Hot Science: Carbon Budgets, Deglaciation & More
In this edition, we explore studies published between November 2022 and January 2023
"Hot Science" is a joint effort of the Bezos Earth Fund and World Resources Institute. While we aim to highlight the most significant climate science literature compiled from leading peer reviewed journals, this is not meant to be comprehensive.
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Hottest Stories
The world will consume the remaining carbon budget for a 1.5 degrees Celsius (2.7 degrees Fahrenheit) future in nine years should CO2 emissions continue at current levels
Updated annually, the Global Carbon Budget 2022 estimates that global atmospheric concentrations of carbon dioxide (CO2) are set to reach a record-breaking high of 417.2 parts per million (ppm) – 2.5 ppm more than in 2021. From 2021 to 2022, global CO2 emissions rose by roughly 0.8%, driven by relatively stable emissions from land use and increasing emissions from fossil fuels.
Annual CO2 emissions from fossil fuels, as well as cement, increased by 1% to hit a new high of 36.6 GtCO2. Oil accounted for much of this growth in CO2 emissions, as travel continued to recover from COVID-19, while CO2 emissions increased only slightly for coal, remained relatively flat for gas and fell slightly for cement. Authors of the study also found that, as CO2 emissions continued to rise from 2012 to 2021, climate change has weakened the world’s carbon sinks, reducing CO2 uptake by roughly 4% in the ocean and by 17% on land.
Widespread mountain deglaciation in a warming world
A new study projects that mountain glaciers (excluding the Greenland and Antarctic ice sheets) will lose roughly 26% of their mass with 1.5 degrees C of warming and 41% with 4 degrees C of warming by 2100. This corresponds to 49% (with 1.5 degrees C) to 83% (4 degrees C) of mountain glaciers disappearing. Not only would this lead to significant sea level rise and flooding but also threaten water resources for the nearly two billion people who depend on glacial runoff as a water resource. Another recent study of mountain glaciers finds that westerly winds shifting towards the poles, combined with warming, will speed up glacial recession.
Speed up of Northeast Greenland Ice Stream
Scientists have documented accelerated melting of the Northeast Greenland Ice Stream, a fast-flowing stream of ice which reaches the interior of the Greenland Ice Sheet. They project that this Ice Stream alone will lead to 13.5-15.5 mm sea level rise (0.53 – 0.61 inches) by 2100, which is equivalent to the contribution of the entire Greenland ice sheet over the past half century. This level of projected sea level rise is six times more than previous models suggested.
Unprecedented fire activity in the Arctic associated with rising temperatures
Scientists have now quantified the burned area across permafrost peatlands in 2019 and 2020: about 4.7 million hectares. This burned area – from these two years alone – was 44% of the total burned area in the Siberian Arctic from 1982-2020. The authors find a near exponential relationship between temperature and annual burned area. Burning of permafrost and peat is particularly problematic given the rich stores of carbon they hold, which can be released with burning, in turn adding to warming.
Climate change could trigger changes in La Niña and El Niño events far sooner than anticipated
The El Niño-Southern Oscillation (ENSO) is the world’s strongest and most significant annual fluctuation in climate, alternating between a cold La Niña phase, a warm El Niño phase and a neutral phase. Among scientists, there is a growing consensus that global temperature rise will increase the sea surface temperature variability of ENSO. However, determining when this variability will be detectable above the natural variations of ENSO has been a far more difficult exercise until now.
Analyzing 70 years of data on ENSO, alongside outputs from 58 climate models, authors of a new study found that climate change’s influence on El Niño and La Niña events via changes in sea surface temperatures across the tropical eastern Pacific will be observable by 2030 – four decades sooner than previously predicted. Stronger La Niña and El Niño events will likely intensify flooding in some parts of the world, while prolonging droughts in others.
