What's with this Global Warming lark? - Quareness Series (4th "Lecture").
Ladies and Gentlemen,
First a belief - in the Universe there's always the same amount of energy which does, however, entail differing concentrations and manifestations at differing times.
Molecule for molecule water is a much more potent greenhouse gas than CO2, since it absorbs energy over a far wider energy-wave spectrum. Methane is also about 20 times more potent than CO2 as a buffer of energy because it absorbs energy over a larger energy-wave spectrum than CO2, but it is present in only minute amounts in the atmosphere. Even for CO2 the actual concentration in the earth's atmosphere is less than 0.038%. It is the fear that human activity will add significantly to this level of concentration over the next 100 years that has provoked the present global warming panic. However, even a doubling or more would still be miniscule in scale.
The sun is the only major source of heat on our planet. When it shines it warms us up. Some of that energy is absorbed by the earth's crust, warming it. Some of that heat diffuses from the surface into the soil and rock below. This is geothermal heat. As the surface of the earth gets hotter, it acts like a radiator, dispersing its heat back into the atmosphere. Because this radiation is in the infrared invisible spectrum, we cannot see it happening, although we can feel its effect. It is the infrared radiation given off by the planet once it has been warmed that is buffered by the greenhouse gases in the atmosphere. They do it by absorbing the energy within their molecules. Those gases with the capacity to absorb energy with a wavelength in the infrared spectrum can buffer energy in this way - CO2, methane and sulphur dioxide. However, it is water molecules which are the most potent because they absorb energy over a very wide range of wave bands, from infrared to visible light.
Were it not for the blanket of greenhouse gases in the atmosphere the temperatures on earth would be boiling hot during the day and freezing at night. It's due to the presence of these gases in our atmosphere that some of the infrared energy that would otherwise reach the surface of the earth when the sun is shining is absorbed, reducing the extreme heat that would otherwise ensue.
Because of the greenhouse gases, much of the earth's warmth acquired during the day is prevented from being dissipated into space at night. The proponents of the theory of anthropogenic global warming point out that as a result of this effect, increasing the amount of greenhouse gas in the atmosphere will reduce the amount of heat dissipated into space at night and therefore over time is likely to cause the earth's temperature to rise. It is almost certain, however, that the levels of atmospheric CO2 would have increaseed rapidly during WW2 and the post war construction period, and that this should have caused a rise in temperature due to the greenhouse gas effect. But the temperatures in Europe actually fell by 0.3 to 0.4 centigrade over the period 1940 to 1975.
It is generally agreed that the water vapour and droplets in the clouds contribute at least 50% of the total global warming effect, although some say it's much higher (up to 93%). The difficulty is that the amount of water vapour in the atmosphere varies from time to time and is impossible to predict. A lot of polluting particles in the atmosphere will enhance the effect of the clouds in insulating earth from the effect of the sun. When huge amounts of debris are released into the atmosphere e.g. due to a major volcanic eruption, the world cools despite the release of large amounts of the greenhouse gases CO2 and sulphur dioxide. The opposite also occurs e.g. with the reduction in the concentration of particle pollutants over London, following on the Clean Air Acts of the 1950s, the sun's rays can now better penetrate the atmosphere and this has led to an average increase in temperature in the city of about 2 degrees celsius (as high as that predicted over the next 100 years by some of the global warming models). And this together with the separate urban warming effect has already resulted in central London being up to 4 degrees warmer than the surrounding countryside.
Scientific controversy centres on the relative importance of the enormous, but impossible to measure, effect of water vapour and clouds, the effect of changes in the sun's activity and the effect of the tiny but increasing 0.038% of CO2 in the atmosphere, in the production of global warming. It is because these effects are impossible to separate and measure that it is so difficult to make reliable mathematical models to predict the behaviour of earth's temperature in the future.
The greenhouse gas effect of a huge CO2 amount in the atmosphere (15% - 20%) up to 500 million years ago (due to constant asteroid bombardment and volcanic eruptions) did not prevent the molten mass of earth from cooling, although it may have slowed the process. By the time of the earliest recognisable animal life forms appearance (about 400 - 500 million years ago) it is calculated that CO2 concentration in the atmosphere had decreased to 4% - 5% and that when the first marine organisms emerged onto swampy land many millions of years later CO2 levels had fallen further to about 1.5% in the atmosphere (i.e. many times higher than today).
