Theory Observation |
Global Warming
IN SHORT - The Earth's atmosphere is naturally generating a greenhouse effect, without which the temperatures at our planet would be less by 30° C. The addition of manmade gases into the atmosphere is thought to add to the effect and to bring an increase of it, hence of the temperatures. Most pessimistic views are warning of dramatic temperature, vegetation zones, and sea level |
changes during the 21st century, as more rationalist views keep questioning such views and ask for science data to be scientifically collected during at last 10 years to make the balance between what effects are really due to the human activity, compared to those due to purely natural cycles. This page is giving views about the main questions related to the global warming |
What is called "global warming" is this trend which, since about 250 years, would be modifying the great balances of Earth's climate. A benevolent, natural greenhouse effect exists at Earth. As a part of sunlight is managing to reach through the atmosphere and clouds the Earth's surface, the Earth is heated. This heat is partly reflected under the form of infrared radiation. A part of this radiation is blocked by some of the gases which are naturally present in the atmosphere, like carbon dioxide, water vapor (the most important component and acting mostly in the upper troposphere), or methane. On the other hand, high-altitude, icy, cirrus clouds are another major actor as they may reflect Sun radiation, or trap the reflected infrared radiation, due to their icy crystals. Such a natural greenhouse effect is benefiting Earth. Without it Earth would endure temperatures 60° F (30° C) lower than the current ones, something like a Mars bound Earth...
The usual thinking about "global warming" is that a manmade greenhouse effect added to the natural one since the Industrial Revolution in the 1750s. Human activities added -and continue to add- gases, mostly carbon dioxide, to the atmosphere, hence more of the infrared re-emitted radiation is blocked, leading to a temperature increase. The human activities, thus, are adding gas to the Earth's natural greenhouse effect. The leading greenhouse gases (GHGs) include carbon dioxide, methane, nitrous oxide, and halocarbons. They are called ‘well mixed’ greenhouse gases because their long lifetime of a decade or more, which allows them to disperse evenly in the Earth's atmosphere. Thus, climate is thought to have changed since at least 1850, this bringing, during one century, 1° F (0.5° C) more around the world and an increase of 8 inches (20 cm) of the sea levels in the last century. Climate changes are complex however as they are due to several factors. Climate would certainly fluctuate even without human interaction, due, for example, to how the Sun's activity is varying along small -and large- periods of time, or to the various modifications of the Earth's orbit or of its axis tilt. The question, if any, is to know what the balance is between such large, slow, natural cycles and the human activity, that is: how significant are greenhouse gases against the backdrop of larger, natural climate changes? Another question is: how "self-correcting"is Earth to possible such changes? That's why most scientists point to that more data are needed, to the effect that a real assessment might be possible of what is really going on. The most pessimistic forecasts about the 21st century are that there might occur an average temperature increase of 6° F (3°. C), ecosystems and crops production disruptions, an increase of extreme weather events, a global sea level elevation of about 3 ft (0.9 meter -the global sea level has been found to have risen by 0.1 inch -3 mm- a year since 1993), and increased health ill-conditions and diseases prevalence. The latest figures, released at NASA in 2006, are stating that the Earth warmed by 0.6° C or 1.08° F over the past 30 years, as it had already warmed by 0.8° C or 1.44° F during the last 100 years. The main part of the excess heat (about 84 percent of it) is absorbed by the mass of the oceans. The temperatures at Earth, unless that, would reach a 49° F (27° C) more!. The melting of the whole of the land ice found at Earth, on the other hand, would raise the sea level by 230 ft (70 meters)
Latest Studies
. A most recent 2005 study by the NASA's Goddard Institute for Space Studies is showing like a certitude that the ocean got warmer in average over the past decade. This is matching the computed climate models which predict that the growing amounts of human-produced greenhoused gases are trapping solar radiation and lead to a warming planet. The energy in excess had not been found until now, as it seems well that the decade-long warming of the ocean is accounting for the energy excess. To increase the temperature of the ocean, on the other hand, it taking much more energy than to raise the one of the atmosphere. A definitely warmer ocean means that there really is a global warming. The study thinks that, even with no further increase of the greenhouse gases, the temperature at Earth will rise by 0.6 degrees centigrade (1.1 degrees Fahrenheit)
