jim(yaoxin)

Friday, March 5, 2010

green house gases

The greenhouse effect is the process by which absorption and emission of infrared radiation by gases in the atmosphere warm a planet's lower atmosphere and surface. It was discovered by Joseph Fourier in 1824 and was first investigated quantitatively by Svante Arrhenius in 1896.^[23] Existence of the greenhouse effect as such is not disputed, even by those who do not agree that the recent temperature increase is attributable to human activity. The question is instead how the strength of the greenhouse effect changes when human activity increases the concentrations of greenhouse gases in the atmosphere.

Naturally occurring greenhouse gases have a mean warming effect of about 33 °C (59 °F).^[24]^[C] The major greenhouse gases are water vapor, which causes about 36–70 percent of the greenhouse effect; carbon dioxide (CO₂), which causes 9–26 percent; methane (CH₄), which causes 4–9 percent; and ozone (O₃), which causes 3–7 percent.^[25]^[26]^[27] Clouds also affect the radiation balance, but they are composed of liquid water or ice and so are considered separately from water vapor and other gases.

Human activity since the Industrial Revolution has increased the amount of greenhouse gases in the atmosphere, leading to increased radiative forcing from CO₂, methane, tropospheric ozone, CFCs and nitrous oxide. The concentrations of CO₂ and methane have increased by 36% and 148% respectively since 1750.^[28] These levels are much higher than at any time during the last 650,000 years, the period for which reliable data has been extracted from ice cores.^[29]^[30]^[31] Less direct geological evidence indicates that CO₂ values higher than this were last seen about 20 million years ago.^[32] 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, particularly deforestation.^[33]

CO₂ concentrations are continuing to rise due to burning of fossil fuels and land-use change. The future rate of rise will depend on uncertain economic, sociological, technological, and natural developments. Accordingly, the IPCC Special Report on Emissions Scenarios gives a wide range of future CO₂ scenarios, ranging from 541 to 970 ppm by the year 2100 (an increase by 90-250% since 1750).^[34] Fossil fuel reserves are sufficient to reach these levels and continue emissions past 2100 if coal, tar sands or methane clathrates are extensively exploited.^[35]

The destruction of stratospheric ozone by chlorofluorocarbons is sometimes mentioned in relation to global warming. Although there are a few areas of linkage, the relationship between the two is not strong. Reduction of stratospheric ozone has a cooling influence, but substantial ozone depletion did not occur until the late 1970s.^[36] Ozone in the troposphere (the lowest part of the Earth's atmosphere) does contribute to surface warming.^[37]

Aerosols and soot

Ship tracks over the Atlantic Ocean on the east coast of the United States. The climatic impacts from aerosol forcing could have a large effect on climate through the indirect effect.

Global dimming, a gradual reduction in the amount of global direct irradiance at the Earth's surface, has partially counteracted global warming from 1960 to the present.^[38] The main cause of this dimming is aerosols produced by volcanoes and pollutants. These aerosols exert a cooling effect by increasing the reflection of incoming sunlight. James E. Hansen and colleagues have proposed that the effects of the products of fossil fuel combustion—CO₂ and aerosols—have largely offset one another in recent decades, so that net warming has been driven mainly by non-CO₂ greenhouse gases.^[39]

In addition to their direct effect by scattering and absorbing solar radiation, aerosols have indirect effects on the radiation budget.^[40] Sulfate aerosols act as cloud condensation nuclei and thus lead to clouds that have more and smaller cloud droplets. These clouds reflect solar radiation more efficiently than clouds with fewer and larger droplets.^[41] This effect also causes droplets to be of more uniform size, which reduces growth of raindrops and makes the cloud more reflective to incoming sunlight.^[42]

Soot may cool or warm, depending on whether it is airborne or deposited. Atmospheric soot aerosols directly absorb solar radiation, which heats the atmosphere and cools the surface. Regionally (but not globally), as much as 50% of surface warming due to greenhouse gases may be masked by atmospheric brown clouds.^[43] When deposited, especially on glaciers or on ice in arctic regions, the lower surface albedo can also directly heat the surface.^[44] The influences of aerosols, including black carbon, are most pronounced in the tropics and sub-tropics, particularly in Asia, while the effects of greenhouse gases are dominant in the extratropics and southern hemisphere.^[45]

Solar variation

Main article: Solar variation

Solar variation over the last thirty years.

