A heat wave in Greenland and a storm in Antarctica. These kinds of individual weather “events” are increasingly being supercharged by a warming climate. But despite being short-term events they can also have a much longer-term effect on the world’s largest ice sheets, and may even lead to tipping points being crossed in the polar regions.

We have just published research looking at these sudden changes in the ice sheets and how they may impact what we know about sea level rise. One reason this is so important is that the global sea level is predicted to rise by anywhere between 28 cm and 100cm by the year 2100, according to the IPCC. This is a huge range – 70 cm extra sea-level rise would affect many millions more people.

Partly this uncertainty is because we simply don’t know whether we’ll curb our emissions or continue with business as usual. But while possible social and economic changes are at least factored in to the above numbers, the IPCC acknowledges its estimate does not take into account deeply uncertain ice-sheet processes.

Sudden accelerations

The sea is rising for two main reasons. First, the water itself is very slightly expanding as it warms, with this process responsible for about a third of the total expected sea-level rise.

Second, the world’s largest ice sheets in Antarctica and Greenland are melting or sliding into the sea. As the ice sheets and glaciers respond relatively slowly, the sea will also continue to rise for centuries.

Photo by Cassie Matias on Unsplash

Scientists have long known that there is a potential for sudden accelerations in the rate at which ice is lost from Greenland and Antarctica which could cause considerably more sea-level rise: perhaps a metre or more in a century. Once started, this would be impossible to stop.

Although there is a lot of uncertainty over how likely this is, there is some evidence that it happened about 130,000 years ago, the last time global temperatures were anything close to the present day. We cannot discount the risk.

To improve predictions of rises in sea level we therefore need a clearer understanding of the Antarctic and Greenland ice sheets. In particular, we need to review if there are weather or climate changes that we can already identify that might lead to abrupt increases in the speed of mass loss.

Weather can have long-term effects

Our new study, involving an international team of 29 ice-sheet experts and published in the journal Nature Reviews Earth & Environment, reviews evidence gained from observational data, geological records, and computer model simulations.

We found several examples from the past few decades where weather “events” – a single storm, a heatwave – have led to important long-term changes.

The ice sheets are built from millennia of snowfall that gradually compresses and starts to flow towards the ocean. The ice sheets, like any glacier, respond to changes in the atmosphere and the ocean when the ice is in contact with sea water.

These changes could take place over a matter of hours or days or they may be long-term changes from months to years or thousands of years. And processes may interact with each other on different timescales, so that a glacier may gradually thin and weaken but remain stable until an abrupt short-term event pushes it over the edge and it rapidly collapses.

Because of these different timescales, we need to coordinate collecting and using more diverse types of data and knowledge.

Historically, we thought of ice sheets as slow-moving and delayed in their response to climate change. In contrast, our research found that these huge glacial ice masses respond in far quicker and more unexpected ways as the climate warms, similarly to the frequency and intensity of hurricanes and heatwaves responding to changes with the climate.

Ground and satellite observations show that sudden heatwaves and large storms can have long-lasting effects on ice sheets. For example a heatwave in July 2023 meant at one point 67% of the Greenland ice sheet surface was melting, compared with around 20% for average July conditions. In 2022 unusually warm rain fell on the Conger ice shelf in Antarctica, causing it to disappear almost overnight.

These weather-driven events have long “tails”. Ice sheets don’t follow a simple uniform response to climate warming when they melt or slide into the sea. Instead their changes are punctuated by short-term extremes.

For example, brief periods of melting in Greenland can melt far more ice and snow than is replaced the following winter. Or the catastrophic break-up of ice shelves along the Antarctic coast can rapidly unplug much larger amounts of ice from further inland.

Failing to adequately account for this short-term variability might mean we underestimate how much ice will be lost in future.

What happens next

Scientists must prioritise research on ice-sheet variability. This means better ice-sheet and ocean monitoring systems that can capture the effects of short but extreme weather events.

This will come from new satellites as well as field data. We’ll also need better computer models of how ice sheets will respond to climate change. Fortunately there are already some promising global collaborative initiatives.

We don’t know exactly how much the global sea level is going to rise some decades in advance, but understanding more about the ice sheets will help to refine our predictions.

Edward Hanna, Professor of Climate Science and Meteorology, University of Lincoln and Ruth Mottram, Climate Scientist, National Centre for Climate Research, Danish Meteorological Institute

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Amid the escalating threats of a warming world, and with the latest annual United Nations global climate conference (COP28) behind us, there is one critical message that’s often left out of the climate change discourse. Halting overfishing is itself effective climate action.

This argument is the logical conclusion of a plethora of studies that unequivocally assert that stopping overfishing isn’t just a necessity, it’s a win-win for ocean vitality, climate robustness and the livelihoods reliant on sustainable fisheries.

The intricate relationship between climate change and ocean ecosystems was the subject of recent collaborative research — led by researchers at the University of British Columbia — that highlighted the crucial links between overfishing and climate change.

