Every month, climate scientists make new discoveries that advance our understanding of climate change's causes and impacts. The research gives a clearer picture of the threats we already face and explores what's to come if we don't reduce emissions at a quicker pace.
Our blog series, This Month in Climate Science, offers a snapshot of the month's significant scientific literature, compiled from some of the leading peer-reviewed journals. This edition explores studies published in January 2020. (To get these updates delivered right to your inbox, sign up for our newsletter.)
Impacts to Species and Ecosystems
- Large-scale seabird die-off: Roughly 62,000 common murres, a North Pacific seabird, were found dead during 2015 and 2016, the largest mass die-off of seabirds ever recorded. Scientists estimate that only a small fraction of the birds washed ashore; total mortality is probably closer to 1 million birds. Scientists now attribute this mortality to a heatwave in the ocean, nicknamed the “blob,” which occurred at the same time and affected food supply. Cold-blooded organisms increased their metabolism as a result of the warmer temperatures, with larger fish demanding unsustainable amounts of smaller fish, the murres’ food supply, contributing to the seabirds’ starvation.
- Whale entanglements: Also during the unprecedented marine heatwave from 2014-2016 in the northeast Pacific, record numbers of whales were entangled by crab fishing gear. Scientists found that warming impacted food availability (such as krill and anchovy), pushing whales’ shoreward into the crab fishery. At the same time, a toxic algal bloom, also caused by the marine heatwave, delayed the opening of the fishery, so peak crab fishing subsequently coincided with the whale migration.
- Coral acidification and fish behavior: A new study challenged previous studies suggesting that ocean acidification would impact coral reef fishes’ vision, hearing, learning, activity levels and susceptibility to predation, among other effects. The new study could not reproduce such behavioral effects.
- Threatened mushrooms: Scientists found that species of ecyomycorrhizal fungi — which include truffles, porcini and other mushrooms— in pine forests in North America will decline by as much as a quarter over the next 50 years due to climate impacts. These fungi play a key role in the health of forests.
- Tropical caterpillar decline: In a study analyzing 22 years of data from a biological research station in Costa Rica, scientists detected a dramatic decline of caterpillars and parasitoids, which control pest populations. One driver is frequent flooding from climate change. Such species losses can have knock-on effects throughout the entire ecosystem.
- Vanishing platypus: About 40% of platypus populations are expected to face localized extinction over the next 50 years due to land clearing and development. Scientists said warming and resultant drought will lead to even greater local extinctions.
Fires and Climate Change
- Siberian fires: Scientists found a link between fires in Siberia and the Arctic Oscillation, a pattern of weather variability that precedes the fires by 1-2 months. The oscillation causes earlier snowmelt, which in turn dries the ground in spring, promoting the spread of fire. In southeastern Siberia, warming and snow retreat led to an increase in area burned. These large-scale forest fires are also releasing carbon from permafrost, which can greatly accelerate warming.
- More Amazon forest fires: A study of Amazon forests found that warming will double the area burned by wildfires by mid-century, affecting up to 16% of the region’s forests and emitting as much as 17 Gt of CO2e (almost 1.5 times the current emissions of China). Avoiding new deforestation could slash these emissions in half.
- Worsened British Columbia fire: A study using an event attribution method and model simulations found that climate change worsened British Columbia’s 2017 fire season, which burned a record 1.2 million hectares. Scientists found that human-induced warming increased the area burned by a factor of 7 to 11.
- More injury-related deaths: Scientists found that even if the world successfully limits global temperature rise to 1.5 degrees C (2.7 degrees F), a goal of the international Paris Agreement, the United States would still see an additional 1,601 injury-related deaths. The large majority (84%) would occur in adolescent and middle-age male populations, e.g., from drownings (swimming becomes more common in warm weather) and drunk driving (warmer weather leads to more cars on the road and increased alcohol consumption).
- More violent crime: Researchers found that by the end of the century, there could be 2.3 million to 3.2 million more violent crimes in the United States resulting from warming. For example, assault and robbery are more frequent when weather is warm.
- Warming and flu: It was previously thought that deaths due to flu would decline with warmer winters, but this was not the case in the very warm winter of 2017-2018. Scientists found that rapid weather variability in autumn is a key determinant of deadly flu in subsequent months in northern mid-latitudes. Rapid weather variability in autumn will become more typical in some northern mid-latitude regions, increasing the risk of flu epidemic in these highly populated areas by 20% to 50% by the later part of the century.
Extreme Weather and Temperature Rise
- 2019 the second-warmest year on record: Both NASA and NOAA confirmed that Earth’s average surface temperature in 2019 was the second-warmest in the 140-year record. The past decade was the hottest on record. NOAA found that Alaska had its warmest year on record in 2019, 6.2 degrees F (3.4 degrees C) above the long-term average, the first time that annual average temperature was at or warmer than freezing.