. A recent study in 2005 thinks that the methane might account for one-third of the man-induced greenhouse effect since 1750! This dramatic increase in proportion of the methane's impact is simply due to that previous studies did not take into account that methane is the main producer of the "tropospheric ozone", this ozone found in the lower strates of the atmosphere. Methane produces ozone by interacting with hydrocarbons, carbon monoxide and nitrogen oxides. Methane, thus, is the main responsible for the "smog". Natural sources of methane range from wetlands to gas hydrates in the ocean floor and permafrost, as fossil fuels, cattle and rice paddies are the main man-related sources
Sea level has risen at an estimated rate of 0.07 inches (2 millimeters) per year during the last 50 years as it seems that in the last 12 years that rate might have increased to 0.12 inches (3 mm) per year. Half of the increase might be attributed to the increase of temperature of the oceans themselves (leading to an expansion of them), as the largest likely factor for the sea level rise might be the increase in the ice melting. The three-fourths of the Earth's freshwater is stored into the glaciers and the polar ice sheets. It's the equivalent of 220 ft (67 m) of sea level which is stored this way! Such ice and water reservoirs might be melting at a much faster pace than thought as over half of the recent sea level rise might be due to the sole melting in Greenland and the West Antarctica Amundsen Sea and glaciers
Such satellites like Topex/Poseidon and Jason (radar-mapping the ocean's surface, measure of the ocean height and monitoring of the ocean circulation), Ice, Cloud and Land Elevation Satellite (IceSat) (mass of polar ice sheets and their contributions to global sea level change, or Gravity Recovery And Climate Experiment (Grace) (mapping Earth's gravitational field, allowing to better understand movement of water throughout the Earth) are allowing NASA and agency partners like the National Oceanic and Atmospheric Administration (NOAA) and the National Science Foundation (NSF) to explore and understand sea level change via global coverage and the ability to examine the various factors involved in the concept of the sea level rise
The ozone hole was first detected in 1985. A natural ozone layer is found in the Earth's stratosphere, this layer of our atmosphere lying 11-31 miles (17-50 km) in altitude. The ozone (O3), an unstable form of the oxygen (O2), is the result there of the interaction between the ultraviolet light from the Sun and the oxygen in the atmosphere. Such a stratospheric ozone layer is protecting us from the ultraviolet radiation from the Sun, as this high-energy light causes sunburns and is associated with skin cancers. The ozone layer is lying at 10-25 miles (15-40 km) of altitude. Earth's mid-latitudes are more rich in ozone
The ozone layer is destroyed when chlorine, cold temperatures, and sunlight mix in the atmosphere between 5-31 mi (8-50 km) of altitude. The main destructor of the ozone layer was traced back to chlorofluorocarbons emitted into the atmosphere (chemical reactions occur with chlorine from such human-produced compounds), as various chemicals and local meteorological conditions as well are interacting with the ozone. Chemically reactive, hydrogen-containing, chemical species are too involved in the ozone destruction, due to chemical reactions about 9 to 12-mile (15-20-km) high. Most of the conditions affecting the ozone hole occur above both poles, inside the polar vortex, this band of winds that forms each winter at high latitudes and isolating the polar regions from the mid-latitudes. The vortex is strong and long-lived above the Antarctica, as it's weaker and shorter-lived above the Arctic. The ozone layer, each year, is seen thinning above both Earth's poles, expanding to surrounding areas, possibily exposing populated areas to health harm. The ozone hole varies from 24 to 29 million square kilometers over Antarctica. Winter contributes as an accelerator of the ozone hole. Mild winters, at the northern or southern pole, bring a weaker hole. (it has to be noticed too that a colder stratosphere over the poles bring a larger ozone layer hole). Despite that the chlorofluorocarbons emissions have now been reduced the ozone layer hole is to persist for at least forty years as the chemicals still persist in the upper atmosphere
The Ozone Layer' Decline Halted, Albeit the Recovery Will Take Longer Than Planned!