Finding the connections

Our collaborative team of international researchers applied a host of methodologies ranging from literature reviews to quantitative and quality analysis. The findings of this research illuminate eight key multifaceted impacts.

1 — Ending overfishing isn’t merely an ecological imperative but a vital climate action. Doing so would bolster marine life resilience in the face of climate shifts and reduce associate carbon emissions.

2 — Large subsidized fishing boat fleets can actually be a burden on small-scale fisheries, leaving them disproportionately vulnerable to shocks. In turn, overfishing not only depletes resources but also escalates carbon emissions, intensifying climate impacts on these fisheries and their communities, particularly women.

Additionally, the vulnerability of shellfish fisheries to climate stressors further underscores the importance of adaptive strategies tailored to local conditions.

3 — Success stories, like the recovery of European hake stocks, reveal a direct tie between stock recuperation and reduced emissions intensity from fisheries. We must champion and also learn from these successes.

4 — Ecosystem-based fisheries management reverses the “order of priorities so that management starts with ecosystem considerations rather than the maximum exploitation of several target species.”

Ecosystem-based fisheries management has considerable potential to enhance sustainable catches while fostering carbon sequestration. This is perhaps best exemplified by the successful implimentation of ecosystem-based fisheries management in the western Baltic Sea.

5 — Heavy metal pollution in the ocean — such as mercury or lead waste — intensifies the negative impacts of warming and overfishing. This pollution reinforces the need for developing multifaceted regulations based around ecosystem and ocean sustainability solutions.

6 — Overfishing exacerbates climate and biodiversity threats. Climate change contributes to less defined and predictable seasons and is causing reproductive challenges and the propagation of diseases in fish populations — among other issues.

Via Pixabay. .

Adding to these problems, overfishing itself is altering ecological dynamics, modifying habitats and opening new pathways for invasive species. These compounding crises further exacerbate the impacts of overfishing on marine ecosystems while at the same time making fish populations more vulnerable to climate change.

The above factors all combine to reduce the catch potential in any given ecosystem. In turn, fishers are forced to venture farther and deeper in the ocean to fish — increasing carbon emissions, personal risk factors to fishers and bycatch concerns.

7 — International fisheries management must play a central role in promoting biodiversity and retaining the ocean’s carbon sequestration potential. While 87 nations have signed the UN’s Biodiversity of Areas Beyond National Jurisdiction Treaty (also known as the High Seas Treaty), only one has ratified it. This treaty must be fully ratified and its effective implementation should be contingent upon the creation of marine protected areas that cover at least 30 per cent of the high seas.

8 — The ocean has huge carbon sequestration potential. Shifting from the generally accepted maximum of sustainable yield management to maximizing carbon sequestration in fisheries management could further advance climate goals.

Future regulations should allocate a percentage of the annual fish quota to maintain the carbon sequestration function of marine animals. Simply put, beyond just being food, fish stocks serve vital carbon sequestration and biodiversity services that directly benefit humanity. Future regulations should reflect this reality.

A simple goal

This joint collaborative research underscores the urgency of this issue. Ending overfishing isn’t just an ecological imperative but a linchpin for climate action. Furthermore, fisheries aren’t mere victims in these dynamics, but have real agency to play a pivotal role in either exacerbating or mitigating climate change.

An ideal governance framework would focus on managing ecosystems with considerations for their diverse benefits, based on the best evidence available. Regulation of fisheries, while controversial, is essential to not overly exploit such a valuable public resource.

As we gear up to the next COP, we would do well to remember these conclusions. Without nurturing ocean life, addressing climate change becomes an uphill battle. Sustainable fisheries management is not just an ecological necessity. It is also the cornerstone of a resilient, sustainable future.

Rashid Sumaila, Director & Professor, Fisheries Economics Research Unit, University of British Columbia

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Superstorms, abrupt climate shifts and New York City frozen in ice. That’s how the blockbuster Hollywood movie “The Day After Tomorrow” depicted an abrupt shutdown of the Atlantic Ocean’s circulation and the catastrophic consequences.

While Hollywood’s vision was over the top, the 2004 movie raised a serious question: If global warming shuts down the Atlantic Meridional Overturning Circulation, which is crucial for carrying heat from the tropics to the northern latitudes, how abrupt and severe would the climate changes be?

Twenty years after the movie’s release, we know a lot more about the Atlantic Ocean’s circulation. Instruments deployed in the ocean starting in 2004 show that the Atlantic Ocean circulation has observably slowed over the past two decades, possibly to its weakest state in almost a millennium. Studies also suggest that the circulation has reached a dangerous tipping point in the past that sent it into a precipitous, unstoppable decline, and that it could hit that tipping point again as the planet warms and glaciers and ice sheets melt.

In a new study using the latest generation of Earth’s climate models, we simulated the flow of fresh water until the ocean circulation reached that tipping point.

The results showed that the circulation could fully shut down within a century of hitting the tipping point, and that it’s headed in that direction. If that happened, average temperatures would drop by several degrees in North America, parts of Asia and Europe, and people would see severe and cascading consequences around the world.