Temperature
2022 ranks among the top five warmest years on record
New data from the European Union’s Copernicus Climate Change Service confirms the World Meteorological Organization’s provisional finding that the last eight years have been the warmest eight on record. And while scientists at the United States’ National Aeronautics and Space Administration agree with this strong, long-term warming trend, they estimate that the past nine years have been the hottest on record since modern observations began in 1880. Despite the cooling influence of La Niña conditions, 2022, specifically, ranks as the fifth hottest year, with its annual average temperature approximately 1.1 to 1.2 degrees C (2.0 to 2.2 degrees F) warmer than pre-industrial levels.
Arctic warming continues to occur more than two times faster than global temperature rise
Surface air temperatures in 2022 were 0.7 degrees C (1.3 degrees F) higher than the region’s average temperature from 1991 to 2020, and unprecedented, late-season warming in September triggered surface-melt conditions over more than a third of the Greenland Ice Sheet, which experienced its 25th straight year of ice loss. Scientists at the United States’ National Oceanic and Atmospheric Administration observed similarly concerning warming trends in the Arctic Ocean, where sea ice extent in 2022 remained well below the long-term average. Wetter, stormier conditions accompanied these above-average temperatures, with the region witnessing a significant increase in precipitation since the 1950s. This past year, for example, ranks third wettest in the past 72 years. Together, these changes are threatening the lives and livelihoods of the region’s communities, including Indigenous Peoples.
Near-term ambition will prove critical to limiting peak global warming
Analyzing Nationally Determined Contributions (NDCs), official long-term strategies (LTSs) and net-zero pledges announced by the end of COP26, authors of a recent article modelled a suite of high-ambition pathways to inform national efforts to strengthen 2030 GHG emissions targets. They found that, should countries fail to adopt more ambitious near-term targets and meet only their stated GHG emissions targets for 2030, the world would need to improve the GHG emissions intensity of gross domestic product by at least 8% each year – a decarbonization rate that far exceeds historically observed changes – to limit warming to 1.5 degrees C (2.7 degrees F).
Failure to ratchet up near-term ambition also risks increasing peak temperatures, as well as the number of years that global warming would overshoot 1.5 degrees C (2.7 degrees F). Absent a step change in ambition, this period of overshoot, the authors estimated, would likely span decades, exposing humans and natural systems to increasingly dangerous and irreversible impacts. But significantly increasing near-term ambition – defined as lowering GHG emissions by 30% below countries’ current 2030 targets in their NDCs – could limit peak warming to roughly 1.7 degrees C (3.1 degrees F) and the years of overshoot to between 47 and 58 years.
Even temporarily overshooting 1.5-2 degrees C (2.7-3.6 degrees F) risks triggering a cascade of tipping points
Much attention has focused on identifying temperature thresholds for tipping points that, once crossed, catalyze changes in parts of the climate system (known as tipping elements) that become self-perpetuating, leading to abrupt, irreversible and increasingly disastrous impacts for people around the world. Building on these analyses, a recent Nature Climate Change paper explores the risk of triggering tipping points at different magnitudes and durations of overshooting the Paris Agreement’s temperature goal.
Focusing on four, interconnected tipping elements, including the collapse of the Greenland Ice Sheet and the West Antarctic Ice Sheet, the shutdown of the Atlantic Meridional Overturning Circulation (AMOC) and the dieback of the Amazon rainforest, the authors found that the risk of crossing at least one tipping point increased as peak temperatures rise.
For example, across all modeled simulations, roughly a third feature a tipping event or cascade of tipping events at a peak temperature of 2 degrees C (3.6 degrees F) and that figure jumps to nearly three-quarters at 4 degrees C (7.2 degrees F). The Greenland and West Antarctic Ice Sheets, in particular, could reach tipping points at relatively small levels of temperature overshoot, although it would take hundreds to thousands of years for these ice sheets to fully melt. Conversely, the shutdown of the AMOC and dieback of the Amazon rainforest will likely occur at higher levels of overshoot, but once their tipping points are crossed, these changes will occur quickly and prove difficult to stop.
