Climate change is unravelling ecosystems and has caused widespread local population extinctions among plants and animals, according to a new report by the Intergovernmental Panel on Climate Change (IPCC) on the effects of global warming, species adaptation and their vulnerability.
In research its team of scientists examined, climate-caused local population extinctions were detected in 47% of 976 species on land and in the ocean, and associated with increases in hottest yearly temperatures.
“Local extinctions at the fine scale are the first steps in the march towards global extinction of species,” said Professor Guy Midgley, an expert in biodiversity and global change science at Stellenbosch University, and an IPCC lead author. “That is a worrying prospect.”
Midgley, who was speaking at a meeting of the Presidential Climate Commission on the key findings of the IPCC report, said that the average global temperature has increased by at least 1.1°C and “it’s very clear that once we start to exceed 2°C, the higher the risk of extinction really is. And so there’s a very strong incentive for us not to test those levels.”
According to the report, climate-driven population extinctions have been higher in tropical (55%), than in temperate habitats (39%), higher in freshwater (74%), than in marine (51%) or terrestrial (46%) habitats and higher in animals (50%) than in plants (39%).
Global extinctions or near extinctions have been linked to regional climate change in three documented cases.
The golden toad, which is found in cloud forests only, was extinct by 1990 in a nature preserve in Costa Rica after successive extreme droughts. In Queensland, Australia, the white sub-species of the lemuroid ringtail possum disappeared after heatwaves in 2005; intensive censuses found only two individuals in 2009. The Bramble Cays Melomys was not seen after 2009 and declared extinct in 2016, with sea level rise and increased storm surge associated with climate change the most probable drivers.
The IPCC report describes how, in the ocean, marine plants and animals, including entire communities, have shifted their distributions poleward at an average speed of 59km a decade because of increasing water temperatures.
“Ocean acidification and decreasing oxygen in the water also play a part. Together all three processes have caused a reorganisation of biodiversity over the past 50 years, especially at the ocean surface.” Those species that cannot adjust or move fast enough are at high risk of vanishing forever.
As a result, it said, the geographic patterns and the regional and local abundance of plants and animals are changing, with potentially severe harm for herders, farmers, fishers, hunters, foragers and other people who directly rely on nature’s services.
A myriad of other harms caused by compound those of climate change, including habitat loss and fragmentation, hunting, fishing and its bycatch, over-exploitation, water abstraction, nutrient enrichment, pollution, human introduction of invasive species, pests and diseases — all of which reduce climate resilience.
Healthy ecosystems and rich biodiversity support human survival by providing food, oxygen, recycling of nutrients and water filtering, among numerous other benefits. They also store large amounts of carbon that limit global warming.
“It’s a big chunk of emissions that are absorbed by our living ecosystems,” said Midgley. “Without them we would have been in a far warmer world than we currently are. Therefore it’s absolutely vital that we understand that we need to protect these systems and their ability to sequester carbon away from the atmosphere.”
In the case of Africa, at about 1.5°C of warming about half the species assessed are projected to lose a third of their populations and a third of their geographic ranges. “At 1.5°C, we’re starting to see some significant adverse effects in Africa particularly in freshwater systems and off the east coast of Africa where our coral systems are under extreme risk even at fairly low levels of warming,” said Midgley.
Current projections imply that at a global warming level of 2°C by 2100, up to 18% of all species on land will be at high risk of going extinct, according to the report’s findings. If the world warms up to 4°C, every second known plant or animal species will be threatened.
The extinction risk is especially high for cold-loving species living in the high mountains or in polar regions, where the effects of climate change are unfolding at global maximum speed and extent.
These bleak trends can still be reversed by restoring, rebuilding and strengthening ecosystems and by managing them sustainably, “which will also support the well-being and livelihoods of people”, said the report.
“To achieve this balance, drastic greenhouse gas emissions reductions are required now to avoid further global warming and its deadly impacts on ecosystems around the world. For indeed, humans are just one of the many living organisms in our beautiful and complex world.”