We also discovered a physics-based early warning signal that can alert the world when the Atlantic Ocean circulation is nearing its tipping point.

The ocean’s conveyor belt

Ocean currents are driven by winds, tides and water density differences.

In the Atlantic Ocean circulation, the relatively warm and salty surface water near the equator flows toward Greenland. During its journey it crosses the Caribbean Sea, loops up into the Gulf of Mexico, and then flows along the U.S. East Coast before crossing the Atlantic.

This current, also known as the Gulf Stream, brings heat to Europe. As it flows northward and cools, the water mass becomes heavier. By the time it reaches Greenland, it starts to sink and flow southward. The sinking of water near Greenland pulls water from elsewhere in the Atlantic Ocean and the cycle repeats, like a conveyor belt.

Too much fresh water from melting glaciers and the Greenland ice sheet can dilute the saltiness of the water, preventing it from sinking, and weaken this ocean conveyor belt. A weaker conveyor belt transports less heat northward and also enables less heavy water to reach Greenland, which further weakens the conveyor belt’s strength. Once it reaches the tipping point, it shuts down quickly.

What happens to the climate at the tipping point?

The existence of a tipping point was first noticed in an overly simplified model of the Atlantic Ocean circulation in the early 1960s. Today’s more detailed climate models indicate a continued slowing of the conveyor belt’s strength under climate change. However, an abrupt shutdown of the Atlantic Ocean circulation appeared to be absent in these climate models.

Ted-Ed Video: “How do ocean currents work? – Jennifer Verduin”

This is where our study comes in. We performed an experiment with a detailed climate model to find the tipping point for an abrupt shutdown by slowly increasing the input of fresh water.

We found that once it reaches the tipping point, the conveyor belt shuts down within 100 years. The heat transport toward the north is strongly reduced, leading to abrupt climate shifts.

The result: Dangerous cold in the North

Regions that are influenced by the Gulf Stream receive substantially less heat when the circulation stops. This cools the North American and European continents by a few degrees.

The European climate is much more influenced by the Gulf Stream than other regions. In our experiment, that meant parts of the continent changed at more than 5 degrees Fahrenheit (3 degrees Celsius) per decade – far faster than today’s global warming of about 0.36 F (0.2 C) per decade. We found that parts of Norway would experience temperature drops of more than 36 F (20 C). On the other hand, regions in the Southern Hemisphere would warm by a few degrees.

These temperature changes develop over about 100 years. That might seem like a long time, but on typical climate time scales, it is abrupt.

The conveyor belt shutting down would also affect sea level and precipitation patterns, which can push other ecosystems closer to their tipping points. For example, the Amazon rainforest is vulnerable to declining precipitation. If its forest ecosystem turned to grassland, the transition would release carbon to the atmosphere and result in the loss of a valuable carbon sink, further accelerating climate change.

The Atlantic circulation has slowed significantly in the distant past. During glacial periods when ice sheets that covered large parts of the planet were melting, the influx of fresh water slowed the Atlantic circulation, triggering huge climate fluctuations.

So, when will we see this tipping point?

The big question – when will the Atlantic circulation reach a tipping point – remains unanswered. Observations don’t go back far enough to provide a clear result. While a recent study suggested that the conveyor belt is rapidly approaching its tipping point, possibly within a few years, these statistical analyses made several assumptions that give rise to uncertainty.

Instead, we were able to develop a physics-based and observable early warning signal involving the salinity transport at the southern boundary of the Atlantic Ocean. Once a threshold is reached, the tipping point is likely to follow in one to four decades.

The climate impacts from our study underline the severity of such an abrupt conveyor belt collapse. The temperature, sea level and precipitation changes will severely affect society, and the climate shifts are unstoppable on human time scales.

It might seem counterintuitive to worry about extreme cold as the planet warms, but if the main Atlantic Ocean circulation shuts down from too much meltwater pouring in, that’s the risk ahead.

This article was updated on Feb. 11, 2024, to fix a typo: The experiment found temperatures in parts of Europe changed by more than 5 F per decade.

René van Westen, Postdoctoral Researcher in Climate Physics, Utrecht University; Henk A. Dijkstra, Professor of Physics, Utrecht University, and Michael Kliphuis, Climate Model Specialist, Utrecht University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The health benefits of eating seafood are appreciated in many cultures which rely upon it to provide critical nutrients vital to our physical and mental development and health. Eating fish and shellfish provides significant benefits to neurological development and functioning and provides protection against the risks of coronary heart disease and Type 2 diabetes.

Over three billion people get at least 20 per cent of their daily animal protein from fish. In countries from Bangladesh to Cambodia, Gambia, Ghana, Indonesia, Sierra Leone and Sri Lanka, fish consumption accounts for 50 per cent or more of daily intake.