Although the ozone hole over Antarctica is remaining opened wide, the ozone layer worldwide was found in May 2006 to have halted its decline. The ozone in the upper stratosphere (above 11 miles -18 km) was found recovered mostly due to the ban of the CFCs, those ozone-destroying gases as in the lower stratosphere (between 6.2 and 11 miles -10 and 18 km), ozone was found to recover much better -as the causes of the recovery there remain unclear. The northern ozone layer however will not be restored to its 1980 levels before about 2068 -or about mid-century. Data are unavailable about the Antarctic hole. The ozone hole, generally, will not be seen shrinking significantly before 2018
The effects of the ozone hole, North, seem to be attenuated, some years, as specific weather conditions -namely stratospheric winds- are bringing ozone from mid-latitudes up to the poles, filling the gap. Strong solar storms however, on the other hand, may affect the ozone layer in the other direction, bringing for example a modification in the activity of the Arctic stratospheric polar vortex. Energetic solar particles are triggering chemical reactions which, in turn, yield nitrogen gases at at least 6 mi (10 km) above the stratosphere. Such gases, like the nitrogen oxide and nitrogen dioxide, together destroy the ozone layer. They are drawn down more quickly than usual by the Arctic's polar vortex upper winds. The main accelerator of the ozone hole remains the increase of carbon dioxide levels anyway, which are bringing a cooler stratosphere. High altitude clouds, at last, which, like the cirrus, cirrostratus, and cirrocumulus, may be found at the lower part of the ozone layer, are related to the ozone destruction too, as Polar stratospheric clouds (PSCs) -these high polar clouds forming when stratospheric temperatures drop below -108°F (-78°C)- and aerosols as well are acting like a medium or host to create ozone-destroying chemicals. Chemical reactions on the surfaces of these clouds activate chlorine, converting it into forms that destroy ozone when exposed to sunlight
A source of ozone, at last, in the lower atmosphere, is due to carbon monoxide like that emitted by cars. Incomplete combustion can generate ozone. Such a low-lying ozone has a relatively long lifetime in the atmosphere and hence is often used for identifying human-induced pollution
El Niño and El Niña are two alternate phases of a global climate cycle in the Equatorial Pacific ocean. This cycle is called the Niño-Southern Oscillation (ENSO) and is a type of disruption of the Pacific ocean weather pattern. Normal climate conditions along the equatorial Pacific Ocean are warm water in the Western Pacific and a westwards cold tongue in the Eastern Pacific starting at the northwestern South America. During an El Niño episode the western warm water extends along the equator up to the California and the Central America coasts. During an El Niña episode it's the cold tongue which extends westwards rendering the equatorial Eastern Pacific cooler than usual. An El Niño means a warm equatorial Pacific, an El Niña means a cold equatorial Pacific.
 Warm waters in the Western Pacific are due to trade winds which are blowing West. They are piling up warm surface water on the other side of the Pacific as, on the other hand, cold, nutrient-rich, water is rising from deeper levels to the surface, off the coasts of South America. The Niño-Southern Oscillation (ENSO) is due to a modification of the trade winds in the Pacific. Easterly trade winds are weakening letting room for westerly ones. In term of local weather each side of the Pacific, an El Niño phenomenon brings rainfalls and flooding in Peru, more rainfalls in the southeastern United States and California, and warmer winters in the northwestern USA. Most recent studies, in 2008, leads to think that the impact of the ENSO patterns unto the US climate are much higher than thought
El Niño and El Niña however may be overtaken by the so-called 'Pacific Decadal Oscillation' (PDO) a pattern of alternating two phases, usually about 20 to 30 years. The PDO is detected as warm or cool surface waters in the Pacific Ocean, North of 20° N. During a "warm", or "positive", phase, the west Pacific becomes cool and a warm horseshoe pattern of waters, running North, East, and South, surrounds it; during a "cool" or "negative" phase, the opposite pattern occurs
Why Such a Mediatization of El Niño As Other Such Oscillations Not? The stress on the El Niño phenomenon might not be innocent as such a mediatization is not as strong for other such similar climate patterns in other parts of the world. A similar pattern to El Niño, for example, is known for the North Atlantic Ocean as it's far less mediatized. The 'North Atlantic oscillation' (NAO) is a fluctuation of the difference of pressure between the Icelandic Low and the Azores high, those permanent zones of lows and highs which control the strength of the westerlies across the North Atlantic towards Europe. The NAO was discovered in the 1920s, with a positive NAO occurring with the difference between the lows and highs large and a negative NAO the difference small. A large difference is increasing the westerlies, bringing cool summers and mild and wet winters in Europe. A small difference suppresses the westerlies, leading to cold winters, as storms are tracking southwards down to the Mediterranean Sea, bringing rainfall there. The NAO is particularly efficient between November and April each year, as it seems to be of consequence too about the eastern part of Northern America: with a strong NAO a southwesterly circulation prevents the Arctic air from descending over the continent and may combine to El Niño
The 'Arctic oscillation' (AO) highly correlates the NAO, as the Arctic oscillation is a pattern of higher-lower of sea-level pressures between the polar and the mid-northern latitudes. A negative AO has a pressure higher than normal over the polar regions and lower than normal at about 45 degrees North and the reverse with a positive AO, which further brings storms North over Scotland and Scandinavia, and to Alaska, as conditions are dry over California, Spain, and the Middle East. Most scientists agree on that the AO to be the cause for much of the changes in the Arctic. More oscillations still are involved over other regions and oceans of the world
Such precisions bring to say that, at least, better models are needed to a comprehensive view of such a complexity!
