by DK
Longer plant growing seasons sound like good news, but warmer temperatures create problems as well as advantages. Not all insects are welcome, and shorter, milder winters kill fewer dormant insects, some of which may consequently undergo explosive population increases and produce damaging infestations. Warmer springs allow pine sawflies, whose larvae eat pine needles, to develop too rapidly for the birds and parasites that feed on them to keep their numbers in check. Out of control, the sawflies strip trees of their needles and stunt their growth.
The leaves of some oak species turn red shortly before they fall in fall. Comparing the date on which this occurs from year to year can provide evidence for climate change.
CAMILLE PARMESAN
Born in 1961, Professor Camille Parmesan is an American academic who has established a reputation as one of the leading climate change scientists. She received her Ph.D. in biological sciences from the University of Texas at Austin in 1995 and her early research concerned the evolution of insect–plant interactions. For the best part of 20 years, she has focused on documenting the shifting geographical ranges of butterflies across North America and Europe, linking these to climate change. Parmesan has been a leading figure in the IPCC and her work has won her many accolades and has been cited in hundreds of academic papers. She is professor in Integrative Biology at the University of Texas at Austin and advises international conservation bodies.
Key works
2003 “A globally coherent fingerprint of climate change impacts,” Nature
2015 “Plants and climate change: complexities and surprises,” Annals of Botany
Migration and hibernation
Birds that migrate in spring to reach rich food sources also face problems. Some have adjusted their flight schedules to benefit from the earlier abundance of insects. After making the long journey from sub-Saharan Africa, the first swallows arrive in the UK about 20 days earlier than they did in the 1970s, and the first Bank Swallows reach their destination 25 days sooner than previously. However, there is evidence that birds migrating from Central America to New England in the US have declined faster than birds that remain in New England all year. This is probably because the migrant birds have been unable to adjust their departure dates from Central America to arrive in time to benefit from the earlier abundance of insects the way local birds do.
Climate change also appears to have changed the behavior of hibernating mammals. Zoologists at the Rocky Mountain Biological Laboratory found that yellow-bellied marmots living in Colorado emerged 38 days earlier in 1999 than they had done in 1975. In 2012, scientists at the University of Alberta found that in the last two decades, late snowfall has delayed the emergence of the Rocky Mountain ground squirrel from hibernation by 10 days. This has cut down the already short active period in which they mate, give birth, and feed to prepare for the next hibernation cycle.
Some bee species now emerge earlier in spring, in line with earlier flowering dates for the plants that they pollinate. Other bees, though, have not been able to synchronize their emergence.
Decoupling
Some organisms’ survival could be threatened by the “decoupling” of interactions between species. This could seriously upset the balance of ecosystems. If flowers appear earlier, the bees that pollinate them can respond in one of two ways: they can emerge earlier; or they can move to a higher latitude to match later flower emergence farther from the equator. Studies of 10 wild bee species in northeast North America have shown that their behavior has changed in line with earlier flowering. However, bumblebees in Colorado have not matched the changes and their population has fallen. If pollinators decline, so may the plants that they pollinate.
There is evidence that many primary consumers have adjusted to changed natural phenomena, but species higher in the food chain seem to find it harder to make the change. Although birds are now nesting earlier than they once did, the timing of insect emergence has advanced more rapidly. This is a problem for birds that depend on peaks in insect abundance. For example, Pied Flycatchers and Great Tits feed their chicks on caterpillars that are abundant for a short period in spring. Due to climate change, the caterpillar peak is now earlier, but the birds have not been able to advance their egg-laying dates enough to take advantage of the glut of food. Studies show that fewer Pied Flycatcher and Great Tit chicks are surviving. Pied Flycatcher numbers have declined in Dutch woodlands, possibly as a result of climate change.
A Great Tit feeds its chicks. If breeding takes place after the peak period for spring caterpillars, there will be less food for the young birds, and fewer will survive to breed.
“We are now sure of what we only suspected years ago. Policy needs to catch up with science.”
Camille Parmesan
Taking action
All of this disturbing evidence has prompted climate scientists worldwide to lobby governments and demand policy change. Spring creep has been used by scientists as a definitive piece of proof that climate change is occurring, and researchers have called upon policy makers to fight global warming to save the familiar species that find their very existence threatened by phenological changes.
“This butterfly I was studying shifted its entire range across half a continent—I said this is big … Everything since then has just confirmed it.”
Camille Parmesan
Wall butterflies and climate change
Climate change sometimes produces unexpected results. For example, in the UK, the life cycle of the wall butterfly has been disrupted by changing climatic conditions. Previously, the butterfly produced two generations every summer. The late-summer adults would mate, the females lay eggs, and the eggs then developed into caterpillars. In September, these caterpillars found sufficient food to grow large and sustain themselves in hibernation through winter. In spring, the caterpillars metamorphosed into pupae, and then became adults. Warmer weather has allowed a third generation to develop in fall, with adults flying as late as mid-October. By the time the third generation caterpillars hatch there is little food, so most starve and die. Scientists call this a “developmental trap” and it is probably responsible for the decline in wall butterflies.
