The Arctic is currently warming nearly four times faster than the global average rate. The new study, published in the journal Earth System Dynamics, aimed to estimate the impact of this faster warming on how quickly the global temperature thresholds of 1.5C and 2C, set down in the Paris Agreement, are likely to be breached.

To do this, the research team created alternative climate change projections in which rapid Arctic warming was not occurring. They then compared temperatures in this hypothetical world with those of the “real-world” models and examined the timing with which the critical Paris Agreement thresholds of 1.5C and 2C were breached. They found that, in the models without fast Arctic warming, the thresholds were breached five and eight years later respectively, than their “real-world” projected dates of 2031 and 2051.

In addition, they found that disproportionately fast Arctic warming, known as Arctic amplification, added disproportionate uncertainty to forecasts, as the variation in model projections for the region is larger than for the rest of the planet.

Alistair Duffey (UCL Earth Sciences), a PhD candidate and lead author of the study, said: “Our study highlights the global importance of rapid Arctic warming by quantifying its large impact on when we are likely to breach critical climate thresholds. Arctic warming also adds substantial uncertainty to climate forecasts.”

“These findings underscore the need for more extensive monitoring of temperatures in the region, both in-situ and via satellites, and for a better understanding of the processes occurring there, which can be used to improve forecasts of global temperature rise.”

The study does not attempt to quantify the ways in which Arctic warming affects the rest of the world, for instance through the retreat of sea ice which helps to keep the planet cool, but instead estimates the direct contribution of Arctic warming to global temperature increases.

Co-author Professor Julienne Stroeve (UCL Earth Sciences, the University of Manitoba, Canada, and the U.S. National Snow and Ice Data Center) said: “While our study focuses on how Arctic warming affects global temperature change, the local impacts should not be overlooked. A 2C temperature rise globally would result in a 4C annual mean rise in the Arctic, and a 7C rise in winter, with profound consequences for local people and ecosystems.

“In addition, rapid warming in the Arctic has global consequences that we do not account for in this study, including sea level rise and the thawing of permafrost which leads to more carbon being released into the air.”

Co-author Dr Robbie Mallett (University of Manitoba and Honorary Research Fellow at UCL Earth Sciences) said: “Arctic climate change is often overlooked by politicians because most of the region is outside national boundaries. Our study shows how much the Arctic impacts global targets like the Paris Agreement, and hopefully draws attention to the crisis that’s already unfolding in the region.”

Arctic amplification, which is strongest in the winter months, is caused by several factors. One is the retreat of sea ice, meaning more sunlight (and heat) is absorbed by water instead of being reflected back into space. Another factor is less vertical mixing of air in the poles than in the tropics, which keeps warmer air close to the Earth’s surface.

For the study, researchers looked at an ensemble of 40 climate models that informed the UN’s 2021 climate change report*. These models divide Earth’s surface into a three-dimensional grid of cells, modelling physical processes occurring within each cell.

The research team modified the output of the models to create an alternative world in which rapid Arctic warming was not occurring, by setting the rate of change of temperature in the region north of 66° North equal to that of the rest of the planet. They looked at how the removal of rapid Arctic warming would affect temperature projections in a plausible intermediate emissions scenario and calculated the average temperature projection across all models.

In addition, they looked at how removing rapid Arctic warming from the models would affect more pessimistic or optimistic scenarios. For example, in a more optimistic scenario, where emissions are cut sharply and net zero is reached shortly after 2050, Arctic amplification causes a seven-year difference in the time of passing 1.5°C.

Temperature projections for the Arctic varied more substantially between the models than for other parts of the globe, accounting for 15% of the uncertainty in projections, despite the region only making up 4% of the global surface area.

The 1.5C and 2C limits are regarded as having been breached when average global temperatures over a 20-year period are 1.5C or 2C higher than in pre-industrial times.

The goal of the Paris Agreement, an international treaty, is to keep the global average temperature to “well below 2°C above pre-industrial levels” and pursue efforts “to limit the temperature increase to 1.5°C.”

The Arctic is thought to have warmed by 2.7C since the pre-industrial era, and this warming is believed to have accelerated since the start of the 21^st century.

The study was supported by the Natural Environment Research Council (NERC), the European Space Agency (ESA), and the Canada 150 Research Chairs Program.

*The Intergovernmental Panel on Climate Change’s Sixth Assessment Report.

