This Month in Climate Science: Migrating Mosquitoes, Marine Heatwaves, More Hay Fever

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 March 2019. (To get these updates delivered right to your inbox, sign up for our Hot Science newsletter.)

Impacts to Ecosystems and Species

• Fish catch declines: While scientists have long known that climate change affects fish and invertebrates, the knock-on effects to food production have not been studied to the same extent. Scientists assessed climate impacts on 124 species—about a third of global fish catch—and found that maximum yields decreased by about 4 percent between 1930 and 2010. Five  ecoregions (Sea of Japan, North Sea, Iberian Coastal, Kuroshio Current and Celtic-Biscay Shelf) witnessed losses on the order of 15 to 35 percent. East Asian ecoregions, home to some of the largest and fastest-growing human populations, saw the greatest losses. These warming-induced losses compound problems from overfishing.
• Marine heatwaves devastate ocean life: Researchers found that recent marine heatwaves have significantly compromised biological processes and negatively impacted many key species, including corals, sea grasses and kelp. The number of marine heatwave days per year increased more than 50 percent in 1987-2016 compared with 1925-1954.
• Marine heatwave kills dolphins: Western Australia’s Shark Bay World Heritage Area experienced an unprecedented marine heatwave in 2011, where water temperatures were 2–4°C above average for more than two months. Scientists found that populations of Indo-Pacific bottlenose dolphins declined 6-12 percent in the area, and remaining females have had significantly fewer calves after the heatwave.
• New insights from 20 years of coral bleaching data: Scientists assessed coral bleaching across more than 3,000 sites from 1998 to 2017, during which time bleaching increased in frequency and intensity. The highest probability of coral bleaching was in tropical mid-latitude areas. Another interesting finding: In the last decade, bleaching occurred at 0.5 degrees C higher temperatures than it had previously. This could mean that sensitive individual corals have already vanished, and/or that they have adapted and now have a higher threshold for bleaching.
• Pines suffer after fires: Climate change is increasing fire activity across the western United States. A new study found that ponderosa pines and Douglas firs, two ecologically and economically critical species, aren’t regenerating after high-severity fires due to the temperature and dryness of the soil. The authors suggest that in the future, we may see forests shift abruptly to other kinds of vegetation as species cross critical thresholds.
• Climate change threatens bird migrations: Researchers found that the Great Basin, a key habitat in the North American Pacific Flyway migration route, can no longer support species that have long depended on it. Water flowing into the wetlands has dropped significantly and shifted in timing, resulting in a marked decline of waterbirds.

Impacts to Health

• Earlier spring brings greater risks of hay fever: Warmer temperatures are bringing earlier Spring and pollen seasons. Scientists found that between 2001 and 2013, adults living in areas of the United States experiencing an earlier Spring had an 18 percent higher chance of suffering from hay fever than adults not experiencing an earlier Spring.
• Migrating mosquitos: Scientists found that Aedes mosquitos, which spread dengue fever, Zika virus and chikungunya, are expected to move poleward.  With severe amounts of warming, almost one billion more people will be exposed to these diseases, with the risk of transmission increasing substantially for most of Europe and high-elevation tropical and subtropical regions. Southeast Asia and west Africa, on the other hand, would see a decrease in one significant _Aedes _species under severe warming (though not with moderate warming).

Impacts to Infrastructure

• Coastal flooding costs Californians: Researchers found that by the end of the century, more than $150 billion of property and 600,000 people could be impacted by coastal flooding in California. The study is novel in its flood assessment because it combined sea level rise projections with the impacts of extreme storms.

Ice

• Rain causes Greenland melting: Studying more than 300 rapid melt increases in Greenland between 1979 and 2012, researchers found that more precipitation triggered melting. Melting caused by precipitation more than doubled over the period, contributing about 28 percent of overall surface melt.
• Some good news for Greenland: Jakobshavn Glacier has been the largest source of mass loss from the Greenland Ice Sheet over the last two decades. Encouragingly, scientists found that Jakobshavn has been re-advancing and thickening since 2016, thanks to cooling ocean waters in Disko Bay due to natural variability. The authors found that ocean cooling can add stability to a glacier, furthering our understanding of the complicated dynamics between the ocean, atmosphere and ice.
• Ice lakes under Antarctica: Scientists from Australia discovered large lakes under eastern Antarctica. It’s a troubling finding, as glaciers can move more quickly when they sit on water as opposed to bedrock.

 Temperature Extremes

• Warmer Arctic brings less rain: The Arctic is warming twice as fast as the global average, and as it does so, there is less of a temperature gradient across latitudes. Temperature gradients affect jet streams and atmospheric stability. Researchers found that a weaker latitudinal temperature gradient could cause substantial declines in rain at the mid-latitudes. In the past, when a similar temperature pattern occurred, central North America experienced drought.

Emissions

• Emissions climb: The International Energy Agency found that global carbon dioxide emissions from energy hit a record high in 2018, the highest annual rate of growth since 2013. Global energy consumption last year increased at a rate that was almost two times the average rate of growth since 2010, with resultant demand for fuels. Energy efficiency improvements were slower than in recent years. U.S. emissions overall rose by more than 3 percent, reversing the previous year’s decline.  Emissions from China, India and the United States made up 85 percent of the net emissions increase, while emissions dropped in France, Germany, Japan, Mexico and the United Kingdom.
• Methane from trees: Researchers found that trees could be a substantial source of methane. A study published last month reviews the flux of methane in living and dead trees. For example, trees transport and emit methane because the gas is present in the soil they grow in. Microorganisms living inside the trees also produce methane, which is then emitted through the trees. Trees are also producing methane directly through a photochemical reaction. The research reveals a complex set of processes that depend on the position in the tree and tissue type among several other variables.
• Methane emissions from lakes: Climate change is expected to increase eutrophication, in which excess nutrients enter estuaries and coastal waters.  A new analysis showed that this increased eutrophication will result in higher aquatic methane emissions. Modelers suggest that methane emissions from lakes will increase substantially over the next century—equivalent to 18-33 percent of annual CO2 emissions from burning fossil fuels.
• Quantifying the oceanic carbon sink: Researchers found that the ocean sequestered 31 percent of global anthropogenic CO2 emissions from 1994 to 2007, though there are large regional differences in the rates of sequestration, likely due to ocean circulation patterns. While the ocean is playing a critically important role in slowing the build-up of carbon dioxide in the atmosphere, ocean acidification has increased as a result.
• Coastal wetlands are an increasingly important carbon sink: Scientists found that carbon accumulation has increased significantly in some tidal marshes exposed to rapid sea level rise over the last few thousand years Such feedbacks have not been included in climate modeling, meaning that coastal wetlands could be more important in the battle against future climate change than previously thought.