Human Impacts on the Biosphere: Climate Change
By studying the Earth’s history and making comparisons with other planets, scientists have determined that
concentrations of gases in our atmosphere, particularly CO2, maintain the average temperature on Earth about 25⁰C
higher than it would be if these gases were absent. This fact emphasis that the composition of our atmosphere is a
key consideration for life on Earth. Unfortunately, human activities are now changing the composition of the
atmosphere in ways that most authorities conclude will be damaging or, in the long run, disastrous. Because of
changes in atmospheric composition, the average temperature of the Earth’s surface is increasing, a phenomenon
called global warming.
Carbon dioxide is a major greenhouse gas
In 1958, the atmosphere was 0.031% CO2. By 2004, the concentration
had risen to 0.03%. All authorities agree that the cause of this steady rise in
atmospheric CO2 is the burning of coal and petroleum products by the increasing
(and increasingly energy-demanding) human population.
Carbon dioxide (CO2). A minor but very important component of the
atmosphere, carbon dioxide is released through natural processes such as
respiration and volcano eruptions and through human activities such as deforestation, land use changes, and burning
fossil fuels. Humans have increased atmospheric CO2 concentration by a third since the Industrial Revolution began.
This is the most important long-lived "forcing" of climate change.
Other greenhouse gases
Methane. Produced in globally significant quantities in anaerobic soils and in the fermentation reactions of
ruminant mammals, such as cows, huge amounts of methane of the permafrost could cause a sudden and large
perturbation in global temperature by releasing methane rapidly.
Nitrous oxide.Agricultural use of fertilizers is the largest source of nitrous oxide emissions, with energy
consumption sezond and industrial use third.
Global temperature changed has affected ecosystems in the past and is doing so now
Evidence for warming can be seen in many ways. For example, on a worldwide statistical basis, ice on lakes
and rivers forms later and melts sooner than it used to; an average, ice-free seasons are now 2.5 weeks longer than
they were century ago. Also, the extent of ice at the North Pole has decreased substantially, and glaciers are
retreating around the world.
Global warming – and cooling – have occurred in past, most recently during the ice ages and intervening warm
periods. Species often responded by shifting their geographic ranges, tracking their environments.
A number of cold-adapted North American tree species that are now found only in the far north, or at high
elevations, lived much farther south or at substantially lower elevations 10,000-20,000 years ago, when
conditions were colder.
Many butterfly and bird species have shifted northward in recent decades.
Many migratory birds arrive earlier at the summer breeding grounds than they did decades ago.
Many insects and amphibians breed earlier in the year.
Many plants flower earlier.
Global warming affects human population as well
1. Rising sea level
The U.S. Environmental Protection agency predicts that sea level is likely to rise two or three times faster in
the 21st century because of two effects of global warming:
a) The melting of polar ice and glaciers, adding water to the ocean
b) The increase of average ocean temperature, causing an increase in volume because water
expands as it warms.
As many as 200 million people would be affected by increased flooding.
2. Other climatic effects
Global warming is predicted to have a variety of effects besides increased temperature. In particular, the
frequency or severity of extreme meteorological events such as:
3. Effects on agriculture
Global warming may have both positive and negative sides
a) Positive side
Warmer temperatures and increased atmospheric carbon dioxide tend to increase growth
of some crops and thus may increase agricultural yields.
b) Negative side
Most crops will be affected by increased frequencies of droughts. Moreover, although
crops in north temperate regions may flourish growing at their maximal temperatures, so
increased temperatures may lead to reduced crop yields. Changes in rainfall patterns,
temperature, pest distributions, and various other factors will require many adjustments.
Such changes may come relatively easily for farmers in the developed world, but the
associated costs may be devastating for those in the developing countries.
4. Effects on human health
Increasingly frequent storms, flooding, and drought will have adverse consequences on human
health. Aside from their direct effect, such events often disrupt the fragile infrastructure of developing
countries, leading to loss of safe drinking water and other problems.
In addition, as temperature rise, area suitable for tropical organisms will expand northward. Of
particular concern are those organisms that cause human diseases. Many diseases currently limited to
tropical areas may expand their range and become problematic in nontropical countries. Diseases
transmitted by mosquitoes, such as malaria, dengue fever, and several types of encephalitis.
5. Solving the problem
Global warming is now recognized, even by former skeptics, as an ongoing phenomenon caused in
large part by human actions. Even formerly recalcitrant governments now seem poised to take action, and
corporations are recognizing the opportunities provided by the need to reverse human impacts. The
resulting “green” technologies and practices are becoming increasingly common. With concerted efforts
from citizens, corporations, and governments, the more serious consequences of global climate change
hopefully can be averted.