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 August 2019. (To get these updates delivered right to your inbox, sign up for our Hot Science newsletter.)
Recent Extreme Events
August brought alarming signs of a changing climate, many of which are in line with projections of a warming world:
- About 90% of the Greenland ice sheet’s surface melted from July 30th to August 3rd. Runoff was 55 billion tons, 40 billion tons more than the average from 1981-2010 for the same time period.
- Arctic sea ice extent was the second-lowest in the satellite record for the month of August, after 2012.
- Anchorage, Alaska had its warmest August on record.
- Hurricane Dorian picked up significant strength, and was one of the five strongest hurricanes on record in the Atlantic Basin.
- NOAA confirmed that July 2019 was the warmest month on record globally.
Ice Loss:
- September Arctic sea ice to disappear with low levels of warming: A new modeling technique estimated that Arctic sea ice will disappear in September with warming of only 2 to 2.5 degrees C (3.6 to 4.5 degrees F). The authors further stated that limiting warming to 1.5 degrees C (2.7 degrees F), a temperature goal in the Paris Agreement, may not be sufficient to prevent ice-free conditions.
- Human-induced climate change melted West Antarctic ice sheet: Researchers have now established a causal link between greenhouse gas emissions and past melting of the West Antarctic Ice Sheet. Human-induced climate change has affected the winds that blow over the nearby oceans, bringing warm waters that melted the West Antarctic Ice Sheet.
- Arctic sea ice loss may not cause cold winters at mid-latitudes: For several years, scientists have linked record-cold winters to shrinking Arctic sea ice cover. A new article questions that connection for cold mid-latitude winters, finding that atmospheric circulation changes occurred before sea ice loss rather than as a result of it. The authors did find that sea ice loss may be contributing to cold winters in East Asia.
- Arctic sea ice decline started earlier than previously thought: Scientists used records of algae, which depend on light availability, as a proxy to study sea-ice cover in the high Arctic. They found the declining sea-ice trend started in the beginning of the 20th century, earlier than previously reported. The lowest sea-ice values over the past 200 years occurred from the 1980s to early 2000s.
- Melting Antarctic icebergs can delay climate impacts: Scientists examined the effect of Antarctic icebergs, which can travel large distances before melting, on meltwater patterns across the Southern Ocean. While they found that meltwater can contribute to accelerated Antarctic ice loss, the iceberg melt also increases surface cooling, slowing down warming in the southern hemisphere. Depending on the rate of ice sheet disintegration, this “iceberg effect” could delay warming in cities such as Buenos Aires and Cape Town.
Extreme Weather
- Hot extremes rise in Europe: Researchers found that across Europe, the number of days with extreme heat and heat stress more than tripled between 1950 and 2018, with temperature extremes warming by 2.3 degrees C (4.1 degrees F) during that period. At the same time, days with extreme cold temperatures decreased by two to three times, and extremely cold temperatures warmed by over 3 degrees C (5.4 degrees F).
- More persistent summer weather: Summer weather will become more persistent as global average temperature increases more than 1.5 degrees C (2.7 degrees F), leading to longer uninterrupted warm, dry periods, especially in eastern North America. Authors also found that warming increases the likelihood of consecutive days of strong precipitation at mid-latitudes.
- Flood incidence a mixed bag in Europe: In some regions of Europe, floods increased about 11% between 1960 and 2011, whereas other areas saw a decline of 23%. More autumn and winter rainfall increased floods in northwestern Europe, while decreased precipitation and increased evaporation led to a decline in floods in southern Europe. Eastern Europe also saw decreased floods due to declining snow cover and snowmelt.
- Thousands more deaths with half a degree of warming in China: Researchers found that limiting warming to 2 degrees C instead of 1.5 degrees C would result in about 28,000 additional-heat related deaths annually in China.