- And 2019 was the warmest year for oceans: Researchers also confirmed that ocean temperature was highest in 2019. The five warmest years in the ocean were 2019, 2018, 2017, 2015 and 2016, in that order.
- Warming and the daily weather: While the climate community is quick to distinguish between weather and climate, a new study detected climate change in “any single day of weather” at the global scale. While local conditions are still variable, when averaged across the globe, scientists found a long-term warming trend evident in daily weather data.
- Warming in the tropics: Modelers have found that the tropics are not only impacted by warming locally, but also strongly influenced by warming outside of the tropics, in sub-tropical areas. As subtropical warming increases, the Hadley cell, an atmospheric circulation pattern, slows down, weakening trade winds, raising sea surface temperatures, and reducing cloud coverage in the tropics.
- Irrigation can mitigate warming: Researchers found that irrigation substantially reduces heat extremes, especially in South Asia. The study’s authors suggested that one billion people currently benefit from this reduction in extreme heat due to expanded irrigation over the past century. However, they question whether such a benefit will continue in future years, given uncertainty in irrigation extent and water use.
- Significant emissions from peat swamp conversion: Tropical peat swamps hold a substantial amount of carbon. The impacts of their conversion to oil palm and other plantations had not been quantified well to date, in part due to a lack of data. New research estimated that the conversion of the Southeast Asian peat swamp forest contributes between 17% and 28% of the combined national greenhouse gas emissions from Malaysia and Indonesia.
- Southern Ocean oxygen depletion: A study found that meltwater from Antarctic ice sheets and intensified winds played a role in reducing oxygen levels in the Southern Ocean. Meltwater and more intense winds have been overlooked by modeling efforts to date. Authors concluded that the ocean could be deprived of nutrients sooner than expected.
- Sea level rise in the Ganges delta higher than we thought: Scientists found that sea level rise since the 1970s in the Ganges-Brahmaputra-Meghna delta (roughly 3 mm/yr (0.12 inch/yr)) was higher than the global average (roughly 2 mm/yr (0.08 inch/yr)). Authors projected that sea level rise could double by the end of the century even under a moderate warming scenario, reaching 85-140 cm (33-55 inches) across the delta as a result of a subsiding coastline. This estimate is twice as high as the most recent Intergovernmental Panel on Climate Change (IPCC) report, which failed to also consider land subsidence. The eastern region of the delta, where 28 million live, is at particularly high risk.
- Extreme sea level events: Researchers studying Antarctic Ice Sheet melt found that even if warming is limited below 2 degrees C (3.6 degrees F), almost half of tide-gauge sites across the globe would be exposed annually to a present-day 100-year extreme sea level event by mid-centuryr. With higher warming scenarios, many tropical sites, including low-lying islands, would face such events even earlier.
- Ozone-depleting substances and Arctic melt: Many have heard of the ozone hole’s impact over Antarctica and nearby regions, but recently researchers discovered that ozone-depleting substances — like chlorofluorocarbons, which were used as solvents and refrigerants among other uses — contributed significantly to recent Arctic warming. They found that if ozone-depleting substances are kept constant, sea-ice loss is only half as large as scenarios where ozone-depleting substances increase. They noted the importance of the Montreal Protocol for mitigating Arctic warming and sea-ice melt.
- Permafrost depends on sea ice: A new study of carbonate deposits in a Siberian cave found that when sea ice is present, permafrost is consistently present. When sea ice is absent, permafrost is prone to thaw because of heat and moisture transport from open Arctic waters. Permafrost thaw releases significant amounts of carbon, creating a positive feedback loop.
- River ice disappearing: Frozen rivers, which occur seasonally, are important to many communities for transportation of food, fuel and equipment. Using satellite observations, scientists found a decline of seasonal river ice duration of about 6 days for every 1 degrees C (1.8 degrees F) increase in surface air temperature. Over the past three decades, river ice declined by 2.5% globally. Researchers projected that under a high emissions scenario, average river ice duration would decline by almost 17 days by the end of the century, as compared to the 2009-2029 average.
- Tidewater glaciers melting quicker than we thought: Presenting new data gathered from autonomous robotic kayaks, scientists estimated that the rate of one critical type of underwater melting under the LeConte Glacier in Alaska is 100 times higher than predicted (∼16 ft/day), instead of 0.16 ft/day. To date, such melting had been difficult to directly observe. This study has implications for other tidewater glaciers.
- Antarctica’s largest glacier may not face extreme melt: Pine Island Glacier, the largest glacier in Antarctica, has contributed more to sea level rise over the last 40 years than any other Antarctic glacier. However, a new study projected more moderate melting than other models suggest, based on satellite observations since 2010.