IS CLIMATE CHANGE] [FACTORS
AFFECTING GLOBAL CLIMATE] [NATURAL FACTORS] [HUMAN
FACTORS] [CLIMATE TRENDS]
Change is a change occurring in the climate during a period
of time that can range from decades all the way up to centuries.
The term refers to changes caused both by nature and changes
that are caused by human beings. The term “climate variability”
refers to shorter periods ranging from years to decades which
show climate fluctuations such as the ones caused by the “El
The United Nations Framework
Convention on Climate Change (UNFCCC) defines this phenomenon
as: "a change of climate which is attributed directly or
indirectly to human activity that alters the composition of
the global atmosphere and which is in addition to natural climate
variability observed over comparable time periods”. In other
words, the UNFCCC is using the term climate change to refer
to changes produced by the activities of human beings.
AFFECTING GLOBAL CLIMATE
There are many factors of
both natural and human origin that determine the Earth’s climate.
The Sun is the primary source
of energy controlling the status of weather and climate on the
Earth. Radiation coming from the Sun is intercepted by the Earth,
and one third of this solar radiation is reflected back into
space. The other two thirds are absorbed by different parts
of the climate system: the atmosphere, the oceans, glacial areas,
soils and different kinds of life.
The Earth also sends its
energy back into space in the form of long wavelength radiation.
Some of this energy is re-absorbed and is therefore kept on
the Earth through a process known as the Greenhouse Effect.
The rest of this energy is lost in space.
There is a delicate balance
between this radiation that is leaving and solar energy that
is arriving. Any change in the factors affecting this balance
of energy that is coming and going, or in the actual distribution
of energy, can change the Earth’s climate. Factors affecting
climate are classified among:
FACTORS AFFECTING CLIMATE
There have been changes in
climate throughout the Earth’s history. The Ice Age and some
other warmer periods are examples of this. Some of these changes
have been on a global scale, while others have been on a regional
or hemispheric scale. The natural factors causing climate changes
are described below:
in the Production of Solar Energy
The amount of energy emitted
by the Sun is not constant. There is evidence that the amount
of energy produced by the Sun varies over an 11 year period,
which affects the Earth’s temperature. It should also be mentioned
that solar periods may be shorter or longer.
in Distance and Position of the Earth with Respect to the Sun
Slow variations in the Earth’s
distance and position with respect to the Sun change the place
and time at which solar energy is delivered to the planet. This
affects the amount of energy that is reflected and absorbed
by the Earth, and determines the seasons.
Changes in the Earth’s
Angle of Inclination
Slight variations in the
Earth’s angle of inclination with respect to the polar axis
can cause variations in the amount of solar energy reaching
the Earth’s surface. It is believed that such variations were
a factor at the beginning of the Ice Age.
energy that is able to get through the atmosphere serves to
heat the Earth’s surface. This energy is then released from
the surface toward space as infrared radiation. The greenhouse
gases (water vapor, carbon dioxide, methane, nitrous oxides,
ozone, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride)
that are present in the atmosphere absorb a large proportion
of the infrared radiation emitted by the Earth, thus preventing
this energy from escaping directly from the Earth’s surface
into space. This radiation is then released into the atmosphere
by air currents, evaporation, rain, etc. If the surface of the
Earth could freely irradiate energy, our planet would be a cold,
lifeless place, so therefore the greenhouse gases help maintain
a proper temperature for life on Earth. When the atmosphere’s
capability for absorbing infrared radiation becomes increased
due to the presence of an excess of greenhouse gases, there
is an alteration in climate because the balance between energy
entering and energy leaving the atmosphere is upset. Global
overheating is then caused when infrared radiation is not able
to leave the Earth. According to the United Nations Environment
Program (UNEP), if greenhouse gases continue to be emitted at
the current rate, during the next decade the Earth will cease
to emit 2% of its energy toward space, which is the same as
retaining the energy content of 3 million tons of petroleum
FACTORS AFFECTING CLIMATE
are different greenhouse gases. The most common one that represents
over 60% of the total amount of these gases is carbon dioxide
(CO2). Carbon dioxide is mainly generated by the
use of fossil fuels such as petroleum, gas and coal, and therefore
the energy sector is the main contributor to global warming.
