Global Change
 According to the National Academy of Sciences, the Earth's surface temperature has risen by about 1 degree Fahrenheit in the past century, with accelerated warming during the past two decades. There is new and stronger evidence that most of the warming over the last 50 years is attributable to human activities. Human activities have altered the chemical composition of the atmosphere through the buildup of greenhouse gases – primarily carbon dioxide, methane, and nitrous oxide. The heat-trapping property of these gases is undisputed although uncertainties exist about exactly how earth's climate responds to them.
  Our Changing Atmosphere
Energy from the sun drives the earth's weather and climate, and heats the earth's surface; in turn, the earth radiates energy back into space. Atmospheric greenhouse gases (water vapor, carbon dioxide, and other gases) trap some of the outgoing energy, retaining heat somewhat like the glass panels of a greenhouse.
Information on how the greenhouse affect effects the earth. Without this natural "greenhouse effect," temperatures would be much lower than they are now, and life as known today would not be possible. Instead, thanks to greenhouse gases, the earth's average temperature is a more hospitable 60°F. However, problems may arise when the atmospheric concentration of greenhouse gases increases. Since the beginning of the industrial revolution, atmospheric concentrations of carbon dioxide have increased nearly 30%, methane concentrations have more than doubled, and nitrous oxide concentrations have risen by about 15%. These increases have enhanced the heat-trapping capability of the earth's atmosphere. Sulfate aerosols, a common air pollutant, cool the atmosphere by reflecting light back into space; however, sulfates are short-lived in the atmosphere and vary regionally.
  Emissions
 Once, all climate changes occurred naturally. However, during the Industrial Revolution, we began altering our climate and environment through changing agricultural and industrial practices. Before the Industrial Revolution, human activity released very few gases into the atmosphere, but now through population growth, fossil fuel burning, and deforestation, we are affecting the mixture of gases in the atmosphere.
 
  What Are Greenhouse Gases?

Some greenhouse gases occur naturally in the atmosphere, while others result from human activities. Naturally occuring greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Certain human activities, however, add to the levels of most of these naturally occurring gases:

Carbon dioxide is released to the atmosphere when solid waste, fossil fuels (oil, natural gas, and coal), and wood and wood products are burned.

Methane is emitted during the production and transport of coal, natural gas, and oil. Methane emissions also result from the decomposition of organic wastes in municipal solid waste landfills, and the raising of livestock.

Nitrous oxide is emitted during agricultural and industrial activities, as well as during combustion of solid waste and fossil fuels.

Very powerful greenhouse gases that are not naturally occurring include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6), which are generated in a variety of industrial processes.
Each greenhouse gas differs in its ability to absorb heat in the atmosphere. HFCs and PFCs are the most heat-absorbent. Methane traps over 21 times more heat per molecule than carbon dioxide, and nitrous oxide absorbs 270 times more heat per molecule than carbon dioxide. Often, estimates of greenhouse gas emissions are presented in units of millions of metric tons of carbon equivalents (MMTCE), which weights each gas by its GWP value, or Global Warming Potential

The chemical composition of the atmosphere has changed dramatically since the pre-industrial era. Emissions of many chemical species have been increased as a result of human activities, specifically in relation with agricultural practices and industrial activities. In the last 150 years, most of these changes have occurred at mid-latitudes in the Northern hemisphere. Today, rapid population growth and economic development in tropical countries including Asia and South America make these regions particularly vulnerable to chemical pollution. The impact of mega cities on the regional and global environment becomes an increasingly scientific and political issue. The role of biomass burning as a source of large-scale pollution, especially in the tropics during the dry season, has also been emphasized at many occasions

 

The tropics (which cover nearly half of the Earth’s surface) play a key role for the chemistry of the global troposphere due to the following reasons:
(1) with the high levels of incoming solar energy, this region is photochemically very active, and contributes efficiently to the oxidizing power of the atmosphere,
(2) because of the high amounts of biomass present on the continents and the high temperatures at the surface, biogenic emissions of natural hydrocarbons are very high,
(3) bio-mass burning provides a major source for many chemical species
(4) the presence of large electrically active storms provides a major source of reactive nitrogen
(5) vertical exchanges of mass are rapid due to the presence of large convective systems, and finally
(6) human-induced changes will be most rapid in this region of the world.

Carbon dioxide is the main culprit.The single human activity that is most likely to have a large impact on the climate is the burning of "fossil fuels" such as coal, oil and gas. As people burn more fossil fuel for energy they add more carbon dioxide to the atmosphere. If this goes on long enough, the average temperature of the atmosphere will almost certainly rise.Coal and oil contain sulfur. When they are burned the sulfur is transformed into fine particles in the atmosphere. This sulfur pollution contributes to various environmental problems.Also the main cause of the hole in the ozone layer is chlorofluorocarbons (CFCs), gases that are used in refrigerators, air conditioners, and industrial applications.
Human activities that are...

* major contributors to possible climate change: coal, oil, and natural gas, when burned release carbon dioxide, the most important greenhouse gas.
* modest contributors to possible climate change: deforestation: when wood is burned, the carbon contained in the trees is released as carbon dioxide. When wood rots in swamps methane can be produced. Living trees remove carbon dioxide from the atmosphere, rice paddies, cattle, coal mines, gas pipelines, and landfills produce methane, another greenhouse gas, which today causes about 30% as much warming as carbon dioxide,  fertilizers and other chemicals release nitrous oxide, which today causes about 10% as much warming as carbon dioxide.
* not significant causes of climate change: aerosol spray cans, nuclear power, the space program,toxic waste
Obviously, climate has a big influence on plants and animals in the natural environment, on oceans, and on human activities, such as agriculture, water supplies, and heating and cooling

 

  Conclusion:
The geographical extent of the climate response to human-induced emissions of chemical species depends primarily on the atmospheric lifetime of these species. Long-lived gases such as carbon dioxide, methane, nitrous oxide and the chlorofluorocarbons have a global impact, while shorter-lived species such as tropospheric ozone and aerosols affect the radiative fields primarily at the regional scale (in the regions of most intense pollution). The overall response of the Earth system to chemical perturbations remains a topic of active research. An important contribution to such studies is the documentation of temporal changes in the chemical composition of the troposphere and of the middle atmosphere, and specifically of long-term trends and interannual variations.