[Fresh Ink] Earth Out of Sync: Rising Temperatures Throwing off Seasonal Timing

[Richard Menec]

http://blog.sustainablog.org/global-warming-effects-seasonal-timing/

Earth Out of Sync: Rising Temperatures Throwing off Seasonal Timing

by Earth Policy Institute on March 29, 2010
in Science

By Janet Larsen

A newly hatched chick waits with hungry mouth agape for a parent to deliver 
its first meal. A crocus peaks up through the snow. Rivers flow swiftly as 
ice breaks up and snows melt. Sleepy mammals emerge from hibernation, and 
early frog songs penetrate the night.

Spring awakening has long provided fodder for poets, artists, and almanac 
writers. Even for a notoriously fickle time of sunshine, rain, and 
temperature swings, some old-fashioned seasonal wisdom was consistent enough 
to be passed down through generations. The first blooming of a specific 
flower, for example, could traditionally signal when to find certain fish 
running the rivers, when to hunt for mushrooms, or when to plant crops. The 
timing of such seasonal events is coordinated in an intricate dance-a dance 
under-appreciated, perhaps, until something jolts it out of step.

With global average temperatures up 0.5 degrees Celsius since the 1970s, 
springtime warming is coming earlier across the earth's temperate regions. 
A number of organisms have responded to the warming temperatures by altering 
the timing of key life-cycle events. The problem, however, is that not all 
species are adjusting at the same rate or in the same direction, thus 
disrupting the dance that connects predator and prey, butterfly and blossom, 
fish and phytoplankton, and the entire web of life.

The timing of seasonal biological events, otherwise known as phenology, has 
been tracked in some places for centuries. Japan's much-feted cherry tree 
blossoming has been carefully recorded since before 1400. The trees showed 
no clear trend in timing until the early 20th century, when they began to 
bloom earlier, with a marked advancement since around 1950.

The meticulous records of Henry David Thoreau help us gauge how spring has 
changed in Concord, Massachusetts, since the mid-1800s. Comparing his notes 
on over 500 species and subspecies of plants with modern surveys and records 
in between, researchers found that springtime blooming advanced by an 
average of one week over the past 150 years as local springtime temperatures 
rose.


Seasonal timing changes: plants

The plant varieties that advanced their timing appear to have thrived over 
the years, while others declined in numbers. The varieties left behind 
include asters, mints, orchids, lilies, and violets. Some native plants 
advanced their blossoming dramatically: the highbush blueberry by three 
weeks and the yellow wood sorrel herb by a month. Yet these native plants 
may be the exception rather than the rule; on average, non-native invasive 
plants advanced their bloom by 11 days more than natives. With exotic 
invasives appearing to adapt more quickly to warming temperatures, the 
concern is that they could out-compete some native plants, leading to their 
disappearance.

Earlier springs and later autumns mean longer growing seasons-as long as 
plants do not succumb to a surprise late cold snap or wilt in the peak 
summer heat.  In Germany, apricot and peach trees now bloom more than half a 
month earlier than in 1961.  Apple trees in the northeastern United States 
moved up flowering by eight days between 1965 and 2001; apple trees require 
chilling time before they flower, and warmer winters have been tied to 
smaller harvests.  Earlier spring blooming has lengthened pollen seasons in 
some places by weeks. Allergy sufferers beware: this trend is likely to get 
worse as the planet gets warmer. (See additional examples at 
www.earthpolicy.org.)

A longer growing season could benefit some crops like the sugar beet. For 
other foods, however, including important cereals like rye, the increased 
early-season temperatures could hurt yields by pushing plants to devote more 
energy to vegetative growth than to the seed that we eat.  The premature 
warming also elevates the risk of damage from late frosts. In 2007, for 
example, a warm March in prime U.S. agricultural regions pushed spring into 
gear early, only to be followed by unusual cold in April. The damage to the 
nascent crops exceeded $2 billion.


