Just How Sensitive Is The Climate To Increased Carbon Dioxide? Scientists Are Narrowing In On The Answer

The Conversation - Richard Betts | Jason Lowe | Timothy Andrews

NASA/Reid Wiseman

Authors Richard Betts is Met Office Head of Climate Impacts Research and Professor, University of Exeter Jason Lowe is Principal Fellow, Met Office Hadley Centre and Professor, Priestley International Centre for Climate, University of Leeds Timothy Andrews is Research Scientist in Atmospheric Physics, Met Office Hadley Centre

At the dawn of the industrial revolution, the Earth’s atmosphere contained 278 parts of CO₂ per million.

Today, after more than two and a half centuries of fossil fuel use, that figure is around 414 parts per million (ppm).

If the build-up of CO₂ continues at current rates, by 2080 it will have passed 560 ppm – more than double the level of pre-industrial times.

Exactly how the climate will respond to all this extra CO₂ is one of the central questions in climate science.

Just how much will the climate actually change?

A major new international assessment of the Earth’s climate sensitivity, now published in the journal Reviews of Geophysics, addresses this question. This research has improved our understanding of how much the world will eventually warm if the carbon dioxide in the atmosphere is maintained at double the level of pre-industrial times.

While an exact figure is still not possible, low levels of warming are now found to be far less likely than previously thought. Very high values are slightly less likely too. There is much greater certainty that, if left unchecked, global warming would be high enough to bring very severe impacts and risks worldwide.

The study, which was organised by the World Climate Research Programme (WCRP) and involving many leading climate scientists (including one of us: Tim), looks at a measure called “equilibrium climate sensitivity”. This refers to how much global average temperatures will increase by in the long-term following a doubling of carbon dioxide concentrations. It can be estimated using three main lines of evidence:

1. Temperature measurements made with thermometers from 1850 (when enough global coverage began) to the near present. By comparing temperatures, CO₂ levels and the effect of other climate drivers in the past and present, we can estimate the longer-term changes.


2. Evidence from paleoclimate records from the peak of the last ice age 20,000 years ago, when CO₂ was lower than now, and a warm period around 4 million years ago when CO₂ was more comparable to today. We can tell how warm the climate was and how much CO₂ there was in the atmosphere based on the make-up of gases trapped in air bubbles in ancient ice cores.


3. Present-day observations – for instance from satellite data – and evidence from climate models, theory and detailed process models that examine the physics of interactions within the climate system.

Despite its importance, equilibrium climate sensitivity is very uncertain and for many years the standard estimate has been 1.5°C to 4.5°C. In its 5th Assessment Report, the Intergovernmental Panel on Climate Change (IPCC) gave these values as the “likely range”, which meant it considered there was at least a 66% chance that it fell within this range. Or, in other words, it judged there was up to a 33% chance that warming would either be less than 1.5°C or more than 4.5°C.

The new study suggests that this “likely range” has narrowed to, at most, 2.3°C to 4.5°C – or possibly an even narrower range*. The lower end of the range has therefore risen substantially, meaning that scientists are now much more confident that global warming will not be small.

Global warming assessments old and new

Ranges of equilibrium climate sensitivity from the IPCC and the new study.

We won’t be saved by low sensitivity

An important implication is that humans would be taking an even bigger risk than previously thought if we relied on low climate sensitivity to allow us to meet the Paris Agreement target of keeping global temperatures to “well below” 2°C above pre-industrial levels, and to “pursue efforts” to limit warming to 1.5°C.

This is therefore further confirmation that CO₂ emissions need to be rapidly reduced and ultimately reach net zero if the Paris targets are to have a good chance of being met.

According to the study, if CO₂ does reach double the pre-industrial level and stays there (or to be precise, if the total effect of all human impact on greenhouse gases and other climate drivers reaches an equivalent level), then there is up to an 18% chance that temperatures will rise to 4.5°C above pre-industrial levels, and a no more than 5% chance that they will go above 5.7°C.

This has important implications for climate change risk assessments. In a risk assessment, it is normal to consider outcomes that are possible even if they are not the most likely.

The latest climate models have a wide range of climate sensitivities, with our own Met Office models at the high end. This happens because climate sensitivity is not something that scientists input to the models, but rather it emerges from the same complex interactions the models simulate.

This diversity of models lets us understand the regional changes in climate and extreme weather associated with different climate sensitivities, and assess their potential impacts. This includes the high sensitivities that are less likely but still possible. At the other end of the range, seeing the minimum changes we can expect will help inform climate change adaptation measures.

