Understanding Climate Change
Content provided by: UCAR / University Corporation for Atmospheric Research
A climate
that's already changing
Current
environmental impacts and prospects for the future
Changes in weather
Heat and heat waves
Rain, snow, and drought
Stormy weatherChanges in ecosystems
Polar and mountainous regions
Plant life
Wildlife
| How will future impacts vary by region? |
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| View an interactive map of potential impacts of climate change. The selected impacts are based on the region-by-region analysis conducted by IPCC Working Group II. Click here or on the image to open a Web page with the enlarged, interactive map. (©UCAR. News media terms of use*) |
A climate that's already changing
Climate is always changing, but the changes we've observed in the last several
decades are best explained as a
combination of natural and human-made causes.
The first IPCC report, issued in 1991, discussed changes we could expect
decades in the future. Some of those are happening now, as reported in the
IPCC's 2007 assessments. Our confidence in projecting future changes has
also improved.
Some of the trends now under way—such as warmer nights during heat
waves and heavier bursts of rain and snow—are expected to continue.
Other changes will be less familiar, and there could be surprises along the
way. This increased uncertainty makes planning for the future more
difficult.
Our ability to adapt is one of our greatest strengths as a species. But
in this case, the medicine could feed the disease. As we adapt to climatic
changes already happening, some of those behaviors will affect the
amount of greenhouse
gases we put into the atmosphere, and thus affect the climate itself.
Population growth, increases or decreases in air
pollution, increased ability to purchase air conditioning or automobiles,
and other social and economic changes are difficult to pin down decades
into the future. This is why IPCC climate scientists have created a number
of emissions scenarios; each
one sketches a different set of possible future social, economic, and
technological developments for use in projecting future changes in the climate.
Here's a look at some of the impacts we're already experiencing and some
of the research at NCAR and in the wider research community that's
focusing on the connections between global warming and Earth's ecosystems.
Current
environmental impacts and prospects for the future
Changes in weather
- What’s happening?
- The IPCC reports that hot days, hot nights, and
heat waves all have become more frequent globally
in the last 50 years.
-
Record-breaking heat across
the United States during July 2006 is shown in red on
this map from NOAA's National Climatic Data Center. Click here or
on the map to open a NOAA Web page with details on the
extreme heat. (Image courtesy NOAA.)Europe’s 2003 heat wave, which resulted
in more than 40,000 deaths, was the hottest in 150 years of
modern record keeping, and possibly the hottest in 500 years,
by some estimates. There is at least double the risk of
such deadly heat waves ocurring in Europe compared
to what it would be if we were not adding greenhouse gases
to the atmosphere, according to a 2004
study in the journal Nature.
-
Sacramento, California, saw its warmest overnight low on record
(84 °F, or 27°C) during a July
2006 heat wave that killed more than 100 people
across the state.
The city’s previous record for warmest low was 79°F
(26°C). Many other western U.S. cities also saw their hottest
day or night ever reported.
- The IPCC reports that hot days, hot nights, and
- What can we expect?
- By the 2040s, the average summer in Europe may
be similar to the scorching one of 2003, according to the Nature study
cited above.
- A report by
two NCAR scientists found that Chicago’s heat waves could
become 25% more frequent by the 2080s. Nighttime lows during
the worst heat waves in the U.S. South and West are projected
to warm by more than 5°F (3°C).
- By the 2040s, the average summer in Europe may
Rain, snow, and drought
- What’s happening?
- On average, precipitation has
increased globally over
the last century, including over the United States.
- Days with heavy rain and snow are becoming more
frequent over most of the globe’s land areas,
including North America, according to IPCC
Working Group I.
- Despite
this, the global extent of drought has
more than doubled worldwide since the 1970s, according to an
NCAR study.
The more precipitation/more drought paradox is
because- rising temperatures allow more water to evaporate from
oceans (adding extra moisture to the air for rain or snow), - but that warming also draws moisture out of the ground,
worsening drought wherever it’s not raining.
- rising temperatures allow more water to evaporate from
- On average, precipitation has
- What can we expect?
- By the 2080s, most land areas north
of latitude 40°N, from Europe
to the northern U.S. states and Canada,
will see a jump in the number of
days with precipitation greater than
0.40 inch (1 centimeter), according
to NCAR research.
- The same NCAR report found that dry
spells could lengthen significantly across
the western United States, southern
Europe, eastern Brazil, and several
other areas.
- Another
study found widespread agreement among computer models
that the U.S. Southwest, from the southern Great Plains to
California, may be entering a semipermanent state of drought,
with "normal" years by the 2030s becoming as dry
as the 1930s Dustbowl or the persistent drought of the 1950s.
- By the 2080s, most land areas north
Stormy weather
- What’s happening?