However, expansive growth of human populations globally puts immense pressure on the health of wild fish stocks. Fish catches peaked in 1996, and one-third are considered overexploited. With less fish available to still more people, the future of fish as an accessible source of nutritious food is at risk, particularly among low-income countries.

Seafood nutrient losses

Threats to seafood access aren’t just due to overharvesting. There is a growing body of research showing that higher water temperatures due to climate change can impact the presence and abundance of the catch, through shifts in species distribution and changes in the species caught. This impacts the amount that can be harvested, as well as the nutritional value of that harvest.

A new study (which Aaron MacNeil contributed to) quantified nutrient availability from seafood through time considering the twin impacts of overfishing and climate change.

Focusing on four key nutrients important to human health — calcium, iron, omega-3 fatty acids and protein — the authors argue that nutrient availability in seafood has been declining since 1990 and will further decline by around 30 per cent by 2100 in predominately tropical, low-income countries with 4 C of warming.

These predicted losses are significant. While global famines are now relatively rare, some 50 million people suffer from “hidden hunger” — nutrient-deficient diets that are masked by being otherwise calorie-sufficient.

For animal-derived nutrients such as B12 and omega-3 fatty acids, nearly 20 per cent of the global population are at risk of becoming nutrient-deficient in coming decades due to reliance on wild-caught fish.

Climate change is also affecting natural cycles of nutrients in the ocean. For example, it has been predicted that increasing water temperatures will cause a decline in natural omega-3 availability from seafood by more than 50 per cent by 2100. At the bottom of the food chain, microalgae that naturally produce omega-3s are less productive at warmer temperatures and this cascades through marine and freshwater food chains resulting in fish having less omega-3s available to eat and store in their bodies.

These kinds of climate-caused losses are expected to disproportionately affect vulnerable populations, especially in inland Africa.

Challenges and strategies for nutritious seafood

Aquaculture can help supply some of these missing nutrients, but it is an industry also vulnerable to the effects of climate change. A recent study predicted that 90 per cent of aquaculture will be impacted by climate change, where warm waters increase disease outbreaks, harmful algal blooms and impact the availability of feed supplies.

Global disparities already exist in food security that will be exacerbated by climate change in the future. Yet the effects of warming waters on nutrient availability from seafood will compound these inequities among tropical and low-income countries.

These results suggest a major challenge to our future nutritional security that demands strong fisheries and aquaculture management to facilitate equitable distribution of nutritious seafoods.

Improvements are possible.

For example, redirecting nine per cent of Namibia’s fisheries toward its coastal population would alleviate the severe iron deficiencies experienced there. Policies that prioritize nutrient supply would help maintain diets as the climate warms.

The recent United Nations call to action for blue transformation emphasizes the need to provide sufficient aquatic food from fisheries and aquaculture for our growing population in a sustainable way.

To do this, strategies are needed to achieve healthy, equitable and resilient food systems that adequately deal with overfishing, strive for equal access to resources and markets and mitigate the environmental impacts of aquatic food production.

Ultimately, these strategies must support the nutritional security of vulnerable nations and consider global health equity and the cultural significance of seafood.

Stefanie Colombo, Canada Research Chair in Aquaculture Nutrition, Dalhousie University and Aaron MacNeil, Professor, Department of Biology, Dalhousie University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Featured Image: (Pexels), CC BY

(The Conversation) – While the Southern Ocean around Antarctica has been warming for decades, the annual extent of winter sea ice seemed relatively stable – compared to the Arctic. In some areas Antarctic sea ice was even increasing.

That was until 2016, when everything changed. The annual extent of winter sea ice stopped increasing. Now we have had two years of record lows.

In 2018 the international scientific community agreed to produce the first marine ecosystem assessment for the Southern Ocean. We modelled the assessment process on a working group of the Intergovernmental Panel on Climate Change (IPCC). So the resulting “summary for policymakers” being released today is like an IPCC report for the Southern Ocean.

This report can now be used to guide decision-making for the protection and conservation of this vital region and the diversity of life it contains.

Why should we care about sea ice?

Sea ice is to life in the Southern Ocean as soil is to a forest. It is the foundation for Antarctic marine ecosystems.

Less sea ice is a danger to all wildlife – from krill to emperor penguins and whales.

The sea ice zone provides essential food and safe-keeping to young Antarctic krill and small fish, and seeds the expansive growth of phytoplankton in spring, nourishing the entire food web. It is a platform upon which penguins breed, seals rest, and around which whales feed.

The international bodies that manage Antarctica and the Southern Ocean under the Antarctic Treaty System urgently need better information on marine ecosystems. Our report helps fill this gap by systematically identifying options for managers to maximise the resilience of Southern Ocean ecosystems in a changing world.

An open and collaborative process

We sought input from a wide range of people across the entire Southern Ocean science community.

We sought to answer questions about the state of the whole Southern Ocean system – with an eye on the past, present and future.

Our team comprised 205 authors from 19 countries. They authored 24 peer-reviewed papers. We then distilled the findings from these papers into our summmary for policymakers.

