Hot Science: Underestimated Aviation Emissions, New Feedback Loops, & Octopuses Under Threat

Warming of Antarctica’s waters likely contributing to sea level rise in the North Atlantic

The Atlantic Meridional Overturning Circulation (AMOC) is a system of ocean currents driven by temperature and salinity differences that, like a conveyor belt, moves water across ocean basins, as well as mixes surface and deeper waters. By distributing heat, nutrients and CO2 across the world’s ocean basins, this circulation system supports all marine life. 

But global temperature rise is disrupting the AMOC, with a new study published in Nature Geoscience shedding light on the impact of these human-induced changes on a specific section of the AMOC called the abyssal limb. This branch of the conveyor belt carries bottom waters from the Southern Ocean — which form as seawater cools during Antarctica’s winter, freezes into ice and leaves behind salty, denser waters that sink to depths greater than 4,000 meters – northward to the Atlantic. 

Analyzing data collected from a network of buoys anchored to the seafloor, floats that sink down to the bottom of the ocean and cruise surveys across the North Atlantic, the authors found this current weakened by 12% between 2000 and 2020. This was likely in response to a slowdown in the formulation of these deep waters in the Southern Ocean. Reduced inflow of cold waters from Antarctica, then, likely contributed to warming thousands of miles away in the North Atlantic, and this increase in ocean heat content has caused water to expand and local sea levels to rise.

Positive feedback identified in West Antarctic Ice Sheet melting

Because a significant amount of the West Antarctic Ice Sheet sits below sea level, the ice is particularly vulnerable to warm waters. New research explores how warm waters are moving towards the ice shelf and transporting heat, in turn driving ice shelf melting. The findings suggest that the waters are being steered towards the ice shelf because of upwelling of meltwater. 

As ice melts, the freshwater leads to a stronger undercurrent, with the transport of more heat from nearby waters to the ice shelf. Accordingly, a positive feedback has been created – with more melting from ice shelves leading to changes in currents, which itself accelerates ice melting. The authors note that this potentially further destabilizes the West Antarctic Ice Sheet.

Glacier loss alters ecosystems and helps the establishment of invasive species

As warming from climate change accelerates, ecosystems are starting to experience novel changes. Research conducted in the South Atlantic on the Island of South Georgia assessed the ability of established introduced species to colonize areas previously covered by glaciers but are now exposed; a process known as deglaciation. The researchers sampled plant communities and invertebrates (animals without a backbone) at multiple locations on the island. 

They found that the number of plant species and cover increased with time since deglaciation. They also found notable presence of introduced plant species and arthropods with known negative ecosystem impacts. Such ecosystem changes demonstrate how climate change drives complex alterations to ecosystems over time.

Deadly ocean cooling events threaten marine life

Analyzing over 30 years of sea surface temperature data and wind records, a new Nature Climate Change study finds that cold upwelling events, where patches of cold water rise from the depths of the ocean, are becoming more frequent and more intense in parts of the Indian and Pacific Oceans due to climate change. These cooling events can be deadly to sharks, rays and many other marine megafauna. 

In 2021 for example, an extreme cold upwelling event off the coast of South Africa was responsible for a across 81 species. Should this trend continue, it could create a “bait and switch” situation for marine life — as warming across the tropics pushes species poleward, they may move into waters that experience more and more deadly cold upwelling events.

Climate change increases fire risk through the “fertilization effect”

Climate change is increasing the frequency, size and duration of fires. Additional atmospheric carbon dioxide can also drive the “fertilization effect”, where elevated carbon availability allows plants to increase their growth and productivity. Current research has not assessed if the increased uptake of carbon by plants will influence fires. 

A study published in Communication Earth & Environment investigated the impact of atmospheric carbon dioxide on future fire activity. They modeled how wildfire activity is projected to change with increases in atmospheric carbon dioxide. They found that biogeochemical changes, such as the fertilization effect, are projected to increase fire activity. The authors suggest that future policy should incorporate ecological drivers when working to mitigate fire risk.

Decreased productivity in soda lakes threatens flamingos

Soda lakes are productive aquatic ecosystems with high alkalinity (pH between 9 to 12) and salinity. In East Africa, they are also home to more than three-quarters of Lesser Flamingos. Research published in Current Biology used satellite observations, abundance counts and climatic data to assess the productivity and health of 22 soda lakes over time. 

The authors found that the abundance of Lesser Flamingos at lake sites is correlated with food availability. They also find that productivity is declining, likely due to rising water levels from increased rainfall, which changes the chemical makeup of the lakes. As climate change alters weather patterns, iconic species like the Lesser Flamingo are at risk of losing critical habitat.

Increasingly rapid Arctic warming reducing dust pollution

High dust levels have caused persistent challenges across West and South Asia, with negative impacts to food security, local air quality and energy supplies. But data collected over the past two decades indicates that dust pollution has steadily decreased. While previous studies attribute this trend to local land-use changes like an increase in tree planting, a new study finds that Arctic amplification — the phenomenon of the Arctic warming much faster than the rest of the planet — is spurring declines in dust levels. 

This amplification reduces the difference in temperature between the Arctic and Northern Hemisphere and is associated with changes to the polar jet stream. Shifts in this east-west air current have disrupted wind patterns that transport dust from Northeast Africa to the Middle East and the Indian subcontinent. Efforts to slow down Arctic warming by reducing GHG emissions, then, could actually increase dust loading in the region, and so implementing local actions to counter desertification, such as reforestation and irrigation management, alongside measures to mitigate climate change will become increasingly important.

Oases artificially expanding but all the more vulnerable

Oases play a critical role for habitats and water sources in drylands, which cover over 40% of the Earth’s land area. Oases sustain 10% of the global population. Researchers have now created a global oasis distribution map from 1995 to 2020 and in doing so found that the global area covered by oasis increased from 1995 to 2020 by 8.65 million hectares. They attribute this growth largely to the conversion of deserts into croplands resulting from irrigation water. 

However, in a changing climate, water resources will be in greater demand given the loss of groundwater, changes in precipitation patterns and glacial loss. Troubling, at the same time, however, they found that 13.4 million hectares of oases studied turned into deserts.