In a paper published today in Nature Climate Change, an international team of academics explore the ways in which research has shown that a changing environment affects how our brains work, and how climate change could impact our brain function in the future. The paper is led by the University of Vienna with input from the universities of Geneva, New York, Chicago, Washington, Stanford, Exeter in the UK and the Max Plank Institute in Berlin. It also explores the role that neuroscientists can play in further understanding and addressing these challenges.

Lead author Dr Kimberly C. Doell, of the University of Vienna, said: “We’ve long known that factors in our environment can lead to changes in the brain. Yet we’re only just beginning to look at how climate change, the greatest global threat of our time, might change our brains. Given the increasingly frequent extreme weather events we’re already experiencing, alongside factors such as air pollution, the way we access nature and the stress and anxiety people experience around climate change, it’s crucial that we understand the impact this could all have on our brains. Only then can we start to find ways to mitigate these changes.”

Since the 1940s, scientists have known from mouse studies that changing environmental factors can profoundly change the development and plasticity of the brain. This effect as also been seen in humans in research looking at the effects of growing up in poverty, which found disturbances to brain systems, including lack of cognitive stimulation, exposure to toxins, poor nutrition, and heightened childhood stress. While not entirely surprising, this research highlights the profound impact that one’s environment can have on their brain.

Now, the authors are calling for research to explore the impact on the human brain of being exposed to more extreme weather events, such as heatwaves, droughts, and hurricanes, and associated forest fires and floods. They believe such events may change brain structure, function, and overall health, and also call for more research to evaluate how this may explain changes in well-being and behaviour.

The paper also explores the role that neuroscience can play in influencing the way we think about climate change, our judgments and how we respond.

Dr Mathew White, of the Universities of Exeter and Vienna, is a co-author on the study. He said: “Understanding neural activity that is relevant to motivations, emotions and temporal horizons may help predict behaviour, and improve our understanding of, underlying barriers preventing people from behaving as pro-environmentally as they might wish. Both brain function and climate change are highly complex areas. We need to start seeing them as interlinked, and to take action to protect our brains against the future realities of climate change, and start using our brains better to cope with what is already happening and prevent the worse-case scenarios.”

In late September of this year, flash-flooding surged down neighborhood streets and subway stairways in New York City, as a historic rainfall led to canceled flights and closed roads and city officials urged people to stay at home or shelter in place. Some areas of the city saw up to 2.58 inches of rain in one day, nearly 50% more than the city sewer system’s maximum capacity, causing wastewater problems for many low-lying homes and businesses.

Intuitively, when an extreme weather event hits a city, the more residents it has, the larger number of people are affected. Currently, 83% of the United States population lives in urban settings, according to the U.S. Census. This number is expected to grow over the coming decades, rendering urban climate resilience extraordinarily important. As a result, many people have the impression that the growing sizes of cities are making weather extremes worse for the people who live there.

However, cities are designed and built by people. So, it stands to reason that if some methods of land development increase population exposures to extreme weather conditions, others might hold the potential to moderate or even reduce population exposures as the climate changes over the coming decades.

To explore this idea, University of Delaware researcher Jing Gao, assistant professor in the College of Earth, Ocean and Environment and a resident faculty member in the Data Science Institute, and colleague Melissa Bukovsky, associate professor in the Haub School of Environment and Natural Resources at the University of Wyoming, investigated how changes in urban land and population will affect future populations’ exposures to weather extremes under climate conditions at the end of the 21st century.

The researchers looked at urban areas across the continental United States, including cities large and small, with various development densities and in different climate regions. They used a data-driven model developed by Gao to predict how urban areas across the country will grow by 2100, based on development trends observed over the past 40 years. The research team considered how these urban land changes might affect weather extremes like heat waves, cold waves, heavy rainfalls and severe thunderstorms. They then analyzed how many people would be exposed to these extremes under different climate and urban development conditions at the end of the century.

The research team’s simulations showed that at the end of the 21st century, how a city is laid out or organized spatially, often called an urban land pattern, has the potential to reduce population exposures to future weather extremes, even for heat waves under very high urban expansion rates. Further, how the urban landscape is designed — meaning how buildings are clustered or dispersed and how they fit into the surrounding environment — seem to matter more than simply the size of a city. This is true even while climate change is increasing population exposures.

These findings apply to all cities, from large metropolitan areas like New York City to smaller towns in more rural contexts, such as Newark, Delaware.

“Regardless of the size of a city, well planned urban land patterns can reduce population exposures to weather extremes,” Gao said. “In other words, cities large and small can reduce their risks caused by weather extremes by better arranging their land developments.”

