To fully understand global warming, one must first understand the operations of the Earth System (described on later pages), since natural sources of temperature-affecting gases play an important role. We can learn about our planet's interacting physical systems by observing the results of such natural phenomena, and use our knowledge to explore human-induced changes. Thus, one factor that may in itself induce and account for some of the regional and global temperature changes is volcanism. Remote sensing is effective at monitoring such events. Consider, for example, the eruption of a volcano, such as Mount Pinatubo in the Philippine Islands in 1991, that happened without human intervention. This volcano had been dormant for more than 600 years.

When a volcano erupts it spews millions of tons of ash, debris, and gases into the atmosphere, not to mention the lava flows from some volcanoes. Because of the presence of instruments - on the ground, at the ocean's surface, and in space - meteorologists/environmentalists observed a cloud of sulfur dioxide (SO₂), emitted by Pinatubo, make its way westward, extending well past India within twelve days of the original eruption. Monitoring has been done by the UARS (Upper Atmosphere Research Satellite). By three months, that cloud had completely encircled the Earth, as shown from space (below), and inside of a year SO₂ particles in the atmosphere were providing gloriously-colored sunsets all over the globe and lowering global temperatures, as well. Clearly, an erupting volcano impacts more people and places than just within its immediate vicinity.

16-4: Why does the Pinatubo ash tend to stay confined to a wide equatorial zone? ANSWER

Mt. Pinatubo offers a stellar example of how monitoring from space can continually update the status of transient ground events (that, in unpopulated areas [not the case in Luzon] may go unnoticed). Below are two SIR-C radar color composites (L-band HH = red; L-band HV = green; C-band = blue) taken in May (left) and September (right) of 1995, both showing the effects of the 1991 eruption. Ash from an earlier phase of the 1991 event appears in red just above the summit of the volcano.

16-5: There is one noticeable change in the right radar image. Find it. Make a guess as to its cause (clue: the volcano didn't erupt between May and September of 1995). ANSWER

Volcanoes are a main source of SO₂ rises in atmospheric chemistry. The TOMS instrument (see page 14-9) has been making measurments of SO₂ in the air for more than 30 years now. The plot below shows the amounts detected for major volcanic eruptions from those on island arcs and others not on a direct plate boundary for the period from 1979 to 2003:

Another fascinating example of a natural phenomenon we know as El Niño, because it occurs with some regularity (although not complete predictability) around Christmas time. El Niño refers to the baby Jesus, whose birthday we celebrate at the end of December. When an El Niño occurs, a pool of warm water from the western Pacific Ocean moves eastward to the western coast of South America. In the process, weather patterns around the world changes often to the detriment of human populations–as do South American fish populations. In non-El Niño years, fish are abundant in this region, because of the cold, nutrient-filled waters. When an El Niño occurs, that cold water flows deep into the Pacific, and fish populations decline dramatically, with concomitant effects on humans whose livelihood depends on those fish.

Other such phenomena abound. Some are readily observable by space sensors, particularly meteorological and oceanographic measurements (see Section 14). As examples, consider these near-global plots. The top from comes from the Seasat Radar Scatterometer and shows prevailing wind patterns over the oceans at supercontinental scales. The bottom one depicts the mean day, night, and day-nite temperatures of the Earth's land and sea surfaces, averaged for January of 1979, from Nimbus 6's High-resolution Infra-red Sensor (HIRS) 3.4 and 4.0 µm channels (page 14-4), integrated with MSU microwave and infrared data. Suffice to say that even without human contributions Earth is a dynamic system, one that changes routinely and often drastically.

Clearly, global mean annual temperatures are rising, and we continue to monitor this condition with space observations to help settle the question: how much is just a natural trend (e.g., inevitable interglacial warming) and how much is due to man's activities? Calculations show that the burning of fossil fuels (mainly coal, petroleum derivatives, and natural gas) add about 6 billion metric tons of carbon (as the element) to the air annually; each year also, deforestation permits an extra 1-2 billion metric tons of carbon to reach the atmosphere.

As an indication of how much worldwide temperatures have risen in the last few years, this next map of the globe shows temperature anomalies, with measurements from various sources as compiled by NASA GISS (Goddard Institute for Space Science), for the year 2006 - the fifth warmest on record. The plot of temperature increase since 1880.

