GLOBAL WARMING CAUSES

• The science of climate change
• Greenhouse effect
• Danger of C02 emissions
• Rundown on greenhouse gases
• Aggregated evaporation
• Rising sea levels

Changes in the shape of the Earth's orbit (or eccentricity) as well as the Earth's tilt and precession affect the amount of sunlight received on the Earth's surface. These orbital processes which function in cycles of eccentricity, tilt and years are thought to be the most significant drivers of ice ages, according to the popular theory of Mulitin Milankovitch, a Serbian mathematician (1879-1958).

Changes occurring within (or inside) the sun can affect the intensity of the sunlight that reaches the Earth's surface. The intensity of the sunlight can cause either warming (stronger solar intensity) or cooling (weaker solar intensity).

According to NASA research, reduced solar activity from the 1400s to the 1700s was likely a key factor in the “Little Ice Age” which resulted in a slight cooling of North America, Europe and probably other areas around the globe.

Volcanoes can affect the climate because they can emit aerosols and carbon dioxide into the atmosphere. Volcanic aerosols tend to block sunlight and contribute to short term cooling. According to the United States Geological Survey (USGS), the eruption of the Tambora Volcano in Indonesia in 1815 lowered global temperatures by as much as 5ºF and historical accounts in New England describe 1815 as “the year without a summer.”

Volcanoes also emit carbon dioxide (CO2), a greenhouse gas, which has a warming effect. While volcanoes may have raised pre-historic CO2 levels and temperatures, according to the USGS Volcano Hazards Program, human activities now emit 150 times as much CO2 as volcanoes.

The heating or cooling of the Earth's surface can cause changes in greenhouse gas concentrations. For example, when global temperatures become warmer, carbon dioxide is released from the oceans. When changes in the Earth's orbit trigger a warm (or interglacial) period, increasing concentrations of carbon dioxide may amplify the warming by enhancing the greenhouse effect. When temperatures become cooler, CO2 enters the ocean and contributes to additional cooling. During at least the last 420,000 years, CO2 levels have tended to track the glacial cycles That is, during warm interglacial periods, CO2 levels have been high and during cool glacial periods, CO2 levels have been low.

THE SCIENCE OF GLOBAL WARMING

The first law of the modern science of global warming and climate change is that is that a warmer Earth is directly related to the release of greenhouse gases and aerosols. The cause has been scientifically sourced to human activities that are changing the amount of radiation coming into and leaving the atmosphere.

The United Nations report by 2000 eminent scientists contends that it’s most likely (more than a 90 per cert probability) that human-made emissions have cause global warming over the past 100 years.

The science of climate change was formulated through studying the history of the Earth’s climate changes by drilling holes into portions of the Antarctic ice sheet several miles deep, consisting of ice that has accumulated over hundreds of thousands of years or longer. Paleoclimatologists (scientists who study the history of the Earth's climate) drill holes into the ice sheets to extract what are called "cylindrical cores," or "ice cores."

Ice cores have provided valuable information about the Earth’s past as they contain trapped air bubbles that can be analyzed to obtain snapshots of the composition of the atmosphere at the time the ice accumulated. Through this analysis, concentrations of greenhouse gases (CO2, CH4, N2O) dating back thousands of years or longer can be obtained with a high level of confidence.

GREENHOUSE GASES

Greenhouse gas concentrations in the atmosphere have historically varied as a result of many natural processes (e.g. volcanic activity, changes in temperature, etc). However, since the Industrial Revolution humans have added a significant amount of greenhouse gases in the atmosphere by burning fossil fuels, cutting down forests and other activities involving carbon emissions. Because greenhouse gases absorb and emit heat, increasing their concentrations in the atmosphere will tend to have a warming effect. But the rate and amount of temperature increase is not known with absolute certainty. Changes in the atmospheric concentration of the major greenhouse gases are listed below:

CO2 EMISSIONS

Carbon dioxide (CO2) concentrations in the atmosphere increased from approximately 280 parts per million (ppm) in pre-industrial times to 379 ppm in 2005, according to the National Oceanic and Atmospheric Administration's (NOAA) 2005 State of the Climate Report. This represents a 35 percent increase in recent history. Currently the CO2 concentration levels are peaking at 390 ppm, which is dangerously close to the 400 ppm - the level regarded by most climate scientists as the threshold for severe, and unmanageable climate change.

Almost all of the recent increases in CO2 atmospheric gasses are due to human activities (IPCC, 2001). The current rate of increase in CO2 concentrations is about 1.8ppmv/year. Present CO2 concentrations are higher than any time in at least the last 420,000 years (IPCC 2001).

CO2 emissions stay in the atmosphere for more than 100 years. That’s the reason for the overriding concern for the aggregated build-up of CO2 concentrations, which according to contemporary climate science, are contributing greatly to global warming.

Other than CO2 there are other emission gases that contribute to the greenhouse effect that precipitates global warming and climate change.

METHANE

Methane (CH4) is more abundant in the Earth’s atmosphere now than at any time in at least the past 420,000 years. Methane concentrations increased sharply during most of the 20th century and are now 151% above pre-industrial levels. In recent decades, the rate of increase has slowed considerably

NITROUS OXIDE

Nitrous oxide (N2O) has increased approximately 18 percent in the past 200 years and continues to increase (see Figure 3). The present concentration of N2O has not been exceeded during at least the last 1,000 years. For more information on N2O emissions and sources, see EPA’s Nitrous Oxide Site.