These findings differ from current common perceptions. For example, existing literature in this area has almost exclusively focused on limiting the amount of urban land development, Gao said.

In contrast, the new findings from this research encourage researchers and practitioners from a wide range of related fields to reconsider how cities are designed and built so that they can be in harmony with their regional natural surroundings and more resilient to potential climate risks over the long run.

Gao likened the effects of climate change and urban land patterns on extreme weather risks to the effects of a person’s diet and activity level on their risk for health problems. Properly designed urban land patterns, she said, are like physical exercises that work to counteract poor dietary choices, contributing to a reduced risk for disease, while helping a person become more fit in general.

“Carefully designed urban land patterns cannot completely erase increased population exposures to weather extremes resulting from climate change, but it can generate a meaningful reduction of the increase in risks,” Gao said.

And the cost to start is small, Gao said. No extravagant measure, such as leveling and rebuilding a large area at once, is required.

“Instead, when building new and renovating existing parts of a city, we should adjust our mindset to consider how the new development and renovation will change the way the city as a whole situates in its natural surroundings, and how the city and its surrounds can be one integrated human-environment system at large scales over the long run,” Gao said. “The key is to start adjusting how we think about development now.”

Next steps in the work

The researchers are working to identify specific characteristics about the spatial arrangement of a city that can make it more — or less — resilient to future weather extremes. Identifying these patterns can help guide development that is more sustainable in the face of increasing instances of extreme weather. Through their efforts, the research team hopes to provide actionable suggestions for how to design and build urban areas that reduce their residents’ exposures to weather extremes in the long run.

Importantly, the researchers emphasized that these characteristics will likely vary from region to region, now and as climate changes. For instance, what works in arid Phoenix, Arizona, will probably differ from what will work in humid New Orleans, Louisiana. Likewise, what might work today for a city could differ from what will work in the future, as climate conditions evolve.

“Eventually, we want our work to be directly useful to urban design and planning efforts, offering insights and tools for decision makers to influence long-term social and environmental well-being at scale,” Bukovsky said. “First, though, we need to identify what development patterns can improve various cities’ long-term climate resilience. We will continue collaborating in the future.”

The escalating plastic pollution crisis and inefficiencies in the plastic recycling system have turned many against single-use plastics and led to national and state bans on some plastic packaging. Now, the fossil fuel and petrochemical industries have launched a category of plastic processing technology called chemical recycling or advanced recycling. The plastic industry describes it as a potential panacea that can clean up millions of tons of plastic waste produced annually. Is it everything claimed?

The Ocean Conservancy recently hosted a forum to discuss their findings after examining chemical recycling. The implications of this technology are intricate, and the technology is still evolving. However, the early evidence is that chemical recycling still requires immense energy, generating large amounts of planet-warming CO2. At the same time, it does not significantly reduce the volume of plastic toxins.

“Chemical recycling is an umbrella term that captures a suite of disparate technologies,” said Dr. Anja Brandon, Associate Director of U.S. Plastics Policy at the Ocean Conservancy. She suggested that fossil fuel and plastic companies fudge these terms to confuse consumers and policymakers. “These terms are constantly changing. Its ‘chemical recycling,’ ‘advanced recycling,’ ‘molecular recycling,’ and ‘renewable technologies.’ Different companies all use different terms.”

One clear message from the event was the importance of reducing the use of plastic. As much as 40% of plastic becomes single-use packaging, which accounts for much of the plastic pollution in the oceans and landfills.

“Recycling mitigates the harm of waste and extraction, but not as much, of course, as reuse and certainly reduction is our primary strategy,” said Lynn Hoffman, Co-President of Eureka Recycling in Minneapolis and National Coordinator for the Alliance for Mission-Based Recyclers.

Hoffman noted that mechanical recycling is not without its environmental flaws but suggests that most plastics, especially single-use plastic packaging, are not recycled because of the broken economics of today’s system. It’s often cheaper to use virgin plastic because of the complexity and cost of sorting and processing plastic.

Chemical Recycling: The Spectrum of Methods

Chemical recycling describes several technologies, each a method of breaking down plastics categorized into three main types: purification, depolymerization, and conversion technologies. Each process converts the polymers in plastic into their underlying monomers, the hydrocarbon building blocks extracted from petroleum.

Purification

This method involves using solvents or heat to dissolve plastic, separating it from additives and impurities without altering its molecular structure. The recovered plastic can then be reprocessed into new materials. This method requires very clean post-consumer plastic supplies, which requires careful sorting and cleaning before the material can be processed. Purification works only with specific types of plastic.