- Increase in tropical cyclone-related flooding in the US: Tropical cyclone-induced flooding is one of the most destructive hazards. Researchers found that in a warming climate, tropical cyclones would impact flood hazards along the U.S. Atlantic and Gulf Coasts significantly, with the largest impacts in the Gulf of Mexico.
- Increased risk of food and water shortages in Upper Nile Basin: While the Upper Nile Basin — which covers South Sudan, Uganda and western Ethiopia — is expected to see more precipitation due to climate change, the increased frequency of hot and dry years will lead to more water shortages, despite increased precipitation. Given the projected rise in hot and dry years (increasing by a factor of 1.5 to 3, even with warming limited to 2 degrees C), agriculture is expected to be stressed, and water scarcity will be exacerbated. The authors conclude that climate change could place the region “at risk of severe food and water shortages.” As many as 250 million people could be affected.
- Link between sea surface temperature and U.S. tornadoes: Using tornado data in the United States from 1954 to 2016, scientists found that global sea surface temperatures increased tornado activity in April across the Southern Great Plains region, when tornado occurrences have peaked in the region.
Impacts:
- Deforestation significantly affects local climate: A new study found that in areas of the Amazon with severe deforestation, surface temperature increased by 0.44 degrees C (0.8 degrees F) between 2000 and 2013.
- Earlier grape harvests: Studying a 664-year-long data record of grape harvest dates in Burgundy, scientists found that between 1354 to 1987, grapes were typically picked from September 28th onwards. In the last three decades, harvests began 13 days earlier than the six-century average. The authors said that the transition to rapid warming in 1988 has made hot and dry years the norm.
- Transformed boreal forests: While evergreen conifers are currently the dominant tree type in Alaska’s boreal forests, by the end of the century, deciduous broadleaf trees will nearly double, making them dominant tree in the ecosystem. Researchers said the expansion of deciduous forest can have several ecological and climatic implications. For example, broadleaf deciduous trees lose their leaves, which can amplify warming as a result of microbial decomposition and increased moisture loss through the leaves.
- Climate change causing bumpier plane rides: Researchers found that climate change has had a larger impact on the North Atlantic jet stream than previously thought, affecting aviation by creating more turbulence. They studied the change in wind speed at higher heights (known as vertical shear), which has increased 15% between 1979 and 2017.
- Marine heatwaves affect corals more than previously thought: Researchers discovered that severe marine heatwaves lead to coral death, as well as the rapid dissolution of the coral skeleton, which transforms reefs’ entire structure. This can have widespread impacts on other animals that depend on the reef.
- Native plant species at risk in Europe: A study of the plant Arabidopsis thaliana in Spain and Germany found that frequent droughts and rising temperatures will put the native plant species at risk. The study suggested that many native plant populations in the transition zone between the Mediterranean and temperate regions could be at risk of perishing.
Ocean Behavior
- Altered ocean waves: Researchers have found that under a high emissions scenario, climate change will alter ocean waves (in terms of height, frequency and/or length) across about half of the world’s coastline. The impacts vary by region. For example, average wave height is to increase in the Southern Ocean and tropical eastern Pacific, but is to decrease in the North Atlantic and part of the Pacific Ocean. Climate change affects wind patterns, which in turn affect waves.
Emissions
- Critical role of land in determining climate change: The Intergovernmental Panel on Climate Change’s (IPCC) Special Report on Climate Change and Land found that land removed a net 6 gigatonnes (Gt) of CO2 per year from 2007 to 2016, equivalent to the annual greenhouse gas emissions of the United States. Further deforestation and land degradation, though, will chip away at this carbon sink. **Read more about the findings in our blog post.
- Carbon dioxide makes plants bigger — to a point: Scientists found that the higher carbon dioxide levels expected by the end of the century could increase plant biomass by about 12% over current levels. This additional biomass could sequester about 59 petagrams of carbon (PgC), roughly six years’ worth of global carbon dioxide emissions. However, if deforestation and land use change continue unabated, or the land carbon sink is weakened or reversed due to further climate change, this effect would be lost.