GISS is continually refining its models. Daily inputs improve the credibility of the predictions. Now that Aqua (page 16-11) is operational, its AMSR instrument can provide global data covering very short time spans. This map is of worldwide surface temperatures on August 27, 2003:

Using temperature data, GISS has now published a map of sea surface heat content anomalies (measured to a water depth of 70 m) integrated over a ten year period from 1993 to 2003. From typical data (top illustration) they have derived a model distribution of temperature variations. Since the upper ocean waters serve as efficient reservoirs for heat storage, the patterns of distribution of excess, normal, and deficient heat (in Watts-year/m²) thus determined are proving helpful in weather and climate forecasting since the temperatures have strong effects on atmospheric heating.

The trend of temperature changes on annual and 5 year-running averages proves that in the second half of the 20th Century the global atmosphere has been slowly warming - cumulatively totaling about 0.5 ° C, as shown here:

A more recent graph released by GISS covers departures of global average annual temperatures from a 30 year average as baseline over the period from 1870 to 2005 (the latter being the warmest year on record):

From the Washington Post

GISS has designed its model to predict both sea surface and surface air temperatures up to 50 years in the future. Here is a recently published forecast, which suggests that under current trends the temperature rise will be somewhat greater (more than 1 °C) than the last 50 years:

Other models predict an even more extreme temperature rise - if little or nothing is done to alleviate the causes. One forecast holds the average temperature will increase by 3 to 5 degrees Fahrenheit in the next 50 years.

Perhaps most alarming of all is the result of an extended study by NASA's GISS. Using a sophisticated model, their researchers projected temperature rises by the year 2085 for the eastern U.S. For comparison, using this model they produced an estimate for the year 1993 (right map) which was closely matched by reality:

The colors denote peak July temperatures as follows: Violet = 79-85° F; Green = 86-92° F; Yellow = 93-99° F; Red = 100 - 107° F; Dark Purple = 108-114°F. Under the 2085 conditions, rainfall in this region will diminish and vegetation will become much like that around Phoenix, AZ today. Available water will become scarce, so that desalination of the Atlantic ocean would have to provide much that is needed.

That this warming trend is already happening elsewhere in North America is convincingly demonstrated by temperature data for the state of California. In the illustration, temperatures (in Fahrenheit) across the state and in Los Angeles have risen more than 2.5° F in places in the last four decades and more generally almost 4° F statewide in the last 120 years:

So, is there any sign this is happening everywhere? Much debate has started in the middle of 2006 because of very intense heat waves during July-August in both the U.S. and Europe (the latter seldom experiences the extremes that occurred then) as shown in these plots obtain from metsats:

These excess temperatures point up the problem that both advocates and disbelievers of global warming face in interpreting the abnormalities. Thus: Does this period of high temperatures (St. Louis, MO had almost a week of temperatures at or above 100° F) reflect the onset of the predicted hotter summers or is this just another of the drastic warm spells that have happened infrequently in the past? The "jury is still out", although the unusual European situation seems to favor the warming hypothesis.

In addition to the observed phenomena described above, scientists have accumulated other relevant environmental recordings. For example, levels of several trace gases in our atmosphere have been rising and continue to rise. This change in atmospheric gas composition may be the most serious threat to the global well-being of Earth's environment. Information about this has been nicely summarized in an October, 1997 pamphlet entitled Climate Change: State of Knowledge, prepared and distributed by the President's Office of Science and Technology (OST), from which information and selected illustrations on this page have been extracted.

One of these gases, carbon dioxide (CO₂) has been increasing at an accelerating rate since the middle of the last century, after many, many years of essentially stable levels. Why is this? A simple explanation is that the Industrial Revolution began at about the time these increases started. With that social upheaval came the use of biomass and coal for fuel to support these new industries. Burning such material generates CO₂.

Other trace gases have been rising, as well. Carbon Monoxide (CO) is particularly deletorious. Methane (CH₄), from rice paddy production and enteric fermentation, is increasing, as are chlorofluorocarbons (CFCs) that have been used for many years as a refrigerant and to produce foam. Methane is a much more potent greenhouse gas that CO₂.

16-6: The carbon dioxide curve shows regular oscillations (much like a sine curve). Why? With what do these three curves best correlate? ANSWER

For those unfamiliar with carbon dioxide and its properties, consult this Wikipedia website

Later in this Section we will familiarize you with satellites that gather data on atmospheric gases and other contributors to global warming. This bears on a main thesis in this Tutorial, that satellites are proving to be a powerful, almost unique, tool for monitoring the whole Earth at the global scale. For now, we will mention the results obtained by the AIRS sensor on the Aqua satellite which led to a global map of carbon dioxide at a height of 8 kilometers (5 miles) above the Earth's surface:

Scientists need to establish a long-term data base for global warming, which includes temperatures from previous centuries. One way to estimate past temperatures is from CO₂ measurements of air trapped in glacial ice that has been accumulating for thousands of years. The plot below shows the general trend in rising CO₂ during the last 160,000 years (includes recent ice ages), with estimates of temperatures (derived from a CO₂ model) shown for comparison.

