Global warming refers to the average gradual increase in planet-wide temperatures.

The temperature of the earth depends on the amount of sunlight received, the amount absorbed by the earth and then reflected back into space and the extent to which the atmosphere retains the heat. There is a natural ‘greenhouse effect’ which keeps the Earth’s average temperature warm enough (about 16 °C or 60 °C) to be habitable. This effect is due to the pressure of water vapour and carbon dioxide as ‘greenhouse gases’ found naturally in the atmosphere. Sunlight penetrates the atmosphere to warm the earth’s surface. The energy radiated from the Earth as infrared radiation is absorbed by the water vapour and carbon dioxide and reradiated back to earth. Thus, greenhouse gases allow incoming solar radiation to reach earth, but absorb some of the heat radiated from the earth, thus maintaining the global temperature. This is called greenhouse effect, without which the earth would be much colder than it is.

The average temperature of the air near earth surface increased 0.74 ± 0.18 °C (1.33 ± 0.32 °F) during the last 100 years. The Intergovernmental Panel on Climate Change (IPCC) concludes, “Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations” via the greenhouse effect. Between 1880 and 1940, the average temperature increased 0.4 °C to 0.6 °C. But between 1945 and 1957, it fell 0.2°C to 0.3 °C during the period of the greatest expansion of fossil fuel use. Why? Cooling during 1950s could possibly have been due to particulates emitted by gigantic volcanic eruptions in Alaska (1953) and USSR (1956) amongst others.

Particulates: An increase in average temperature due to increase in carbon dioxide and other greenhouse concentrations was counteracted by reflection of sunlight by particulates (however other factors may have been important such as solar radiation not being constant as it follows an eleven year cycle). Particulates are produced by nearly all combustion and industrial processes, heavy industry and incinerators. Particulates have the effect of cooling the earth as small particles are effective scatterers of radiation; thus less radiation reaches the earth leading to decrease in temperature. Also, particulates helps as nuclei in condensation of water vapour in the atmosphere. This leads to increased cloudiness and more precipitation. The increased cloudiness also causes a decrease in the average temperature near the surface of the earth. Thus, we come t the statement- ‘Particulates can lower the temperature by reflecting the sunlight’

Climate models referenced by the IPCC project that global surface temperatures are likely to increase by 1.1 to 6.4 °C (2.0 to 11.5 °F) between 1990 and 2100. The range of values results from the use of differing scenarios of future greenhouse gas emissions as well as models with differing climate sensitivity. Although most studies focus on the period up to 2100, warming and sea level rise are expected to continue for more than a millennium even if greenhouse gas levels are stabilized. This reflects the large heat capacity of the oceans.

An increase in global temperatures is expected to cause other changes, including sea level rise, increased intensity of extreme weather events, and changes in the amount and pattern of precipitation. Other effects of global warming include changes in health, water resources, agricultural yields, glacier retreat, species extinctions and increases in the ranges of disease vectors.

Remaining scientific uncertainties include the amount of warming expected in the future, and how warming and related changes will vary from region to region around the globe. There is ongoing political and public debate worldwide regarding what, if any, action should be taken to reduce or reverse future warming or to adapt to its expected consequences.

Greenhouse gases in the atmosphere:

Existence of the greenhouse effect as such is not disputed. Naturally occurring greenhouse gases have a mean warming effect of about 30 °C (54 °F), without which Earth would be uninhabitable. The debate centres on how the strength of the greenhouse effect is changed when human activity increases the atmospheric concentrations of some greenhouse gases.

On Earth, the major greenhouse gases are water vapour, which causes about 36–70% of the greenhouse effect (not including clouds); carbon dioxide (CO₂), which causes 9–26%; methane (CH₄), which causes 4–9%; and ozone, which causes 3–7%. Some other naturally occurring gases contribute very small fractions of the greenhouse effect; one of these, nitrous oxide (N₂O), is increasing in concentration owing to human activity such as agriculture. The atmospheric concentrations of CO₂ and methane have increased by 31% and 149% respectively above pre-industrial levels since 1750. These levels are considerably higher than at any time during the last 650,000 years, the period for which reliable data has been extracted from ice cores. From less direct geological evidence it is believed that CO₂ values this high were last attained 20 million years ago. Fossil fuel burning has produced about three-quarters of the increase in CO₂ from human activity over the past 20 years. Most of the rest is due to land-use change, in particular deforestation.