Despite these very high levels of carbon dioxide in the planet's atmosphere when it was born, the earth cooled down, basically because it was originally much hotter than the surrounding atmosphere. Indeed large parts of the planet came to be eventually covered with ice and known as the "Snowball Earth" period, just before multi-cellular life forms appeared. And this period was followed by several million years of warming. The Antarctic was warm enough to support animal life about 15 million years ago (as shown by the finding of the fossil remains of gastropods in the trans Antarctic mountains near the South Pole). The huge glaciation that formed the Antarctic must have occurred when the CO2 levels in the atmosphere were over 0.5% - 1%. Although we cannot be fully certain of these levels back then or of the exact extent of the duration of glaciation, it is evident that in the past the earth has cooled to very low temperatures in spite of very much higher levels of CO2 than at present. And this does indicate that high levels of CO2 in the atmosphere are not incompatible with global cooling. It's true of course that much of this is based on assumptions and calculations rather than accurate measurings and that is why much of the current argument about global warming and the part played by CO2 as a global greenhouse gas, has centred on what is happening now and how this relates to the period we can measure with some accuracy i.e. the past 1,000 - 2,000 years.
Evidence from ice core samples indicates that for the past 500,000 years the level of CO2 has been roughly stable at around the present less than 0.04% and over this period the earth has cooled slightly although from time to time the temperatures have fluctuated through swings of 3% - 4%. To trace back....primitive cellular animal life evolved between 500 and 300 million years ago and as life developed and photosynthesis occurred large amounts of CO2 were relatively rapidly sequestrated from the atmosphere by plant and animal life and deposited as chalk, peat, shale, coal and oil, producing a fall in CO2 concentration from a high of around 4% to the 0.038% found today. Throughout this time the earth was cooling and, although the CO2 levels were falling, they were many times higher than today.
The CO2 produced today when we burn fossil fuels is merely returning into the atmosphere a minute part of the CO2 sequestrated by plant and animal life over hundreds of thousands of years.....it's simply being recycled. If we were to burn all the available fossil fuel, coal, oil and gas in the world at one go, it would raise the atmospheric CO2 by only a small amount to nowhere near the level it was 500 million years ago when global cooling caused much of the earth's surface to be covered with ice.
It is almost entirely due to the apparent link between the temperature and CO2 levels over the past 500,000 years, revealed by the analysis of ice cores drilled in the ice caps, that the present concern about the effect of human activity on the CO2 levels in the atmosphere has been given some scientific credence. While it is likely that the CO2 levels measured in one place will not differ significantly from that in the rest of the world, the same cannot be said for the temperature. It is unlikely that the relative hot and cold spells found in the Antarctic ice core samples accurately reflect what was happening in the rest of the world. It is only in the past 50 years that advances in technology have allowed us to measure the change in CO2 levels accurately and record temperatures continuously. And in the past 15 years we have also been able to obtain accurate reproducible data on ocean levels, global temperatures and the behaviour of clouds, thanks to the use of earth orbiting satellites.
Over the past decade the measurements from European remote sensing satellites have demonstrated that there has been a rise in sea level of 0.5 - 0.1mm a year (within the margin of scientific error) and that the increase is not accelerating. Although there is some evidence that the levels of the oceans have risen slowly, possibly by about 5cm over the past 150 years, it is a process that started long before industrialisation produced an increase in atmospheric CO2. And the acceleration in the rate at which some glaciers in Greenland have been melting, adding to the ocean mass, started long before the motor car and industrialisation. Although the Arctic ice cap has probably been getting smaller since the Little Ice Age (16th and 17th centuries), most evidence points to an increase in the amount of ice in the Antarctic.
The best model is only as good as the weakest information used in its construction, and many parameters used in climate modelling are immeasurable or unknown e.g. exact contribution of water vapour and of the clouds to global warming. In addition many of the factors that might determine the global weather pattern, such as cosmic radiation and solar magnetic effects, are omitted because they are uncertain or unpredictable. All the models have failed to predict past events such as the Little Ice Age or the 0.4%C fall in global temperatures since 2000 (instead of the expected increase). Essentially the models are meant to be "what-if" scenarios but unfortunately many who do not appreciate the level of uncertainly in their predictions treat them as proven facts. The longer the time frame of these projections, the greater will be the magnification of any initial error. It's little wonder, therefore, that these models produce widely differing predictions of future events - some differ by as much as 300%.
