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


Kelly Levin, Sophia Boehm, Tovah Siegel, Emma Grier, and Dennis Tirpak
(Photo credit: iStock / Nigel Marsh)

Welcome to Hot Science, a joint effort of World Resources Institute and Bezos Earth Fund. This edition features studies published in April 2024 and is not meant to be comprehensive. Rather, this newsletter aims to highlight ten of the most significant climate science papers published in leading peer-reviewed journals each month, with a focus on global temperature rise and surface albedo; greenhouse gas (GHG) emissions and carbon removals; climatic changes across ice, permafrost and the ocean; extreme weather events; and climate risks and impacts. If you find this newsletter useful, please encourage your colleagues and friends to subscribe to Hot Science. 

Ten of the Hottest Stories

New estimates of global GHG emissions from aviation significantly higher than those reported by countries

Together, domestic and international flights currently account for 2.4% of annual carbon dioxide (CO2) emissions globally, and when combined with non-CO2 effects from (e.g., non-CO2 emissions and cloud formations), air travel’s contribution to climate change rises to 4%. By 2050, aviation may cause a total of 0.1°C (0.2°F) in global warming. Yet the majority of countries that have ratified the United Nations Framework Convention on Climate Change (UNFCCC) do not regularly disclosure emissions from domestic and international flights. 

GHG emissions reporting for developing countries, specifically, is voluntary, and for all countries, inventorying air travel emissions based on different methods (e.g., by where the flight originated, by the nationality of the individual that took the flight) can yield vastly different estimates. Consequently, few national inventories for domestic and international aviation emissions that are consistent with UNFCCC reporting standards exist for all countries. 

A study published last month aims to fill this gap by using a high-resolution model for air travel emissions and data from 36.2 million individual flight paths in 2019 to estimate CO2 emissions from international and domestic flights for each country in the same year. It finds that Parties to the UNFCCC emitted 911 MtCO2 in 2019 – about 50% higher than the 604 MtCO2 collectively reported by governments. The United States, China, the United Kingdom, Japan and the United Arab Emirates top the list of countries with the highest CO2 emissions from departing flights, and together, accounted for almost half of these air travel emissions in 2019.

Global temperature rises risks transforming tundra ecosystems from carbon sinks to carbon sources

Arctic and alpine tundra ecosystems, which are warming far faster than the global average, hold large amounts of carbon within their soils, and the fate of these reservoirs will be decided by the balance between uptake of carbon via photosynthesis and release of carbon via ecosystem respiration. Yet the magnitude of climate change’s impact on ecosystem respiration, as well as the factors that drive variability in ecosystem respiration across the tundra, remains highly uncertain. 

To help improve our understanding of this feedback loop, more than 70 scientists worked together to analyze data collected from 56 experiments that use mini-greenhouses that trap heat and simulate local warming across 28 arctic and alpine tundra sites. Published in a recent Nature article, their findings show that an average warming of 1.4°C (2.5°F) in air temperature and 0.4°C (0.7°F) in soil temperature, together, spurred a 30% rise in ecosystem respiration during growing seasons that continued for at least 25 years. 

As the study’s lead author noted, “[this] remarkable increase [was] nearly four times greater than previously estimated.” Yet these respiration rates, the authors underscore, varied widely across tundra ecosystems, with site-specific soil conditions (e.g., nitrogen concentrations and pH levels) driving differences in local warming’s impact on respiration and, therefore, carbon release.

Pools of tundra water just beginning to freeze for the winter in the Alaskan Arctic in a valley in the Brooks Range
(Photo credit: troutnut / iStock)

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.

An iceberg floats in front of South Georgia Island Coastal Mountains.
An iceberg floats in front of South Georgia Island Coastal Mountains. (Photo credit: Mlenny / iStock)

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.

A large group of Lesser Flamingos in Kenya's Lake Elementatia.
(Photo credit: nikpal / iStock)

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.

Honorable Mention

A warmer world is a blurrier and deadlier world for the octopus

Many animals are particularly vulnerable to warming in their early life stages, which are often not the subject of research efforts. A recent study exposed octopus embryos and their mothers to future projected temperatures and found that key eye protein levels were reduced, impairing vision. An estimated 70% of octopuses’ brains are devoted to vision, and the animals rely heavily on sight for communication and spotting predators and prey. 

In addition to eyesight impairment, the octopuses activated a stress response which redirected energy resources from growth, digestion and other critical functions. The authors found a higher mortality rate in adult females and octopus embryos, implying a limit to their thermal tolerance. Given the compounding effects of fishing and warming, octopus could struggle to survive by the end of the century. This contradicts earlier studies which found that cephalopods, including octopuses, were highly adaptable to warming.

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