- The strongest U.S. tornadoes have
not become more frequent in the last 50 years. Reports
of weaker tornadoes are increasing as more people watch
for them.
- Based on data since the 1970s, the most intense hurricanes (those
ranked Category 4 or higher on the Saffir-Simpson scale)
make up an
increasing fraction of tropical cyclones worldwide.
- Sea-surface temperatures have increased
in the parts of the Atlantic and Pacific where warm water fuels hurricanes
over the last century. The warming is more likely due to
human-produced climate change than natural cycles, according to research
reported in June and September 2006.
- The strongest U.S. tornadoes have
- What can we expect?
- Research continues on the effects of climate
change on tornadoes, severe thunderstorms, and hurricanes.
The trends should become more clear as the length
of observation records grows. Because extremes
are by definition rare, it takes a long time to gather
enough data to make definitive statements.
- Computer models of the
global climate cannot directly simulate tornadoes and other small-scale
weather features. More progress will emerge as
fine-scale models that depict hurricanes and severe
storms are linked to global simulations, as with the Nested
Regional Climate Model now being developed
at NCAR.
- Research continues on the effects of climate
Changes in ecosystems
Even gradual warming can have dramatic impacts on ecosystems. By crossing
important thresholds, such as when freezing or thawing occur, small
shifts in climate can transform the way plants, animals, and landforms
interact.
The polar and mountainous regions of Earth are especially vulnerable to
climate change. The huge amounts of snow and ice in cold regions act
as natural
air conditioners—not because they're frozen, but because their
light-colored surfaces span vast areas, reflecting most of the sunlight
that hits them. If the ice melts, the darker surface underneath (whether
land or sea) absorbs much more of the sunlight, like asphalt paving
does on a hot day. That helps to speed further warming and melting
in what’s
known as a positive
feedback loop.
Many plants and animals survive within a narrow range of very specific climate
conditions. As climate zones shift, some plants and animals are adapting,
but others are less-well equipped to do so.
- What’s happening?
- During recent summers, the
ice that covers the Arctic Ocean has
been retreating further
than ever measured. The
extent of Arctic ice in September 2006 was only about 80–85%
of what it was in the 1980s and 1990s.
- Many glaciers on the coasts of
Greenland and West Antarctica are melting at an accelerating
clip. When ice shelves and glacier tongues break away from the
coast (as in the spectacular Larsen
B collapse of 2002), it allows the ice upstream to flow
more quickly toward the sea. A major chunk of Antarctica's
Wilkins Ice
Shelf collapsed in the
spring of 2009 and is being monitored for further losses. For
time lapse video of melting glaciers around the world, see
the Extreme
Ice Survey website.
- Over frigid and desolate East Antarctica, the
ice cover may be increasing as
temperatures warm and snow becomes heavier. Ironically, this
increased precipitation could also be related to global warming.
- Permafrost (permanently frozen soil) is thawing
in parts of Canada, Alaska, and Siberia. The impacts include
building and road damage, sinkholes, and “drunken
forests” in and near such cities as Fairbanks, Alaska,
and Irkutsk, Russia. The thawing is destabilizing both modern
and traditional ways of life in Arctic regions.
- Glaciers are also retreating in midlatitude and
tropical mountains such as the Andes, Himalayas,
and Alps. Based on the available data, this appears to be mainly
due to gradual warming, but in some cases—such as Mt. Kilimanjaro
in Africa—reduced precipitation
may be a more significant factor.
- During recent summers, the
-
View an animation,
based on simulations produced by the Community Climate
System Model, showing the year-to-year variability of Arctic
sea ice from 1990–2049. Click here or
on the image to open a Web page with two stills and the animation,
which can be launched in a variety of formats. (©UCAR.
News media terms of use*)What can we expect?
- Summer sea ice in the Arctic could
decrease dramatically by the 2020s, according to climate-model
studies that
also suggest virtually ice-free Arctic summers are possible by 2040.
The ice loss threatens the survival of polar bears and other
Arctic species.
- The melting of ice from Greenland, West Antarctica,
and glaciers elsewhere will add to sea-level rise, which could
range from 7 to 24 inches by 2100 according to the IPCC’s
most recent estimates. However, some aspects of melting that
could speed glacial loss are not fully represented in models
or in the IPCC’s
own estimates because they remain poorly understood. An NCAR study
in 2006 found
that the Arctic’s summer warmth
by 2100 could match that of 130,000 years ago, when sea levels
were rising to 20 feet above today’s
levels. Even if levels rise far less than that, a 2009 study suggests
the coastal United States, and particularly the northeast from
New York up through Canada, is especially vulnerable.
- Most of the world’s permafrost could thaw
by the end of this century, an
NCAR study found in 2004.
- Tropical and midlatitude glaciers will continue
to retreat. Some projections show, for example, that the namesakes
of Glacier National Park could be gone by 2030.
