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 July 2019. (To get these updates delivered right to your inbox, sign up for our Hot Science newsletter.)
Recent Extreme Events
The past few months have brought alarming signs of a changing climate, many of which are in line with projections of a warming world:
Global average temperatures for July were the highest since records began in 1880, 0.95 degrees C (1.71 degrees F) above the 20th-century average. This makes July 2019 the warmest month on record for the globe.
A heat wave slammed Europe, breaking temperature records in Germany, the Netherlands, the UK, Belgium and France. Paris saw temperatures reach 108.7 degrees F (42.6 degrees C) . The World Weather Attribution project found that heatwaves in France and the Netherlands had “extremely little chance” of occurring without human-caused emissions.
The UK Met Office announced that the region’s 10 hottest years since records began in 1884 all occurred since 2002. Relatedly, Europe’s five hottest summers in the last 500 years have all happened in the last 15 years.
Arctic sea ice extent in July reached record low levels, dropping 80,000 square kilometers (30,900 square miles) below the previous record-low set in 2012 and 1.88 million square kilometers (726,000 square miles) below the average from 1981 to 2010.
In an annual census of wild reindeer on Svalbard, scientists found carcasses of about 200 animals that had starved to death over the winter. They attributed the deaths to more rain falling instead of snow. When rain freezes over, it makes plants inaccessible for grazing.
Warming fuels California wildfires: A study found that from 1972-2018, California saw a five-fold increase in the amount of area burned annually and an eight-fold increase in the extent of its summer fires. Scientists concluded that human-induced warming is increasing the potential for such wildfires.
More extreme heat in the US:Scientists estimated that the annual number of days exceeding 100 degrees F (38 degrees C)and 105 degrees F (41 degrees C) in the United States will double and triple by mid-century, compared to 1971-2000.
Flood risks to U.S. East Coast: The U.S. National Oceanic and Atmospheric Administration (NOAA) found a significant acceleration of high-tide flooding events in more than 40 locations. The current national average for high-tide floods is 5 days per year; scientists expect the frequency to reach 7-15 days by 2030 and 25-75 days by 2050 (the range depends on the level of future emissions), with much higher rates in many locations.
Extreme weather batters Australia’s coasts:Scientists documented extreme events like marine heat waves and high rainfall along the coast of Australia between 2011 and 2017. They found that along more than 45% of the coastline, there had been abrupt and extensive mortality of key marine species, such as corals, mangroves, seagrasses and kelp forests. The authors noted that the heightened frequency and intensity of extreme events have been associated with climate change.
The warmest period in 2,000 years: Researchers have now established that the warmest period of the past two milliennia happened during the 20th century, affecting more than 98% of the globe. They concluded that both temperatures and extent of warming are unprecedented and human-induced.
Climate change altering Japanese forests: A new study relying on almost 40 years’ of data revealed that warming and greater rainfall in northern Japan has reduced the growth rate of conifers and increased that of broad-leaved tree species. This shift in species composition can impact the services that forests provide, including carbon storage and habitat provision.
Raccoons thriving in a changing climate: A new study found that raccoons’ suitable range will expand further north. With the species spreading out, raccoons could eventually outcompete native species.
Salmon at risk: Scientists found that several salmon species in the U.S. West Coast are very vulnerable to warming and ocean acidification. Furthermore, other stressors like dams and other migration barriers have reduced species’ ability to adapt to warmer temperatures.
Climate connection with fungal disease: A drug-resistant fungus, Candida auris, which can cause infections, has emerged on three continents. Scientists said it may be the first fungal disease that emerged due to climate change, given its thermal tolerance.
Species on the move in the UK: Researchers analyzed a decade’s worth of data from 2008 to 2018 and found that at least 55 species changed their ranges due to climate change. Changing ranges has implications for ecosystem composition, such as competition with native species and crop damges.
Climate change to hamper nutrient growth: The global availability of nutrients like iron and zinc is expected to increase due to technological advancements, carbon dioxide fertilization (increased photosynthesis with higher levels of carbon dioxide) and market responses. However, modelers have now found that increased levels of carbon dioxide will decrease such nutrient growth; researchers expert a 20% drop in protein, 14.4% drop in iron and 14.6% drop in zinc relative to what’s expected due to technological and market gains by 2050. Already, a quarter to a third of the global population is deficient in at least one micronutrient.