Rise in atmospheric dust masks the GHG warming effect
Driven primarily by desert storms across Asia and North Africa, the amount of dust in the atmosphere has increased by roughly 55% since pre-industrial levels, and this rise in microscopic airborne particles can have opposite effects on the climate. By scattering sunlight back to space and dissipating high clouds that would otherwise increase global temperatures, dust can cool the planet. But it can also spur warming through other mechanisms, such as darkening snow and ice to enhance absorption of solar radiation.
Until recently, dust’s net impact on the global climate was uncertain. Authors of a new study were the first to demonstrate that, this increase in atmospheric dust concentrations, has had an overall, slight cooling effect globally. Because climate models do not account for this net impact of dust, they may be underestimating the amount of warming that GHGs, alone, could cause, the lead author warned, and should dust levels stop rising, warming could accelerate slightly.
GHG Emissions and Carbon Removals
Carbon losses from forest degradation across the Amazon are comparable to those from deforestation
Much of the recent literature on CO2 emissions from the Amazon has focused on deforestation. Yet human-caused disturbances, from timber extraction, fire, extreme drought intensified by climate change and habitat fragmentation resulting from deforestation, are also driving degradation across this critical forest. Relying on recently published, spatially explicit datasets on these four drivers of degradation, authors of a new paper assessed the extent of forest degradation from 2001 to 2018, as well as associated carbon losses.
Their analysis shows that more than a third of the remaining Amazon forest (38%) experienced some form of degradation during this period, and these disturbances resulted in carbon losses of 0.05-0.20 petagrams per year. This figure is roughly equivalent to losses from deforestation, which were 0.06 to 0.21 petagrams of carbon per year. The authors project that degradation will remain a significant source of CO2 emissions in the coming decades, independent of deforestation rates.
Scientists warn that the world’s largest tropical peatlands are close to a tipping point
A recently published study in Nature finds that, thousands of years ago, climate change triggered a shift in peat accumulation and decomposition across the central Congo Basin, effectively transforming these peatlands from a major carbon store to a significant carbon source. Analyzing six-meter-long samples of peat from across the region, scientists were able to reconstruct rates of peat accumulation and decomposition, organic carbon stores and precipitation trends over the last 17,500 years.
Data from these samples suggests that, roughly 5,000 years ago, the central Congo Basin began to dry. As water table levels fell, peat likely became exposed to the oxygen-rich air, which spurred decomposition and the release of CO2. However, 3,000 years later, this drying trend reversed, and wetter conditions enabled carbon-rich peat to accumulate again.
The implications for this study are significant. Peatlands across the central Congo Basin store roughly 30 gigatonnes of carbon, and recent evidence suggests that dry seasons in the region are growing longer. One author of the study warned that, “we know today that these peatlands are very close to that tipping point where they could release billions of tonnes of carbon to the atmosphere,” but “we don’t know exactly how close.”
Largely overlooked, fjords play an important role in the global carbon cycle
Although they cover just 0.1% of the ocean’s surface area, fjords store between 11 and 12% of marine organic carbon. New research, however, shows that, while these deep ocean inlets may be hotspots of carbon sequestration during interglacial periods, burying 18 teragrams of carbon each year, they become carbon sources during glacial periods. After collecting sediment samples rich with organic carbon from 25 fjords around the world, scientists used an instrument, colloquially known as a “dirt burner,” to measure how quickly organic carbon in these soil samples breaks down as temperatures rise — or how “reactive” it is. This reactivity, in turn, serves as a proxy for organic carbon’s sensitivity to biogeochemical decomposition.
Essentially, they found that organic carbon in fjords is more reactive than organic carbon buried in other global sediments, which means that, once exposed to air, it can re-mineralize to become CO2. During glacial periods, advancing glaciers can push sediments rich in organic carbon up into sills that are exposed to the air, helping spur the shift of fjords from a carbon sink to a carbon source.