We deliberately modelled the multi-disciplinary assessment process on a working group of the IPCC to distill the science into an easy-to-read and concise narrative for politicians and the general public alike. It provides a community assessment of levels of certainty around what we know.

We hope this “sea change” summary sets a new benchmark for translating marine research into policy responses.

So what’s in the report?

Southern Ocean habitats, from the ice at the surface to the bottom of the deep sea, are changing. The warming of the ocean, decline in sea ice, melting of glaciers, collapse of ice shelves, changes in acidity, and direct human activities such as fishing, are all impacting different parts of the ocean and their inhabitants.

These organisms, from microscopic plants to whales, face a changing and challenging future. Important foundation species such as Antarctic krill are likely to decline with consequences for the whole ecosystem.

The assessment stresses climate change is the most significant driver of species and ecosystem change in the Southern Ocean and coastal Antarctica. It calls for urgent action to curb global heating and ocean acidification.

It reveals an urgent need for international investment in sustained, year-round and ocean-wide scientific assessment and observations of the health of the ocean.

We also need to develop better integrated models of how individual changes in species along with human impacts will translate to system-level change in the different food webs, communities and species.

What’s next?

Our report was tabled at an international meeting of the Commission for the Conservation of Antarctic Marine Living Resources in Hobart.

The commission is the international body responsible for the conservation of marine ecosystems in the Southern Ocean, with membership of 26 nations and the European Union.

It is but one of the bodies our new report can assist. Currently assessments of change in habitats, species and food webs in the Southern Ocean are compiled separately for at least ten different international organisations or processes.

The Southern Ocean is a crucial life-support system, not just for Antarctica but for the entire planet. So many other bodies will need the information we produced for decision-making in this critical decade for action on climate, including the IPCC itself.

Beyond the science, the assessment team has delivered important lessons about how coordinated, collaborative and consultative approaches can deliver ecosystem information into policymaking. Our first assessment has taken five years, but this is just the beginning. Now we’re up and running, we can continue to support evidence-based conservation of Southern Ocean ecosystems into the future.

Andrew J Constable, Adviser, Antarctica and Marine Systems, Science & Policy, University of Tasmania and Jess Melbourne-Thomas, Transdisciplinary Researcher & Knowledge Broker, CSIRO

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Featured Image: Courtesy Pat James, Australian Antarctic Division.

As oceans waves rise and fall, they apply forces to the sea floor below and generate seismic waves. These seismic waves are so powerful and widespread that they show up as a steady thrum on seismographs, the same instruments used to monitor and study earthquakes.

That wave signal has been getting more intense in recent decades, reflecting increasingly stormy seas and higher ocean swell.

In a new study in the journal Nature Communications, colleagues and I tracked that increase around the world over the past four decades. These global data, along with other ocean, satellite and regional seismic studies, show a decadeslong increase in wave energy that coincides with increasing storminess attributed to rising global temperatures.

What seismology has to do with ocean waves

Global seismographic networks are best known for monitoring and studying earthquakes and for allowing scientists to create images of the planet’s deep interior.

These highly sensitive instruments continuously record an enormous variety of natural and human-caused seismic phenomena, including volcanic eruptions, nuclear and other explosions, meteor strikes, landslides and glacier-quakes. They also capture persistent seismic signals from wind, water and human activity. For example, seismographic networks observed the global quieting in human-caused seismic noise as lockdown measures were instituted around the world during the coronavirus pandemic.

However, the most globally pervasive of seismic background signals is the incessant thrum created by storm-driven ocean waves referred to as the global microseism.

Two types of seismic signals

Ocean waves generate microseismic signals in two different ways.

The most energetic of the two, known as the secondary microseism, throbs at a period between about eight and 14 seconds. As sets of waves travel across the oceans in various directions, they interfere with one another, creating pressure variation on the sea floor. However, interfering waves aren’t always present, so in this sense, it is an imperfect proxy for overall ocean wave activity.

Image by Elias from Pixabay

A second way in which ocean waves generate global seismic signals is called the primary microseism process. These signals are caused by traveling ocean waves directly pushing and pulling on the seafloor. Since water motions within waves fall off rapidly with depth, this occurs in regions where water depths are less than about 1,000 feet (about 300 meters). The primary microseism signal is visible in seismic data as a steady hum with a period between 14 and 20 seconds.

What the shaking planet tells us

In our study, we estimated and analyzed historical primary microseism intensity back to the late 1980s at 52 seismograph sites around the world with long histories of continuous recording.

We found that 41 (79%) of these stations showed highly significant and progressive increases in energy over the decades.

The results indicate that globally averaged ocean wave energy since the late 20th century has increased at a median rate of 0.27% per year. However, since 2000, that globally averaged increase in the rate has risen by 0.35% per year.

We found the greatest overall microseism energy in the very stormy Southern Ocean regions near the Antarctica peninsula. But these results show that North Atlantic waves have intensified the fastest in recent decades compared to historical levels. That is consistent with recent research suggesting North Atlantic storm intensity and coastal hazards are increasing. Storm Ciarán, which hit Europe with powerful waves and hurricane-force winds in November 2023, was one record-breaking example.