The new study allows a key aspect of climate models, their climate sensitivity, to be seen in the context of other evidence. While there is still more to be done to assess more precisely how the global climate will respond to further increases in greenhouse gases, these advances provide a much more solid base of evidence on which climate change policy can be further developed.

* WCRP provides two sets of ranges. The first is based on a “baseline” calculation which represents a single interpretation of the evidence and may be over-confident. The second set of “robust” ranges are designed to bound the range of plausible alternative interpretations of the evidence and statistical modelling assumptions. The numbers quoted in this article are from the robust range. For further details, see Sherwood et. al, 2020

Links

• Explainer: How scientists estimate ‘climate sensitivity’
• Climate Change: Atmospheric Carbon Dioxide
• An assessment of Earth’s climate sensitivity using multiple lines of evidence (pdf)
• The Keeling Curve
• Mauna Loa carbon dioxide forecast for 2020
• The Paris Agreement
• Climate Change Risk Assessment 2022
• HadGEM3 family: Met Office climate prediction model

World’s Largest Falcon Faces A Threat It Can’t Flee: Climate Change

National Geographic - Text Douglas Main | Photographs Kiliii Yüyan

Scientists are working to better understand gyrfalcons, the only raptors that stay year-round in the Arctic, the fastest-warming region on Earth.

A gyrfalcon soars over the cliffs and tundra of Alaska’s Seward Peninsula. The birds are especially vulnerable to climate change because many stay year-round in the Arctic, the fastest-warming region on Earth.

The gyrfalcon is the world’s largest falcon, and one of the fastest: During long flights, it can surpass speeds of 80 miles per hour. Weighing more than three pounds, with a wingspan of four feet or more, it can take down prey twice its size.

It’s also the only Arctic raptor that doesn’t need to head south for the winter, staying behind instead to hunt prey in a frigid, dark landscape. “Any organism that can live in such a hostile environment has my respect,” says Travis Booms, a raptor biologist with the Alaska Department of Fish and Game.

But the gyrfalcon faces a challenge it cannot flee or take down: The Arctic is warming more than twice as fast as the rest of the planet, and biologists consider gyrfalcons one of the region’s most vulnerable species, in part because they’re ultra-specialized to survive in the cold. While many species are shifting their ranges toward the cooler poles as temperatures climb, the gyrfalcon can’t go any farther north. Though they’re not currently classified as threatened with extinction, recent research in Alaska suggests there’s cause for concern.

“The population is stable for now but may possibly be declining,” Booms says, though it’s unclear by just how much. “There are some pretty clear threats on the horizon.” He is part of a long-term study in the Seward Peninsula, in western Alaska—home to 70 to 80 nesting pairs of gyrfalcons, or about one-tenth of the state’s total population—to understand how the birds are adapting to climate change.

Source: IUCN

Photographer Kiliii Yüyan accompanied researchers visiting gyrfalcon nests on the peninsula in June 2019. His photos provide an unprecedented glimpse of the birds in their natural habitat, where they are very difficult to find and observe. He was drawn to the project by the birds’ beauty and their role as top predators in the Arctic, he says, as well as to the importance of the research.

Gyrfalcons and golden eagles compete for nesting spots on cliffs across vast, uninhabited stretches of the Arctic. This former eagle’s nest sits on a bluff over a river on the Seward Peninsula. The region is uniquely suitable for gyrfalcon research because its network of roads allows researchers easier access.

Left: These gyrfalcon chicks are about 25 days old and ready to be banded by biologists so they can be identified in the future. The researchers must hike for miles and rappel down cliffs to band the chicks and take measurements and blood samples.
Right: The youngsters are not immune to swarms of mosquitoes that arise during the heat of the summer. Scientists worry that avian diseases like West Nile virus, spread by mosquitoes, could migrate north as the area warms.

“We frankly still know so little about gyrfalcons,” he says, including how they manage to survive the winter and where they go then.

“I wanted to give people a close glimpse of this beautiful animal. There are so few images of gyrfalcons out there,” Yüyan says. “What does a gyrfalcon, aerial queen of the Arctic, look like in its own domain?”

Aeries, canaries

The Seward Peninsula is an ideal place to study gyrfalcons because it has a robust network of roads, a rarity in the Arctic. These extend from the small town of Nome and run within hiking distance of several gyrfalcon nesting sites, or aeries, perched high on rocky cliffs that rise above vast, uninhabited stretches of tundra.

Since 2014, the Peregrine Fund, an organization devoted to raptor conservation and research, has been studying the peninsula’s gyrfalcons in tandem with Booms and the Alaska Department of Fish and Game, which has been studying raptors there for 20 years.