Depolymerization

This process breaks plastic down into its constituent monomers using solvents, heat, catalysts, or enzymes. Like purification, depolymerization requires pure feed-stocks, and there are limits on the types of plastics that can be run through the process.

Conversion Technologies

Two older technologies, pyrolysis and gasification, are being repurposed and rebranded under the chemical recycling banner. Both rely on extreme heat to “crack” the polymers, breaking them down into hydrocarbon monomers. And most of that heat is produced by burning oil, coal, or natural gas.

Pyrolysis relies on intense heat and pressure to break plastic molecules into shorter-chain hydrocarbons, not monomers, resulting in a substance known as pyrolysis oil. This process is energy-intensive, requiring temperatures between 600 to 1,600 degrees Fahrenheit.

Like pyrolysis, but operating at even higher temperatures between 1,000 and 2,000 degrees Fahrenheit, gasification breaks plastic into synthetic natural gas.

Chemical Recycling Impacts and Policy Considerations

Despite its potential to address the plastic pollution crisis, chemical recycling has significant environmental and social impacts, especially concerning carbon emissions. Current data suggests that the carbon footprint of chemical recycling is significantly higher than that of traditional mechanical recycling that grinds and melts plastic for reuse. Because chemical recycling facilities are built near oil refineries and plastic factories, they are usually next to low-income communities of color. The emissions and other toxins these chemical recycling facilities may produce raise critical questions about the technology’s role in a sustainable future.

The Ocean Conservancy panelists said that policy implications also need to be at the forefront of the discussion. The classification and regulation of chemical recycling facilities, whether treated as manufacturing entities or solid waste management facilities, have significant implications for where they are placed and the reviews required for permitting. So far, 24 states in the U.S. have passed laws reclassifying chemical recycling facilities as manufacturing entities. In other words, these states decided it is not a form of recycling.

The Challenges of Tracking Success and State Laws

Tracking the success of chemical recycling is a complex task, because the oil and gas produced is not directly comparable to recycled plastic.

The recycling industry has long relied on mass balance accounting, which compares the volume of materials sent to a recycling facility with the output. That works well for mechanical recycling, which ingests plastic and produces plastic that is weighed to estimate the percentage of materials recovered. However, because chemical recycling turns a solid plastic into an oil or gas, there is no easy way to estimate yields. Consequently, petrochemical companies can make audacious claims about the efficacy of chemical recycling that cannot be compared with mechanical recycling.

State laws will play a crucial role in shaping the recycling landscape. They help finance improvements in recycling systems and establish accountability for producers of packaging materials. However, how chemical recycling is defined and regulated by different states varies. California, for example, excludes chemical recycling, treating it as a form of manufacturing rather than recycling. On the other hand, Oregon may treat chemical recycling as a waste management practice but imposes a high burden of proof that the technology is effective before allowing a facility to operate.

Addressing the Textile Industry and Community Impacts

The ever-growing issue of textile waste, particularly from fast fashion, has made chemical recycling appear to be an attractive solution. Startups are exploring depolymerization to tackle the challenge of recycling polyester materials. However, as Dr. Brandon notes, the priority should be reducing production and consumption.

Chemical recycling facilities, like all recycling operations, have proven environmental and health impacts. As the technology evolves, it may become cleaner. For example, oil companies have suggested the CO2 emitted by depolymerization and conversion processes may be captured by a scrubber and sequestered permanently. The potential to extract additives and other impurities from mixed plastic waste using purification could produce more food-grade plastics, albeit at the potential cost of more plastic packaging.

But do we need more plastic? By reducing plastic use, society can remove a substantial amount of the problem. That’s a question each of us answers when we are shopping.

Chemical recycling’s effectiveness, environmental impacts, and societal implications require careful consideration and transparent discussion. As humanity strives to create a sustainable future, the panelists emphasized that all options must be assessed carefully with a critical eye to ensure that solutions like chemical recycling are responsibly and equitably implemented.

Dig Into Related Stories and Interviews

The researchers came to that conclusion after running thousands of computer simulations on the steps needed to decarbonize passenger and freight travel, which make up the largest contributor to greenhouse gases. While they advised that “no single technology, policy, or behavioral change” is enough by itself to reach the target, eliminating tailpipe emissions would be a major factor.

“There are reasons to be optimistic and several remaining areas to explore,” said Chris Hoehne, a mobility systems research scientist at NREL and lead author of a new paper detailing the routes that could be taken. “In the scientific community, there is a lot of agreement around what needs to happen to slash transportation-related greenhouse gas emissions, especially when it comes to electrification. But there is high uncertainty for future transportation emissions and electricity needs, and this unique analysis helps shed light on the conditions that drive these uncertainties.”

