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 recent research, compiled from some of the leading peer-reviewed scientific journals. This edition explores studies published in June and July 2020. (To get these updates delivered right to your inbox, sign up for our Hot Science newsletter.)
Recent Extreme Events
The last two months brought alarming signs of a changing climate, many in line with projections of a warming world.
For example, this summer in the Arctic has been one of extremes:
- In only two days at the end of July, the last fully intact ice shelf in the Canadian Arctic, the Milne Ice Shelf on Ellesmere Island, lost 40% of its area.
- Following a record-breaking heatwave in June, fires have raged across Siberia, burning an area larger than Greece. Notably about half of the fires in Russia’s Arctic are burning through peat soils which not only can burn longer than other soil types but release significant amounts of carbon and methane when they burn.
- Svalbard set an all-time heat record at 21.7 degrees C (71.1 degrees F). In Nunavut Canada, the temperature reached 21.9 degrees C (71.4 degrees F), which may be the highest ever recorded so far north.
- Arctic sea ice extent in July was the lowest in the satellite record for the month.
- The Northern Sea Route’s opening date – when it became ice-free — was the earliest on record this year.
The Arctic is not alone. In the Middle East several countries experienced record highs. Baghdad reached 51.7 degrees C (125 degrees F). And aptly named Death Valley, California, may have reached the hottest temperature ever recorded at 130 degrees F.
- Advancing understanding of climate sensitivity: A seminal paper uses multiple lines of evidence to narrow the range of equilibrium climate sensitivity – how much the Earth will warm with a doubling of pre-industrial carbon dioxide levels – which is essential for understanding likely future temperature change. About 40 years ago, scientists had established the range to be between 1.5 and 4.5 degrees C (2.7 to 8.1 degrees F), but the new study finds that it is most likely between 2.6 and 4.1 degrees C (4.7 to 7.4 degrees F), with a best estimate slightly above 3 degrees C (5.4 degrees F). Notably the scientists find that the lowest and upper levels of warming are not likely.
- South Pole’s exceptional warming: Researchers have found that the South Pole has experienced record warming of roughly 0.61 degrees C (1.1 degrees F) per decade, three times the global average. They find that the warming was driven by increasing sea surface temperatures in the western tropical Pacific.
- New models running hot likely due to clouds: Some of the newest generation of earth systems models show more warming associated with carbon dioxide concentrations, and are therefore running hotter than previous models. A review of various possible explanations finds that the models are likely doing so because of cloud feedbacks and cloud-aerosol interactions.
- Methane emissions at all time high: Global emissions of methane, a greenhouse gas that is 28 times more powerful than carbon dioxide, reached their highest level on record. The researchers describe their findings on the global methane budget from 2000 to 2017 in two papers. Since 2012, methane emissions have tracked the worst scenario of the Intergovernmental Panel on Climate Change.
- Slow response of climate system to halting emissions: If one were to remove human-induced greenhouse gas emissions altogether, a new study finds that we still likely wouldn’t see a discernible impact before mid-century. This is because of the inertia and variability of the climate system. The build-up of greenhouse gas emissions dictates our current climate. That means that even after significant mitigation efforts are put in place, surface temperature changes would not occur until decades afterwards. Even fully removing short-lived climate forcers like black carbon would not have a discernible impact for a decade. The authors note that the paper’s findings can help “manag[e] our expectations.”
- Carbon removal via enhanced rock weathering: A new study finds significant potential for the application of enhanced silicate rock weathering on croplands. Enhanced weathering is a process which crushes rocks, in this case adding it to soil, and thereby accelerating rocks’ natural sequestration of carbon dioxide. They find the greatest potential in China, India and the US and the method could sequester 0.5-2 gigatonnes of carbon dioxide a year (equivalent to the combined emissions of Germany and Japan) at $80-180 per tonne of carbon dioxide.
- New means for estimating fossil fuel emissions: An independent evaluation of emissions through NOAA’s air sampling network reveals higher fossil fuel emissions than estimated in the US national inventory, but within the bounds of error of another government estimation. The study demonstrates the feasibility of independent observations directly from atmospheric air samples, as opposed to accounting methods based on economic relationships and emissions factors, which are used in national inventories.
- Arctic Ocean acidification worse than anticipated: A new study estimates 20% more acidification in the Arctic Ocean over the century than previous studies. Ocean acidification can have serious consequences for calcifying organisms, like mussels, as the shells break down in acidic waters.
- Human signal in Arctic Ocean freshening: It has been established that the surface waters of the Arctic Ocean are fresher – less salty – than other oceans. This is due to freshwater runoff entering the oceans. Researchers have now demonstrated that this phenomenon is being driven by human-induced climate change and that we can soon expect to see changes beyond those experienced with past natural variability, with implications for ocean behavior.
- Weaker ocean circulation could delay ice-free Arctic: Scientists have advanced understanding of the impacts of a slowdown of the Atlantic Meridional Overturning Circulation, an ocean current that could slow down and weaken due to freshwater inputs from melting ice. Notably, they find that it would delay an ice-free Arctic by six years and cool global average surface temperatures by 0.2 degrees C (0.36 degrees F) by 2061-2080.
