In the past century, the surface temperature of our earth has risen by about one degree Fahrenheit; with the result that warming has accelerated during the past two decades. Most of the warming over the last 50 years is owing to human activities that have altered the chemical composition of the atmosphere through the buildup of greenhouse gases primarily carbon dioxide, methane, and nitrous oxide.
Solar energy that drives the earths weather and climate radiates and heats the earths surface. Some solar radiation is reflected by the earth and the atmosphere back into space. Likewise, some of the infrared radiation passes through the atmosphere, and some is absorbed and re-emitted in all directions by greenhouse gas molecules. Thus the earths atmosphere and the lower atmosphere are considerably warmed up. This is called Global Warming. Human activities in enhanced agriculture, deforestation, landfills, industrial production, and mining are also responsible for global warming. 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.
Without this natural greenhouse effect temperatures would be much lower than they are now, and life as known today would not be possible. But thanks God, due to greenhouse gases, the earths average temperature is rather hospitable to the extent of 60%. Problems may, however, 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 earths atmosphere. Why are greenhouse gas concentrations increasing? Scientists believe that the combustion of fossil fuels and other human activities are the primary reasons for the increased concentration of carbon dioxide. Plant respiration and the decomposition of organic matter release more than 10 times the CO2 released by human activities; but these releases have generally been in balance during the centuries leading up to the industrial revolution with carbon dioxide absorbed by terrestrial vegetation and the oceans.
What has changed in the last few hundred years is the additional release of carbon dioxide by human activities. Fossil fuels burned to run cars and trucks, heat emitted by homes and industrial production, and power factories are responsible for up to 98% of carbon dioxide emissions, 24% of methane emissions, and 18% of nitrous oxide emissions. As already mentioned, enhanced agriculture, deforestation, landfills, industrial production, and mining also contribute a good deal of emissions. The United States emitted about one-fifth of total global greenhouse gases in 1997.
Estimating future emissions is difficult, because it depends on demographic, economic, technological, policy, and institutional developments. Several emissions scenarios have been developed based on differing projections of these underlying factors. For example, by 2100 in the absence of emissions control policies project carbon dioxide concentrations may be 30-150% higher than todays levels.
Global mean surface temperatures have increased 0.5-1.0°F since the late 19th century. The 20th century’s 10 warmest years all occurred in the last 15 years of the century. Of these, 1998 was the warmest year on record. The snow cover in the Northern Hemisphere and floating ice in the Arctic Ocean has decreased. Globally, the sea level has risen 4-8 inches over the past century. Worldwide precipitation over land has increased by about one percent. The frequency of extreme rainfall events has also increased throughout the world.
Increasing concentrations of greenhouse gases are likely to accelerate the rate of climate change. Scientists expect that the average global surface temperature could rise 1-4.5°F(0.6-2.5°C) in the next fifty years, and 2.2-10°F (1.4-5.8°C) in the next century, with significant regional variation. Evaporation will increase as the climate warms, which will increase average global precipitation. Soil moisture is likely to decline in many regions, and intense rainstorms are likely to become more frequent.
Sea level has risen worldwide approximately 15-20 cm (6-8 inches) in the last century. Approximately 2-5 cm (1-2 inches) of the rise has resulted from the melting of mountain glaciers. Another 2-7 cm has resulted from the expansion of ocean water that resulted from warmer ocean temperatures.
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. New surveys from satellites and aircraft document an alarming acceleration in the melting of glaciers around the world. The swift retreat of these great ice streams is helping to raise ocean levels and is threatening significant changes in human, animal, and plant life.
Our Changing Atmosphere
Rising global temperatures are expected to raise the sea level and change precipitation and other local climate conditions. Changing regional climate could alter forests, crop yields, and water supplies. It could also affect human health, animals, and many types of ecosystems. Deserts may expand into existing rangelands, and features of some of our National Parks may be permanently altered.
Scientists currently are unable to determine which parts of any country will become wetter or drier, but there is likely to be an overall trend toward increased precipitation and evaporation, more intense rainstorms, and drier soils. Unfortunately, many of the potentially most important impacts depend upon whether rainfall increases or decreases, which can not be reliably projected for specific areas.
What Are Greenhouse Gases
Some greenhouse gases occur naturally in the atmosphere, while others result from human activities. Naturally occurring 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.
What Are Sinks?
A sink is a reservoir that uptakes a chemical element or compound from another part of its cycle. For example, soil and trees tend to act as natural sinks for carbon each year hundreds of billions of tons of carbon in the form of CO2 are absorbed by oceans, soils, and trees.
Today, action is being taken at every level to reduce, to avoid, and to better understand the risks associated with climate change. Many cities and states across the country have prepared greenhouse gas inventories; and many are actively pursuing programs and policies that will result in greenhouse gas emission reductions.
What difference can we make?
A little change in our lifestyle and behavior can make some big changes in greenhouse gas reductions. What difference can we make? Faced with this question collectively as individuals we can really make a lot of difference. Think back to the days before recycling became popular when everyone threw everything out in the trash. In less than 20 years, most households have gone from recycling little to nothing to recycling newspapers, plastics, glass and metal. Many businesses recycle paper and buy recycled products and many industries practice source reduction in their packaging efforts. An entire mindset has changed in one generation!
Our actions can reduce greenhouse gas emissions in addition to other benefits, including saving of money! The actions range from changes in the house, in the yard, in the car, and in the store. If we arrange to grow evergreen plants in the house and use gas kit in stead of consuming petrol in the car, we can certainly make a difference.
Researchers have discovered that as rice plants produce higher yields, they make less of the potent greenhouse gas methane. Plants that use the carbon they absorb from the atmosphere efficiently put less carbon into the soil, where it can be converted into methane. Methane is the second most important greenhouse gas, responsible for about 20% of global warming. The scientists say their findings could lead to new ways of growing rice that will curb global warming as well as producing higher yields. For Pakistan the good news is that our soil is more suitable for producing higher yields of rice.