The best place to see one of South Africa’s national treasures — the iconic “living stones’’ — is on a gentle rolling plain at the Knersvlakte in Namaqualand, says professor Guy Midgley, an expert in biodiversity and global change science at Stellenbosch University.
It’s here where the tiny, cryptic succulents — the lithops — hug the hard desert ground. “You think, looking across the landscape, that you’re just looking at little klippies, but they’re actually plants,” he says.
“There’s nothing to eat there and if you can disguise yourself you can protect yourself from herbivores. These plants are fascinating and beautiful.”
But this group of highly specialised plants, which are “exquisitely” tied into the climate of the winter rainfall Karoo, along with other endemic species, are most under threat from a warming world. (Endemic plants and animals are unique to one geographic location, such as one island or one country.)
Midgley is one of the authors of a new study warning that numerous animals and plants that are unique to the world’s biodiversity-rich natural places face extinction if greenhouse gas emissions continue to climb.
The global team of scientists analysed 273 biodiversity hotspots — places with exceptionally high numbers of animal and plant species — on land and at sea.
They concluded that if the planet heats by more than 3°C then a third of endemic species living on land and about half of endemic species in the sea will disappear forever. Overall, 92% of land-based endemic species and 95% of marine endemics face negative consequences, such as a reduction in numbers, at 3°C.
Their warning is stark, considering current policies put the world on track for about 3°C of heating. Human activity has warmed the world by about 1°C since preindustrial times.
If greenhouse gas emissions keep rising, the Caribbean islands, Madagascar, and Sri Lanka could see most of their endemic plants go extinct as soon as 2050.
The tropics are especially vulnerable, with more than 60% of tropical endemic species facing extinction from climate change alone.
On mountains, 84% of endemic animals and plants face extinction at these temperatures, while on islands that number rises to 100%.
Endemic species most at risk include lemurs in Madagascar, giant tortoises in the Galápagos, snow leopards in the Himalayas, the vaquita porpoise in the Gulf of California, the orange-breasted sunbird, well-known in the Cape Floristic Region, as well as blue cranes and multiple bee species that are critical to pollination in South Africa, the third-most biodiverse country in the world, with high levels of endemism.
For the living stones succulents, warming could bring devastation, Midgley says, “This is a whole super genus that is endemic basically to the Namaqualand area.”
The tiny plants put huge effort into their once-a-year flowering events.
“The seeds are very specialised. They’ve got these special fruit capsules that only open when it rains so they only release seeds during rainfall events. A little raindrop has got to drop into the capsule, pop, and then it pops the seeds out, and then they disperse a few inches.”
But as the climate warms, the lower reliability of winter rainfall, as well as overheating, puts the succulents at risk. “They’re one of these niche endemics that is entirely dialled into the climatic regime and that’s why they’re so vulnerable … That incredible link to climatic cues become strained and finally broken and then we will lose them all.”
The study describes how climate change is already affecting biodiversity and is likely to intensify over the next few decades unless substantive mitigation efforts are implemented.
For widespread species, geographic range shifts, expansions and contractions are among the most common responses of species to climate change.
But in contrast, the more restricted ranges of endemic species means that they are often at greater risk of extinction from local impacts, including habitat loss and interactions with introduced species, the effects of which are being worsened by changes in climate.
Introduced species may either be unaffected or benefit from climate change, according to the study. “It suggests that you could potentially end up with biodiversity hotspots that have depleted in endemics but then become much more homogenised through invasive species,” Midgley says.
Reducing extinction risks requires both adaptation responses in biodiversity-rich spots and better mitigating climate change, says the study.
Midgley says he is concerned about a mass bird and bat mortality event in northern KwaZulu-Natal in November last year.
“Getting these mass mortality events is really a bit of a wake-up call,” he says.
The authors say remaining within the climate goals of the Paris Agreement, which aims to keep global warming well below 2°C, ideally at 1.5°C, would save most species.
In total, just 2% of endemic land species and 2% of endemic marine species face extinction at 1.5°C, and 4% of each at 2°C.
The authors say: “Strong commitments from global leaders ahead of the climate change summit in Glasgow later this year could put the world on track to meet the Paris Agreement, and avoid the widespread destruction of some of the world’s greatest natural treasures.”