Causes and feedbacks:

1. Carbon Dioxide From power Plants

One of the largest contributors to global warming is said to be pollution from power plants. Every time you turn on a light, you add to the tons of carbon spewed into the sky by long tubes connected to these massive coal or oil driven “machines”. According to recent studies, approximately 40% of all carbon dioxide emissions comes form power plants. Natural gas, coal, and oil are the 3 types of polluting power plants. Coal is the biggest contributor out of the 3 because of it releases more carbon than the rest of them per capita. Studies, like the one done in the film, “An Inconvenient Truth”, show that the levels of carbon in the atmosphere has increased drastically in recent years and will probably continue to increase in the years to come.

Some people believe that the levels of carbon are completely normal. According to Geocraft.com, the levels of carbon found in the atmosphere today mirror those found hundreds of thousands of years ago. They believe the scientific “proof” that global warming exists is taken out of cortexes because they look at the past 100 years instead of the bigger picture. The earth has been around of billions of years; earthquakes, monsoons, ice ages, meteors, and so forth, have all affected the earth without destroying every living thing on it.

Despite what others say, many people have created solutions for the pollution caused by power plants. For example, products that help to reduce the green house emissions have emerged. Filters that improve the quality of the air released into the atmosphere have been created to solve this problem. In addition, government regulations have been placed to force owners of large industrial buildings to improve the quality of the air produced by their buildings. Finally, hydrogen power has also become a way of reducing carbon. According to Tom Simonite using carbon is better than using water to generate power, and it is completely environmentally friendly.

2. Pollution Emitted from Cars

Driving to work in the morning is one example of this. When your stuck in traffic, how long does your car stay idle on the road, releasing it’s pollution into the air? There are approximately, 3 billion vehicles being used today. Similarly with the power plants, cars also emit carbon into the air. Cars emit millions of tons of pollutants into the air. In some dense cities, this causes some of the smog and ozone problems. 1,500 cases of cancer are reported each year from pollution according to USA based National Safety Council.

Luckily, solutions are available. Many ask, “What can I do.” One thing that can be done is a switch to more environmentally friendly vehicles such as hybrid or electric cars. Some countries are even using cars that run on hydrogen. In the near future, talk about ethanol to replace gasoline in cars seems to be a promising change.

3. Pollution from Trucks

Trucks, although less in volume, make up for a large portion of the earth’s pollution with each truck’s individual output of pollutants. The difference between cars and trucks is the type of fuel used to run them. Diesel, the standard for trucks and other vehicles used for carrying large loads, is known to be less clean than gasoline. Trucks roaring down streets can bee seen from a mile away with a tiny smoke stack blowing out the product of having to carry large amounts of goods from one place to the other.

How can our society get rid of trucks? They are vital for the economic health of certain companies. They are used to build homes and carry supplies, People go camping and carry gear with them, and the list goes on. According ucsusa.org, diesel is reaching a point where it can no longer meet the standards of government regulations. What kind of alternative can be used instead?

4. Pollution from Airplanes

Airplanes are indispensable to today’s society. Businessmen fly across the country on a daily basis to meet the demand of industry. In less than 24 hours, you can fly across the circumference of the planet traveling from the US to China. So how can you possibly blame these amazing gravity defying machines of global warming? 10% of the green house gas emissions come from airplanes. You might be going to a vacation or to a business meeting but those airplanes you travel on are releasing their pollution directly into the air they fly in.

According to the Christian Science Monitor, during the 3 days after 9/11, there was a difference of 4°F in the average highs and lows compared to other days. What caused this change? It is believed that the contrails of the air crafts are the cause of this. Following 9/11, all airplanes were grounded. This allowed scientists to see the difference in the temperatures with contrails in the sky and without them. Although airplanes do pollute the sky, they accidentally reflect some sunlight.

5. Pollution from Buildings

Although many believe those large SUV’s and Airplanes are the cause for all the commotion going on about global warming, the houses we live in may be a larger contributor. Unlike cars and airplanes, homes have a long lifespan of 50- 100 years meaning that changes in this area may be difficult to accomplish. Houses are mainly built to burn oil, or run on coal. In most houses, coal is used for electricity because it is the cheapest and most abundant resource.

