Climate Change Scientists predict
increasing droughts, floods and extreme weather and say there is growing
evidence that human activities are to blame. What Is Climate
Change The planet’s climate is constantly changing. The
global average temperature is currently in the region of 15℃. Geological and
other evidence suggests that, in the past, this average may have been as high as
27℃ and as low as 7℃. But scientists are concerned that the
natural fluctuation (波动) has been overtaken by a rapid human-induced warming
that has serious implications for the stability of the climate on which much
life on the planet depends. What Is the "Greenhouse Effect"
The greenhouse effect refers to the role played by gases which effectively
trap energy from the Sun in the Earth’s atmosphere. Without them, the planet
would be too cold to sustain life as we know it. The most
important of these gases in the natural greenhouse effect is water vapor, but
concentrations of that are changing little and it plays almost no role in modern
human-induced greenhouse warming. Other greenhouse gases include
carbon dioxide, methane (甲烷) and nitrous (含氮的) oxide, which arc released by
modern industry, agriculture and the burning of fossil fuels. Their
concentration in the atmosphere is increasing-the concentration of carbon
dioxide has risen by more than 30% since 1800. The majority of
climate scientists accept the theory that an increase in these gases will cause
a rise in the Earth’s temperature. What Is the Evidence of
Warming Temperature records go back to the late 19th
century and show that the global average temperature increased by about 0.6℃ in
the 20th century. Sea levels have risen 10～20 cm-thought to be
caused mainly by the expansion of warming oceans. Most glaciers
in temperate regions of the world and along the Antarctic Peninsula are in
retreat, and records show Arctic sea-ice has thinned by 40% in recent decades in
summer and autumn. There are anomalies (异常) however-parts of the
Antarctic appear to be getting colder, and there are discrepancies between
trends in surface temperatures and those in the troposphere(对流层) (the lower
portion of the atmosphere). How Much Will Temperatures Rise
If nothing is done to reduce emissions, current climate models predict a
global temperature increase of 1.4～5.8℃ by 2100. Even if we cut
greenhouse gas emissions dramatically now, scientists say the effects would
continue because parts of the climate system, particularly large bodies of water
and ice, can take hundreds of years to respond to changes in temperature. It
also takes greenhouse gases in the atmosphere decades to break down.
It is possible that we have already irrevocably(不可撤回地) committed the
Greenland ice sheet to melting, which would cause an estimated 7m rise in sea
level. There are also indications that the west Antarctic ice sheet may have
begun to melt, though scientists caution further research is
necessary. How Will the Weather Change Globally, we
can expect more extreme weather events, with heat waves becoming hotter and more
frequent. Scientists predict more rainfall overall, but say the risk of drought
in inland areas during hot summers will increase. More flooding is expected from
storms and rising sea levels. There are, however, likely to be
very strong regional variations in these patterns, and these are difficult to
predict. What Will the Effects Be The potential
impact is huge, with predicted freshwater shortages, sweeping changes in food
production conditions, and increases in deaths from floods, storms, heat waves
and droughts. Poorer countries, which are least equipped to deal with rapid
change, will suffer most. Plant and animal extinctions are
predicted as habitats change faster than species can adapt, and the World Health
Organization has warned that the health of millions could be threatened by
increases in malaria, water-borne disease and malnutrition. What Don’t We
Know We don’t know exactly what proportion of the observed
warming is caused by human activities or what the knock-on effects of the
warming will be. The precise relationship between concentrations
of carbon dioxide (and other greenhouse gases) and temperature rise is not
known, which is one reason why there is such uncertainty in projections Of
temperature increase. Global warming will cause some changes
which will speed up further warming, such as the release of large quantities of
the greenhouse gas methane as permafrost(永久冻结带) melts. Other
factors may mitigate(减轻) warming. It is possible that plants may take more
carbon dioxide from the atmosphere as their growth speeds up in warmer
conditions, though this remains in doubt. Scientists are not
sure how the complex balance between these positive and negative feedback