Each summer, a team of researchers visits some 20 gyrfalcon nests on the peninsula at three different times: in May, when the eggs have been laid; in June, when chicks are about 25 days old; and in mid-July, after the chicks have fledged.

It’s not easy work. An average day requires hours of hiking through difficult terrain, crossing rivers, climbing and descending cliffs, and enduring swarms of mosquitoes. The June tour—when they take blood samples and measurements from the chicks, and place leg bands on them—is particularly difficult. The parents aren’t exactly pleased with the human visitors.

“It’s somewhat intimidating rappelling down a cliff toward a nest and having these large birds swooping at you [while] constantly screaming,” says Devin Johnson, a doctoral student at the University of Alaska Fairbanks who’s writing his dissertation on the links between gyrfalcons’ diet and reproductive success. (The researchers’ remote cameras show the birds quickly return to the nest and to a sense of normalcy after they leave.)

Data gathered from these field visits will illuminate how gyrfalcons are reacting to environmental changes in the area. These include more intense spring storms—which can kill nestlings—and the growth of new bushes and small trees across the tundra, which gives their prey more places to hide. The scientists have also begun sampling the raptors’ blood for diseases such avian malaria and West Nile virus, to which gyrfalcons are likely more vulnerable than other raptors.

“If environmental change is occurring, it will be manifested in the biology of gyrfalcons,” says David Anderson, who runs the Peregrine Fund’s gyrfalcon research program. “We use them as a canary in the coal mine.”

Young gyrfalcons high up in a cliffside nest devour prey delivered by their mother. A camera trap placed by the Peregrine Fund biologists helps researchers to monitor the chicks and see what they eat.

Four million photos

Learning more about gyrfalcons’ diet is an important part of the project because the birds prey almost exclusively on other animals that, like themselves, are specially adapted to live in the cold north. And like gyrfalcons, their prey are increasingly vulnerable in the warming Arctic, says Mike Henderson, a raptor biologist with the Peregrine Fund who manages the research program in the field.

Motion-activated cameras the researchers place at the nests every May capture photos of all the prey gyrfalcons bring back. Since 2014, the project has accrued more than four million photos of prey items—including ptarmigans, ground squirrels, lemmings, and songbirds. “We currently have more gyrfalcon diet photos than anyone in the world,” Henderson says.

Left: Feathers litter the ground alongside wildflowers growing near a gyrfalcon aerie. The raptors specialize in hunting ptarmigans, chicken-like ground birds, as well as ground squirrels, lemmings, and songbirds.
Right: This gyrfalcon, in Nome, Alaska, is cared for by local falconer John Earthman. "They're very engaging birds, highly intelligent," Earthman says. Many raptors used by falconers are caught “on the wing” after fledging in late summer or fall and released in the spring.

Their research shows the diet of gyrfalcons is more varied than previously thought. But as to whether their diet has already changed due to climate conditions, “it’s something we’re looking into—we really need a longer-term data set to know for sure,” Johnson says.

Hunters and guides

Though gyrfalcon populations appear stable globally, Booms says “there are some indications the species may be declining locally in western Alaska and the Yukon Territory.” The southernmost population being studied appears to be doing the worst, he says. The declines may be due in part to difficulty finding prey and more intense spring storms. But he says it’s too early to make definitive conclusions.

Michael Henderson, who manages the Peregrine Fund's gyrfalcon research project, cradles a recently banded juvenile gyrfalcon at a nest site.

The uncertainty is yet another reason why it’s important to monitor Alaska’s birds, to get baseline data before the area warms even more, Booms says.

Furthermore, a small number of gyrfalcons are legally taken from the wild each year for use in falconry, in which people train the raptors to help them hunt. Between about one and five are taken from nests in the state each year, in a highly regulated fashion, Booms says.

Gyrfalcons are not only valued hunters but they’re also spiritual guides for many Indigenous Arctic people. And that’s personal for Yüyan, because his ancestors are Nanai, Native people in the Siberia region.

“Some of the most powerful [spirit helpers] are falcons,” he says, including gyrfalcons. He says he wants to help people understand that the Arctic is more than a big expanse of ice. “It’s the last vast wilderness we have, with so much incredible life and Indigenous culture. If we don’t know what’s out there, we just assume there’s nothing. And keeping the Arctic exotic will doom it to exploitation.”

A female white gyrfalcon soars through the air near Nome. In certain areas, 10 percent of gyrfalcons have such bright white coloration. “Gyrfalcons, especially the ghostly white-morph birds, are so stunning visually,” says photographer Kiliii Yüyan. “Their size and ferocity intrigue me. They have an intensity and awareness that reminds me that wild creatures have a vastly different perspective than humans.”