This may be a very important graph bearing on the arguments for and against global warming. The graph shows a temperature maximum about 130,000 years ago, with a steady decline thereafter until a rapid rise beginning about 15,000 years ago. This rise resembles the same increase leading to the 130,000 peak. The question that must be asked: Is this just a repeat in the normal cycle associated with Pleistocene glaciation? The follow-up question: Is there any strong evidence that the more rapid temperature rise of the last 50 years (or, going back to the Industrial Revolution) is abnormal? The closest to the truth may be that there is now a temperature spike added to a trend that has natural causes related to glacial processes.

Even more impressive is the correlation between CO₂ content in cored ice and derived temperatures during the last 400,000 years, as shown in this plot:

Note: These high and low range values of temperature correlate well with the periods of continental glaciation in the northern hemisphere and the warm interglacial intervals over this extended time period.

The next graphs provide more details on the increasing levels of CO₂ during the last 140 years. The top shows carbon dioxide concentration increases, based on ice core measurement until 1960 and Mauna Loa Observatory measurements thereafter. Below it is the measured temperature changes averaged for the entire world; the trend upwards, amounting to about 1.5° F, shows some irregularities (not smoothly cyclic) which result from other climatic factors. The Mauna Loa level in 2006 was 384 ppm.

These gases contribute to the greenhouse effect that is warming our atmosphere to the levels we now record. The greenhouse effect results from the trapping of solar radiation that reflects from the Earth’s surface by these (and other) gases. This is illustrated below.

The atmosphere is essentially transparent to incoming solar radiation. After striking the Earth's surface, the wavelength of this radiation increases as it loses energy. The gases we discussed are opaque to this lower energy radiation, and therefore trap it as heat, thereby increasing the atmospheric temperature. As these gases increase, due to natural causes and human activity, they enhance the greenhouse effect, and may raise temperatures even more. If the climate warms, the vegetation belts will tend to move northward, changing global ecological and biome patterns. Other effects may be discerned in precipitation patterns, sea level changes, and more.

Armed with the data that relate CO₂ increase to temperature rise, models allow prediction of the global distribution of changing temperatures if the total amount of carbon dioxide in the air were to double or quadruple from today's values (arbitrarily set at 275° F). The 4x case could be truly catastrophic, leading to worldwide deserts unless the added heat in the atmosphere also notably increase vegetation growth (to tropical forms). Thus:

One obvious consequence of the significant rise in CO₂ in the northern polar latitudes would be melting of Arctic Ocean and Greenland Ice Cap ices, releasing huge quantities of stored water that would have an extremely serious impact on global sea levels. A rise to 550 ppm CO₂ by the end of year 2100 would bring about rises from 8 to 37 inches, enough to greatly modify present beach and shoreline configurations and even submerge such cities and New Orleans and Venice (which is also presently sinking because of groundwater withdrawal).

Evidence has been building, through satellite and ground measurements, that the Arctic region of the northern hemisphere has been steadily warming. The main consequence has been the shrinking of the area capped by ice in the Arctic, as shown in this plot based on ground data:

The general change pattern of Arctic temperatures is summarized in this map of the upper northern hemisphere using data from the last 30 years. The Arctic ice shelf has responded both by thinning and loss of ice at the margins. Further south, the western U.S. and Siberia are both in a warming trend. Note that the only region that has cooled during this time is in eastern Canada-Greenland.

A somewhat more precise map of temperature changes in the Arctic covering the two decades between 1972 and 1992 has been constructed from meteorological satellite data as shown here:

The net effect has been an overall shrinkage of the outer extent of the main sea ice cover within the Arctic Circle:

Owing to greater precipitation, the sea ice around the North Pole increased somewhat in 2008. But surrounding waters were more open. This meant that the famed Northwest Passage shipping lanes were even better suited to navigation by cargo ships from Europe to the Orient for the summer months, obviating the need to transit through the Panama Canal.

This ice fluctuation can be displayed visually using data from the SSM/I (Special Sensor Microwave Imager) instrument (on the U.S. Air Force Defense Meteorological Satellite series), taken in 1979 and again in 2003. The Arctic Ocean appears to be opening up off eastern Siberia and northern Alaska.

More recent observations have increased the alarm. NASA's Quikscat satellite has produced a map of the Arctic's perennial sea ice (ice that remains through the summer) for the years 2004 and 2005:

The reduction of the most stable ice - perennial, in white - amounts to about 14% in one year - the largest yet observed. The remaining ice has thinned from an average of 3 meters to less than 2 m.

