Essay by Eric Worrall
Past global warm epochs were bursting with abundance and life, but apparently this time the computer models tell us we’re all going to die.
Climate change: if warming approaches 2°C, a trickle of extinctions will become a flood
Published: December 11, 2023 11.37pm AEDT
Principal Research Fellow, Centre for Biodiversity and Environment Research, UCL
Our world has warmed by roughly 1.2°C since the pre-industrial period. Many species are already exposed to increasingly intolerable conditions, driving some populations to die off or contract at the hottest edges of their geographic ranges. Biodiversity is feeling the heat in all ecosystems and regions, from mountain tops to ocean depths.
Are there thresholds of warming beyond which the risks to wildlife accelerate? And if so, where and when might we cross them? In short, what does the future hold for Earth’s biodiversity?
My colleagues and I overlaid the projections of climate models with data on the geographic distributions of more than 35,000 species on land and in the ocean. We found that the area over which each species will be exposed to intolerable temperatures is likely to increase abruptly during the coming decades.
Most populations may initially appear safe. But then, suddenly, a threshold of global warming is crossed beyond which multiple populations across widespread areas face intolerable conditions in rapid succession.
This scenario is already playing out on coral reefs. Just a few decades ago, coral bleaching events driven by extreme sea surface temperatures were rare and localised. Today, these events degrade reefs globally on an almost annual basis.
Burying our heads in the sand will not alter the hard biophysical limits that govern life on Earth – and through which we are rapidly crashing.
Read more: https://theconversation.com/climate-change-if-warming-approaches-2-c-a-trickle-of-extinctions-will-become-a-flood-219182
The abstract of the paper;
Abrupt expansion of climate change risks for species globally
Alex L. Pigot , Cory Merow , Adam Wilson & Christopher H. Trisos
Climate change is already exposing species to dangerous temperatures driving widespread population and geographical contractions. However, little is known about how these risks of thermal exposure will expand across species’ existing geographical ranges over time as climate change continues. Here, using geographical data for approximately 36,000 marine and terrestrial species and climate projections to 2100, we show that the area of each species’ geographical range at risk of thermal exposure will expand abruptly. On average, more than 50% of the increase in exposure projected for a species will occur in a single decade. This abruptness is partly due to the rapid pace of future projected warming but also because the greater area available at the warm end of thermal gradients constrains species to disproportionately occupy sites close to their upper thermal limit. These geographical constraints on the structure of species ranges operate both on land and in the ocean and mean that, even in the absence of amplifying ecological feedbacks, thermally sensitive species may be inherently vulnerable to sudden warming-driven collapse. With higher levels of warming, the number of species passing these thermal thresholds, and at risk of abrupt and widespread thermal exposure, increases, doubling from less than 15% to more than 30% between 1.5 °C and 2.5 °C of global warming. These results indicate that climate threats to thousands of species are expected to expand abruptly in the coming decades, thereby highlighting the urgency of mitigation and adaptation actions.
Read more: https://www.nature.com/articles/s41559-023-02070-4.epdf
The study admits they didn’t consider migration in their study, because of their belief that global warming is happening too fast?
… A gradual spread of thermal risks would provide more time for species to adapt via dispersal12 or evolution13, and more opportunity to implement conservation interventions and adaptation policies once the adverse effects of thermal exposure are first detected. ……. While species will be adversely impacted by exposure to multiple abiotic and biotic variables, we focus our analysis on temperature, which provides a universal driver of species distributions across both marine22 and terrestrial23 realms; thus, it is a logical starting point for understanding the spatiotemporal dynamics of climate change risks to species. We do not consider processes of evolutionary adaptation, changes in phenology and behaviour or dispersal to new locations. While these processes will determine the resilience of species to climate change, in this study we focus on the first key step of understanding the spatial and temporal dynamics of thermal exposure that will ultimately drive these biological responses. …
Read more: Same link as above
The paper assumes abrupt pulses of global warming.
The paper admits shortcomings in terms of considering short term responses to these assumed pulses of global warming.