Image by Joe from Pixabay

The decadeslong microseism record also shows the seasonal swing of strong winter storms between the Northern and Southern hemispheres. It captures the wave-dampening effects of growing and shrinking Antarctic sea ice, as well as the multi-year highs and lows associated with El Niño and La Niña cycles and their long-range effects on ocean waves and storms.

Together, these and other recent seismic studies complement the results from climate and ocean research showing that storms, and waves, are intensifying as the climate warms.

A coastal warning

The oceans have absorbed about 90% of the excess heat connected to rising greenhouse gas emissions from human activities in recent decades. That excess energy can translate into more damaging waves and more powerful storms.

Our results offer another warning for coastal communities, where increasing ocean wave heights can pound coastlines, damaging infrastructure and eroding the land. The impacts of increasing wave energy are further compounded by ongoing sea level rise fueled by climate change and by subsidence. And they emphasize the importance of mitigating climate change and building resilience into coastal infrastructure and environmental protection strategies.

Richard Aster, Professor of Geophysics and Department Head, Colorado State University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The global climate is changing and the Arctic is warming rapidly. These are objectively true statements that most people have come to accept.

But it is also true that Earth’s climate has never been stagnant and climate anomalies have been frequent throughout the past.

How then, do we understand our current situation relative to past climate shifts? Are the impacts of modern climate change comparable to those of the medieval warm period (MWP) or the little ice age (LIA)?

Our recently published study in Anthropocene demonstrates a much more substantial impact to polar bears resulting from recent climate change compared to observations over the last 4,000 years. This suggests that current climatic changes are, indeed, unprecedented in human history.

Ecosystem background

Predators at the top of the food chain, like polar bears, reflect changes across the entire ecosystem, all the way down to microscopic algae.

In the Arctic, the base of the food web is sourced from two categories: sea ice-associated algae and open-water phytoplankton, which are distinguishable through their carbon isotopes.

In our study area — centred on Lancaster Sound in the Canadian Arctic Archipelago — the food web is fed by a combination of both sea ice algae and phytoplankton. We can assess the relative importance of these two sources through the stable isotopes incorporated into the tissues of animals.

The relative abundance of carbon isotopes does not change as they are transferred through the food web, so these isotopes tell us about the carbon sources at the base of the food web. Nitrogen isotopes do change as they are passed up the food chain, which tells us who is eating whom.

Results from our study

In our study we examined stable carbon and nitrogen isotopes in polar bear bone collagen.

The polar bears were all from the Lancaster Sound sub-population and spanned the last 4,000 years. We acquired samples of modern polar bear (1998-2007) obtained through hunting and we were able to compare them to samples from archaeological excavations conducted in the region.

The span of time captured by the archaeological samples was vast, but by dividing them into time bins associated with the cultural traditions in the region we were able to compare the samples across time before present (BP): pre-Dorset (4000-2800 years BP), Dorset (1500-700 BP) and Thule (700-500 BP).

The Dorset/Thule cultural transition occurred at the onset of the medieval warm period, so a comparison of these time bins allows us to look at the state of the food web before and during a known climate shift. The Thule time bin also extends into the beginning of the little ice age giving us a glimpse into that period as well.

What it all means

First, the good news. The results of the nitrogen isotopes showed that throughout time, 4,000 years BP to the present, the structure of the Lancaster Sound food web was relatively unchanged. Polar bears eat seals, seals eat cod, cod eat zooplankton, et cetera. There were no surprising shifts in the diets of polar bears despite past and present climate change. This is comforting.

The results of the carbon isotopes tell a less encouraging story, however. Throughout the four millennia encapsulated by the ancient time bins, we saw stability in the mixture of sea ice algae and open water phytoplankton. We did not detect a difference in the origin of carbon at the base of the food web resulting from the medieval warm period or the little ice age.

The modern samples, however, showed a significant difference in the source of carbon, resulting from a greater proportion of open water phytoplankton and less reliance on sea ice algae.

Evidence of a warming climate

Sea ice is an important habitat in the high Arctic. For polar bears it is a platform for hunting. For ringed seals, the primary prey of polar bears, it is a platform for denning and raising young.

The algae that grows in association with sea ice is also very important for jumpstarting biological productivity before the open water season. Our study shows that the loss of biological productivity associated with sea ice is unprecedented on a very long timescale.

Archaeological materials can provide valuable context to the ongoing climate discussion. Much of the valuable work being undertaken is tracking ecosystem changes on a short timescale, seasons to decades. But as we have demonstrated, the Arctic has already changed, so we should not always assume that we are looking at a pristine or undisturbed state.

Image by Peter Fischer from Pixabay

Adding a lens that looks back into the distant past gives resolution and context to our collective understanding of our situation.