- Delayed monsoons: More than two-thirds of people on Earth live in areas impacted by monsoons. A new modeling study finds that monsoons in nine regions across the Americas, Asia, Africa and Australia will be delayed up to a month by the end of the century, with the strongest delay over South America. For those regions with substantial delays, pre-monsoon precipitation will also decline. At the same time, more precipitation is more likely over a shorter period, which could exacerbate flooding. Many communities depend on the seasonality of monsoon rains for critical activities such as agriculture and hydropower.
- Significant increase in flooding with warming: A study of the impacts of a high-emissions scenario (RCP 8.5) finds that without further adaptation or coastal protection, there would be 52% more of the global population (totally 2.5-4.1% of the population), 46% more global assets (totaling 10-20% of global GDP), and 48% more land at risk of flooding by the end of the century, compared to today’s risks of flooding. More than two-thirds of the flooding is due to tide and storm events. Northwestern Europe and Asia are at greatest risk.
- Unprecedented flooding in Europe: Using a new database, scientists have now found that the last 30 years of flooding in Europe were among the highest periods of flooding in the region over the past 500 years. The recent flooding has been exceptional in terms of its extent, timing and associated air temperature.
- Unprecedented extreme precipitation in South America: Data from tree rings were used to reconstruct hydroclimatic conditions since 1400 and show that the frequency of widespread severe droughts and extreme rainfall since the 1960s is unprecedented in South America. The researchers suggest that increased greenhouse gas emissions may cause more extreme rainfall and droughts in the region over the course of the century.
- Acceleration of heatwaves: A comprehensive assessment of heatwaves finds that since the 1950s, the frequency, duration and cumulative heat of heatwaves has accelerated over many regions.
- Human footprint in North American extreme rainfall: Scientists have now established that human-induced climate change has contributed to extreme precipitation in North America. They further state that warming will lead to more frequent and intense precipitation extremes in the future.
- Upper Missouri River drought: New research has established that the drought experienced in the Upper Missouri River Basin from 2000 to 2010 was potentially unprecedented in 1200 years and warming likely played a role in altering streamflow.
- North Atlantic climate more predictable than we thought: A new paper finds that uncertainty in models related to North Atlantic wind patterns can be reduced significantly, increasing confidence in projections.
- Whales on the move: A new study of a decade’s worth of acoustic observations finds that the range of baleen whales in the North Atlantic Oceans has shifted, mirroring climatic shifts in the ocean and prey distribution. This has implications for protection plans as whales move into new areas known for shipping and fisheries.
- Amphibians left vulnerable to changes in temperature and precipitation: Water availability is critical for amphibians. Given changes in temperature and precipitation, a new paper suggests that water- and shade-seeking amphibians may be left with few ideal habitats. In areas where water may be available for amphibians, scientists have found that future temperatures may be above what they can tolerate. On the other hand, where temperatures are more tolerable in the shade, these areas may be too dry.
- Earlier springs give wolf spiders time for an additional clutch: Spring is coming earlier to the high Arctic and snowmelt is advancing. Scientists have now found that high-Arctic wolf spiders now have time to have a second clutch of eggs, like their neighbors at lower latitudes. This is the first evidence of invertebrates having additional clutches in response to warming. Given that wolf spiders are distributed widely, the authors posit that this could have implications for the broader food web.
- Water temperature too hot to tolerate for many fish: A study of almost 700 species of marine and freshwater fish globally find that the stage during which fish species are most vulnerable to temperature change is when they are spawning or are embryos. Researchers suggest that by the end of the century, depending on the level of warming, 10%-60% of fish species could be affected by water temperatures that are beyond what they can tolerate for reproduction.
- Decline of phytoplankton due to warming in the Northeast: Researchers have uncovered a 50% decline in the abundance of small aquatic crustaceans called copepods over the last six decades in the Northeast U.S. They find that changes in summer weather have altered nutrient supply to surface water, which can not sustain these larger, more nutritious phytoplankton. They suggest this could have knock on impacts to the food web.
- On the other hand, in the Arctic, more phytoplankton: In another study, scientists find that sea ice loss has increased phytoplankton, tiny organisms which support the marine food web, with primary production increasing by 57% between 1998 and 2018. The authors suggest that over this period new nutrients were transported into the Arctic Ocean, and a future Arctic Ocean may be even more productive.
- Failure of mangroves to thrive with sea level rise: A new study finds that mangroves are unlikely to be able to grow with rates of sea level rise that could result within 30 years under a high-emissions scenario. Mangroves provide critical habitat to a wide range of species, provide storm surge protection and are an important carbon sink.
- More crabs: As a result of sea level rise, salt marshes are getting inundated for longer across the southeastern U.S. This makes marshes softer and provides more optimal habitats for crab burrowing. A recent study finds that a previously inconspicuous marsh crab is now reshaping the salt marsh ecosystem.