The paper, “Exploring decarbonization pathways for USA passenger and freight mobility,” appears in the journal Nature Communications. Hoehne’s co-authors from NREL are Matteo Muratori, Paige Jadun, Brian Bush, Artur Yip, Catherine Ledna, and Laura Vimmerstedt. Two other co-authors are from the U.S. Department of Energy.

While most vehicles today burn fossil fuels, a zero-emission vehicle (ZEV) relies on alternate sources of power, such as batteries or hydrogen. Transportation ranks as the largest source of greenhouse gas emissions in the United States and the fastest-growing source of emissions in other parts of the world.

The researchers analyzed in detail 50 deep decarbonization scenarios, showing that rapid adoption of ZEVs is essential alongside a simultaneous transition to a clean electric grid. Equally important is managing travel demand growth, which would reduce the amount of clean electricity supply needed. The researchers found the most dynamic variable in reducing total transportation-related emissions are measures to support the transition to ZEVs.

Using a model called Transportation Energy & Mobility Pathway Options (TEMPO), the researchers performed more than 2,000 simulations to determine what will be needed to decarbonize passenger and freight travel. The study explores changes in technology, behavior, and policies to envision how passenger and freight systems can successfully transition to a sustainable future. Policy changes may require new regulations that drive the adoption of electric vehicles, for example. Technology solutions will call for continued advancements in batteries, fuel cells, and sustainable biofuels, among others. Behavior comes into play in considering shifts in population and travel needs. Someone moving away from an urban core, for example, might have to travel longer distances to work.

“The transportation sector accounts for about a quarter of greenhouse gas emissions in the United States, and about two-thirds of all that is from personal vehicle travel,” Hoehne said.

By employing a combination of strategies, the study shows that the maximum potential for 2050 decarbonization across the simulated scenarios is a staggering 89% reduction in greenhouse gases relative to 2019, equivalent to an 85% reduction from the 2005 baseline.

“Recent progress in technology coupled with the pressing need to address both the climate crisis and air quality issues have elevated the importance of clean transportation solutions,” said Muratori, manager of the Transportation Energy Transition Analysis group and architect of the TEMPO model. “This shift has made transitioning the entire sector towards sustainability an achievable goal and a top priority in the United States and worldwide.”

Funding was provided by the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Strategic Analysis Team.

Their approach, which uses AI applied to DNA-based biodiversity, climate variables and pollution, could help regulators to protect the planet’s existing biodiversity levels, or even improve them.

Researchers from the University of Birmingham, in collaboration with Goethe University in Frankfurt, used sediment from the bottom of a lake in Denmark to reconstruct a 100-year-old library of biodiversity, chemical pollution, and climate change levels. This lake has a history of well-documented shifts in water quality, making it a perfect natural experiment for testing the biodiversity time machine.

Publishing their findings today (7 Nov) in eLife, the experts reveal that the sediment holds a continuous record of biological and environmental signals that have changed over time — from (semi)pristine environments at the start of the industrial revolution to the present.

The team used environmental DNA — genetic material left behind by plants, animals, and bacteria — to build a picture of the entire freshwater community. Assisted by AI, they analysed the information, in conjunction with climate and pollution data, to identify what could explain the historic loss of species that lived in the lake.

Principal investigator Luisa Orsini, Professor of Evolutionary Systems Biology and Environmental Omics at the University of Birmingham and Fellow of the Alan Turing Institute, explained: “We took a sediment core from the bottom of the lake and used biological data within that sediment like a time machine — looking back in time to build a detailed picture of biodiversity over the last century at yearly resolution. By analysing biological data with climate change data and pollution levels we can identify the factors having the biggest impact on biodiversity.

“Protecting every species without impacting human production is unrealistic, but using AI we can prioritise the conservation of species that deliver ecosystem services. At the same time, we can identify the top pollutants, guiding regulation of chemical compounds with the most adverse effect. These actions can help us not only to preserve the biodiversity we have today, but potentially to improve biodiversity recovery. Biodiversity sustains many ecosystem services that we all benefit from. Protecting biodiversity mean protecting these services.”

The researchers found that pollutants such as insecticides and fungicides, alongside increases in minimum temperature (a 1.2-1.5-degree increase) caused the most damage to biodiversity levels.