The El Niño brings drought in Indonesia, Australia, and the northeastern Amazon basin as there is a decrease of the hurricanes in southeastern USA (with an increase of them in the Eastern Pacific). An El Niña episode bring colder temperatures in northwestern USA, drier than usual conditions in the southeastern USA and California. The El Niña brings excessive rains in Indonesia and northeastern Amazon basin. Generally, during an El Niño, a rainfall pattern is seen stretching from the northwestern coasts of South America up to the East of New Guinea as during an El Niña, this pattern is shifted West, that is that it stretches from the Pacific Ocean's center up to Borneo, Indonesia and the Philippines. Last El Niño episodes occurred in 1986-1987, 1991-1992, 1993, 1994, and 1997-1998. Usually El Niños may not occur at such a frequency as between 1990 and 1994 but along a periodicity of roughly 4 to 12 years relative to the neutral state of the Pacific weather system. A strong El Niña occurred in 1988-1989, a weaker one in 1995-1996. El Niñas do not necessarily follow an El Niño. The warm water event off the coasts of South America was first recognized by a fisherman around Christmas, hence the name "El Niño" which is the name for the Christ child in Spanish. El Niño is impacting too the Pacific Ocean jet stream winds and leads to weather changes in various parts of the world
The La Niña episodes, on the other hand, are bringing that the "marine desert" of the Pacific Ocean, that is the equatorial zone there, is blooming during about one month with phytoplankton. It seems like that an El Niño episode, at the opposite, is accentuating the void in plankton in the equatorial Pacific. These effects of the El Niño/La Niña events on the phytoplankton is likely due to that iron, the fuel for the phytoplankton, in the central Pacific is weak, as such regions are remote from any land, where sediments and dust are sources of iron. Another source of iron is found in some regions of the ocean, like off coast South America, where deeper ocean waters are upwelling, and bringing nutrient to the ocean's surface to replace the surface waters which are blown away West when the winds regime is normal. In case of an El Niño event, such easterly winds cease and the upwelling too. Such concentrations of plankton are of importance too as when such plants die, they are sinking down to the bottom of the ocean, increasing the amount of carbon, there and leading to a possible lack of viable conditions for the other plants and organisms
The climate oscillation in the Pacific Ocean has wider effects, forcing changes in weather in regions far away from the Pacific ocean. On another hand it seems that the El Niño/Niña phenomenons are linked to a large oceanic currents system which is named the "Great Ocean Conveyor". The Great Ocean Conveyor is a larger Gulf Stream of sort. It's working on a 15-20 year cycle and it is transporting warm water from the Pacific Ocean into the Atlantic Ocean through the Indian one. When the conveyor is active, the Atlantic Ocean climate is warmer and wetter as the Pacific Ocean one is colder and dryer (that is that El Niño phenomenon). And the reverse (El Niña in the Pacific Ocean) when the conveyor is inactive. We should now have entered an active phase since about 1995. The Great Ocean Conveyor does not seem to be concerned by Arctic ice thawing in its Pacific Ocean part. Waters there are just cold water rising to surface, and where the phenomenon takes place is far South Bering Strait. Nor is it by a possible Antarctic thawing neither, as the cold, eastwards, part of the conveyor there is underwater only, along the Antarctic coasts
A late, February 2006, NASA-funded study, using the atmosphere-ocean coupled climate computer model known as "GISS Model E-R", has been showing that the last massive climate change which occurred 8200 years ago due to a large flood of freshwater in Northern America did not modify that much the Earth's climate. Such a flood was due to retreating glaciers opening a route for two ancient meltwater lakes, known as Agassiz and Ojibway, to suddenly and catastrophically drain from the middle of the North American continent. This took place after the end of the last Ice age, that is as our current, warm period had begun. The flood was equivalent to 25 to 50 times the flow of the Amazon river as it's in North Atlantic and Greenland that temperatures showed the largest decrease, with slightly less cooling over parts of North America and Europe. The rest of the northern hemisphere showed very little effect however as temperatures in the southern hemisphere remained largely unchanged. It's the ocean circulation which seems to have been most hit as it initially dropped by half after the flood, taking 50 to 150 years to rebound. Such a study is of importance as the current melting of the ice sheets at Earth's both poles might be of a less quantity than the flood 8200 years ago. Should such studies prove true, this might be the indice that the current climate change might be mostly natural, on one hand, and mostly of a low level and impact, on the other hand