Early explorers had hoped for at least a short season when the Arctic ice cap had melted enough to provide open water through which ships could pass - the famed Northwest Passage. In recent years this is now happening on an annual basis, as seen in this image in northern Canada:

This progressive diminishing of ice cover has been increasing steadily in the last few years, with 2005 now showing the least amount of frozen ice. Data acquired by satellite and ground truth lead to this plot:

Evidence is growing that ice in the Arctic Ocean is accelerating its loss. Near Ellesmere Island in northern Canada, the Ayles Ice Shelf began to break up in 2006. Here are a series of space observations that show the breakaway of a 64 square kilometer (41 sq miles) section of the Shelf over a period of just weeks:

Experts studying the ice shrinkage in the Northern Hemisphere have, using projected temperature rises, produced a plot of area decrease during the full 20th Century and a prediction for loss in the 21st Century. The loss trend started around 1970:

The subcontinental Greenland land mass, mostly covered with ice, is also serving as a proving grounds for detection of widespread melting. Despite the interior cooling of Greenland (suggesting enough snow to increase the ice cap's thickness), the edge of this ice cap is currently shrinking as confirmed by several separate aerial/ground/satellite studies in which remote sensing played a part. Most recent is the map produced by the GRACE satellite that uses gravity data to calculate the mass of ice that has melted, or increased, on Greenland:

A NASA team made survey passes across Greenland by air using a laser altimeter to measure elevations. A second group used the Global Positioning System (GPS) (page 11-6) to track movements of ice. When both results were analyzed, the map shown below was constructed. It shows increase in ice in the central part of this huge island (possibly related to the recent winter cooling) but significant shrinking near the edges (increases in summer temperature). The net loss of ice is estimated to be 51 cubic kilometers a year, enough to fill a lake 30 miles long, 30 miles wide, and 70 feet deep (spread globally to the oceans this would cause a rise of 0.005 inches a year; this contributes 7% of the total rise now being measured).

This map shows similar results from a different perspective:

Scientists visiting Greenland in the last few years have remarked about significant increases in the onset of melting along the edge of the western fringes. This is visible in MODIS images taken from 2001 into 2003, with the zone of active melting showing up as a darker gray (presence of water):

Individual glaciers along the edges of the Greenland ice cap, especially on its western side, have been undergoing retreat and flow rate increases (caused by increased water within the glacier that lubricates its movement) as the ice melts. Three big glaciers on both sides of Greenland are shown in this map:

This Terra ASTER image illustrates the loss through melting at the Jakobshavn Glacier:

This aerial photo shows the positions of the Jakobshavin glacier's toe or frontal boundary in the 21st Century. This front is now rapidly moving at a rate of 15 m/yr (49 ft/yr), as it calves off ice that enters the ocean along Greenland's western shore.

The two glaciers flowing into the sea along the southeast coast (see above map), Kangerdugssquaq and Helheim, from the latest ground measurements are now flowing (even as their fronts retreat) at 40 m (131 ft) and 25 m (82 ft) per year respectively for the period 2004-05 - the fastest movement rates ever observed for this pair:

Recent reports indicate that the amount of ice released from the Greenland sheet to the sea has nearly doubled in the last 10 years - the highest rate yet observed. This may be another sign that overall Arctic ice is wasting away at an accelerated pace. In the 21st Century, if this increase continues, worldwide sealevel can rise - from arctic melting alone - by about a meter (3 feet). This space image shows the coast around Helheim with a large raft of icebergs beyond the shoreline:

The concern is one of "volume", not just "area". While the areal coverage in the Arctic has decreased significantly - and looks dramatic - the volume loss in Greenland exceeds that of the sea ice. This is the kind of loss, if it accelerates, that will have the most impact on sealevel rise.

Ice melting is worldwide. Thus, melting is being observed in the Southern Hemisphere, mainly in South America and the Antarctic. Here is a ground photo pair showing the Qon Kalis glacier in the Peruvian Andes:

Glaciers in Asia also show notable retreats, as shown here for the Ganglotri glacier:

On page 14-14 evidence of major changes - mostly as thinning of ice along the fringes - in Antarctica was discussed. This is in response to notable rises in temperature in sea water along its coastal shelves; in the Antarctic Peninsula, a cumulative rise between 2 to 3°C (3.6 to 5.4°F) has occurred in recent years. This map, made from NOAA AVHRR data, shows that the exterior parts of the Antarctic and surrounding waters has warmed in the last 22 years, yet the interior has cooled. Perhaps the increased evaporation in the seas, where ice calving has exposed more open ocean, has produced more inland precipitation, accounting for the cooling.

