted away the hundreds of flightless little
blue penguins that washed up on New Zealand beaches at half their typical
weight.

Compressed and
compiled, these death tolls collapse into senselessness; it’s a familiar
feeling to the modern writer or reader. “While statistical shock and awe is
abundant, we are often unable to grasp the true meaning of such figures—stymied
by basic
innumeracy, the incomprehensible scale of our present crises, and the profound mismatch between hard data and human feeling,”
Eleanor Cummins wrote
of Covid-19 for this magazine in 2020. But a careful look at any mass mortality
event can restore its contours. Take the hundreds
of Cape fur seal carcasses that washed up on Namibia’s coastline early last
year. On a single February day, more than 400 appeared along the water’s edge.
In one photograph taken by biologists during the aftermath, a dark, wet seal
pup lies as flat as a slipper near a tape measure indicating it never grew to
be longer than 75 centimeters long; in another, 14 dead seals are spread on the
beach in a lonely colony of dark, lifeless curves. “It’s been mentally and
emotionally taxing,” a conservationist said at the time. “It truly feels like a war zone
out there.”

Unfortunately,
experts say it’s fair to categorize mass mortality events as a phenomenon on
the historic upswing. “They’re happening more often, and more individuals are
dying each time they happen,” Tye said. In 2015, Fey and his colleagues
reviewed more than 7,000 mass mortality events since 1940 and found that reported die-offs have, indeed, become more
common for birds, fish, and marine invertebrates. The scientists attributed one
in four mass mortality events to disease (like the avian flu), one in five to
human perturbation (like contamination), and about one in six to biotoxicity
(like harmful algae blooms). One in four, they found, was directly influenced
by climate: weather, heat stress, oxygen stress, starvation. Other research on
North American freshwater lakes and the Mediterranean
Sea demonstrates a link between rising environmental
temperatures, extreme heat events, and die-offs.