Links

• Climate Change Endangered:  Raptors (pdf)
• Climate Change Vulnerability of Migratory Species
• Climate Change and Raptors
• What a 100-degree day in Siberia really means
• Conserving Birds of Prey Worldwide
• A falcon war in Greenland’s frigid north is a preview of habitat contests to come
• Climate Threatened: Gyrfalcon
• Wikipedia: The Gyrfalcon

(AU) How Coastal Communities On Victoria's Bellarine Peninsula Are Dealing With The Reality Of Sea Level Rises

ABC News - Nicole Mills

Vicki Perrett's home in Indented Head is at risk of going underwater during high tides or storm surges as a result of rising sea levels. ABC News: Steven Schubert

Key Points The Victorian Government has instructed all councils to plan for a 0.8m sea-level rise by the year 2100 The City of Greater Geelong has identified 1,614 properties that will face inundation, and has submitted an overlay to the Planning Minister The overlay would require new buildings and renovations to meet certain conditions, such as ensuring floors were above predicted flood levels

As Vicki Perrett plays with her granddaughter Rachel on the beach in front of her home on Victoria's Bellarine Peninsula, she knows she has to cherish these moments.

And not just because children grow up so fast.

She also knows the beach they play on may not be there forever.

"The beach is coming closer towards us, towards the road and towards our property," Ms Perrett says.

"It's very prone to sea level rise here and to storm surges."

This stretch of coastline at Indented Head has already been earmarked as at risk of going underwater by 2100.

Ms Perrett's house is also in the danger zone.

The foreshore at Indented Head is being slowly eroded, and the road and homes are now at risk. ABC News: Steven Schubert

It was identified as one of 1,614 properties across the Greater Geelong region that may be faced with future flooding under a 0.8-metre sea level rise.

"Our property is about 20cm above sea level. There are others along the foreshore here that are actually below sea level," Ms Perrett says.

"Probably not in our lifetime will the actual property be flooded, I would like to hope, but clearly, the foreshore is getting slowly eroded."

Councils ordered to plan for sea level rises

The Victorian Government has instructed all councils to plan for a 0.8m sea level rise by the year 2100.

That figure is based on a 2007 report from the United Nations Intergovernmental Panel on Climate Change, which agreed on the projected rise, but could not rule out larger increases.

Although the worst impacts of sea level rises may still be decades away, this bayside community, about an hour-and-a-half south of Melbourne, has already had a taste of what is to come.

Four years ago, a "triple whammy" of a low-pressure system, strong onshore winds and very high tides battered the coastline.

"Parts of the foreshore all the way from where we're living down to Portarlington [about 6 kilometres away] were inundated ... so we know what happens and what it does to infrastructure," Ms Perrett says.

Homes in the predicted inundation zone will require a special planning permit for new buildings and renovations. ABC News: Steven Schubert

The City of Greater Geelong recently submitted its Land Subject to Inundation Overlay to the State Planning Minister for approval.

Once signed off, it means any properties within the predicted inundation zone, including Ms Perrett's home at Indented Head, will require a planning permit for new buildings and renovations, with permit conditions usually requiring floor levels to be above the predicted flood levels.

Ms Perrett says she understands councils need to mitigate their risk, and the overlay would be useful information for anyone buying or building a property within the inundation zone.

But she feels more needs to be done to support residents whose property prices may be affected in the long term.

"I can't mitigate my risk. I've rung my insurer, they won't change my insurance policy so we just have to suffer the consequences," she says.

"For the existing property owners, we're being told that, 'Oh don't worry, it's not going to affect your property value.' But I think the subtext to that is we don't want to have to reduce your rates.

"That clearly would impact on Council's revenue."

What can we expect from sea level rises?

Dr Kathleen McInnes is the group leader for CSIRO's climate extremes and projections group. (ABC News: Steven Schubert)

CSIRO climate scientist Dr Kathleen McInnes said previous predictions estimated sea level rises between 0.5m and 1m by the end of the century.

The 0.8m predicted sea-level rise quoted in the Victorian Government's directive to councils is "towards the upper range" of those predictions, she says.

But a report released last year by the Intergovernmental Panel on Climate Change increased the predicted sea level rise range to between 0.6m and 1.1m.

Dr McInnes said it coincided with data that showed sea level rises were accelerating.

"Sea levels rose about 1.8 millimetres per year over the 20th century," Dr McInnes said.

"But in the last 30 years, the rate of rise has increased to about 3.6mm per year."