Ice along the Antarctic Peninsula (west-northwest of the South Pole) is largely melting and thus retreating, although some measurements show ice advance

In the last few years parts of the fringing Antarctic ice shelves have broken loose as massive ice bergs floating northward. Use of laser altimetry and interferometric measurements of data obtained by InSAR (Interferometric SAR) are showing up as annual velocities of ice movement both within the continent and along its edges, as seen in this composite image:

The Antarctic ice shelves appear in gray in this map. Letters indicate 33 named glaciers. As the ice sheets thin and break off, the glaciers respond by increased (accelerating) outward flow.

The Ross ice shelf was one of the first in the western Antarctic to show dramatic changes. It greatly diminished by 2006. Here are a series of MISR (Terra) images of parts of the Ross shelf as these broke off and entered the sea as ice(berg) sheets:

In February of 2008, most of the Wilkins ice shelf disintegrated, as ice cover the size of Rhode Island broke loose. The changes were imaged by the Terra satellite.

Formosasat, operated by the Taiwanese, obtained this detailed view of the disrupted Wilkins ice shelf:

Here is an aerial photo showing broken ice and separated slabs within the now detached Wilkins ice shelf:

The West Antarctic ice shelfs (primarily the Ross Shelf) are losing ~65 cubic kilometers per year, enough to raise ocean levels by 0.16 mm/yr; worldwide sealevel is rising by 1.8 mm/yr (0.7 inches/yr), primarily from Arctic, Antarctic, and Greenland sources. Scientists have calculated that if all of the ice in Greenland and the Antarctic were to completely melt through significant warming the worldwide sealevel would rise 70 meters (230 feet), which would be catastrophic to the large fraction of global populations living near the coasts.

Like the other evidence, a shrinking ice cover in each hemisphere does not confirm a direct response to global warming. Critics of the global warming hypothesis have challenged the conclusion reached from the now verified evidence of the linkage between warming and ice melting. Their argument is simple: Studies of global ice distribution during the last few million years have revealed a cyclic trend of advances and retreats. Debate still continues as to the cause(s) of these cycles. The periodicity is revealed by measuring the ratio of O¹⁸/O¹⁶ in ice cores retrieved from deep drilling into ice caps. O¹⁸ will increase during times of warming. This diagram displays the trends of warming and cooling determined by this method (individual core segments are dated by C¹⁴ and other radioactive isotopes):

Thus, natural cycles of freezing/thawing as continental glaciation waxes and wanes may indeed explain the current lines of evidence disclosed by temperature and ice retreat indicators. The crux of the argument between global warming advocates and those conservative thinkers who still believe the recent observations are not alarming and to be expected is this: The Earth may just be undergoing its latest natural warming in the cyclic sequence. But taken with other signs of temperature rises, and their effects, one can certainly postulate that global warming is a credible factor in these changes. Some argue that both cyclic warming and human-induced global warming are occurring concurrently. The present situation then may be made worse by the added effects of CO₂ and other gases that are driving the atmosphere into a warmer than "normal" temperature rise.

As stated before, ice melting will lead to sealevel rises, both regionally and worldwide. A good overview of this subject is found at Wikpedia's review of sealevel change.

As an illustrative example of how a specific region would be affected, this predictive map of southern Florida shows the extent of inundation if sealevel were to rise just 5 meters (about 16 ft):

But is sealevel actually rising? Data from the last decade, using satellite imagery, points to a strong affirmation of this change:

Some other lines of evidence are shown in these figures, taken from the aforementioned Wipedia website:

The first shows sealevel rise trends for the last 125 years as measured at 23 marine gauges:

But this question can be raised: Have comparable rises been observed in the past?

From observations made at various islands and continental seaports, sealevel has steadily risen since the end of the last major continental glacial advance over the northern hemisphere; note that sealevel rise has approximately leveled off in the last few thousand years.

The trends in temperature and sealevel fluctuations over the last 900000 years is shown in this next diagram, which has an enlargement showing the changes during the last 140000 years. The impression is that there has been a cyclic pattern that makes it difficult to say that the current observations are unusual:

Over the last 500 million years or so, sealevel has undergone some broad patterns of change (as determined in a study supported by Exxon and in a separate study by Halam et al. that has used worldwide data and attempts to compensate for shifts of continents driven by plate tectonics). Higher general levels have occurred at the beginning of the Paleozoic and the end of the Mesozoic, with a minimum during the Pangaea breakup at the end of the Paleozoic. Note that the rise/fall trend during the glacial activity in the Neogene (N) is much less in magnitude than during earlier maxima.