See also: Animal ecology • Animal behavior • The foundations of plant ecology • Global warming • Endangered habitats • Halting climate change
IN CONTEXT
KEY FIGURE
Malcolm McCallum (1968–)
BEFORE
1989 The formerly common golden toad of Costa Rica is declared extinct. Various explanations are proposed.
1998 In the US, many poison-dart frogs die at the National Zoo in Washington DC. The chytrid fungus is implicated as a cause.
AFTER
2009 The Kihansi spray toad of Tanzania is declared extinct in the wild as a result of chytrid infection.
2013 A second species of chytrid fungus causes the near- extinction of fire salamanders in the Netherlands.
2015 The chytrid fungus is detected in amphibians in 52 out of 82 countries sampled.
Since the 1980s, hundreds of species of amphibians have suffered population crashes and localized extinctions—at a rate thought to be more than 200 times the natural, “background” extinction rate unaffected by modern human activity. This alarming phenomenon first attracted public attention in 1999, when American environmental scientist Malcolm McCallum published his findings about the dramatic increase in deformities in frogs. He went on to produce landmark studies on amphibian decline and extinction.
The causes of the problem are wide-ranging, and include habitat destruction and pollution, as well as competition from nonnative species. But one of the most devastating causes is undoubtedly disease, with two particularly lethal culprits.
Chytrid and ranavirus
Chytridiomycosis is a disease caused by the chytrid fungus, and it has ravaged populations of frogs and toads in particular. The fungus affects amphibians’ skin, such that they are not able to breathe, hydrate, or regulate their temperature. The exact origin of
the fungus is not known, but the global trade in live amphibians for various uses, be it pets, food, fishing bait, or research, has been a major factor in its spread.
Ranaviruses evolved from a fish virus. They infect amphibians and reptiles, and have caused mass mortality in frogs since the 1980s. The common midwife toad ranavirus causes bleeding, skin sores, lethargy, and emaciation. It is notably virulent as it has the ability to “jump” from one species to another.
The North American bullfrog is resistant to the chytrid fungus, but acts as a deadly carrier of the infection to other species of amphibians.
See also: Biomes • Pollution • Endangered habitats • Deforestation • Overfishing
IN CONTEXT
KEY FIGURES
Kenneth Caldeira (1960–), Michael E. Wickett (1971–)
BEFORE
1909 Danish chemist Søren Sørensen develops the pH scale for measuring acidity.
1929 American biologists Alfred Redfield and Robert Goodkind discover that excess carbon dioxide in water suffocates squid.
1933 German chemist Hermann Wattenberg makes the first global survey of ocean acidity, as he analyzes results from the Atlantic expedition of the Meteor research vessel.
AFTER
2012 In the US, oceanographer James C. Zachos and his colleagues use fossil evidence from marine sediments to show that past acidification of the ocean has led to mass extinctions of sea creatures.
Adding carbon dioxide (CO2) to the air not only triggers climate change but also makes the oceans more acidic. So far, the oceans have buffered the worst effects of global warming, absorbing up to half of the carbon dioxide added to the atmosphere by human activity. However, the gas alters the oceans’ chemistry.
In 2003, American climate scientists Ken Caldeira and Michael E. Wickett investigated the effects of CO2 pollution on the oceans. They took samples of seawater from around the world, and found that the acidity had increased measurably in the past 200 years of industrialization. They coined the term “ocean acidification” and predicted that this change could accelerate over the next 50 years, with damaging results.
Many sea creatures rely on the natural alkalinity of seawater to maintain carbonates for building their shells and skeletons. Even a slight decrease in alkalinity seriously disrupts growth, especially for sensitive creatures such as corals and plankton. Acidification might wipe out corals within decades; if they go, so do the reef ecosystems. Phytoplankton are the foundation of the ocean food web, and are vital to maintaining global oxygen levels.
Ocean acidification is far harder to reverse than the atmospheric effects of CO2 emissions, and its devasting impact on biodiversity, fisheries, and food security remains a serious concern.
“Most carbon dioxide released into the atmosphere as a result of burning fossil fuels will be absorbed by the ocean.”
Ken Caldeira and
Michael Wickett
See also: Global warming • Pollution • Endangered habitats • Acid rain • Halting climate change
IN CONTEXT
KEY FIGURE
Robert Bruegmann (1948–)
BEFORE
1928 British architect Clough Williams-Ellis compares London’s growth to an octopus devouring the countryside.
1950s With postwar prosperity and increased car ownership in the US, the middle classes leave cramped city centers and move to new, low-density areas in the suburbs.
AFTER
2017 A housing crisis in the UK prompts calls for the lifting of restrictions on new building on the greenbelts around major UK cities.