Variations in solar output have been the cause of past climate changes,^[46] but solar forcing is generally thought to be too small to account for a significant part of global warming in recent decades.^[47]^[48]

Greenhouse gases and solar forcing affect temperatures in different ways. While both increased solar activity and increased greenhouse gases are expected to warm the troposphere, an increase in solar activity should warm the stratosphere while an increase in greenhouse gases should cool the stratosphere.^[4] Observations show that temperatures in the stratosphere have been cooling since 1979, when satellite measurements became available. Radiosonde (weather balloon) data from the pre-satellite era show cooling since 1958, though there is greater uncertainty in the early radiosonde record.^[49]

A related hypothesis, proposed by Henrik Svensmark, is that magnetic activity of the sun deflects cosmic rays that may influence the generation of cloud condensation nuclei and thereby affect the climate.^[50] Other research has found no relation between warming in recent decades and cosmic rays.^[51]^[52] A recent study concluded that the influence of cosmic rays on cloud cover is about a factor of 100 lower than needed to explain the observed changes in clouds or to be a significant contributor to present-day climate change.^[53]

temperature change

The most common measure of global warming is the trend in globally averaged temperature near the Earth's surface. Expressed as a linear trend, this temperature rose by 0.74 ± 0.18 °C over the period 1906–2005. The rate of warming over the last half of that period was almost double that for the period as a whole (0.13 ± 0.03 °C per decade, versus 0.07 °C ± 0.02 °C per decade). The urban heat island effect is estimated to account for about 0.002 °C of warming per decade since 1900.^[10] Temperatures in the lower troposphere have increased between 0.13 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 regionally varying fluctuations such as the Medieval Warm Period and the Little Ice Age.^[11]

Estimates by NASA's Goddard Institute for Space Studies and the National Climatic Data Center show that 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.^[12]^[13] Estimates prepared by the World Meteorological Organization and the Climatic Research Unit show 2005 as the second warmest year, behind 1998.^[14]^[15] Temperatures in 1998 were unusually warm because the strongest El Niño in the past century occurred during that year.^[16] Global temperature is subject to short-term fluctuations that overlay long term trends and can temporarily mask them. The relative stability in temperature from 2002 to 2009 is consistent with such an episode.^[17]^[18]

Temperature changes vary over the globe. Since 1979, land temperatures have increased about twice as fast as ocean temperatures (0.25 °C per decade against 0.13 °C per decade).^[19] Ocean temperatures increase more slowly than land temperatures because of the larger effective heat capacity of the oceans and because the ocean loses more heat by evaporation.^[20] The Northern Hemisphere warms faster than the Southern Hemisphere because it has more land and because it has extensive areas of seasonal snow and sea-ice cover subject to ice-albedo feedback. Although more greenhouse gases are emitted in the Northern than Southern Hemisphere this does not contribute to the difference in warming because the major greenhouse gases persist long enough to mix between hemispheres.^[21]

The thermal inertia of the oceans and slow responses of other indirect effects mean that climate can take centuries or longer to adjust to changes in forcing. Climate commitment studies indicate that even if greenhouse gases were stabilized at 2000 levels, a further warming of about 0.5 °C (0.9 °F) would still occur.^[22]

global warming cause

Global warming is the increase in the average temperature of Earth's near-surface air and oceans since the mid-20th century and its projected continuation. Global surface temperature increased 0.74 ± 0.18 °C (1.33 ± 0.32 °F) between the start and the end of the 20th century.^[3]^[A] The Intergovernmental Panel on Climate Change (IPCC) concludes that most of the observed temperature increase since the middle of the 20th century was very likely caused by increasing concentrations of greenhouse gases resulting from human activity such as fossil fuel burning and deforestation.^[3] The IPCC also concludes that variations in natural phenomena such as solar radiation and volcanic eruptions had a small cooling effect after 1950.^[4]^[5] These basic conclusions have been endorsed by more than 40 scientific societies and academies of science,^[B] including all of the national academies of science of the major industrialized countries.^[6]

Climate model projections summarized in the latest IPCC report indicate that the global surface temperature is likely to rise a further 1.1 to 6.4 °C (2.0 to 11.5 °F) during the 21st century.^[3] The uncertainty in this estimate arises from the use of models with differing sensitivity to greenhouse gas concentrations and the use of differing estimates of future greenhouse gas emissions. Most studies focus on the period leading up to the year 2100. However, warming is expected to continue beyond 2100 even if emissions stop, because of the large heat capacity of the oceans and the long lifetime of carbon dioxide in the atmosphere.^[7]^[8]

An increase in global temperature will cause sea levels to rise and will change the amount and pattern of precipitation, probably including expansion of subtropical deserts.^[9] Warming is expected to be strongest in the Arctic and would be associated with continuing retreat of glaciers, permafrost and sea ice. Other likely effects include changes in the frequency and intensity of extreme weather events, species extinctions, and changes in agricultural yields. Warming and related changes will vary from region to region around the globe, though the nature of these regional variations are uncertain.

Political and public debate continues regarding global warming, and what actions to take in response. The available options are mitigation to reduce further emissions; adaptation to reduce the damage caused by warming; and, more speculatively, geoengineering to reverse global warming. Most national governments have signed and ratified the Kyoto Protocol aimed at reducing greenhouse gas emissions.