To assist with this problem, architects will have to start using materials that can reduce the consumption of fuels by making them better ventilated or better at holding in heat. Government regulators must pass laws forcing contractors to follow stricter guidelines when building homes to reduce energy consumption. Finally, individuals can reduce the amount of frivolous energy they use on a daily basis.

6. Methane Stored in Water and Ice

With the increase in temperature, a fear of methane being released into the air arises. Methane is approximately 60 times stronger than carbon dioxide as a green house gas. According to scientists, in the past, a rapid release of methane has led to immense heating of the earth. In the past, when the earth’s temperature rose to a certain level, such as 8 degrees above normal, the earth’s temperature then increased an additional 14 degrees.

Methane is stored in the earths oceans and is released when the temperature increases and pressure reduces. Also, methane can be found in ice. When ice melts, methane stored in the ice is released. Scientists fear that if the earth reaches a certain temperature, it would be impossible to turn back and prevent a massive increase in temperature.

Solar variation:

Hypotheses have been proposed that variations in solar output, possibly amplified by cloud feedbacks, may have contributed to recent warming. A difference between this mechanism and greenhouse warming is that an increase in solar activity should warm the stratosphere while greenhouse warming should cool the stratosphere. Cooling in the lower stratosphere has been observed since at least 1960, which would not be expected if solar activity were the main contributor to recent warming. (Reduction of stratospheric ozone also has a cooling influence but substantial ozone depletion did not occur until the late 1970s.) Phenomena such as solar variation combined with changes in volcanic activity have probably had a warming effect from pre-industrial times to 1950, but a cooling effect since 1950. A related hypothesis is that cosmic rays may affect climate by influencing the generation of cloud condensation nuclei.

A few papers suggest that the Sun’s contribution may have been underestimated. Two researchers at Duke University have estimated that the Sun may have contributed about 40–50% of the global surface warming over the period 1900–2000, and about 25–35% between 1980 and 2000. Stott and coauthors suggest that climate models overestimate the relative effect of greenhouse gases compared to solar forcing; they also suggest that the cooling effects of volcanic dust and sulfate aerosols have been underestimated. Nevertheless, they conclude that even with an enhanced climate sensitivity to solar forcing, most of the warming during the latest decades is attributable to the increases in greenhouse gases.

In 2006, a team of scientists from the United States, Germany, and Switzerland found no net increase of solar brightness over the last thousand years. Solar cycles lead to a small increase of 0.07% in brightness over the last 30 years. This effect is far too minute to contribute significantly to global warming.A 2007 paper by Lockwood and Fröhlich found no relation between global warming and solar radiation since 1985, whether through variations in solar output or variations in cosmic rays.

Temperature changes:

Recent:

Global temperatures on both land and sea have increased by 0.75 °C (1.35 °F) relative to the period 1860–1900, according to the instrumental temperature record. This measured temperature increase is not significantly affected by the urban heat island effect. Since 1979, land temperatures have increased about twice as fast as ocean temperatures (0.25 °C per decade against 0.13 °C per decade). Temperatures in the lower troposphere have increased between 0.12 and 0.22 °C (0.22 and 0.4 °F) per decade since 1979, according to satellite temperature measurements. Temperature is believed to have been relatively stable over the one or two thousand years before 1850, with possibly regional fluctuations such as the Medieval Warm Period or the Little Ice Age.

Sea temperatures increase more slowly than those on land both because of the larger effective heat capacity of the oceans and because the ocean can lose heat by evaporation more readily than the land. Since the northern hemisphere has more land mass than the southern it warms faster; also there are extensive areas of seasonal snow cover subject to the snow-albedo feedback. Although more greenhouse gases are emitted in the northern than southern hemisphere this does not contribute to the asymmetry of warming as the major gases are essentially well-mixed between hemispheres.

Based on estimates by NASA’s Goddard Institute for Space Studies, 2005 was the warmest year since reliable, widespread instrumental measurements became available in the late 1800s, exceeding the previous record set in 1998 by a few hundredths of a degree. Estimates prepared by the World Meteorological Organization and the Climatic Research Unit concluded that 2005 was the second warmest year, behind 1998.