Dr McInnes leads the CSIRO's climate extremes and projections group, which has contributed to the mapping of high-risk areas.

Publicly available mapping tools, such as Coastal Risk Australia, allow anyone to find out how their local area would fare under different sea-level rise scenarios.

Dr McInnes said it was important for local communities to know whether they were at risk so they could decide whether to invest in adaptation strategies, such as infrastructure, to protect the coastline, or simply retreat from the danger zone.

"Land subject to inundation is land that is low-lying, that is potentially at risk from inundation during extreme sea-level events or even potentially high-tide events in the future," Dr McInnes said.

"We know that from our projections … that we can expect a two to threefold increase in the frequency of inundation events as a result of a projected sea-level rise."

Sea level rises visualisation

Dr McInnes says while the worst impacts will be felt during storm surges, there might be some areas that will suffer more permanent flooding.

"If [the land] is low enough, it could be permanently inundated," she said.

"Parts of Swan Bay [on the Bellarine Peninsula] could potentially become quite affected by inundation, certainly high-tide inundation, in the future."

And it's not just regional areas.

Dr McInnes says Melbourne suburbs such as Elwood, Aspendale and Mordialloc are also at risk of more-regular flooding in future.

The insurance impacts of identifying risk

You may think an overlay such as this would have consequences for a property's insurance costs.

But Insurance Council of Australia spokesman Campbell Fuller says overlays that show future sea-level rises should have no impact on current insurance premiums.

"Insurers price risks for the duration of the policy, typically 12 months, and climate change is not a component of premiums," he said.

And actions of the sea are one of the most common policy exclusions.

"However, measures that seek to anticipate and prepare for sea-level rises caused by climate change are positive," he said.

"Overlays will help inform communities about the impact of climate change and may encourage governments and property owners to invest in mitigation, resilience and adaptation programs."

But what it means for property values is yet to be seen.

Many of the submissions the City of Greater Geelong received from residents spoke of a fear their property's value would be significantly decreased.

Councillor Trent Sullivan says the overlay is about "taking a proactive attitude towards protecting our coastal areas and communities" and is based off scientific reports, hazard assessments and inundation mapping.

"We all know how vulnerable our coastal communities are to climate change and storm surge events, so this is an added layer of protection for our residents," he said.

"This should reduce the risk to public safety, private property, agricultural losses and protects our residents."

'We don't want to move'

Ms Perrett worries her granddaughter Rachel's generation will not be able to enjoy the same carefree coastal lifestyle she had. ABC News: Steven Schubert

Ms Perrett is resigned to the fact that her property's value may decrease as the risk goes up in coming years, meaning her family's inheritance may not be as valuable as it is now.

But the dedicated community member, who heads a local environmental group, is vice-president of the community association and previously sat on the local coastal committee, says she just wants to make sure she's doing everything in her power to address climate change.

"We're mindful that we won't be leaving much of a legacy to our children," she said.

"I hate to think that [my granddaughter] won't get to enjoy the summers that I had when I was her age growing up here and holidaying here — it was just a very carefree lifestyle and very idyllic, swimming and sailing and fishing and exploring the beach.

"I certainly do have a lot of friends that are telling me, 'You should move now'. [But] we don't want to move. We love our community. We're probably more connected to our community than with anywhere we've lived in our lives. So it's a very special place."

Ms Perrett says she feels more needs to be done to encourage homeowners and businesses across the region to reduce their carbon emissions.

"We can live our lives with as small a carbon footprint as possible," she said.

"It's all of our responsibility. We all make choices and, clearly, we need to solve the problems together."

Links

• (AU) Wild Weather Leaves NSW Homes At Risk Of 'Structural Collapse Due To Beach Erosion'
• Sea level rise will see 40pc of Australia's beaches lost, predicts new study
• Sea level rise began accelerating in the 1960s, researchers find
• Australia's largest ever bushfire, like you've never seen it before
• A pocket guide to climate change
• (AU) Erosion From Surging Seas Threatens Roads, Homes And Beaches
• Climate Crisis: Sea Level ‘On Course To Rise By One Metre By 2100’ If Global Emissions Targets Are Missed
• (AU) Thousands Of Kilometres Of Australia's Beaches At Risk From Rising Seas
• Rising Sea Levels Pose Threat To Homes Of 300m People – Study
• Extreme Sea Level Events ‘Will Hit Once A Year By 2050’
• Rising Sea, Erosion To Wreak Havoc In Low-Lying Suburbs: Report
• Rising Seas Threaten Australia’s Major Airports – And It May Be Happening Faster Than We Think
• Climate Change Predicted To Wipe $571 Billion Off Property Values