effects will play out. What about the Skeptics Global
warming "skeptics" fall into three broad camps: · those who
maintain temperatures are not rising; · those who accept the
climate is changing but suspect it is largely down to natural
variation; · those who accept the theory of human-induced
warming but say it is not worth tackling as other global problems are more
pressing. Nevertheless, there is a growing scientific consensus
(舆论) that, even on top of the natural variability of the climate, something out
of the ordinary is happening and humans are to blame. A
scientific report commissioned by the U.S. government has concluded there is
"clear evidence" of climate change caused by human activities. The report, from
the federal Climate Change Science Program, said trends seen over the last 50
years "cannot be explained by natural processes alone". It found
that temperatures have increased in the lower atmosphere as well as at the
Earth’s surface. However, scientists involved in the report say better data is
badly needed. Observations down the years have suggested that
the troposphere, the lower atmosphere, is not warming up, despite evidence that
temperatures at the Earth’s surface are rising. This goes against generally
accepted tenets (原则) of atmospheric physics, and has been used by "climate
skeptics" as proof that there is no real warming. The new
report, Temperature Trends in the Lower Atmosphere, re-analyses the atmospheric
data and concludes that tropospheric temperatures are rising. This means, it
says, that the impact of human activities upon the global climate is clear. "The
observed patterns of change over the past 50 years cannot be explained by
natural processes alone, nor by the effect of short-lived atmospheric
constituents (such as aerosols and tropospheric ozone ) alone," it
says. Holes in the Data But there are some big
uncertainties which still need resolving. Globally, the report concludes,
tropospheric temperatures have risen by 0.10 and 0.20℃ per decade since 1979,
when satellite data became generally available. The wide gap between the two
figures means, says the report, that "...it is not clear whether the troposphere
has warmed more or less than the surface." Peter Thorne, of the
U.K. Meteorological Office, who contributed to the report, ascribes this
uncertainty to poor data "Basically, we’ve not been observing the atmosphere
with climate in mind," he told the BBC News website. "We’re looking for
very small signals in data that are very noisy. From one day to the next, the
temperature can change by 10℃, but we’re looking for a signal in the order of
0.1℃ per decade." The report shows up a particular discrepancy
concerning the tropics, where it concludes that temperatures are rising by
between 0.02 and 0.19℃ per decade, a big margin of error.
Additionally, the majority of the available datasets show more warming at
the surface than in the troposphere, whereas most models predict the
opposite. For Fred Singer, of the Science and Environmental
Policy Project, a prominent climate skeptic, this suggests that the report’s
support for the concept of human-induced climate change is spin rather than
substance. "The basic data in the report is quite OK," he said, "but the
interpretation that’s been given is different from what the data says." No
Inconsistency Measuring tropospheric temperatures is far
from a simple business. Satellites sense the "average" temperature of the air
between themselves and the Earth, largely blind to what is happening at
different altitudes. To compound matters, instruments on board
satellites degrade over time, orbits subtly drift, and calibration (校准) between
different satellites may be poor. Weather balloons (or
radiosondes) take real-time measurements as they ascend, but scientists can
never assess instruments afterwards; they are "fire-and-forget"
equipment. Correcting for all these potential sources of error
is a sensitive and time-consuming process. The report makes
clear recommendations for the kind of infrastructure needed to produce
higher-quality data and resolve remaining uncertainties. Key recommendations
include: · establishing reference sites for radiosonde
measurements which would increase consistency between datasets;
· making sure the operating periods of satellites overlap so instruments
can be cross-calibrated; · observing factors such as wind,
clouds, and humidity in the troposphere to make sure they are consistent with
temperature data. Such observations could produce an unambiguous
picture of tropospheric warming, removing discrepancies over the scientific
picture and providing better data which can be used to improve computer
models. In the past, the global average temperature may have been 27℃.