2050 The date by which, according to UN estimates published in 2014, the urban population of the world is set to rise to 6.34 billion out of a projected total population of 9.7 billion.
Since the 1950s, the term “urban sprawl” has been widely used to describe the growth of low-density suburbs beyond high-density city cores. The term was first used by The Times newspaper in the UK in 1955 to describe the spread of London’s suburbs. At this time, the British planning authorities were introducing “green belts” around cities, where new building was almost entirely banned. Green belts were designed to stop cities from spreading and merging with other towns.
Modern definitions of urban sprawl vary, but it generally has negative overtones. At its most extreme, it has created megacities—defined by the United Nations as cities of more than 10 million people. Examples of such megacities include Tokyo-Yokohama (38 million), Jakarta (30 million), and Delhi (25 million).
“The old city is submerged in a far-flung, multicentered, mostly low-density, highly heterogeneous urban region.”
Robert Bruegmann
Ecological upset
Some researchers claim urban sprawl is the most serious threat to biodiversity from any human activity. The new suburbs house relatively few people, yet require extensive and disproportionate levels of infrastructure, such as power and water supplies and transportation networks. As cities swell, valuable farmland is covered in concrete and natural habitats are disrupted or lost entirely. Sprawl can also disturb local fauna and flora through the introduction of pets and invasive plants that threaten indigenous species. Limited public transportation in low density areas also means that suburban populations tend to be multiple car owners, which adds to the levels of air pollution in cities—as do the wood- and coal-burning stoves of the poor in outlying shanty towns.
The area of the world currently covered in urban development is one-and-a-half times the size of France. Mexico City has expanded more than any other city in the West. Spreading far beyond its official boundaries to become the home of more than 21 million people, it has also grown disproportionately: in 1970–2000, the surface area of the city grew 1.5 times faster than its population. While 59 percent of the city’s territory is conservation land, illegal logging and urban sprawl continue to degrade urban forest, grassland, and water supplies.
It is estimated that 37 percent of all urban growth by 2050 will occur in China, India, and Nigeria alone. In Beijing and other cities in China, densely populated hutongs (alleyways), where the urban poor used to live, are being demolished to make way for low-density luxury blocks, pushing the city limits—and the urban poor—far from city centers. The reliance on cars in the new neighborhoods, and the lack of central hubs, means there is little opportunity for community life.
Aware of the problems caused by urbanization, the Chinese government is now trying to limit the population of Shanghai to 25 million and that of Beijing to 23 million by restricting land available for building and controlling the inflow of people, forcing out low-skilled workers. China is also building higher-density neighborhoods with narrower streets, more intersections, and more public transport that will help the formation of communities.
Toluca was once a picturesque old town to the west of Mexico City. Now a city of more than 800,000 people, it is gradually merging into the sprawl of Mexico City—at a high ecological cost.
The endangered axolotl
One of the victims of the urban sprawl of Mexico City has been the tiny axolotl, a pale-colored salamander that looks like a fish but is actually an amphibian, and is sometimes known as the Mexican walking fish. Capable of growing up to 1 ft (30 cm) long, the axolotl feeds on aquatic insects, small fish, and crustaceans, and has the ability to regenerate severed limbs—a quality that has made captive specimens an important subject of scientific research. The captive version is also a familiar pet in aquariums around the world.
Historically, the wild axolotl lived in the urban canals created by the Aztecs as they built their capital city in the 13th century, and in the network of lakes around the city that fed these canals. As Mexico City has expanded, these canals have been lost, and the wild axolotl has declined. In 2006, it was added to the list of critically endangered species and by 2015 it was thought that the creature may have been extinct. However, specimens have since been found in Lake Xochimilco in southern Mexico City.
See also: Pollution • Endangered
habitats • Deforestation • Depletion of natural resources • Amphibian viruses
IN CONTEXT
KEY FIGURE
Charles J. Moore (1947–)
BEFORE
1970s Scientists begin to research plastic litter at sea after reports in the journal Science describe large numbers of plastic pellets in the North Atlantic.
1984 The first International Marine Debris Conference, held in Hawaii, raises awareness of the growing problem of litter in the oceans.
AFTER
2016 The documentary A Plastic Ocean, directed by Australian journalist Craig Leeson, highlights the global effects of plastic pollution.
2018 The Earth Day Network, an organization committed to spreading the environmental movement worldwide, makes End Plastic Pollution the theme of Earth Day, on April 22, 2018.
When plastics were first mass produced in the early 20th century, the world marveled at the versatility and durability of a material that could be molded into any shape, used, and then thrown away. The problem with plastic, however, is that most of it never goes away. According to the British business publication The Economist, only 20 percent of the 6.3 billion tons of plastic produced in the world since the 1950s has been burned or recycled. This means that 80 percent—5 billion tons—is in landfills or elsewhere in the environment.
A “seabin” is emptied in Sydney harbor. The Seabin Project, introduced in Australia in 2015, helps counteract plastic pollution by filtering surface water in ports and harbors.