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Although large creatures such as the Southern Right Whale can migrate over great distances, they are part of a complex marine food chain that is vulnerable to changes in temperature and other climate-induced impacts. (Photo: Steve Benjamin / WILDOCEANS)
Just as governments have struggled at the last minute to seal their borders against the coronavirus crisis, a similar sense of urgency is needed to delay the imminent risk of “sudden and severe” impacts of the climate crisis, scientists warned the Wednesday.
There are still widespread perceptions that the more severe effects of climate change can only manifest gradually towards the end of the century.
But a new study in the leading scientific journal Nature suggests that serious disruptions to critical elements of global ecology (and the people who depend on it) may start much more abruptly than anticipated, possibly within the next 10 years, unless concerted steps are taken to “crush [climate change] curve”.
Lead author Dr. Christopher Trisos of the University of Cape Town suggests that, in a scenario of continuous high carbon emissions, such abrupt events, including “catastrophic” extinctions of terrestrial and marine species, could even begin before 2030 in the tropical zone. oceans of Africa and then spread to tropical forests and higher latitudes by 2050.
Trisos, Rhodes Scholar and principal investigator of the UCT African Climate and Development Initiative, and their fellow authors, Dr. Cory Merow (University of Connecticut) and Dr. Alex Pigot (University College London), say that nature Summarized from various projections of climate change can mask abrupt impacts in particular places.
Citing a number of studies at a more localized level, they say that temperature warming in recent decades has already been associated with marked declines in population and local extinctions of some species.
“At a minimum, our results show that within 30 years, continued high emissions will drive a sudden shift across many ecological assemblies to climatic conditions in which we are almost unaware of the ability of their constituent species to survive,” they say.
Ecological assemblies are groups of creatures or plants that live in the same area and interact closely through different relationships, such as pollination or mutual feeding.
Trisos and colleagues say that if global warming is kept below 2 ° C, less than 2% of these assemblies globally are projected to experience abrupt exposure events of more than 20% of their constituent species. However, the risk accelerates with the magnitude of warming, threatening 15% of assemblies at 4 ° C.
“This almost simultaneous exposure between multiple species could have sudden and devastating effects on local biodiversity and ecosystem services. The catastrophic deaths of multi-species corals caused by a record-breaking marine heat wave in 2016 are a recent example. ”
To carry out the study, Trisos and his colleagues used a database of more than 30,000 species, including birds, mammals, reptiles, amphibians, marine fish, krill, corals and seagrasses, and more than 20 climate models that project precipitation and average temperature increases of between 1.75 ° C and 4.4 ° C before the end of the century.
However, reducing greenhouse gas emissions and delaying the onset of exposure to hazardous weather conditions, even for a few decades, could create valuable time for ecological assemblies to adapt, potentially reducing the magnitude of the disturbances ecological.
In their study, they observed the different ecological niches formed by suitable temperature or humidity ranges to demarcate the historical climatic limits of the studied species.
“For each species in one place [that is, in a 100km grid cell], we define the exposure time of the local species as the year after which the projected local temperatures constantly exceed, for at least five years, the maximum temperature experienced by the species in its geographic range during historical climatic projections (1850–2005) ”
Under high emission scenarios of 4.4 ° C, they project that 81% of the land and 37% of the marine group would have at least one species exposed to unprecedented temperatures beyond historical niche limits before 2100.
Marine organisms, especially seagrasses, corals, cephalopods, marine reptiles, and marine mammals, appeared to be more vulnerable to abrupt changes.
Evidence from laboratory and field studies also suggests that the onset of unprecedented climate change can lead to local extinctions.
The suddenness of exposure to climate change also varied by location, but some of the places most likely to be affected were the Sahel region of North Africa, the Amazon, India, Northern Australia, and the tropical oceans. .
“In some places, such as the Caribbean and the Coral Triangle, the exhibition is predicted to be underway, with these exposure hot spots expanding in spatial extent over time.
“By 2050, the exhibition extends beyond ocean ecosystems to iconic terrestrial ecosystems, such as the Amazon, Indonesian, and Congolese rainforests.”
In a separate statement issued by the University of Cape Town, Trisos said: “Billions of people depend on ecosystems for their livelihood and nutrition. We fish in the coral reefs. We depend on ecotourism. We depend on healthy forests for carbon storage and water filtration.
“If there is a sudden collapse of these ecosystems in a single decade, you could lose most or all of these services. Your income is at risk. Your food security is at risk. Your mental and spiritual well-being could be at risk if those ecosystems are culturally important to you, “said Trisos.
In South Africa, several locations were at particular risk of abrupt disruption of biodiversity in a high-emission scenario, including the coast from Cape Agulhas to Mozambique, inland areas on the western side of the Western Cape to the border with Namibia, all the North Cape and parts of the Free State.
Trisos said he hoped the investigation would be a serious wake-up call for policymakers and other key actors.
“I hope that by showing how terribly widespread and close the risk to biodiversity is globally, this will help us reach positive tipping points in our response to divesting from fossil fuels and the transition to renewable energy.” DM
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