Abrupt disruptions to Earth's climate thousands of years ago that caused extreme sea-level rise and mass ice cap melting can serve as an early warning system for today's planetary tipping points, according to new research.

Climate tipping points -- which are irrevocable over centuries or longer -- are thresholds past which large and rapid changes to the natural world may occur.

They include looming catastrophes such as the melting of the ice sheets atop Greenland and West Antarctica, which contain enough frozen water to lift oceans more than a dozen metres (40 feet).

But they are notoriously hard to anticipate, given the relatively small or incremental changes in variables such as atmospheric carbon concentrations that trigger them.

In a review of past climate events published in the journal Nature Geoscience, an international team of scientists examined two major instabilities in the Earth system, caused by changes in ice, oceans, and rainfall patterns.

They looked at the conditions that led to the Bolling-Allerod warming event nearly 15,000 years ago, which saw surface air temperatures soar up to 14 degrees Celsius over Greenland.

The team also studied the end of the so-called African humid period around 6,000-5,000 years ago, which led to regional changes in ecosystems and pre-historic human societies.

They found that various past climate systems, such as ocean dynamics and rainfall patterns, tended to slow as they reached a tipping point, after which they failed to recover from perturbations.

"Earth's recent past shows us how abrupt changes in the Earth system triggered cascading impacts on ecosystems and human societies, as they struggled to adapt," said Tim Lenton, review co-author and director of the University of Exeter's Global Systems Institute.

"We face the risk of cascading tipping points again now -- but this time it is of our own making, and the impacts will be global," said Lenton.

"Faced with that risk, we could do with some early warning systems."

- Compound changes -

While current atmospheric CO2 levels of around 412 parts per million have some precedent -- at least 800,000 years ago -- the rate of CO2 accumulation does not.

Scientists are divided on when or if most tipping points will be triggered, but many believe effects such as ice-sheet melt is already "locked-in" due to carbon pollution.

Authors of the review, which was published online Thursday, said it showed evidence that the impacts of past abrupt changes to the Earth system combined to create planet-wide disruption.

Changes to ice levels and ocean currents, for example, at the start of the Bolling-Allerod warming lead to cascading impacts such as low ocean oxygen levels, vegetation cover, and atmospheric CO2 and methane levels.

"It sounds counterintuitive, but to foresee the future we may need to look into the past," said lead author Victor Brovkin from the Max Planck Institute for Meteorology.

"The chance to detect abrupt changes and tipping points -- where small changes lead to big impacts -- increases with the length of observations," he said.

"This is why analysis of abrupt changes and their cascades recorded in geological archives is of enormous importance."

Climate scientists tally 'mortality cost of carbon'
Washington DC (UPI) Jul 29, 2021 - If there is one thing all climate models agree on, it's that the more carbon that's released into Earth's atmosphere, the worse the outcome for the planet's warming climate.

According to new research, more carbon also translates to higher death totals.

Numerous studies have explored the relationship between carbon emissions and sea level rise -- or other variables like temperature, extreme weather, flood damage and viral transmission.

Now, a new study, published Thursday in the journal Nature Communications, has established a "mortality cost of carbon" -- the number of lives lost or saved by increases or decreases in carbon emissions.

Previously, climate scientists have worked hard to develop more accurate estimates of the "social cost of carbon," a tally of the economic damages caused by climate change.

But according to the author of the latest study, these estimates have largely ignored the impacts of climate change on human health and mortality.

"Based on the decisions made by individuals, businesses or governments, this tells you how many lives will be lost, or saved," lead study author R. Daniel Bressler said in a press release.

"It quantifies the mortality impact of those decisions. It brings this question down to a more personal, understandable level," said Bressler, a doctoral candidate at Columbia University's Earth Institute and the university's School of Public and International Affairs.

For the study, Bressler focused only on temperature-related mortality like heat stroke.

Though climate change is predicted to increase the risk of floods and other types of extreme weather, all of which will undoubtedly kill humans, such risks are difficult to quantify and forecast.

Using a handful of large public-health studies on the link between temperature and mortality to guide his analysis, Bressler arrived at a number for his mortality cost of carbon metric.

The calculations showed that for every additional 4,434 metric tons of carbon dioxide added beyond the 2020 baseline, one person will die prematurely between 2020 and 2100 -- the "equivalent to the lifetime emissions of 3.5 average Americans," according to the new study.

When accounting for the effects of carbon emissions and subsequent temperature increases, Bressler showed the true social cost of carbon is $258 per metric ton. Current estimates peg the social cost of carbon at approximately $37 per metric ton.

Bressler's analysis assumes that carbon emissions will continue at their current pace, raising global temperatures above 2 degrees Celsius by 2050 and 4.1 degrees by 2100. Such a scenario would result in 83 million excess deaths by 2100, according to Bressler's new metric.

If world governments take a more aggressive approach to climate change mitigation and emissions reductions, limiting warming to 2.4 degrees by 2100, Bressler's analysis suggests excess deaths can be limited to 9 million by the end of the century.

Though Bressler quantified his new metric in terms of the lifetime emissions of the average American, he said climate change requires systematic change, not individual reforms.

"My view is that people shouldn't take their per-person mortality emissions too personally," he said. "Our emissions are very much a function of the technology and culture of the place that we live."

Though local reforms can make a difference, Bressler said the climate crisis requires "large-scale policies such as carbon pricing, cap and trade, and investments in low-carbon technologies and energy storage."

Related Links
Climate Science News - Modeling, Mitigation Adaptation

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India skips key London climate meet; UK gets warmer and wetter
New Delhi (AFP) July 28, 2021
India, the world's third biggest emitter of greenhouse gases, skipped a key climate meeting of more than 50 countries, the environment ministry said Wednesday, citing technical and other difficulties. The two-day conference in London was the first face-to-face talks among governments in more than 18 months and offered a chance of compromise ahead of the pivotal COP26 climate summit in November. The talks on Sunday and Monday followed a G20 meeting last week in Naples where the leaders failed to ... read more