Advances made in understanding brown algae’s role in carbon removal
Scientists have previously estimated that brown algae take up more carbon per hectare than terrestrial forests. Yet these algae also release much of this carbon back into the ocean through various mechanisms, for example, as dissolved organic carbon or as organic carbon stored within plant detritus. The fate of this carbon — how much of it reaches deep ocean sediments, where it remains stored for hundreds to thousands of years, versus how much of it returns to the atmosphere — remains uncertain.
Authors of a recent paper shed light on an important piece of this puzzle by studying fucoidan, a mucus-like, carbon-rich substance that brown algae secrete. Focusing on one species of brown algae in the Baltic Sea, they found that up to 50% of the carbon that these algae fixed and excreted became fucoidan, and this mucus “ is so complex that it is very hard for other organisms to use it.” Carbon stored in fucoidan, then, cannot return to the atmosphere very quickly, the authors argue, making it a “likely overlooked contribution of brown algae to carbon removal.”
Ocean
Ocean warming reached a record-breaking high (again) in 2022
Analyzing data from a global network of buoys across seven ocean basins, authors of a new paper estimated that ocean heat content, which describes the amount of heat stored in the upper 2,000 meters of the water column, surpassed 2021’s record-breaking value by at least 9.1 ± 8.7 zetta joules (a measure of energy). This amount of added heat to the world is roughly equivalent to 100 times the total amount of electricity generated globally in 2021.
Unsurprisingly, the authors found that annual increases in ocean warming have accelerated in recent decades, with average yearly gains in ocean warming from 1986 to 2022 at least threefold higher than those that occurred from 1958 to 1985. The salinity-contrast index, which measures the “salty gets saltier” and the “fresh gets fresher” pattern, also achieved its record high in 2022. Together, these increases in heat and salinity have helped spur increasing ocean stratification, which limits the mixing of deeper, cooler and more nutrient-rich waters with surface waters.
The impacts of these changes will likely be significant to human and natural systems, from rising sea levels to supercharged storms to stronger marine heatwaves.
Slowdown of critical circulation system threatens ocean’s ability to sequester CO2
By increasing ocean heat content and intensifying differences in salinity, climate change disrupts the meridional overturning circulation (MOC) — a system of ocean currents driven by temperature and salinity differences that, like a conveyor belt, moves water across ocean basins, as well as between surface waters and deeper, nutrient-rich waters. Not only does this circulation system support marine life, but it also plays a critical role in the ocean’s uptake of CO2.
Relying on a suite of Earth Systems models, authors of a recent study analyzed the impact of rising GHG emissions on the MOC and, relatedly, on CO2 sequestration and storage across the ocean. They found that, across low-warming scenarios, the MOC stabilizes after 2100 but at significantly reduced rates relative to pre-industrial levels, while in high-warming scenarios, the MOC’s Southern component collapses entirely by 2300. Across all scenarios, climate change’s disruptive effect on the MOC reduces net uptake of CO2, and over time, nutrients that support marine ecosystems become trapped in the deep ocean, triggering a decline in primary productivity.
Ice & Permaforst
Modern temperatures in central-north Greenland warmest in past millennium
With a high quality reconstruction of central and north Greenland temperatures from ice cores, scientists show that the warming of the recent decade exceeds anything in the past millennium. They find modern temperatures are on average 1.5 degrees C warmer than the twentieth century. Notably, the warming documented in central and north Greenland pose risks to overall Greenland mass ice loss.
Melting ice shelves causing instability to downstream neighboring ice shelves in Antarctica
Recent research finds that meltwater from the Pine Island Ice Shelf fed into the cavity under the nearby Thwaites Eastern Ice Shelf in West Antarctica between January 2020 and March 2021. This in turn transported heat to the Thwaites Ice Shelf, melting its base, which has thinned in recent decades.
Extremes
Human-induced warming increased the odds and intensity of West African floods
In 2022, the West African rainy season was particularly devastating. Rains arrived early and were above average, triggering large floods – among the deadliest in Nigeria’s and Niger’s history. Hundreds were killed; millions of people were affected, with 1.5 million displaced; and several hundreds of thousands of hectares of land were inundated.
