Observations
Evidence
of Warming:
- The global mean surface temperature increased
by about
.6º C over the 20th century.
(IPCC Scientific Basis Report 2001)
- Glaciers have retreated.
(Global Warming: Opposing Viewpoints)
- The sea level has risen 10 - 25 cm over the past
century.
(Global Warming: Opposing Viewpoints)
- The 9 warmest years on record have all occurred since
1980.
(Global Warming: Opposing Viewpoints)
- Studies show animals/plants changing their distribution,
behavior and migration patterns in
response to climate shift.
(Union of Concerned Scientists)
- 1998 was the single warmest year of the millenium.
(EPA)
Greenhouse
Gas Concentrations:
- Since 1750, carbon dioxide concentrations have increased
31% (to 360 parts per million). This
concentration has
not been exceeded in at least 420,000 years,
and it's likely
(66-90%) that they have not been exceeded in
the past 20
million years.
- The current rate of carbon dioxide increase hasn't been
seen in
at least 20,000 years.
- About 3/4 of human emissions of carbon dioxide during
the past
20 years are due to burning fossil
fuels. about 1/4 are due to
land-use changes (deforestation, for
example).
- Currently, the ocean and land are able to remove about
1/2 of
human emissions of carbon dioxide
from the atmosphere.
- Since 1750, methane concentrations have
increased 151%; or
1060 ppb (parts per billion). This
concentrations exceeds any
in the past 420,000 years.
- Slightly more than 1/2 of methane emissions are
human-induced (fossil fuel use, cattle
raising, rice agriculture,
landfills and carbon monoxide
emissions).
- Since 1750, concentrations of nitrous oxide has
increased by
17% (46 ppb). The present concentrations has
not been seen in
1,000 years.
- About 1/3 of nitrous oxide emissions are human-induced
(through agricultural soils, cattle feed lots
and chemical
industry).
- Since 1995, many halocarbon gases (which are both ozone
depleting and greenhouse gases) are either
increasing more
slowly, or decreasing. Their substitutes
(which are not ozone
depleting, but are still greenhouse gases) are
increasing.
- Ozone in the troposphere is estimated to have increased
by
36% since 1750 due to human emissions.
-IPCC Scientific Basis Report 2001
- For the last 10,000 years, we've had a constant
concentration
of carbon dioxide in our atmosphere;
approximately 280 ppm
(parts per million). About 100 years ago, as
we burned more
coal and oil, the concentration began to
increase. Today it's
risen to 360 ppm. A concentration this high
has not been
seen in at least 420,000 years.
-E-Magazine & the EPA
Human
Activity:
- Computer models show that the warming over the
past 100
years is very unlikely (1-10% chance) to be
due to natural
causes alone.
- While simulations show that natural processes (such as
solar
and volcanic activity) contributed to the
global warming
experienced in the 1st half of the 20th century, the
natural
occurrences cannot explain the warming in the
2nd half of the
20th century.
- The best agreement between the model simulations and the
actual recorded observations over the last 140
years can be
found when both the natural and anthropogenic
(human)
forcings (impacts on the climate) are
included.
- The IPCC concludes that ". . . most of the observed
warming
over the last 50 years is likely (66-90%
chance) to have been
due to the increase of greenhouse gas
concentrations."
-IPCC Scientific Basis Report 2001
Ice/Snow
Cover:
- Satellite data show that it is very likely
(90-99% chance) that
snow and ice cover has decreased about 10%
since the late
1960s.
- Data show a widespread retreat of mountain glaciers in
non-polar regions in the 20th century.
- There are no significant trends in Antarctic sea-ice
(reduction
or increase) since 1978.
- Since the 1950s, the amount of spring and summer sea-ice
present in the Northern Hemisphere has
decreased by
about 10 to 15%.
- It's likely (66-90% chance) that there has been a 40%
decline
in Arctic Sea Ice thickness in late
summer/early autumn over
recent decades.