OZONE 03

Tropospheric ozone (O3) is created by chemical reactions from automobile, power plant and other industrial and commercial source emissions in the presence of sunlight. It is estimated that O3 has increased by about 36% since the pre-industrial era, although substantial variations exist for regions and overall trends. Besides being a greenhouse gas, ozone can also be a harmful air pollutant at ground level, especially for people with respiratory diseases and children and adults who are active outdoors.

CFC COMPOUNDS

* Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are used in coolants, foaming agents, fire extinguishers, solvents, pesticides and aerosol propellants. These compounds have steadily increased in the atmosphere since their introduction in 1928. Concentrations are slowly declining as a result of their phase out via the Montreal Protocol on Substances that Deplete the Ozone Layer.

HFC GASES

Fluorinated gases such as hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6) are frequently used as substitutes for CFCs and HCFCs and are increasing in the atmosphere. These various fluorinated gases are sometimes called "high global warming potential greenhouse gases" because, molecule for molecule, they trap more heat than CO2. For more information, visit EPA’s High Global Warming Potential Gases Site.

The burning of fossil fuels and biomass (living matter such as vegetation) has resulted in aerosol emissions into the atmosphere. Aerosols absorb and emit heat, reflect light and, depending on their properties, can either cool or warm the atmosphere. NASA’s Earth Observatory describes how aerosols can also affect how clouds form.

Sulfate aerosols are emitted when fuel containing sulfur, such as coal and oil, is burned. Sulfate aerosols reflect solar radiation back to space and have a cooling effect. These aerosols have decreased in concentration in the past two decades resulting from efforts to reduce the coal-fired power plant emissions of sulfur dioxide in the United States and other countries.

BLACK CARBON SOOT

Black carbon (or soot) results from the incomplete combustion of fossil fuels and biomass burning (forest fires and land clearing) and is believed to be a major contributor to global warming. Though global concentrations are likely increasing, there are significant regional differences.

RADIATIVE FORCING

Greenhouse gases have a positive radiative forcing because they absorb and emit heat.

Radiative forcing is the change in the balance between solar radiation entering the atmosphere and the Earth's radiation going out. Radiative forcing from greenhouse gases has increased 21.5% since 1990 as of 2006. Much of the increase (63%) has resulted from the contribution of CO2.

AGGREGATED EVAPORATION

Increasing temperatures tend to increase in aggregated evaporation, which leads to more precipitation. As average global temperatures have risen, average global precipitation has also increased, according to the IPCC.

The following precipitation trends have been observed:

* Precipitation over land has increased by about 2 percent globally since 1900 but trends have varied regionally and over time.
* Records of land-surface precipitation show an increase of about 0.5 to 1 percent per decade over much of the Northern Hemisphere's mid- and high latitudes.
* There is evidence of precipitation increases over the tropical oceans and tropical land areas during the 20th century.

In the Northern Hemisphere's mid and high latitudes, the precipitation trends are consistent with climate model simulations that predict an increase in precipitation due to human-induced warming. Observations compiled by the National Climatic Data Center show that total annual precipitation over the U.S has increased by 6.1 percent in the last century.

RISING SEA LEVELS

Sea levels are rising worldwide. Tide gauge measurements suggest that sea level has risen worldwide approximately 6-8 inches (15-20 cm) during the last century, according the UN IPCC. A significant amount of sea level rise has likely resulted from the observed warming of the atmosphere and the oceans.

The primary factors driving the past century's sea level rise include:

* The expansion of ocean water caused by warmer ocean temperatures (contributing approximately 1-3 inches or 3-7 cm)
* The melting of mountain glaciers and small ice caps (contributing approximately 1-2 inches or 2-4 cm)

Other factors may also be responsible for part of the historic rise in sea level, including the pumping of ground water for human use and the melting of polar ice sheets in response to the warming that has occurred since the last ice age.

While the global average sea level rise of the 20th century was 6-8 inches, the sea level has not risen uniformly from region to region.

Globally:

    * Australia, New Zealand, and Pacific atoll nations appear to have average rates of sea level rise, suggesting that they are neither sinking nor uplifting.
    * Bangkok, Thailand is experiencing above average sea level rise due to the rapid sinking that has arisen from groundwater pumping.
    * Bangladesh is experiencing unusually high rates of sea level rise due to river delta subsidence.
    * Many coastal areas outside of the U.S., Europe and Japan have too few tide gauges to be sure about regional sea level rise.
In the United States:

In the USA
* Sea level has been rising 0.08-0.12 inches per year (2.0-3.0 mm per year) along most of the U.S. Atlantic and Gulf coasts.
* The rate of sea level rise varies from about 0.36 inches per year (10 mm per year) along the Louisiana Coast (due to land sinking), to a drop of a few inches per decade in parts of Alaska (because land is rising). See Figure 1 for sea level trends in selected cities.

Is the rate of sea level accelerating?

In the few locations where the tide gauge record (used to determine sea level changes) is longer than 150 years, sea level rose 1-3 inches more during the 20th century than during the 19th century.

According to the National Aeronautics and Space Administration’s (NASA) Earth Observatory, satellite measurements estimate that sea level rose from 9 to 13 inches over the last 100 years.