… While strong local adaptation in space greatly increases risks, other factors could lead to risks from thermal exposure being overestimated in our models. In particular, many species will be limited by environmental23 or biotic33 factors other than temperature and have fundamental thermal tolerances that exceed their upper realized limit4,34. Species can also be buffered against warming (at least temporarily) by behaviours to exploit cooler microclimates35, changes in phenology36,37, the evolution of higher thermal tolerance13,32 or the contraction of populations into thermal refugia38, such as higher elevations on land or greater depths in the ocean. Thus, while the abruptness of projected thermal exposure is a ubiquitous phenomenon occurring across all terrestrial and marine organisms we studied, our simple temperature-based model of exposure will not be equally useful in understanding climate risks for all species39. However, uncertainty in thermal tolerances and heterogeneity in responses to thermal exposure is unlikely to alter our conclusion that thermal risks will expand abruptly across species’ existing geographical ranges under future warming. …
Read more: Same link as above
The biggest problem with the claim that species are at risk from abrupt climate change is such a change has already occurred – and species did just fine.
The Younger Dryas was a severe and abrupt cooling event which occurred 12,900 years ago, and lasted for around 1200 years – possibly triggered by the collapse of Lake Agassiz, the giant glacial lake which once covered much of Canada and North America, though the exact cause is still hotly debated.
The abruptness and severity of the cooling event cannot be overstated – the full impact was possibly experienced in as little as a couple of months.
… Around 12,800 years ago the northern hemisphere was hit by the Younger Dryas mini ice age, or “Big Freeze”[which] lasted around 1300 years.
Until now, it was thought that the mini ice age took a decade or so to take hold, on the evidence provided by Greenland ice cores. Not so, say William Patterson of the University of Saskatchewan in Saskatoon, Canada, and his colleagues.
The group studied a mud core from an ancient lake, Lough Monreagh, in western Ireland. Using a scalpel they sliced off layers 0.5 to 1 millimetre thick, each representing up to three months of time. No other measurements from the period have approached this level of detail.
Carbon isotopes in each slice revealed how productive the lake was and oxygen isotopes gave a picture of temperature and rainfall. They show that at the start of the Big Freeze, temperatures plummeted and lake productivity stopped within months, or a year at most. “It would be like taking Ireland today and moving it up to Svalbard” in the Arctic, says Patterson. …
Read more: http://www.newscientist.com/article/mg20427344.800-mini-ice-age-took-hold-of-europe-in-months.html
But the Younger Dryas is not described in the scientific literature as an extinction event. The Younger Dryas was no dinosaur killer. Animals and plants adapted just fine to the abrupt change in temperature, other than some large macrofauna which proved too tempting a target for hungry humans armed with spears. Human populations declined in North America during the Younger Dryas, as the land became less productive, then rebounded as temperatures recovered.
The natural world is resilient. You can see this just by watching your own garden lawn.
In wet, cold weather, my neglected house lawn sprouts broad leafed weeds, which take advantage of the damp conditions. In scorching hot dry weather, the broad leafed plants recede, and the lawn is dominated by long, thin stemmed grasses with yellowed tops, which reflect the sunlight. The biome of my back yard, which is heavily shaded, is wildly different to the biome of the grass in my front yard which receives the full blast of subtropical sunlight. The biome of lawn plants near my citrus trees, which I love and water regularly, is also very different to the biome of lawn plants further away from the water source.
You know the most interesting thing about my lawn? Our urban kangaroos don’t care what kinds of plants dominate my lawn. They eat the hot weather thin stemmed grass just as happily as they munch on the broad leafed wet weather weeds.
Northern Hemisphere animal and plant species survived the Younger Dryas, because the abrupt temperature drop of the Younger Dryas didn’t kill everything, it just shifted some balances. It was an opportunity to plants which had always been in the background to dominate and outcompete formerly dominant plants which prefer warmer conditions. Then when the Younger Dryas receded, so did the plants which preferred extreme cold – but we see them again whenever there’s a cold Summer.
It takes a lot more than a few degrees of abrupt temperature change to set off a mass extinction.
Professor Pigot and the other authors admitted in their study that their work didn’t consider several important factors, and that the study might be overestimating the risks. It’s a pity this qualification didn’t come through clearly in Pigot’s press release.