In this case, we have illustrated the magnitude of difference occurring in the modern Arctic, relative to past climate anomalies. The medieval warm period and onset of the little ice age were not visible in the isotopes of the Lancaster Sound food web but modern warming is very apparent. We can, therefore, not dismiss calls to action on climate change on the basis that the climate has always fluctuated.

Jennifer Routledge, PhD Candidate, Environmental and Life Sciences, Trent University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Like the heat waves on land we have all grown familiar with, marine heat waves are being amplified by climate change. These extreme warm water events have ushered in some of the most catastrophic impacts of climate change and are now a major threat to ocean life.

Coral reefs, which are home to a quarter of all life in the ocean, are the most vulnerable.
This is a dire situation, given the vast number of people who depend on coral reefs for their sustenance and livelihoods.

As climate change pushes corals beyond their limits, a key question is why different corals vary in their sensitivity to warm waters.

In our new study in Science Advances, we examined the genetics of hundreds of individual corals during the 2015-16 El Niño-driven heat wave. Our results suggest that heat waves have hidden impacts on the genetic composition of reef-building corals. Understanding this could help scientists bolster reef resilience to future heat waves.

Pushing corals out of their comfort zones

Corals are highly adapted to the temperature of their local waters, with temperatures even 1 C warmer than normal pushing them out of their comfort zone.

Unusually warm water disrupts the vital relationship between stony corals (the reef-builders) and their symbiotic partners, microscopic algae that provide food to the corals. This causes coral bleaching, and in many cases mortality.

The tropical heat wave at our study site in the central Pacific Ocean, Kiritimati (Christmas Island), lasted for ten months, a world record. This led to extensive coral bleaching, presenting an opportunity to determine why some corals died and others survived.

Cryptic diversity within a widespread coral species

We focused on the widespread lobed coral (Porites lobata). This species is amongst the most heat-tolerant corals, and despite almost 90 per cent of all coral cover being lost on Kiritimati, over half of lobed corals survived.

In fact, some Porites colonies didn’t bleach at all.

Why?

Using genomic tools, we identified three distinct types of Porites lobata on Kiritimati. These lineages, which may represent distinct species, are indistinguishable by eye but genetically different.

Such biodiversity is known as “cryptic diversity” or “hidden diversity.” Although cryptic diversity is widespread across corals, its ecological implications remain unclear.

Marine heat waves threaten cryptic diversity

We found that one genetic lineage of Porites was highly sensitive to the heat wave: only 15 per cent of its colonies survived compared to 50-60 per cent in the other lineages. Thus, even in a coral widely considered to be stress tolerant, heat waves can have hidden impacts, threatening diversity that is invisible to the naked eye.

If future marine heat waves continue to have similar effects, eventually sensitive genotypes like this one could be completely lost, reducing the genetic diversity of coral reefs.

Because interbreeding between cryptic lineages and species can offer a potential avenue for future adaptation, losses of genetic diversity could make a bad problem even worse by limiting future adaptation to changing environments.

A forced breakup

So why did Porites lineages on Kiritimati differ in survival?

One hypothesis is that they house symbiotic partners with different heat sensitivities. Using metabarcoding, a technique that attempts to identify everything found living in the coral tissue, we identified which symbionts were partnered with which corals before, during and after the heat wave.

We found that the distinct Porites lineages had different partnerships before the heat wave. Porites species pass on their symbionts from one generation to the next and so these relationships likely arose over many generations.

By the end of the heat wave, however, one of Porites’ unique algal partners had been virtually eliminated. The survivors of all lineages had similar symbionts, suggesting specialized relationships between the partners had been lost under extreme temperatures.

Thus, not only was a cryptic coral lineage left teetering on the edge of local extinction, but its specialized symbiotic relationship had also been forcefully broken up.

Implications for conserving coral reefs

Due to climate change and other threats, we are currently experiencing a biodiversity crisis. Our findings underscore that this crisis extends beyond what the eye can see.

Cryptic species often occupy unique ecological niches and play specific roles within ecosystems. Discovering these hidden differences can enhance our understanding of how ecosystems function. But worryingly, we may be losing this critical diversity before it is even discovered.

Continued study of cryptic diversity could prove essential to building climate resilient ecosystems. Using heat tolerant cryptic lineages in restoration approaches, for example, could help make reefs more tolerant to future warming.

Ultimately, greenhouse gas emissions must be rapidly reduced to curb planetary warming. While targeted efforts to bolster coral reefs against climate change may buy limited time, the current heat waves blanketing the world’s oceans underscore that the ocean is simply becoming too hot for corals and we need to act rapidly to mitigate the damage.

Samuel Starko, Forrest Research Fellow, The University of Western Australia and Julia K. Baum, Professor of Biology, University of Victoria

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Featured image: A healthy reef on Kiritimati (Christmas Island, Republic of Kiribati).
(Danielle Claar), Author provided

Those following the latest developments in climate science would have been stunned by the jaw-dropping headlines last week proclaiming the “Gulf Stream could collapse as early as 2025, study suggests” — which responded to a recent publication in Nature Communications.

