搜尋結果
List of S&P 500 companies. Appearance. The S&P 500 is a stock market index maintained by S&P Dow Jones Indices. It comprises 503 common stocks which are issued by 500 large-cap companies traded on American stock exchanges (including the 30 companies that compose the Dow Jones Industrial Average ).
Renewable energy (or green energy) is energy from renewable natural resources that are replenished on a human timescale. The most widely used renewable energy types are solar energy, wind power and hydropower. Bioenergy and geothermal power are also significant in some countries.
Recycling is the process of converting waste materials into new materials and objects. This concept often includes the recovery of energy from waste materials. The recyclability of a material depends on its ability to reacquire the properties it had in its original state. [1] .
Academi, formerly known as Blackwater and Blackwater Worldwide, is an American private military contractor founded on December 26, 1996, [2] by former Navy SEAL officer Erik Prince. [3] [4] It was renamed Xe Services in 2009, and was again renamed to Academi in 2011, after it was acquired by a group of private investors. [5]
- Properties and Mechanisms
- Contributions of Specific Gases to The Greenhouse Effect
- List of All Greenhouse Gases
- Factors Affecting Concentrations
- Monitoring
- Types of Sources
- History of Discovery
- Other Planets
- See Also
- External Links
Greenhouse gases are infrared active, meaning that they absorb and emit infrared radiation in the same long wavelength range as what is emitted by the Earth's surface, clouds and atmosphere.: 2233 99% of the Earth's dry atmosphere (excluding water vapor) is made up of nitrogen (N2) (78%) and oxygen (O2) (21%). Because their molecules contain two at...
Anthropogenic changes to the natural greenhouse effect are sometimes referred to as the enhanced greenhouse effect.: 2223 This table shows the most important contributions to the overall greenhouse effect, without which the average temperature of Earth's surface would be about −18 °C (0 °F), instead of around 15 °C (59 °F). This table also specifie...
The contribution of each gas to the enhanced greenhouse effect is determined by the characteristics of that gas, its abundance, and any indirect effects it may cause. For example, the direct radiative effect of a mass of methane is about 84 times stronger than the same mass of carbon dioxide over a 20-year time frame. Since the 1980s, greenhouse ga...
Atmospheric concentrations are determined by the balance between sources (emissions of the gas from human activities and natural systems) and sinks (the removal of the gas from the atmosphere by conversion to a different chemical compound or absorption by bodies of water).: 512
Greenhouse gas monitoring involves the direct measurement of atmospheric concentrations and direct and indirect measurement of greenhouse gas emissions. Indirect methods calculate emissions of greenhouse gases based on related metrics such as fossil fuel extraction. There are several different methods of measuring carbon dioxide concentrations in t...
Natural sources
The natural flows of carbon between the atmosphere, ocean, terrestrial ecosystems, and sediments are fairly balanced; so carbon levels would be roughly stable without human influence. Carbon dioxide is removed from the atmosphere primarily through photosynthesis and enters the terrestrial and oceanic biospheres. Carbon dioxide also dissolves directly from the atmosphere into bodies of water (ocean, lakes, etc.), as well as dissolving in precipitation as raindrops fall through the atmosphere....
Human-made sources
The vast majority of carbon dioxide emissions by humans come from the burning of fossil fuels. Additional contributions come from cement manufacturing, fertilizer production, and changes in land use like deforestation.: 687 Methane emissions originate from agriculture, fossil fuel production, waste, and other sources. If current emission rates continue then temperature rises will surpass 2.0 °C (3.6 °F) sometime between 2040 and 2070, which is the level the United Nations' Intergovernmental P...
In the late 19th century, scientists experimentally discovered that N2 and O2 do not absorb infrared radiation (called, at that time, "dark radiation"), while water (both as true vapor and condensed in the form of microscopic droplets suspended in clouds) and CO2 and other poly-atomic gaseous molecules do absorb infrared radiation. In the early 20t...
Greenhouse gases exist in many atmospheres, creating greenhouse effects on Mars, Titan and particularly in the thick atmosphere of Venus. While Venus has been described as the ultimate end state of runaway greenhouse effect, such a process would have virtually no chance of occurring from any increases in greenhouse gas concentrations caused by huma...
Media related to Greenhouse gasesat Wikimedia CommonsAtmospheric spectra of GHGs and other trace gases. Archived 25 March 2013 at the Wayback Machine.Alibaba Group Holding Limited, branded as Alibaba, is a Chinese multinational technology company specializing in e-commerce, retail, Internet, and technology.
IP code. The IP code or ingress protection code indicates how well a device is protected against water and dust. It is defined by the International Electrotechnical Commission (IEC) under the international standard IEC 60529 [1] which classifies and provides a guideline to the degree of protection provided by mechanical casings and electrical ...