Scientists have now assessed whether human-induced climate change played a role. They find that the rainfall event was made about twice as likely and 5% more intense over the lower Niger Basin as a result of warming. In the Lake Chad region, the event was made 80 times more likely and roughly 20% more intense.
Climate change also made a record-breaking heatwave in South America 60 times more likely
Following an unusually cold spring, parts of Argentina, Bolivia, Chile, Paraguay and Uruguay experienced two consecutive heatwaves in late November and early December 2022. Weather stations across northern Argentina recorded temperature anomalies exceeding 5 degrees C (9 degrees F) in late November, with some observing maximum temperatures of over 40 degrees C (104 degrees F).
Just days later in December 2022, these anomalies climbed even higher to more than 10 degrees C (18 degrees F) above average conditions, with some stations registering maximum temperatures of over 45 degrees C (113 degrees F). Nine locations in Argentina recorded their highest temperatures in December since observations began in 1961, and maximum temperatures also broke records in Paraguay and Chile.
A new report from World Weather Attribution finds that climate change substantially increased both the likelihood and intensity of this December heatwave.
Climate fingerprint in recent North American extreme summer heat
A new study attributes the extreme North American 2021 summer heat in part to long-term regional temperature changes and drying soil. The heat wave killed more than 1000 people, smashed temperature records in the region and led to catastrophic wildfires. The authors found that this “virtually impossible” event was now a 1-in-200-year event. And with future warming, they said, it could become a 10-yearly occurrence if warming rises by 2 degrees C over pre-industrial levels, which may be reached by 2050.
Climate change makes Southern Hemisphere stormier
Recent research finds that the Southern Hemisphere has become stormier due to ocean energy transport changes, consistent with climate model projections. The Northern Hemisphere has not witnessed significant changes in storminess, also consistent with projections. Here, increased storminess due to ocean changes has been offset by polar changes, in which there is an increased absorption of sunlight due to loss of sea ice and snow. This article was first of its kind in explaining the mechanisms behind the differences between the two hemispheres’ storminess.
Climate impacts to winter storms in the United States
Winter storms cause billions in economic losses in the western United States. A new modeling study projects that the precipitation volume associated with the top 20% winter storms will increase by up to 40% by the end of the century across the region under a high emissions scenario. The modelers also examine the prospects of “storm sharpening” with an increase of precipitation in the storm center compared with an increase in storm area.
Impacts
Warming to wreak havoc on insects, with knock on impacts to ecosystem functioning
A new review article paints a bleak picture of climate impacts on insects, including on their survival, distributions and abundance. The authors find that warming could destabilize inset communities and lead to species extinction, which have repercussions on ecosystem stability and functioning and the provisioning of critical ecosystem services. The authors suggest that if no further action is taken, we will “drastically reduce our ability to build a sustainable future based on healthy, functional ecosystems.”
Climate and land use change leading to a cascade of extinctions
Land use change and climate change will not only lead to primary extinctions of species but also “coextinctions” as a result of impacted community resilience and changed ecological interactions, for example as predators lose prey. A new study finds that by the end of the century, local vertebrate diversity globally will decline by 17.6%, with coextinctions increasing the effect of primary extinctions by 184.2% on average.
Major blowdown events due to warming to uproot more trees in Amazon
Forecasts indicate that climate change will lead to more extreme thunderstorms in the Amazon. Recent research suggests that this will in turn increase “windthrow events”, in which trees are uprooted or broken. The research finds that the Amazon will witness 43% more blowdown events by the end of the century under a high warming scenario, compromising the rainforest’s carbon sink.
Two thirds of native Antarctic species under threat
Recent research finds that roughly 65% of native terrestrial species and land-associated seabirds are likely to decline by the end of the century if warming continues unabated. Empire penguins were found to be most vulnerable. On the other hand, if tailored management strategies equivalent to an annual cost of $23 million are embraced, 84% of Antarctic taxa could benefit. This suggests that conservation techniques must change to keep up with warming to mitigate impacts on Antarctic biodiversity.