Warmer climate brings more female turtles: Scientists found that 84% of loggerhead turtle hatchlings in Cape Verde are female. By the end of the century, they predict sex ratios could be more than 99% female, with three islands not producing males at all. They also note that by 2050, more 90% of Cape Verde’s turtle nests will be exposed to lethally high temperatures.
Corals redistributing themselves: Exploring data from 1974 to 2012, researchers found an 85% reduction of coral recruitment (when coral larvae settle and become part of an adult population) throughout the tropics, while there has been an increase in the sub-tropics. Corals may be shifting to the poles, which authors said may not be able to support the same diversity of species as the tropics.
Good news for the blue crab: Scientists project that warmer winters will allow the Chesapeake Bay blue crab, an ecologically and economically valuable species, to have longer and more productive seasons.
Trees can’t shift ranges: It is well established that warming will push species to move to more hospitable climates. Researchers have now found that 62% of tropical forest area (roughly 10 million square kilometers) cannot shift to their future hospitable climate range, in part due to extensive deforestation. The authors suggest that it will be important to not only limit future forest loss, but also focus efforts on creating “climate corridors” to improve tropical forest resilience.
Freshwater fish die off: Scientists analyzed a database of 502 freshwater fish die-offs and found that they occurred during periods of extreme heat and in lakes with warmer-than-average temperatures. They expect fish die-offs could double by mid-century for north temperate lakes and increase four-fold by the end of the century, especially at southern latitudes.
Geoengineering the Antarctic ice sheet: If the West Antarctic ice sheet disintegrates, it would cause seas to rise more than 3 meters, inundating coastal cities like Calcutta, Shanghai, New York and Tokyo. Scientists posited that pumping ocean water on top of a Costa Rica-sized area of the ice sheet—either in the form of liquid or snow—could improve its stability. They noted that their model simulations neglected several mechanisms and feedbacks that could compromise ice sheet stability, and there is significant uncertainty and logistical hurdles to their approach.
Tidewater glaciers losing mass much faster than previously thought: Scientists found that models are significantly underestimating the melting from glaciers terminating at sea. Studying an Alaskan tidewater glacier, they found that observational data indicate a melt rate up to a 100 times faster than existing models predict.
Antarctic sea ice declining precipitously: Compiling four decades of satellite observations, a scientist found that while Antarctic sea ice extent had been gradually increasing since the late 1970s, as of 2014, it reversed course. The rates of decline between 2014 and 2017 far exceeded rates in the Arctic.
Energy infrastructure will blow the carbon budget: A study estimated that emissions from existing and proposed fossil fuel energy infrastructure across eight sectors will exceed the carbon budget associated with limiting warming to 1.5 degrees C (2.7 degrees F). The authors concluded that existing infrastructure may need to be retired early or retrofitted with carbon capture and storage to keep temperature rise to safe levels. They also note that carbon dioxide emissions related to the extraction and transport of fossil fuel, as well as non-energy carbon dioxide emissions, such as those related to deforestation, are not included. If these were included in the estimates, the carbon budget would be even further reduced.
Solving the climate problem through forest restoration: Using measurements of forest cover, scientists found that the world could restore forests to 900 million hectares, an area of land the size of the United States. Doing so could store 205 gigatonnes of carbon, which constitutes two-thirds of the total emissions from human activity since the Industrial Revolution. However, they also found that climate impacts could reduce restoration potential by 223 million hectares, and that restoring such a large area is not without significant challenges and tradeoffs. Restoration efforts would need to be carried out with care to take into account the choice of species, socioeconomic implications, impacts to food and land security, and effects on ecosystems.
Elephants indirectly help with carbon sequestration: The presence of forest elephants changes forests, leading to fewer and larger trees with high wood density and carbon-storage potential. Modelers projected that if forest elephants were to go extinct, aboveground biomass in central African rainforests would decline by 7%, causing a decline in carbon stocks.