“Be very worried: Gulf Stream collapse could spark global chaos by 2025” announced the New York Post. “A crucial system of ocean currents is heading for a collapse that ‘would affect every person on the planet” noted CNN in the U.S. and repeated CTV News here in Canada.

One can only imagine how those already stricken with climate anxiety internalized this seemingly apocalyptic news as temperature records were being shattered across the globe.

This latest alarmist rhetoric provides a textbook example of how not to communicate climate science. These headlines do nothing to raise public awareness, let alone influence public policy to support climate solutions.

We see the world we describe

It is well known that climate anxiety is fuelled by media messaging about the looming climate crisis. This is causing many to simply shut down and give up — believing we are all doomed and there is nothing anyone can do about it.

Image by StockSnap from Pixabay

Alarmist media framing of impending doom has become quintessential fuel for personal climate anxiety, and when amplified by sensational media messaging, it is quickly emerging as a dominant factor in the collective zeitgeist of our age, the Anthropocene.

This is also not the first time such headlines have emerged. Back in 1998, the Atlantic Monthly published an article raising the alarm that global “warming could lead, paradoxically, to drastic cooling — a catastrophe that could threaten the survival of civilization.”

In 2002, editorials in the New York Times and Discover magazine offered the prediction of a forthcoming collapse of deep water formation in the North Atlantic, which would lead to the next ice age.

Building on the unfounded assertions in these earlier stories, BBC Horizon televised a 2003 documentary entitled The Big Chill, and in 2004 Fortune magazine published “The Pentagon’s Weather Nightmare,” piling on where previous articles left off.

Seeing the opportunity for an exciting disaster movie, Hollywood stepped up to created The Day After Tomorrow in which every known law of thermodynamics was ever so creatively violated.

The currents are not collapsing (anytime soon)

While it was relatively easy to show that it is not possible for global warming to cause an ice age, this still hasn’t stopped some from promoting this false narrative.

The latest series of alarmist headlines may not have fixated on an impending ice age, but they still suggest the Atlantic meridional overturning circulation could collapse by 2025. This is an outrageous claim at best and a completely irresponsible pronouncement at worst.

The Intergovernmental Panel on Climate Change has been assessing the likelihood of a cessation of deep-water formation in the North Atlantic for decades. In fact, I was on the writing team of the 2007 4th Assessment Report where we concluded that:

“It is very likely that the Atlantic Ocean Meridional Overturning Circulation (MOC) will slow down during the course of the 21st century. It is very unlikely that the MOC will undergo a large abrupt transition during the course of the 21st century.”

Almost identical statements were included in the 5th Assessment Report in 2013 and the 6th Assessment Report in 2021. Other assessments, including the National Academy of Sciences Abrupt Impacts of Climate Change: Anticipating Surprises, published in 2013, also reached similar conclusions.

The 6th assessment report went further to conclude that:

“There is no observational evidence of a trend in the Atlantic Meridional Overturning Circulation (AMOC), based on the decade-long record of the complete AMOC and longer records of individual AMOC components.”

Understanding climate optimism

Hannah Ritchie, the deputy editor and lead researcher at Our World in Data and a senior researcher at the Oxford Martin School, recently penned an article for Vox where she proposed an elegant framework for how people see the world and their ability to facilitate change.

Ritchie’s framework lumped people into four general categories based on combinations of those who are optimistic and those who are pessimistic about the future, as well as those who believe and those who don’t believe that we have agency to shape the future based on today’s decisions and actions.

Ritchie persuasively argued that more people located in the green “optimistic and changeable” box are what is needed to advance climate solutions. Those positioned elsewhere are not effective in advancing such solutions.

More importantly, rather than instilling a sense of optimism that global warming is a solvable problem, the extreme behaviour (fear mongering or civil disobedience) of the “pessimistic changeable” group (such as many within the Extinction Rebellion movement), often does nothing more than drive the public towards the “pessimistic not changeable” group.

A responsibility to communicate, responsibly

Unfortunately, extremely low probability, and often poorly understood tipping point scenarios, often end up being misinterpreted as likely and imminent climate events.

In many cases, the nuances of scientific uncertainty, particularly around the differences between hypothesis posing and hypothesis testing, are lost on the lay reader when a study goes viral across social media. This is only amplified in situations where scientists make statements where creative licence is taken with speculative possibilities. Possibilities that reader-starved journalists are only too happy to play up in clickbait headlines.

Through independent research and the writing of IPCC reports, the climate science community operates from a position of privilege in the public discourse of climate change science, its impacts and solutions.

Climate scientists have agency in the advancement of climate solutions, and with that agency comes a responsibility to avoid sensationalism. By not tempering their speech, they risk further ratcheting up the rhetoric with nothing to offer in terms of overall solutions or risk reduction.

Andrew Weaver, Professor, School of Earth and Ocean Sciences, University of Victoria

This article is republished from The Conversation under a Creative Commons license. Read the original article.