In 2014, as temperatures topped 40deg Celsius, or 104deg Fahrenheit, in eastern Australia, half of the region's black flying fox (Pteropus alecto) population perished, with thousands of the bats succumbing to the heat in one day.
The decline of wild populations doesn't just translate into species loss but can also heighten extinction risk.
This die-off is only one example of the catastrophic loss of wildlife unfolding globally. On average, wildlife populations tracked by scientists shrank by nearly 70% between 1970 and 2018, a recent assessment b WWF and the Zoological Society of London (ZSL) found.
"When wildlife populations decline to this degree, it means dramatic changes are impacting their habitats and the food and water they rely on," WWF chief scientist, Rebecca Shaw, said in a statement. "We should care deeply about the unraveling of natural systems because these same resources sustain human life."
WWF's "Living Planet Report 2022," launched this October, analyzed populations of mammals, birds, amphibians, reptiles and fish. "It is not a census of all wildlife but reports how wildlife populations have changed in size," the authors wrote.
A million species of plants and animals face extinction today, according to a landmark 2019 report from the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), an international scientific body. The new analysis uncovers another aspect of this biodiversity crisis: The decline of wild populations doesn't just translate into species loss but can also heighten extinction risk, particularly for endemic species found only in one location.
Instead of looking at individual species, the Living Planet Index (LPI) on which the report is based tracks 31,000 distinct populations of around 5,000 species. If humans were considered, for example, it would like tracking the demographics of countries. Population declines in one country could indicate a localized threat like a famine, but it was happening across continents, that would be cause for alarm.
The steepest species declines occurred in Latin America and the Caribbean, where wildlife abundance dropped by 94% on average. In this region, freshwater fish, reptiles and amphibians were the worst affected.
Freshwater organisms are at very high risk from human activities worldwide. Most of these threats are linked to habitat loss, but overexploitation also endangers many animals. In Brazil's Mamiraua Sustainable Development Reserve, populations of Amazon pink river dolphin or boto (Inia geoffrensis) fell by 65% between 1994 and 2016. Targeted fishing of these friendly animals for their use as bait contributed to the decline.
Climatic changes render terrestrial habitats inhospitable too. In Australia, in the 2019-2020 fire season, around 10 million hectares (25 million acres) of forestland was destroyed, killing more than 1 billion animals and displacing 3 billion others. For southeastern Australia, scientists showed that human-induced climate change made the fires 30% more likely.
These losses are happening not just in land-based habitats but also out at sea. Coral reefs and vibrant underwater forests are some of the most threatened ecosystems in the world. But they're being battered by a changing climate that makes oceans warmer and more acidic. The planet has already warmed by 1.2degC (2.2degF) since pre-industrial times, and a 2degC (3.6degF) average temperature rise will decimate almost all tropical corals.
However, the bat deaths in Australia, Brazil's disappearing pink river dolphins, and the vulnerability of corals are extreme examples that can skew the index, which averages the change in population sizes. In fact, about half of wildlife populations studied remained stable and, in some cases, even grew. Mountain gorillas (Gorilla beringei beringei) in the Virunga Mountains spanning Rwanda, the Democratic Republic of Congo and Uganda number around 604 today, up from 480 in 2010.
Despite these bright spots, the overall outlook remains gloomy. Even after discounting the extremes, the downward trend persists. "After we removed 10 percent of the complete data set, we still see declines of about 65 percent," Robin Freeman, an author of the report and senior researcher at ZSL, said in a statement.
Even in cases where a changing climate proves favorable, the multitude of threats can prove insurmountable.
Often, habitat loss, overexploitation and climate change compound the risk. Even in cases where a changing climate proves favorable, the multitude of threats can prove insurmountable. Take bumblebees, for example. Some species, like Bombus terrestris or the buff-tailed bumblebee, could actually thrive as average temperatures rise. But an assessment of 66 bumblebee species documented declining numbers because of pesticide and herbicide use.
The report emphasizes the need to tackle these challenges together. Protecting habitats like forests and mangroves can, for example, maintain species richness and check greenhouse gas emissions. The kinds of plants and their abundance directly impact carbon storage because plants pull in carbon from the atmosphere and store it as biomass.
One of the deficiencies of the LPI is that it doesn't include data on plants or invertebrates (including insects like bumblebees).
The report was released in the run-up to environmental summits that will see countries gather to thrash out a plan to rein in climate change in November and later in the year to reverse biodiversity loss. Government leaders are set to meet for the next level of climate talks, called COP27, in Egypt from Nov. 6-13. At the last meeting of parties, known as COP26 in Glasgow, U.K., last year, nations committed to halt biodiversity loss and stem habitat destruction, partly in recognition that this would lower humanity's carbon footprint.
In December, the 15th meeting of the Conference of the Parties to the U.N. Convention on Biological Diversity (CBD) will be held in Montreal. Representatives from 195 states and the European Union will meet to decide the road map to 2030 for safeguarding biodiversity.