Seasonal timing changes: animals

Exactly how these changing plant communities will interact with pollinators 
and foragers that may or may not be changing at the same pace remains 
unanswered. Members of the animal kingdom are responding to warming in 
different ways. A quintessential early bird, the American robin, now 
sometimes makes an even earlier springtime debut.  In the Colorado Rocky 
Mountains, where robin migration is not just south-to-north but also up to 
higher elevations, the birds have responded to warming in their wintering 
grounds by traveling to their high-altitude summer breeding grounds two 
weeks earlier in 2009 compared to the early 1980s. In some years the robins 
arrive long before the snow has melted-making it far more difficult for this 
early bird to catch the worm.

For pied flycatchers that breed in the Netherlands, migration timing from 
their West African wintering grounds has not changed, but earlier spring 
warming has caused the birds to breed about as soon after their arrival as 
possible. Unfortunately, their caterpillar food has been able to respond 
even more strongly, advancing hatching in one woodland by an average of 15 
days over two decades, while the birds only advanced by 10 days. At sites 
where the caterpillar populations still peak somewhat late, flycatcher 
populations have dropped by 10 percent, but where the caterpillars have 
advanced hatching the most, flycatcher populations have plummeted about 90 
percent.

Across Europe as a whole, populations of birds that did not advance their 
migration time along with earlier spring warming have shrunk since 1990. 
Short-distance migrants seem to be faring better than those traveling long 
ways.  Milder winters have even prompted growing numbers of some birds, like 
the Pacific brant and Canada goose, to skip migration altogether. Like the 
early crops, however, the birds that stay are in danger of being wiped out 
by a sudden cold spell.

As evidenced by the caterpillars in the Netherlands, short-lived insects 
have some of the fastest life-cycle responses to global warming. In Central 
Europe, where almost every summer since 1980 has been hotter than the 
long-term average, warming has allowed some species of butterflies and moths 
to become active earlier and actually add an extra generation in the 
year-something not seen among those species in records dating back to the 
1850s. If predation does not increase, a population explosion could 
overstress the plants that the butterfly and moth caterpillars eat.

High-altitude mountain pine beetles in western North America present a 
similar case. In warmer weather they can complete their life cycles in one 
year instead of two. Insects that once were active for just two weeks a year 
now can be found flying for up to six months, leaving devastated forests in 
their wake.  Earlier springs and milder winters are also linked to an 
increased incidence of tick-borne encephalitis and other diseases spread by 
insects that do well in the warmer conditions.


Geographical range shifts

In addition to or instead of adjusting life-cycle timing, some organisms 
have responded to warming temperatures by shifting their geographical 
ranges, often poleward or upward. Bird and butterfly range shifts averaging 
6 kilometers per decade have already been observed, with some species moving 
quite faster.  There are, of course, limitations to all these adaptations. 
Even more-mobile species can gain only so much altitude before running out 
of mountain or can travel only so far before becoming blocked by pervasive 
human development.

Some wildlife take their timing cues from environmental factors other than 
temperature. The snowshoe hare, for instance, appears to rely on changes in 
day length to signal when to transform its coat color from winter white to 
summer brown. While day-length patterns are the same from year to year, snow 
in the hare's Montana wilderness habitat now melts up to a month early. If 
hares are not able to speed up their coat change, they will be in trouble: a 
stark white hare on bare ground is a remarkably easy target. And as go the 
hares, so go the lynxes that feed almost exclusively on them.

Tinkering with an incredibly complex and interconnected system is fraught 
with risk. These mismatches are just some examples of how a hotter world is 
a world unlike any we have known. It is still too early in this global 
experiment to tell which creatures will be the climate winners and losers, 
but the signs indicate that the losers will be the majority. Turning down 
the global thermostat by cutting greenhouse gas emissions is the only way to 
avoid the risk of throwing nature further out of sync.

Janet Larsen is the Director of Research for the Earth Policy Institute. 
Data and additional information are available at http://www.earthpolicy.org

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