- Too warm for tropical plant germination: A recent study of 1,312 tropical plant species from Kew Gardens finds that by 2070, over half of the species studied could experience temperatures higher than their optimum temperatures for germination, with 20% of species at risk of exceeding their maximum germination temperature. Those closest to the equator are most vulnerable.
- Near extinction of polar bears by the end of the century: Polar bears depend on sea ice to hunt. Researchers have now identified the number of days that polar bear subpopulations can fast and coupled this information with model projections of sea ice loss. They find that between 1979 and 2016 such thresholds may already have been exceeded in some populations, meaning that the number of days that the bears were forced to fast was more than what they were capable of. With high greenhouse gas emissions, by the end of the century “all but a few” high-Arctic subpopulations will no longer be able to reproduce or survive.
- Ice-free conditions allow for Adelie penguin success: Research has now found that Adelie penguins are taking advantage of ice-free environments, which allow them to swim rather than walk, cutting down the time and energy spent on foraging. Their dive durations have declined and they capture more krill with each dive. As a result, their adult body mass, growth rates of chicks and breeding success have increased.
- More yellow fever: Yellow fever, which is transmitted by mosquitoes, currently kills almost 80,000 people in Africa every year. A new study of climate impacts to yellow fever transmission finds that even in the least severe warming scenario, there is a high likelihood that annual deaths would increase due to warming by mid-century. The projections increase yellow fever for most African countries. The Central African Republic is one of the countries most likely to see an increase in transmission.
- Expanded range of zika: Modelers studied future transmissions risk of zika, which is carried by mosquitoes, and find risk beyond the current observed range. Specifically, new transmission risk could occur over southern and eastern Europe, the northern U.S., northern China and southern Japan in future climate scenarios.
- Beavers moving into Arctic tundra: Scientists have documented that beavers are colonizing low Arctic tundra areas in Alaska and Canada and, as a result of their dams on lakes and streams, are creating expanded waterbodies, which could worsen permafrost thawing.
- Central European forests left vulnerable by drought: In 2018, Central Europe witnessed one of its most severe summer drought and heat waves. New research finds long-lasting drought stress on the forests. The authors suggest the forests, which include ecologically and economically critical species, are left vulnerable to insect and pathogen attacks and are more vulnerable than previously thought.
- Tropical Asian forests to turn more evergreen: A new modeling study has found that by the end of the century, vegetation in tropical Asia will increasingly transition from deciduous to evergreen and grow in height. Their projections suggest that the vegetation will remain a carbon sink, although conversion of ecosystems poses a risk to the carbon sink.
Ice and Permafrost
- More rain leads to wetter, more vulnerable permafrost: A new study assessed rain-induced thaw in permafrost in the interior of Alaska, and found evidence of deeper thaw. The authors suggest that the projected increase in summer precipitation across most of the Arctic could lead to substantial permafrost thaw.
- Carbon dioxide from permafrost underestimated: Researchers have found that thawing permafrost soils can be flushed into water bodies, such as lakes and rivers, and subsequently release carbon dioxide when exposed to sunlight. This pathway for release of carbon dioxide can lead to 14% more emissions than current estimates, and models currently fail to incorporate such a feedback.
- Significant recent ice loss from Greenland and Antarctica: New estimates from NASA’s ICESat and ICESat-2 satellites show that between 2003 and 2019, 320 gigatons (Gt) of ice per year (200 Gt from Greenland; 118 Gt from Antarctica) was lost, contributing to 14 mm (0.55 inches) of sea level rise. Losses surpassed any gains.
- “Alarming” loss of Arctic sea-ice cover: Scientists have quantified the loss of Arctic sea-ice cover since 1979, finding that the twelve lowest extents of sea-ice cover on record occurred during the last twelve years and that sea-ice volume in September 2018 was three times lower than that of September 1979.
- Decline of summer sea ice in the Weddell Sea, Antarctica: In 2016-17, summer sea ice in the Weddell Sea Antarctica hit an almost record low. Scientists attribute the loss to the reappearance of an area of open water – called the Maud Rise polynya – which allowed for more absorption of solar radiation, which in turn increased ocean temperatures and slowed down the creation of new ice. At the same time, westerly winds carried sea ice from the area. The researchers estimate that the extent of summer sea ice in the Weddell Sea is now 1 million square kilometers less (twice the size of Spain) than in 2013-14. Many species depend on sea ice for breeding and food, including penguins and seals.
- Ice retreat in East Antarctica during past warm periods: Previous research had suggested that East Antarctica’s Ice Sheet was relatively stable during previous warm periods of the Earth’s history. New research, however, has found evidence of significant ice loss in East Antarctica during an interglacial period about 400,000 years ago, raising new questions about its stability. This finding could have major implications for sea level rise, given how much ice the Ice Sheet holds.
- Greenland’s warming rate signals abrupt climate change: A new study uses observations and climate models to place the current rate of warming in Greenland in the context of past changes in the paleoclimate record. The authors find that warming rates that were similar to today’s were accompanied by abrupt glacial episodes. They conclude by arguing that the abrupt rate of temperature change in the Arctic is comparable only to that of the last ice age, and that models are underestimating the rapid rate of change in the region.