For the third year in a row the Arctic perennial sea ice has been found disappearing at about 13 percent a year relative to the average in 2004. As the Arctic ice cover have been monitored since 1978, it was found melting at the important rate of 9 percent per decade. It should have disappeared by 2070! The period between early spring and late fall -that is when the ice is melting- is getting longer over the years as the Arctic regions are warming at the impressive rate of 2.5° C per decade. Its off coast of Northern Alaska, in the Baffin Strait, and on a line running from Iceland to the New Zemble that the increase is the largest. Northern part of North America and Scandinavia are also affected as the Russian coasts of the Artic are safe. This modification of Arctic conditions might be related to global warming as well as to variations in climate patterns in the region. The thinning of the Arctic ice cover might be the real translation of the burning of fossil fuels or it might be due to changes in air pressure and wind patterns over the pole. The ice cover -what is called the perennial sea ice- should recover during winter time, but it's not the case. This loss of the Arctic ice may affect the climate as the albedo of ocean versus ice's allows more heat still to be stored in the region. Most pessimistic views state that Arctic summer ice might be reduced to the half of its thickness during the 21st century, and that further developments might bring a 3 ft (one-meter) surge of seas -Greenland ice melting included, and a disruption of the Gulf Stream mechanism. According to these views, the additional average temperature increase would be of 3-5° degrees over land and up to 7° over the Arctic as the increase is estimated to have been 4° over the last 50 years. As far as Greenland is concerned, data are showing that a steadily thinning of the ice sheet is seen at elevations of under 1,200 ft (2,000 meters) only. Ice cover in the higher elevations of central Greenland stay mostly in balance. On the other hand some thickening has been observed lately in lower locations of southeastern Greenland due to unusual heavy snowfalls (warm air has more capability to retain moisture, hence to produce precipitation). There like elsewhere, scientists warn that data on a longer period of time are required for definite conclusions as a late study, which re-assesses the ice loss through the glaciers calving over the last ten years 1996-2005, is showing that the total Greenland ice loss doubled during the period
As far as the Antarctica is concerned, it mostly cooled during the last 30 years but is expected to warm during the next 50. The cooler episode, lasting since the late 1960s, was due to depleted ozone levels and greenhouse gases. Such elements are contributing to a typical atmospheric climate pattern called the Southern Annular Mode (SAM). A positive phase of the SAM is trapping colder air above the Antarctic due to stratospheric and tropospheric westerly winds circling around the Antarctica. A recovery of the ozone level in the coming decades might paradoxically promote a negative phase of the SAM leading to a warming. A higher ozone level would reject much more ultraviolet radiation. Such a change could obviously become a threat if ice sheets there melt and slide into the ocean, raising greatly the global sea levels. Ice sheets as big as Rhode Island have already collapsed into the ocean from the Antarctic Peninsula as the westerly, warmer, winds existing at 60-65° of latitude South are reaching this part of the South Pole. The same climate oscillation pattern is seen above the Arctic and known as the Arctic Oscillation or the Northern Annular Mode (NAM)