However, the DNA present in the sediment also showed that over the last 20 years the lake had begun to recover. Water quality improved as agricultural land use declined in the area surrounding the lake. Yet, whereas the overall biodiversity increased, the communities were not the same as in the (semi)pristine phase. This is concerning as different species can deliver different ecosystem services, and therefore their inability to return to a particular site can prevent the reinstatement of specific services.

Niamh Eastwood, lead author and PhD student at the University of Birmingham said: “The biodiversity loss caused by this pollution and the warming water temperature is potentially irreversible. The species found in the lake 100 years ago that have been lost will not all be able to return. It is not possible to restore the lake to its original pristine state, even though the lake is recovering. This research shows that if we fail to protect biodiversity, much of it could be lost forever.”

Dr Jiarui Zhou, co-lead author and Assistant Professor in Environmental Bioinformatics at the University of Birmingham, said: “Learning from the past, our holistic models can help us to predict the likely loss of biodiversity under a ‘business as usual’ and other pollution scenarios. We have demonstrated the value of AI-based approaches for understanding historic drivers of biodiversity loss. As new data becomes available, more sophisticated AI models can be used to further improve our predictions of the causes of biodiversity loss.”

Next the researchers are expanding their initial study on a single lake to lakes in England and Wales. This new study will help them understand how replicable the patters they observed are and, therefore, how they can generalise their findings on pollution and climate change on lake biodiversity.

“Looking at recent, natural climate anomalies helps to understand the processes and mechanisms that human-induced global warming may trigger,” says Dr Anastasia Zhuravleva, lead author of the study. She was a PhD student at GEOMAR and received the Annette Barthelt Prize for her dissertation in 2019. She then worked as a post-doctoral researcher at GEOMAR and Dalhousie University, where the study was completed.

“Researchers often consider an increase in sea ice extent and desalination in the subpolar North Atlantic as possible triggers for past cold periods, but processes in the tropical Atlantic appear to be equally important,” says Dr Zhuravleva. “In fact, in contrast to the northern and mid-latitudes, there is little information on these recent climate events from the subtropical-tropical Atlantic and their impact on regions in the Northern Hemisphere,” adds Dr Henning Bauch, paleoclimatologist at AWI and GEOMAR, co-initiator and co-author of the study. “This is where our research comes in.”

So, what happened in the tropical Atlantic during historical climate anomalies, and how might potential changes there have affected ocean circulation and climate much further north? To answer these questions, the team worked on a sediment profile from the southern Caribbean and reconstructed the salinity and temperature of the surface water over the last 1700 years. Among other things, the researchers determined the isotopic and elemental composition of the calcareous shells of plankton.

The results show a cooling of about 1°C during the Little Ice Age. “It is a significant temperature change for this region,” says Dr Mahyar Mohtadi, co-author of the study and head of the Low Latitude Climate Variability group at MARUM. “Particularly noteworthy is the occurrence of another pronounced cooling for the 8th-9th centuries. Colder temperatures in the otherwise warm tropical ocean led to lower regional rainfall, which coincided with severe droughts in the Yucatan Peninsula and the decline of the Classic Maya culture.”

In addition, the researchers found that the cold climate anomalies in the subpolar North Atlantic and Europe were accompanied by weaker ocean circulation and increased salinity in the Caribbean. “Advection, or the movement of tropical salt to high northern latitudes, is essential for maintaining high surface densities in the subpolar North Atlantic. This is a prerequisite for the overall stability of the large-scale ocean circulation, including the transfer of warm Gulf Stream water, which is responsible for our mild temperatures in Europe,” says Dr Bauch.

The data on the historical past thus allow a reconstruction of the connection across the North Atlantic. Initial cooling can be caused by volcanic eruptions, low solar activity and feedbacks between sea ice and the ocean in the north. The new study provides evidence that a decrease in salt movement to high northern latitudes will amplify and prolong these climate events. Conversely, the slow movement of positive salinity anomalies from the tropics will eventually increase the density at the surface of the subpolar North Atlantic. This may favour the northward transport of heat by ocean currents, resulting in milder temperatures over Europe and North America.

“Such a salinity feedback is known from models and has been assumed for the Little Ice Age. However, in the absence of tropical ocean data, these assumptions have been based on less direct precipitation records,” says Dr Zhuravleva.

There is evidence that the Gulf Stream is weakening and that human-induced warming is a likely cause. What is certain is that the consequences of this change will be global. The extent to which the different climate mechanisms interact has been an open question. This study now confirms that the south-north transport of salt is a key factor in the processes involved.