Warming compromises reproductive success in California songbirds
When studying cavity-nesting songbirds in California’s Central Valley, researchers found that reproductive success, nestling weight and clutch size were negatively associated with higher maximum nesting season temperatures. They indicate that future warming and increased spring temperature can reduce the fitness of cavity-nesting songbirds in the region.
Phytoplankton more resilient than we thought
Marine phytoplankton play an essential role in regulating CO2, nitrogen and phosphorous. It has been thought that warming of surface waters and water stratification would lead to reduced nutrient supply, which would in turn compromise net primary production. However, new research finds that phytoplankton adjust to the lower levels of phosphorous, sustaining productivity. The study shows that phytoplankton are able to adapt to nutrient poor ocean conditions better than we thought.
Low oxygen waters in lakes on the rise due to warming
Studying more than 400 lakes, mostly across the United States, researchers have found over three quarter of the lakes exhibited an increase in the length of water stratification during the summer, which provides more time for oxygen depletion in deep water habitats. As a result, most of the lakes have experienced an increase in oxygen-depleted water – called hypoxia – or no oxygen conditions – called anoxia -- reducing habitat for many species and altering lake chemistry.
Plants struggle to acquire nutrients in a higher CO2 world, resulting in less nutritious crops
A new study finds that elevated atmospheric levels of CO2 compromise some plants’ abilities to acquire nutrients. In particular, the nitrogen content of plant tissue is lowered when CO2 levels are elevated, which in turn can threaten crop quality and lessen nutritional value of crops. The authors note that the reasons are largely unknown. However, it may be possible to identify those individual plants that maintain nutrients, which could lead to more successful breeding for a changing climate.
Cliff erosion to accelerate following sea-level rise
New research has explored the stability of rock coasts – which make up more than half of global coastlines - after sea level rise. They find that over the century, cliff retreat will increase by up to an order of magnitude, exceeding earlier predictions. The authors find that rock coasts - long considered stable, especially when compared with sandy coasts and softer cliffs - are highly sensitive to sea level rise, posing risks to lives, property and infrastructure. The authors suggest that their findings inform future planning.
Extreme temperatures lead to greater risk of mortality from cardiovascular disease
Cardiovascular disease is the leading cause of death globally. Examining a database of daily cardiovascular-related deaths from 567 cities across 27 countries from 1979-2019, researchers found that extreme heat and cold led to a higher risk of dying. The authors find that for every 1000 cardiovascular deaths, 2 excess deaths were attributed to extreme hot days and 9 excess deaths were attributed to extreme cold days.
Warming causing fetal strain in pregnant subsistence farmers
A study of pregnant subsistence farmers working under extreme heat stress in the Gambia found a strong association between heat stress exposure and fetal strain. The authors suggest several possible factors including dehydration, blood being diverted from the placenta to the skin and inflammation. They find that with every degree C increase, there was a 17% rise in fetal strain. They note that heat exposure of agricultural workers is an increasing concern given warming.
Microbes being released by glacial melting
Glacial meltwater can have large effects on microbe communities and biogeochemical cycles. In particular, glacial meltwater delivers organic carbon to downstream ecosystems. Studying meltwaters from eight glaciers across North America, Europe and Greenland, researchers forecast that 650,000 tonnes of carbon will be delivered to downstream ecosystems each year over the next eight decades. While ecosystems can be fertilized by the release of these microbes, scientists warn that potential pathogens must also be watched for.
Parasites witnessing one century decline due to warming
A new study analyzing 85 parasitic species – species that live in or on a host and depend on it for their survival - found that the majority suffered population declines over the past 140 years. Between 40 to 50% of all animals are parasites, and they play key roles in maintaining healthy ecosystems. Until this study, however, few datasets had been collected to assess long-term health of parasite species, and the few that did exist were marred with issues related to completeness, accessibility and other factors.
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