Anthropogenic emissions of other pollutants—notably sulphate aerosols—can exert a cooling effect by increasing the reflection of incoming sunlight. This partially accounts for the cooling seen in the temperature record in the middle of the twentieth century, though the cooling may also be due in part to natural variability.

Paleoclimatologist William Ruddiman has argued that human influence on the global climate began around 8,000 years ago with the start of forest clearing to provide land for agriculture and 5,000 years ago with the start of Asian rice irrigation. Ruddiman’s interpretation of the historical record, with respect to the methane data, has been disputed.

Pre-human climate variations:

Earth has experienced warming and cooling many times in the past. The recent Antarctic EPICA ice core spans 800,000 years, including eight glacial cycles timed by orbital variations with interglacial warm periods comparable to present temperatures.

A rapid buildup of greenhouse gases caused warming in the early Jurassic period (about 180 million years ago), with average temperatures rising by 5 °C (9 °F). Research by the Open University indicates that the warming caused the rate of rock weathering to increase by 400%. As such weathering locks away carbon in calcite and dolomite, CO₂ levels dropped back to normal over roughly the next 150,000 years.

Sudden releases of methane from clathrate compounds (the clathrate gun hypothesis) have been hypothesized as a cause for other warming events in the distant past, including the Permian-Triassic extinction event (about 251 million years ago) and the Paleocene-Eocene Thermal Maximum (about 55 million years ago).

Climate:

Scientists have studied global warming with computer models of the climate. These models are based on physical principles of fluid dynamics, radiative transfer, and other processes, with some simplifications being necessary because of limitations in computer power. These models predict that the effect of adding greenhouse gases is to produce a warmer climate. However, even when the same assumptions of future GHG levels are used, there still remains a considerable range of climate sensitivity.

Including uncertainties in future greenhouse gas concentrations and climate modelling, the IPCC anticipates a warming of 1.1 °C to 6.4 °C (2.0 °F to 11.5 °F) between 1990 and 2100. Models have also been used to help investigate the causes of recent climate change by comparing the observed changes to those that the models project from various natural and human derived causes.

Current climate models produce a good match to observations of global temperature changes over the last century, but do not simulate all aspects of climate.These models do not unambiguously attribute the warming that occurred from approximately 1910 to 1945 to either natural variation or human effects; however, they suggest that the warming since 1975 is dominated by man-made greenhouse gas emissions.

Most global climate models, when run to project future climate, are forced by imposed greenhouse gas scenarios, generally one from the IPCC Special Report on Emissions Scenarios (SRES). Less commonly, models may be run by adding a simulation of the carbon cycle; this generally shows a positive feedback, though this response is uncertain (under the A2 SRES scenario, responses vary between an extra 20 and 200 ppm of CO₂). Some observational studies also show a positive feedback.

The representation of clouds is one of the main sources of uncertainty in present-generation models, though progress is being made on this problem. There is also an ongoing discussion as to whether climate models are neglecting important indirect and feedback effects of solar variability.

Attributed and expected effects:

Though it is difficult to connect specific weather events to global warming, an increase in global temperatures may in turn cause other changes, including glacial retreat and worldwide sea level rise. Changes in the amount and pattern of precipitation may result in flooding and drought. There may also be changes in the frequency and intensity of extreme weather events. Other effects may include changes in agricultural yields, reduced summer streamflows, species extinctions and increases in the range of disease vectors.

Some effects on both the natural environment and human life are, at least in part, already being attributed to global warming. A 2001 report by the IPCC suggests that glacier retreat, ice shelf disruption such as the Larsen Ice Shelf, sea level rise, changes in rainfall patterns, increased intensity and frequency of extreme weather events, are being attributed in part to global warming. While changes are expected for overall pattern intensity, and frequencies, it is difficult to attribute specific events to global warming. Other expected effects include water scarcity in some regions and increased precipitation in others, changes in mountain snowpack, and adverse health effects from warmer temperatures.