The main conclusion one reaches after looking at the sealevel change data for a long interval of geologic time (assuming the patterns shown are generally accurate) is that short-term changes are highly variable but over millions of years trends of rise or fall proceed more gradually. The current rise may indeed be due to man's activities but alternate explanations (natural fluctuations, etc.) remain competitive. But it is clear that global warming is now taking place, owing probably to several causes, and as a result coastal areas are likely to be inundated (requiring either relocation of cities or emplacement of elaborate dike systems).

Another possible sign of global warming would be shifts in the distribution of both natural vegetation and food crops. Consider this next diagram which is a map pair showing, on the left, the current range of the common sugar maple with the shift that could occur from just the predicted temperature rise associated with a CO₂ increase to 700 ppm, and, on the right, a more drastic withdrawal northward if soil moisture reduction is included. This happens simply because the climate zone that favors this maple is sensitive to specific temperature and moisture ranges.

This shift in vegetation is still being demonstrated. Measurements of green leaf distribution and other measures of vegetation (various Veg. Indices) over the last 20 years using satellite data have now revealed a substantial increase in the "greening effect". A study reported in the journal Science includes a map that shows the regions of the world that have experienced greater vegetation development and areas losing vegetation, largely as a result of climate changes:

In parts of the Northern Hemisphere, the greatest increase (red is highest) in vegetative cover seen in this summary diagram shows a distinct concentration in the northern parts of Europe, Asia, and North America. To the south, the first Spring leafing is now about 1 week earlier and Fall loss of leaves is almost a week later. The most likely explanation is the warming effect of greenhouse gases and the greater availability of CO₂.

Even more affecting would be the changing conditions suited to supporting certain staple crops. A CO₂ rise to 550 pm would redistribute crop yields worldwide for common grains, as shown below. Note that warming in the higher latitudes of the Northern Hemisphere would favor increases in crop production in Canada/Alaska, Scandinavia, and most of Europe and Russia but changes in South America and most of Africa would move towards drops in yield.

After all the "hoopla" over global warming as synopsized above, it came as a surprise to NMS, and to the scientific community in general, to learn recently (as I did from a PBS Nova telecast) that there is another major atmospheric phenomenon known as global dimming. This refers to the now demonstrated fact that there has been an average decrease in solar irradiation reaching the Earth's surface of 10-15% since the 1950s. In some regions the number is less; in a few places the drop has been as high as 36%. This plot indicates the change (the abscissa, not identified is probably latitudes north and south of the equator):

Solar irradiation at the surface is measured quantitatively by pyranometers, such as shown in this cluster;

The decrease in irradiation varies, being generally less over the open oceans and more on land. The average drop in heavily populated regions is 0.41 W/m²/year compared with rural regions at 0.16 W/m²/year. The global dimming effect was first noticed by the English/Israeli climatologist Gerald Stanbill whose published reports were largely discounted. More recent studies by Atsumu Ohmura confirmed the postulate by Stanbill of dimming.

The overall effect of this reduction in irradiation has been to cool the atmosphere by 1 to 1.5 °C. This in turn causes a decrease in water evaporation, and - although not yet verified - shifts in precipitation including less rainfall. Droughts in Ethiopia and West Africa have been attributed, in part at least, to disturbances of the mechanism by which monsoon rains are developed and sent northward from equatorial spawning grounds. A drop in irradiation can mean that plant life will experience less irradiation and hence photosynthesis, now a subject of real concern.

The cause of global dimming is largely due to increased soot, ash, and sulphur particles released to the atmosphere by industrial activity and automobile use. The particles serve as nuclei for water droplets that make up clouds. The clouds in turn become more reflective, sending a greater percentage of incoming irradiation back into space. Much of the particulate matter is carbon-rich, being soot caused in part by regional burning of forests and grasslands (both controlled crop-management burning and wildfires). MODIS on Terra and Aqua produced this global map of carbon soot in the atmosphere; wildfires in northwest Siberia account for the high readings there.

Another factor which seems important in moderating temperatures is the large number of contrails from airplanes, as seen here:

While the contrails may seem insignificant, their role was indirectly verified as a side effect of 9/11 (the Sept. 11, 2001 terrorist attacks in the U.S.). For almost 4 days after the government grounded all commercial flights in the U.S., the amount of measured irradiation increased enough to raise average temperatures by a degree Celsius. Upon resuming flights, this increase was reversed.

