* Global dimming is the gradual reduction in the amount of global direct irradiance at the Earth’s surface. Global dimming involves reduction of heat reaching the earth. It occurs when clouds reflect the sun’s rays back to space. This is being caused by use of fossil fuels, which also contribute to global warming.
* Global dimming is defined as the decrease in the amount of sunlight reaching the surface of the earth, believed to be caused by pollution in the atmosphere.
* It is the ironic counterpoint to global warming, both caused from burning fossil fuels, and both a serious potential threat to our future climate.
What is Global Dimming?
* Global Dimming is a term describing the reduction in incoming sunlight or isolation reaching the earth’s surface in the last 50 years. Studies of sunlight data show that isolation reaching the earth’s surface decreased by around 5% during the second half of the twentieth century.
* The sun shines down on the Earth, providing two of the essential elements of life: light and heat. But we live in a world of “quanta”; of measurable matter and energy. Thus, the sunlight radiating upon the earth is a matter of specific measurement. These specific measurements of the quantity of sunlight reaching the Earth’s surface did not begin in any scientifically viable way until the 1950’s. Since then, the on-going measurement shows a steady decline of solar irradiance. A “Global Dimming” of the sun of an average of 4% between 1960 and 1990.
* Global dimming, also referred to as solar dimming, is a new buzz word in the scientific community.
* Fossil fuel use, as well as producing greenhouse gases, creates other by-products. These by-products are also pollutants, such as sulphur dioxide, soot, and ash. These pollutants however, also change the properties of clouds.
Clouds are formed when water droplets are seeded by air-borne particles, such as pollen. Polluted air results in clouds with larger number of droplets than unpolluted clouds. This then makes those clouds more reflective. More of the sun’s heat and energy is therefore reflected back into space. This reduction of heat reaching the earth is known as Global Dimming.
How was it discovered?
* The global dimming effect was first brought to the attention of the scientific community in the 1980s when “Dr. Gerry Stanhill” was updating data he had collected in Israel in the 1950s. When comparing the original data with that of the 1980s, he found that the amount of sunlight reaching Israel had fallen by an astounding 0.22% per year. Based on this data, Stanhill published the finding that from 1958 to 1985 the earth had dimmed by 5.3%.
* In 1997, a similar effect was detected from research conducted on solar irradiance in Germany and subsequent research using US data over the period 1961-1990 indicated that the globe had dimmed by 4% over the period.
* The most compelling evidence of global dimming was discovered in the days immediately following the September 11,2001, terrorist attack on the World Trade Centre (commonly known as 9/11 attack) in New York.
* The 9/11 study showed that removing contrails resulted in a large increase in the daily temperature range – in other words warmer days and cooler nights. The study does not really provide a clear-cut answer to the question of whether the overall effect of the contrails is a net warming or a net cooling averaged over the whole 24 hours. This question is controversial. But what seems clear is that contrails contribute to a reduction in the amount of daytime solar radiation reaching the surface, and that this has significant effects on temperature.
Causes of Global Dimming
* Burning of Fossil Fuels & Wood:
* Two effects of fossil fuel productions are:
* Greenhouse gases that cause global warming
By-products which are pollutants that causes global dimming. The incomplete combustion of fossil fuels (such as diesel) and wood releases black carbon into the air. Though black carbon, most of which is soot, is an extremely small component of air pollution at land surface levels, the phenomenon has a significant heating effect on the atmosphere at altitudes above two kilometres (6,562 ft). Also, it dims the surface of the ocean by absorbing solar radiation.
* Presence of Aerosol Particles:
* Atmospheric aerosols from anthropogenic air pollution are considered important contributors to global dimming.
* Aerosol particles cause water droplets in clouds to be smaller and more numerous, changing the properties of the clouds to reflect more sunlight upwards instead of down onto Earth.
* Some climate scientists have theorized that aircraft contrails (also called vapour trails) are implicated in global dimming, but the constant flow of air traffic previously meant that this could not be tested.
* Hot humid from the jet exhaust air mixes with environmental air causing global dimming.
* The near-total shutdown of civil air traffic during the three days following the September 11, 2001 attacks afforded a unique opportunity in which to observe the climate of the United States absent from the effect of contrails. During this period, an increase in diurnal temperature variation of over 1 °C was observed in some parts of the U.S.
* Airborne volcanic ash:
* Airborne volcanic ash can reflect the Sun’s rays back into space and thereby contribute to cooling the planet. Dips in earth temperatures have been observed after large volcano eruptions such as Mount Agung in Bali that erupted in 1963, El Chichon (Mexico) 1983, Ruiz (Colombia) 1985, and Pinatubo (Philippines) 1991. But even for major eruptions, the ash clouds remain only for relatively short periods.
Effects of Global Dimming
* With water’s temperature getting down less rain is generated and the required amount of rain is failed to reach.
* The phenomenon underlying global dimming may also have regional effects. While most of the earth has warmed, the regions that are downwind from major sources of air pollution (specifically sulphur dioxide emissions) have generally cooled.
* Black carbon will actually increase global warming, being second only to CO2. They believe that soot will absorb solar energy and transport it to other areas such as the Himalayas where glacial melting occurs. It can also darken arctic ice reducing reflectivity and increasing absorption of solar radiation.
* Human health problems from the soot/smog.
* Environmental problems such as acid rain, drought.
* Ecological problems such as changes in rainfall patterns (as the Ethiopian famine example above reminds us) which can kill millions, if not billions.
* Vegetation will die off even more quickly.
* Soil erosion will increase and food production will fail.
* The positive effect of Global Dimming is that it covers the drastic effects of global warming.
Difference between Global Dimming and Global Warming
Global Dimming Global Warming
* Is the cooling effect.
* Is caused by fossil fuel emission, aerosols etc.
* It blocks sunlight.
* Effects of global dimming have masked the effect of global warming to some extent.
* Is the warming effect
* Is caused by greenhouse effect
* It traps sunlight
* Resolving global dimming may therefore lead to increases in predictions of future temperature rise.
Measures to prevent Global Dimming
* Global dimming can be dealt with by cleaning up emissions to reduce pollutants that create smog and other problems along with reducing the greenhouse gas emissions in parallel.
* Recycling is to return to process an object which its utility life is finished for return to make it works. It allows us to save energy and money.
* Coal is the main cause of CO2; also emission methane leads to Global Warming. We cannot stop Global Warming but we can reduce it. Shortly when we will reduce global warming, it also decreases Global Dimming.
* It is stopped by decreased by pollution.
* Global dimming is a phenomenon not well known by most of people but it has an important effect. It can be easily “repaired” but this will mean that the global warming would be even worse.
* The common thing between global warming and global dimming is that, they both are destructive to our earth. They both cause environmental and ecological problems to earth.
* If we assume that in about 20 year time developing countries will accept standards for preservation of air quality like western countries, this would be ideal conditions for acceleration of global warming. The problem lies in the fact that western countries have not limited greenhouse gases emissions; they only limited emission of tiny particles into atmosphere. Result of those measures is decreased global dimming effect, but global warming effect is still increasing because of greenhouse gases. And if this example is followed by developing countries then global dimming effect will be returning to levels before industrialization, but in the same time global warming effect will be increased because of the greenhouse gases emissions. To put it in other words, current effect of global dimming that moderate the intensity of global warming will be lost.
* Environmental Pollution and Hazards by L.R. Patro
* The complete guide to climate change by Brian Dawson
* Global Warming Cycles: Ice Ages and Glacial Retreat By Julie Kerr Casper
* Name: Shalini Raghav