-IPCC Scientific Basis Report 2001
Natural
Variables:
- Positive radiative forcing (warming) due to solar
activity occurred
mostly during the 1st half of the 20th
century.
- Aerosols from volcanic eruptions produce negative
forcing
(a cooling). Major eruptions occurred
from 1880 to 1920 and
from 1960 to 1991.
- When the enhanced greenhouse effect is left out, and
both
the solar and volcanic events combined,
the overall effect on
the earth's climate is negative
(cooling), at least for the
past 2 to 4 decades.
-IPCC Scientific Basis Report 2001
Precipitation:
- During the 20th century, it's very likely (90-99% chance)
that
precipitation has increased by about .5-1% per
decade over
most mid-high latitudes in the Northern
Hemisphere. It's also
very likely (90-99% chance) that there has
been a 2-4%
increase in frequency of heavy precipitation
events over the
same area/time frame.
- It's likely (66-90% chance) that during the 20th century,
precipitation over tropical land has increased
by .2 -.3% per
decade. It's also likely (66-90% chance) that
rainfall over
sub-tropical land areas in the Northern
Hemisphere has
decreased about .3% per decade.
- There is insufficient data to make any conclusions
concerning
precipitation over oceans, and the
Southern Hemisphere has
seen no consequential change over the
20th century.
-IPCC Scientific Basis Report 2001
Sea
Level:
- Tide gauge data show that the global average sea level
rose
about .1 to .2 meters over the 20th century.
- The global ocean heat content has increased since the
1950s.
-IPCC Scientific Basis Report 2001
- The sea level has risen 3 times faster over the past 100
years
compared to the past 3,000 years.
-Union of Concerned Scientists
Temperatures:
- Over the 20th century, the global average surface
temperature
has increased by about .6º C (± 2º
C). these numbers take into
account the urban-heat island effect.
- It's very likely (90-99% chance) that the 1990s were the
warmest
decade, and 1998 the warmest year since
1861. It's likely
(66-90% chance) that these have also
been the warmest
decade/year of the millenium.
- From 1950 to 1993, nighttime minimum temperatures over
land
masses have increased about .2º C per
decade.
- From 1950 to 1993, daytime maximum temperatures over
land
masses have increased about .1º C per
decade.
- A few areas of the globe have not warmed, mainly over some
parts of the Southern Hemisphere's
oceans, and Antarctica.
- Weather balloon data from 1950 to the present show a .1º C
increase in warming per decade in the
lowest 8 km of the
atmosphere.
- Since 1979, satellite/weather balloon data show
that the global
average temperature in the lowest 8 km
of the atmosphere has
increased by about .05º C (± .10º C)
per decade, while surface
temperatures increased by about .15º C
(± .05º C). The
difference between the atmospheric
temperatures and the
surface temperatures occurred mainly
over tropical/subtropical
regions. The lowest 8 km of the
atmosphere and the surface of
the earth are influenced differently by
ozone depletion, aerosols
and El Ninos, therefore it is reasonable
to expect some
differences, however the matter is not
fully resolved.
- IPCC Scientific Basis Report 2001
- Up until the 1970s, the earth was warming at a rate of 1
degree
Fahrenheit per century. In the last 20 years,
it's been warming at
a rate of 4 degrees F.
- E - Magazine
- The rate of warming in the 20th century has been greater
than
at any other time in the past 400-600 years.
- Union of Concerned Scientists
Weather:
- It's likely that there has been a 2% increase in cloud
cover at
mid-high latitudes during the 20th century.
- El Ninos have been more frequent/intense since the
mid-1970s
compared w/previous 100 years.
- From 1900 to 1995, there were small increases in areas
receiving extreme drought or wetness.
- In some regions; like parts of Asia and Africa,
frequency/intensity of droughts has increased
in recent
decades.
- There are no significant trends in
tropical/extra-tropical storm
intensity/frequency.
- There have been no systematic changes in the frequency
of
tornadoes, thunder days of hail in the
few areas studied.
-IPCC Scientific Basis Report 2001
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