What is the main import of this recognition that global dimming is real? The answer is that temperature increases due to global warming are partially offset by dimming (dimming counters about half the increase due to warming). Thus, it follows that warming has been slowed by dimming which if the latter were not acting would mean that the rate of warming (by itself) would have been higher. One might suppose that dimming is therefore a good thing. In some respects, yes. But the consequences of dimming as influences rainfall and crop production may be detrimental and even a major threat to global ecology and various regions which could become both hotter and drier. The most obvious conclusion: Reduction in both particulates and greenhouse gases should overall be a mandatory necessity for mankind to survive in safety and comfort even as population grows. The corollary: emissions from all major sources MUST be reduced, preferably more than halved present and projected amounts. Since warming and dimming are global, it follows that this is an international threat and should therefore be met head-on by all nations. It also stands to reason that an efficient monitoring system for atmosphered "health" is vital; using satellites and remote sensing is an essential component.

Another observable global change, caused by certain trace gases in the atmosphere, including the CFCs, is the depletion of stratospheric ozone. Ozone in the stratosphere absorbs incoming solar ultraviolet radiation (UVR) that is dangerous to living systems. This UVR causes damage to the genetic material in living systems. Ozone prevents the UVR from reaching the Earth’s surface , and so protects us from its harmful effects. Spacecraft sensors have observed ozone depletion during the Antarctic winter, an observation that helped determine the chemistry underlying this process. Over the South Pole, the right combination of cold stratospheric temperatures, ice crystals (or other solids with surfaces upon which the destruction chemistry occurs), and the global wind patterns intensify the process. Space sensors have observed similar (although smaller) depletions in the Arctic, and some of the chemical agents are increasing over mid-latitude regions, i.e., where most humans live.

These depletions have come to be known as "ozone holes". That this is an apt description is evident in this image of the Antarctic variations in ozone level that have been depicted in 3-D by "contouring" the different values:

The size and extent of the "hole" varies with time as is obvious in this series of October Antarctic ozone maps taken between the years 1979 and 1992.

16-7: Comment on the patterns of ozone change you decipher from the above October sequence. ANSWER

Other gases, including those that contain sulphur compounds, contaminate the atmosphere. One of the products of vegetation decomposition, fossil fuel burning, and even animal flatulation is methane (CH₄). Although present only as traces near the surface and in the stratosphere, this gas rarely is concentrated locally at a toxic level. Using various sources of data, a NASA program has now produced a global map of surface and upper atmosphere distribution of methane:

UARS has measured summer and winter concentrations of several gas contaminants in both earth hemispheres. The first pair of plots on the left are temperature distributions. Note particularly the changes around the polar regions.

Other human activities may increase the rate of global change. One activity now grabbing attention is deforestation, whereby humans slash and burn, or just clear-cut, huge tracts of trees to use the land for agriculture or the wood for building shelters. As developers denude these large regions, biodiversity decreases, and land-use, water run-off patterns, and local weather phenomena change. Satellite remote sensing has produced dramatic images of progressive deforestation, as witnessed in these two scenes taken five years apart over the State of Rondonia in the Brazilian Amazon Basin by NOAA's AVHRR.

16-8: Estimate the percentage increase in deforestation in the middle of the image pair (eastern Rondonia).ANSWER

In recent years, awareness of the effect on global warming of changing landuse has come to the fore. The argument centers around this: Vegetation serves as a sink for carbon, which in turn influences the amount of carbon dioxide that re-enters the atmosphere. Although a complicated mix of positive and negative feedbacks, this changing cycle of carbon redistribution is strongly tied to the vegetation land cover that is affected by populations determining how the land must be used to support and feed the inhabitants.

This is neatly illustrated by a historical reconstruction of the clearing of the eastern half of the United States over an extended time frame: from 1850 to 1920 - approximating the period of greatest expansion of that country's people as the railroads spread westward from the Eastern Seaboard. Consider these diagrams:

The principal change was removal of natural growth, disturbing the pristine land cover, and converting much of the land to farming. Although the replacement of woodland vegetation with crops kept some of the capacity for carbon storage, the balance that applied to carbon dioxide release was modified. Similar results have occurred both in the U.S. and worldwide as Earth's human population has notably increased over the last 100 years. Worldwide vegetation cover is decreasing, reducing the capacity to intake carbon from the carbon gases being added to the atmosphere from burning of fossil fuels and other "smokestack" activities.