- Summer sea ice in the Arctic could
Plant life
- What’s happening?
-
Can't
we just plant more trees?Planting trees is one suggested
response to climate change, because trees absorb
carbon dioxide, the most abundant greenhouse
gas produced by human activity, as they grow.
But new research shows that, depending
on where they grow,
some forests
can intensify global warming, rather
than easing it.
(Image © Bruce
Molnia, Terra photographics.)At higher latitudes, such as
Canada and Russia, snow cover reflects sunlight
back into space, which helps cool the region. But
trees block the process and so contribute to warming.In
the tropics, forests catch rainfall and evaporate
it back into the air, helping cool that region.In midlatitudes, where the bulk
of the United States is located, tree planting
appears to have little overall
effect on climate,
even when the carbon absorption is taken into account.Huge swaths of forest in Canada, Alaska, and
Russia have been ravaged over the last decade by forest fires,
fed by record summer heat and drought. These fires add large
amounts of carbon dioxide, which is also the major human-produced greenhouse
gas, to the atmosphere. However, a
2006 study found that high-latitude fires may have an overall
cooling effect in the long term, as snowfall on the newly exposed
ground reflects
winter sunlight for many years afterward.
- As the climate warms, forests are also moving
north into
land that was once Arctic tundra. These trees will act to
warm the climate by darkening the surface.
-
In some northern high latitudes, the growing
season is up to two weeks longer than in the
1950s. Sakura, Japan's most common species of
cherry blossom, now blooms five days earlier. Some
plant species are moving northward in search of the
cooler climate they need to reproduce.
- Warmer winter nights and
fewer cold snaps in New
England have helped reduce yields of maple syrup.
This climate-related decline is one of several
factors involved in shifting syrup production
from the United States to Canada over the last 40 to 50 years.
-
- What can we expect?
- Periods of high fire risk will continue
to lengthen across northern forests, with
large increases in the areas burned, according
to the IPCC.
- New England’s climate will no longer
support maple trees by later this century,
according to the
U.S. National Assessment of climate.
- Agriculture will continue to be affected by changes
in growing season, precipitation patterns, number of frost days,
number and intensity of heat waves, ranges of predatory insects,
and more.
- Periods of high fire risk will continue
Wildlife
- What’s happening?
- Some animal species are already shifting
toward higher elevations or higher latitudes, as warming
intersects with other natural and human-produced environmental
change. A landmark 2003
survey found that more than a third of 677 species examined
had been affected by climate change, moving an average of 3.7
miles poleward per decade and/or 20 feet up in elevation. Pika,
diminutive rodents found in mountainous parts of North America
and Asia, have disappeared from more than half of their range
in the U.S. Great Basin in the last century. A 2006 report based
on 800 scientific studies concludes that many species cannot
keep pace with climate change and face extinction.
- Warmer ocean temperatures, most evident during El
Niño events, have weakened or killed off
coral species during "bleaching" incidents.
More than 15% of the world’s reefs were damaged
by ocean warming associated with the 1997–98 El
Niño. Warming waters and related changes are also
helping push some algae, plankton, and fish species poleward.
- Another threat to coral reefs arises from changes
in the chemistry of ocean water that make the water less alkaline
as it absorbs carbon dioxide from the atmosphere. Scientists
are investigating the potential harm to marine life from this
process of ocean
acidification.
- A reduction in the intensity of winter cold snaps
is expanding the range where some insects can
flourish. Mountain pine beetles and spruce budworm have invaded
forests across western North America. The U.S. range of fire
ants has expanded each year since the 1960s by an area
the size of New Hampshire.
- More than 30% of amphibian
species have been
recognized as vulnerable, endangered, or critically
endangered. There are multiple causes, including
the interaction of warming temperatures with rainfall
cycles and seasonality, as well as ozone depletion,
pollution, and other environmentally induced stresses.
- Bird species never before noted
in the traditional knowledge of the Inuit people, such as robins
and sparrows, are now being observed in the
far north.
- Some animal species are already shifting
- What can we expect?
- Many species now stressed by climate change
will continue to be affected. According to
the IPCC, some 20–30% of plant
and animal species assessed thus far are likely
to be at increased risk of extinction if the global average
temperature warms more than about 2.7–4.5°F (1.5–2.5°C), which may occur
by later this century.
- Temperature and precipitation change
will influence the territory of mosquitoes
and other disease-carrying insects. For
some ailments, such as malaria, the areas
of prevalence may expand in some regions
and contract in others. Climate is one
of many factors influencing insect-borne
diseases. Scientists are working to better
understand a variety of issues involving climate
and health.
- Coral reefs are expected to continue
declining as ocean temperatures warm and
ocean chemistry becomes less alkaline.
- Many species now stressed by climate change