Increasing deaths, displacements, and economic losses projected due to extreme weather attributed to global warming may be exacerbated by growing population densities in affected areas, although temperate regions are projected to experience some minor benefits, such as fewer deaths due to cold exposure. A summary of probable effects and recent understanding can be found in the report made for the IPCC Third Assessment Report by Working Group II. The newer IPCC Fourth Assessment Report summary reports that there is observational evidence for an increase in intense tropical cyclone activity in the North Atlantic Ocean since about 1970, in correlation with the increase in sea surface temperature, but that the detection of long-term trends is complicated by the quality of records prior to routine satellite observations. The summary also states that there is no clear trend in the annual worldwide number of tropical cyclones.

Additional anticipated effects include sea level rise of 110 to 770 millimeters (0.36 to 2.5 ft) between 1990 and 2100, repercussions to agriculture, possible slowing of the thermohaline circulation, reductions in the ozone layer, increased intensity and frequency of hurricanes and extreme weather events, lowering of ocean pH, and the spread of diseases such as malaria and dengue fever. One study predicts 18% to 35% of a sample of 1,103 animal and plant species would be extinct by 2050, based on future climate projections. Two populations of Bay checkerspot butterfly are being threatened by changes in precipitation, though few mechanistic studies have documented extinctions due to recent climate change.

Economics:

Some economists have tried to estimate the net economic costs of damages from climate change across the globe. Such estimates have so far failed to reach conclusive findings; in a survey of 100 estimates, the values ran from US$-10 per tonne of carbon (tC) (US$-3 per tonne of carbon dioxide) up to US$350/tC (US$95 per tonne of carbon dioxide), with a mean of US$43 per tonne of carbon (US$12 per tonne of carbon dioxide). One widely-publicized report on potential economic impact is the Stern Review; it suggests that extreme weather might reduce global gross domestic product by up to 1% and that in a worst case scenario global per capita consumption could fall 20%. The report’s methodology, advocacy and conclusions have been criticized by many economists, primarily around the Review’s assumptions of discounting and its choices of scenarios, while others have supported the general attempt to quantify economic risk, even if not the specific numbers.

In a summary of economic cost associated with climate change, the United Nations Environment Programme emphasizes the risks to insurers, reinsurers, and banks of increasingly traumatic and costly weather events. Other economic sectors likely to face difficulties related to climate change include agriculture and transport. Developing countries, rather than the developed world, are at greatest economic risk.

Adaptation and mitigation:

The broad agreement among climate scientists that global temperatures will continue to increase has led nations, states, corporations and individuals to implement actions to try to curtail global warming or adjust to it. Many environmental groups encourage action against global warming, often by the consumer, but also by community and regional organizations. There has also been business action on climate change, including efforts at increased energy efficiency and (still limited) moves to alternative fuels. One important innovation has been the development of greenhouse gas emissions trading through which companies, in conjunction with government, agree to cap their emissions or to purchase credits from those below their allowances.

The world’s primary international agreement on combating global warming is the Kyoto Protocol, an amendment to the United Nations Framework Convention on Climate Change (UNFCCC), negotiated in 1997. The Protocol now covers more than 160 countries globally and over 55% of global greenhouse gas emissions.

Only the United States (historically the world’s largest greenhouse gas emitter), Australia, and Kazakhstan have not ratified the treaty. In the absence of clear concerted action by the U.S. Federal government, various state, local, and regional governments have begun their own initiatives to indicate support and compliance with the Kyoto Protocol, on a local basis. For example, the Regional Greenhouse Gas Initiative (RGGI) is a state-level emissions capping and trading program involving eight Northeastern states, which was founded on December 20, 2005.

China (which is expected to soon overtake the U.S. in greenhouse gas emissions) and India have ratified the treaty, but as developing countries, are exempt from its provisions. Chinese Premier Wen Jiabao has called on the nation to redouble its efforts to tackle pollution and global warming.

This treaty expires in 2012, and international talks began in May 2007 on a future treaty to succeed the current one.

The world’s primary body for crafting a response is the Intergovernmental Panel on Climate Change (IPCC), a UN-sponsored activity which holds periodic meetings between national delegations on the problems of global warming, and issues working papers and assessments on the current status of the science of climate change, impacts, and mitigation. It convenes four different working groups examining various specific issues. For example, in May 2007, the IPCC held conferences in Bonn, Germany, and in Bangkok, Thailand.