As a consequence: All in all, the evidence seems to be mounting that there is a definite increase in regional and global temperatures. One sign, not commonly cited, is the progressive migration toward the poles of various animals and birds. In North America, rattlesnakes (very sensitive to temperatures) have moved into New England and the Canadian Great Plains. Tropical and desert birds previously almost exclusive to Mexico are now spilling over into Texas and Arizona. Populations of the Snowy Owl have been decreasing in the Arctic (ecologists surmise that this is due to a large drop in the lemning population, the owls chief food source). Some of this temperature rise may by natural (warming trends during interglacial intervals are the norm); some is now recognized by experts as the consequence of manmade perturbations to the atmosphere.

Thus, many observations and other data seem to point to humans as a major causative source, having at least the potential for modifying global phenomena. However, we are not always sure of this. Scientists continue to wonder if some of the observed changes, such as an apparent increase in atmospheric temperature, are really due to human activities? Or are they part of a natural cycle that we are only now observing in detail, because of the presence of instruments and sensors that were hitherto not available? (Most likely, they are some combination of both a natural trend [as observed in previous interglacial climate histories] and Man's deletorius contributions of wastes to the atmosphere and hydrosphere.) Concerned individuals also must ask whether the current trends will continue and how detrimental they may be.

Comment by NMS: The evidence presented on this page may seem "alarmist". But what if the general conclusions and predictions being made by more and more scientists have significant elements of TRUTH. The potential is for Calamity. We still are somewhat in the dark as to what may occur if certain ill-defined thresholds of change when temperatures exceed some value(s) - will threatening conditions of climate and responses to its change actually cascade (the above-mentioned accelerating rate of glacial flow over just a few years in Greenland glaciers may be an example). The writer is one who feels great concern that there is trouble ahead if politicians, globalists, and the public turn their backs to the dangers and languish in the status quo. I strongly recommend that YOU read Al Gore's new book: "An Inconvenient Truth", keeping an open mind and perhaps some skepticism. But if you come away with some conviction that he's largely right, then resolve to take action, raise your protest, and demand the needed rectifications.

We close this page with a conjectural map of the World in which global warming has induced many major changes (those coming from coastal submergence are omitted). (The map as shown is large but reducing it using the offloaded image file causes the lettering to become blurred.)

Mankind can probably live with these changes as we adjust and find ways to accommodate them. But the Gore book describes some climate-influenced events that will be devastating and considers certain possible effects that may be catastrophic. The many varied observations described on this page seem to favor the global warming hypothesis. But we must reiterate one statement made above: This warming may just be (largely) a natural effect of an interglacial temperature process (but nevertheless there clearly seems to be a component of the observed temperature increase that correlates well with humans' adverse contributions). If so, not to worry excessively (but some protective response is in order); if not, then the Gore conclusion - that very serious damage to global environments is about to occur - should be a warning that seems to cry out for a quick and drastic response by the planet's polluting nations.

In early 2007, a panel of more than a thousand scientists released a pair of reports summarizing what Science can state with high reliability about global warming. To paraphrase some of their conclusions:

1. Over the past few million years, natural climate changes, driven mainly in response to factors that cause widespread glaciation and alternate interglacial periods, are marked by intervals of slowly rising temperatures (interglacials) and then falling temperatures (continental glaciation). Rates of change are usually less than 1 degree per thousand years, and the total range is probably less than 20° F.

2. During interglacials, some animal or plant species adapted to colder weather have died off (the same may happen during warm weather; new species can develop during either cold or warm climes).

3. During interglacials, sealevel tends to rise and vegetation distribution varies; many biomes migrate poleward; productivity of edible plants may increase or decrease.

4. It is likely that mankind has blossomed since the end of the last glaciation and has become both numerous and dispersed in the last ten thousand years. Now humans are in such abundance as to begin to affect (impact) natural conditions that control the weather, moderate the environment, and otherwise maintain healthy living conditions.

5. In all probability, some of the temperature rise whose rate is increasing is just a consequence of the natural interglacial warming. But a proportion of that rise (amount still guesswork) is almost certainly the influence of detrimental atmospheric gases that are being added from fossil fuel burning and other sources. The rise may be abnormal - it is the sum of both natural and manmade contributions.

6. Since the human factor was not present in earlier interglacial warming trends, its current role in causing global warming cannot be evaluated in terms of outcomes. Many scientists believe that the rate and extent of temperature rise can be excessive enough to cause global equilibrium (adjustments of life to the changes) to be upset, perhaps to a stage that will lead to catastrophe. Work must be done to predict what might happen.

7. Because of the uncertainties, the scientists strongly urge that mankind plays it safe and reduces or eliminates the known causes of atmospheric warming.

SCARED??!!

If so, continue onto the next ADD-ON page which delves into the evidence for current warming owing to both natural and human causes.

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Primary Contact: Nicholas M. Short, Sr.