Feeling the heat
Why the warming climate should be of concern to birdwatchers
Published: June 24, 2011
|Climate change remains a hot topic these days, especially between people hewing to opposing political ideologies. Among scientists, however, there is general agreement that it is real and that Earth is warming. |
Climate change is caused mostly by an increase in global-warming gases emitted largely by human activity. The best science organizations in the world endorse this statement, while none opposes it. The changing climate will present many challenges to birds, as I’ll describe here, but first we need to consider the causes.
The best explanation for historical changes in climate — including ice ages and warm interglacial periods — is a combination of physical factors first described by Serbian mathematician Milutin Milankovitch in 1920. The factors include the changing shape of Earth’s orbit around the sun, the varying inclination of Earth’s axis, and the wobble of the rotating planet.
Milankovitch calculated that these changes would cause variations in the amount of solar radiation that strikes Earth at different latitudes. The variations would create two extremes — cooling, causing snow to accumulate throughout the year (ultimately forming glaciers), and warming, which would cause glacial melt. These phenomena are cyclic; Milankovitch predicted, accurately, that ice ages would last about 100,000 years.
The cycles are still operating today, but something happened about 250 years ago that is dramatically affecting the climate: Human populations began to increase rapidly, reaching 1 billion in 1803, 3 billion in 1960, and 6 billion in 1999. The world’s population should hit 7 billion in 2012 and is projected to be about 9 billion in 2050.
Population growth was accompanied by an industrial revolution, and fossil-fuel consumption increased in a similar pattern, resulting in a dramatic rise in carbon-dioxide emissions. The emissions far outstripped natural carbon-dioxide production.
According to the U.S. Geological Survey, volcanoes — including both submarine and terrestrial — produce an average of about 150-270 million tons of carbon dioxide every year. In 2008, human activities produced about 200 times this amount — 36.3 billion tons of carbon dioxide.
Carbon dioxide and other warming gases in the atmosphere absorb long-waved radiation that is emitted from Earth and serves as a cooling mechanism. Warming gases reduce how efficiently the planet cools and, therefore, cause Earth’s temperatures to rise.
Warming temperatures vary by region. While Earth increased a little over 1°F over the past century, it is now increasing that much every three or four decades. Temperature changes are greatest where temperatures are colder, such as in the Arctic and Antarctic.
The Arctic has warmed 4-7°F during the past 50 years. Arctic sea ice has been reduced significantly both in extent and thickness. If the polar bear and walrus are the poster mammals for climate change, Kittlitz’s Murrelet and the small, white Ivory Gull are likely candidates for the poster birds. Foraging activities for both species are associated with sea ice.
Birds like the Red-breasted Goose of Siberia and the Yellow-billed Loon from Alaska and the Canadian Arctic rely on tundra ponds near the shoreline of the Arctic Ocean. The ponds hold water because of frozen ground (permafrost) underneath. As the permafrost melts, the ponds drain.
In the extreme south, regions near the Antarctic Peninsula have increased 9°F during the past 50 years. Emperor and Adélie Penguins have been hit especially hard. Some Emperor populations have been reduced by half, and some Adélie populations even more. In some Adélie colonies, nests, made of small pebbles, and eggs have been found under water from melting ice.
Krill, a shrimp-like crustacean, is an important food source for most penguins, and an essential source for some, including Emperors and Adélies. Young krill feed on algae attached to the underside of sea ice, a location that they use as a kind of nursery. Unfortunately, sea ice of the West Antarctic Peninsula has shrunk about 40 percent over the past 20 to 30 years. Generally, in the Southern Ocean, krill populations have declined about 80 percent since the 1970s, with warming temperature and loss of sea ice thought to be the major cause.
Waterfowl are of concern, too, because most climate models show an increase in temperature and a decrease in precipitation in their most important breeding area — North America’s Prairie Pothole Region, which extends from north-central Iowa to central Alberta. Studies of songbirds in the arid southwest show reductions in nest success and number of fledged young when rainfall is significantly reduced. And the plains are expected to become even drier with climate change.
Many species, including Rose-breasted Grosbeak, Black-throated Blue Warbler, and Tree Swallow, are arriving on the breeding grounds up to three weeks early. Since most species have timed migration to coincide with optimum opportunities for nesting and feeding young, the advances are troubling. And other species, like Blue-winged, Prothonotary, and Hooded Warblers, are expanding their ranges, resulting in changes in habitat or ecosystem structure and interspecific relationships.
The changes brought by the warming world are having a negative effect on birds now, and the effects will be greater in the future. Birds’ success will depend in part on how much we can do to minimize these changes. Clearly, the world’s carbon footprint must be reduced if birds are to survive with healthy populations. The current climate trends should be unacceptable to all.
Eldon Greij is professor emeritus of biology at Hope College, located in Holland, Michigan, and the founding editor of Birder's World (now BirdWatching) magazine.|
Read more by Eldon Greij.