2012/12/21

What's Supposed to Happen in 2012?

by Vanessa Tencati

Depending on who's doing the prophesying, the winter solstice in the year 2012 could usher in a day of celebration — or a day of chaos. December 21, 2012 has been marked as a special day since the time of the Maya, whose calendar first touted it as the end of a great 5,126 year cycle. Now, just a few years before the day of reckoning is upon us, the human race is forced to consider the possibility of an approaching apocalyptic nightmare. Only time will tell whether 2012 will be the end, a new beginning, or just a year like any other.

Image: Temple of the Warriors; Chichen Itza, Mexico THEORY: The End of the Maya Calendar Cycle
This is where it all begins. The Maya Long Count calendar comes to the end of a 5,126 year cycle soon—possibly on December 21, 2012. The exact date is debated, as is what will happen when we hit that date. There is no record telling us exactly what the ancient Maya expected to happen when this cycle ended and the next began. But some think they would have been worried about the end of mankind as we know it.

Image: Open Bible THEORY: Bible Code Prophecy
At least one interpretation of the Bible tells us that in the year 2012, God will destroy Earth. With the help of computers, Israeli mathematicians have discovered a supposed secret code in the Bible's text. Michael Drosnin, author of The Bible Code, also decoded the text based on the mathematicians' work. According to Drosnin's interpretations, comets are due to rain down upon Earth in both 2010 and 2012.

Image: Mathematical formula THEORY: Terrence McKenna's Timewave Zero
In the early 1970s, Terence McKenna took a trip to the Amazon rainforest, where he experienced mind-bending drugs. Upon his return, he utilized the I Ching, the ancient Chinese book of divination, to determine a mathematical formula he called "timewave zero." According to his research, this formula predicts that time will form into tighter and tighter spirals until a "final time" is reached. When this happens, the laws of physics as we currently experience them will no longer apply, and the world will suddenly enter a new era with new, unknown laws. Originally set to occur on November 17, 2012, McKenna later moved the date when he determined the occurrence of the next galactic alignment: December 21, 2012.

Image: Drawing of Nostradamus THEORY: Nostradamus' Prophecies
The infamous seer's writings have been cited as predicting such historical events as the reign of Napoleon, the tyranny of Hitler, both World Wars, and September 11th. His writings also contain a number of end of the world prophecies which have yet to occur. His written quatrains prophesize everything from earthquakes and rampant disease to the coming of an antichrist and the onset of World War III. While not specifically pinpointed to the year 2012, many believe that Nostradamus' prophecies will coincide with the end of the Maya calendar.

Image: Planet in sky THEORY: Rogue Planet Collision
Author Zecharia Sitchin wrote of a 5,000-year-old tale of planet Nibiru, home to a race of beings called the Annunaki, orbiting the sun beyond Pluto. Although dismissed by many as a myth, some believe that because of an unusual orbit, Nibiru is set to disrupt Earth in 2012. Recent science has indeed discovered a planetary body that is slightly larger than Pluto and three times farther from the sun, named Eris. Despite assurances from NASA that Eris is not headed anywhere near Earth, followers of Sitchin’s ideas fear that Eris is indeed Nibiru and will follow a rogue orbit, coming close enough to the solar system that its gravitational pull could dramatically alter the face of the Earth, wreaking unprecedented havoc on our gravity and electromagnetic fields.

Image: Blue galaxy THEORY: Galactic Alignment
In the galactic alignment, the winter solstice sun will line up perfectly with the galactic equator, an invisible line that denotes the center of the Milky Way galaxy. According to researcher John Major Jenkins, this precise alignment only occurs once every 26,000 years—and the next one is scheduled to take place by 2016. Jenkins asserts that rather than doomsday, the galactic alignment will bring about a shift in the human psyche toward a more conscious state.

Image: Solar flare THEORY: Solar Storms on Earth
Approximately every 11 years, the number of sunspots on our sun peaks at what we call a solar maximum. These sunspots, giant magnetic storms which appear as dark splotches on the sun's surface, release solar flares that vary in intensity. The next solar maximum is due to occur in 2012, and if powerful solar flares manage to penetrate Earth's weakening magnetic shield, damaging radiation could wreak havoc on the health on humankind.

Image: Glass globe upside-down THEORY: Pole Shift Hypotheses
Due to a variety of environmental or man-made factors, the north and south poles of Earth are not entirely static. There are many theories as to why this is, and what this means. The occurrence of a pole shift, where the poles would move dramatically, could cause the Earth's crust to move over the mantle and core—like an orange skin floating around above the pulpy fruit. This could result in major tsunamis, dramatic earthquakes and volcanoes, and intense climate change as the continents are pushed halfway across the globe from their current locations. A pole shift of this magnitude was predicted by psychic Edgar Cayce in 1934, who said it would start happening in the early 21st century.