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.
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). There are many who feel 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. Both writers of this Section 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.
As you might gather from the above discussion, global warming is one of the "hottest" topics going on today in both U.S. and International societies. The American people are divided right down the middle on whether manmade global warming is a reality. One recent poll among the general population has 48% of those questioned choosing to be skeptical - they do not believe that human contributions to global warming are a major threat; instead they suspect the trend is due primarily to normal interglacial warming. Most of those polled are not scientists and hence lack the special expertise a scientific background provides, but some scientists themselves have challenged the conclusions cited above and a few even the evidence itself. The subject of global warming is certainly not trivial - it may be vital to survival of the way of life as modern man now lives by. And called for solutions are troubling: they may involve trillions of dollars in expenses and lost revenue, and perhaps even fundamental changes in lifestyles in both developed and emerging nations.
Part of the problem is that the data supposedly corroborating global warming can be contradictory and confusing. If one goes onto the Internet and types in various phrases associated with "global warming", a huge number of 'hits' in both text and illustrations comes up. Some are similar to one another; some are disparate. Some seem to support the 'human factor'; others support the idea that warming is just a part of the natural variability. Obviously, NO CONSENSUS.
But, the dire warnings that many scientists and others are putting forth today indicate that the "worse case scenario" is realistic enough to warrant immediate and in-depth attention, since its projected outcome would be catastrophic. During the week of the International Climate Conference in Copenhagen (December 2009), the writer (NMS) has decided to expand this page with what may seem redundant relative to the coverage earlier on the page. However, I wish to provide a synoptic overview of what I consider the gist of the argument. I have extracted some key illustrations from the Internet to serve this purpose. Read through the next several paragraphs with an open mind.
The first figure puts the warming history of the last 4400 years in perspective with respect to human history. It seems to favor the natural cycle hypothesis pertinent to climate behavior. It gives little detail on the temperature history of the last 100 years or so.
The next two figures cover the climate history of the last 350000 years (top) and the last 1000 years (bottom). The top illustration once more re-enforces the cyclical interpretation of global warming. The bottom illustration is dramatic - it is very similar to one used by Al Gore in making his supportive argument for possible runaway warming - in that temperature is rising in the last 100 years at a rate that is far greater than any previous time in the second millenium.
The next two illustrations are examples of data conflict. Both are plots of temperature variations over the last 30 years. The upper one seems to show warming in the early '80s whereas the lower plot seems to indicate cooling. This conflict is unexplained but it could mean different behavior in different (not corresponding) places on Earth. What they do tell the viewer: the data can seem inconsistent and therefore misleading.
Two global maps are frequently cited on the Internet as indicative of the recent and the future temperature changes worldwide. Examine these:
TO THE WRITER, THE BEST EXPLANATION OF THESE OBSERVATIONS (APPLYING OCCAM'S RAZOR [the simplest explanation is usually the most likely one]) IS THAT THE ATMOSPHERE IS ON THE UPSWING OF A NATURAL INTERGLACIAL WARMING CYCLE BUT HUMANS ARE (THROUGH MISMANAGEMENT OF THE ENVIRONMENT) RESPONSIBLE FOR CAUSING NOTABLY HIGHER TEMPERATURE RISE RATES THAT WILL EVENTUALY POSE SERIOUS THREATS TO SIGNIFICANT NUMBERS OF THE WORLD'S POPULATION.
So, what are the likely consequences of all this: Here is 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.)
Such maps are disturbing in themselves but do not necessarily cause outright alarm. They are rather benign. What does get the "worry beads" in hand are illustrations such as this:
This next "photo" is obviously a fake since New York City isn't now underwater. But it does bring home dramatically the effect of the sea level rise predicted for the worse-case scenario. If in fact the oceans receive water from Greenland and the Antarctic to the extent that some forecast, then many coastal cities would be inundated. Probably New York City would escape the fate shown here because dikes would be built to protect it. Nevertheless, this, and other cities along coasts, would experience radical changes.
While damage resulting from slow but inexorable inundation would occur in the low areas along the coasts, the entire land mass of each continent will be affected. Temperature increases and amounts of seasonal rainfall will modify and displace geographically the major biomes on the Earth's land surfaces. We repeat here a diagram shown on page 3-1. It shows the dependence of any biome on temperature and precipitation. These biomes should survive global warming but they will shift to different regions of the continents. In all likelihood, people will gradually respond to the shifts and relocate but animals may be more unable to adjust and some species may verge on extinction.
Critics of global warming, i.e., those who claim it is not really happening or that the changes are just an interglacial warming trend, cite various lines of evidence they consider as proof that manmade warming is not dominating climate changes. The winter of 2009-2010 is one such instance. In parts of the eastern U.S., record snowfalls (since such records began in the 1800s) in cities like Washington, Baltimore, and Philadelphia are cited as indications that the climate is really not warming. On February 10, 2010 a snowfall of 30 to 30+ inches fell on these cities, as displayed in this MODIS image:
So, is this a valid claim? The brief answer is that the hallmark signature of a "cold climate", namely snow and ice, is not proof in itself that global warming is not underway or that we are entering a period of cooling or perhaps a mini-glaciation. The several heavy snows in the East are the direct consequence of a more active and strong El Niño in the eastern Pacific ocean. This has led to greater evaporation of seawater and hence more moisture-laden storms that travel across North America. In winter, these storms encounter cold Canadian or Arctic air (which is in place as normal) and therefore are resulting in the snow events. Thus, this is a temporal and locational anomaly. Other parts of the world have had a warmer winter than usual. This simply goes to show that proving global warming requires observations over decades and must be evaluated in terms of evidence that can be clearly related to human activities.
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.