North Atlantic weather patterns are ruled by an ocean circulation system. Warm waters coming from tropics are yielding a mild climate along western Europe and Labrador coasts. Such a pattern is better known under the name of "Gulf Stream", starting off the southeastern coast of the USA. Further studies showed that this current pattern has an underwater part, starting about Labrador and bringing cold water back to tropics. Late alarming reports are stating that the North Atlantic currents modification would be a consequence of the melting of the perennial Arctic ice as they would bring doomsday next day and abrupt climate changes on the shores of the Atlantic Ocean. An addition of fresh water either directly, either under the form of increased precipitations in the region, would render waters more buoyant. Such a buoyant water would not sink anymore, hindering the Gulf Stream process. A thorough scientific study of the North Atlantic Ocean circulation system's part which is dubbed the "sub polar gyre" is showing that this current weakened considerably in the late 1990s compared to the 1970s and 1980s however. Sub polar gyre belongs to the Gulf Stream system. It is moving water in a counterclockwise pattern from Ireland to Labrador. Once there waters are plunging downwards, heading back slowly to equator as an intermediate depth current. Such a journey may take about 20 years. Sub polar gyre is sensitive to local weather conditions and particularly to perennial ice Arctic melting. A modification of this current might bring a change to North Atlantic climate system and perhaps to global climate. Waters in the 1990s have been found warmer about Labrador, decreasing contrast with warmer southern latitudes waters, hence reducing the driving force behind ocean circulation. Until now a sub polar gyre weakening had already be observed but was linked to oscillations of a large-scale atmospheric pressure system known as the North Atlantic Oscillation (NAO), and considered normal. This study is showing that current weakening continued despite the fact that NAO switched twice in the 1990s. Sub polar gyre might have an evolution of its own. Scientists are stressing that they need a further 5 to 10 years to definitively assess what is going on, that is whether the current weakening is part of a natural cycle or is resulting of factors related to global warming
Another Natural Cycle Discovered in the Arctic!
An oceanic current called the 'Arctic Ocean circulation' is now back to clockwise -like it was before 1990, as, since the 1990s, it had passed to counterclockwise. That change might be linked to the weakening of the 'Arctic Oscillation', a large scale atmospheric feature of the region, which reduced the salinity of the water there and induced the circulation change. There too, that discovery is showing how, on lengths of time of 10 years, changes are due to natural cycles and not the global warming. The thinning of the Arctic ice of those recent years might be due too to the process. The Arctic Oscillation was stable until 1970, then varied according to decadal rythmes, as it eventually stabilized in the 1990s. It now tends, itself too, to accentuate a trend to counterclockwise
The Indian "brown cloud" is a thick cloud of sooth and ozone pollutants which is generated over India and trapped along the Himalayan Range, over the Gange, by the summer monsoon, these earthward winds. This cloud of pollutants is generated by agricultural fires, home heating, and industrial and vehicle emissions. In winter the cloud is transported over the Bay of Bengal by the reversed monsoon, with seaward winds. On the other hand at the same season, farmers in Southeast Asia are performing agricultural burnings, as Chinese people are burning more energy to fight the cold of winter. All this leads to that a large belt of pollution forms, spreading both sides of the region, in the Pacific Ocean on one hand, and towards Africa on the other. Moreover, this season is the season too when African farmers are performing their own agricultural burnings. This eventually, each winter, contributes to a vast zone of pollutants stretching from China to West Africa! A well-known consequence of it is the high concentration of pollutant, low-lying ozone over the South Atlantic Ocean. The 'brown cloud' proper, in Asia, on the other hand, is contributing, by 50 percent, to the melting of the Himalayan glaciers, leading to a threat to the region water sourcesPollution, on the other hand, is a global problem, with pollution yielded in one part of the world maybe travelling to other parts. Like an example, pollution from East Asia is finally found over western North America, where it represents up to 15 percent of the pollution there, with the largest load in spring, and least in summer
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