Industries are generating 21% of this gas, while electric power
generation is emitting 36% and transportation is contributing
with 27% of total CO2 emissions coming from combustion
second most important gas is methane (CH4). Methane
is mainly generated by agricultural and livestock activities,
and amounts to between 15 and 20% of the planet’s greenhouse
United States is the largest producer of greenhouse gases on
the American continent, and it is also at the top of the world’s
list of emitters, with a production of 5,324 million tons of
CO2 emitted in 1996. Canada is in second place in
emissions with 469 million tons emitted and is followed by Mexico
with 342 million tons emitted for the same year.[ii] Therefore, the northern part of the continent is the largest
generator of emissions, but there is a big difference between
Mexico, which is emitting approximately 2% of the total and
the United States, which is emitting over 20%. On the other
hand, there are countries like Costa Rica that are emitting
close to 4 million tons annually of CO2, which are
also vital due to their wealth of forest resources.
human beings continue to turn the forests and jungles into lands
for agriculture and livestock raising or to pave them over with
asphalt and concrete, the way in which the Earth’s surface reflects
sunlight and allows heat to escape will continue to become substantially
altered. Forests are also absorbers of CO2 and generators
of oxygen, and between 20 and 50 times more carbon is absorbed
by unit of area in forests than on lands used for agricultural
beings are filling the atmosphere with large amounts of fine
particles (aerosols) coming from both agricultural and industrial
activities. Although most of these aerosols are quickly removed
by gravity and rain, they are affecting the radiation balance
in the atmosphere.
review of temperature records shows that the Earth has been
heating up by an average of 0.5° C during the last 100 years.
This warming seems to have continued up to the forties. Afterwards,
there was a moderate cooling trend that continued up to the
first half of the seventies, followed by another continuous
warming from the eighties on. The eleven hottest years of the
20th century have been 1981, 1983, 1987, 1989, 1990,
1991, 1994, 1995, 1996, 1998 and 1999. During this period there
have also been changes in several of the Earth’s regions. For
example, there has been greater warming during the winter and
spring in areas of middle latitude. Cooling has also been recorded
in the North Atlantic area. Precipitation has increased in Northern
Hemisphere latitudes, especially during the colder seasons.
steady trend in global warming has been growing due to the greenhouse
effect and aerosols. However, this variation in temperature
could be within acceptable limits and could be considered to
be a natural variation.
to the United Nations Intergovernmental Panel on Climate Change,
climate change caused by “greenhouse” gases has brought about
the following effects during the most recent years of industrial
The Earth’s median temperature
has increased by 0.5° since the last century, which has caused
changes at the Earth’s surface..
Sea level has gone up about
30 cms. as a result of the thermal expansion of oceans and the
melting of polar ice.
According to the Panel, made
up of members of the United Nations Environment Program and
the World Meteorological Association, there was a consensus
in the following predictions:
There is a recognition that
the problem does exist. Although exact predictions cannot be
precisely calculated, there are alarming estimates that have
resulted in this problem being recognized by 165 countries.
If greenhouse gases continue
to be emitted at the same increasing rate, it is estimated that
the temperature will go up by between 1° and 4° C in the next
A temperature increase of
this magnitude would cause sea level increases ranging between
50 and 95 centimeters, flooding large portions of coastal areas.
Climate change also causes
droughts, storms, heat waves, changes in rainfall precipitation
National Communications, Tables of Inventories of Anthropogenic
Emissions and Removals for 1990-1995 and Projections up to 2020.
Table A.4, FCCC/SBI/1997/19/Add.1. Document available at the
World Wide Web: http://www.unfccc.int/resource/docs.html.
Internet Terra News: http://www.terra.com.mx/noticias/articulo/015758/pagina8.htm.
World Resources Institute. Climate Notes. October 1998.