When considering the consequences of the present and future levels of CO2 we need to know (1) if the world is actually getting hotter, and (2) if so whether it is doing so at a historically unusual rate. As for (1) the answer depends on the length of the period studied e.g. on a very long timescale of say 400 million years the answer is no (the earth is at least 10 degrees colder today), on a shorter period of say 10,000 years the answer is yes (the world has been slowly getting a little bit warmer). In the hundred years 1900 - 2000 the world has warmed up by about 0.6%C, mainly as a result of warmer and shorter winters. However, between 1940 and 1975 there was a reversal of this warming trend and Europe cooled by around 0.3%C - 0.4%C. It should be noted also that until recent times only maximum and minimum temperatures were recorded in many places. In addition the places used as weather stations often changed over the years and many being near town centres may be affected by urban warming. On the break up of the Soviet Union many stations were closed. During the 25 years from 1975 the world warmed up by about 0.5%C although this started to plateau off in 1998. Since 2000 accurate monitoring of global temperature by orbiting satellites has shown that this period of global warming has come to an end. Instead of rising there has been a fall in temperature of about 0.4%C. In hindsight the net increase in temperature recorded over the past 100 years, appears to have been the result of fewer very cold nights and only modest increases in the daytime temperatures.
Much of the present anxiety about global warming is less to do with the actual increase in world temperatures - after all 0.5%C is rather less than the variation between town and countryside - than with the rate of this increase in the 1980s and 1990s and the real question is whether this very recent rise represents a departure from the recurring ups and downs of our weather and presages a permanent and increasingly rapid shift towards a warmer world. And if so, can we or should we try to counter the effect. We do know that climate changes have occurred from the beginning of time and there have been floods, drought and storms ever since the world began. It can be reasonably argued that the world has seen the present changes over and over again during its history and that a modest rise in temperature would provide an extra source of energy at relatively little cost, to the potential benefit of mankind. The majority currently appear to take the view that the changes we are seeing are real and may possibly be made more severe by industrialisation and they advocate caution suggesting that we should do what we can to moderate the effects of anthropogenic changes by anticipating any adverse effects that may ensue. Whatever the view, no one really knows whether the rise in global temperature over the past century is the result of human activity or just another blip in the history of our planet.
This raises another important question - what might happen were the CO2 levels in our atmosphere to fall?
Carbon dioxide is heavier than air and dissolves in water, which is why the world's oceans are such an important buffer against a rapid rise in CO2. At the same time as the temperature of the seas increases, their capacity to dissolve CO2 decreases. Over the ages huge amounts of carbon dioxide have been taken out of the atmosphere and transformed into chalk and coral, into the hydrocarbons of coal, peat, methane and oil, into graphite, diamonds and charcoal. When we burn fossil fuels we are merely recycling atmospheric carbon dioxide in various chemical guises - we are not producing any new carbon. The atmospheric CO2 is constantly taken up by plants in the process of photosynthesis. The plants are then eaten by animals and the carbon they contain is then given off when the animals metabolise fuels such as sugar and fat in order to produce energy. Carbon dioxide, like oxygen, is part of our atmosphere and is essential for life here. Without CO2 plant life would cease to exist and most species of animal, including man, would die out. Leaving aside the effects of our "industrial" activity, the amount of CO2 in the atmosphere is a balance between animal and plant life - an increase in the amount of animal life relative to plants will increase the CO2, while a relative increase in plant life will reduce it. The giant rainforests of the world take up some 30% - 40% of carbon dioxide produced. In the recovering state, the rapidly growing saplings are more efficient sinks of CO2 than mature trees. Human activity and industrialisation contribute just 2.5% - 3% of the total CO2 output, although this amount is increasing.
The concentration of CO2 in the atmosphere is a historically low 380 parts per million (0.038%). Even at this tiny level it is about 0.008% higher than it was a hundred years ago with some of this increase due to the surface water of our oceans warming up, some due to volcanic activity but most of it attributed to human activity. However, it's important to stress that the actual total amount of CO2 in the atmosphere is still tiny. It's estimated that if no new CO2 were added to the atmosphere it would take only 5 years to reduce its level below what would sustain plant life, and that if plant life did adapt and continue at this low level of CO2 all the gas would be used up in about 7 or 8 years. The CO2 level found in our blood is essential to our wellbeing. A sudden reduction would cause many to feel sick and faint and to develop headaches due to a constriction in the blood vessels supplying vital organs. We are physiologically far better adapted to dealing with a rise in CO2 than with an acute reduction. Indeed this may be an evolutionary footprint reflecting the fact that animal evolution occurred during periods of higher rather than lower atmospheric CO2.
The only compelling evidence that CO2 is linked to the recent rise in the earth's temperature due to its greenhouse gas effect comes from the studies of ice core samples drilled in the ice caps. The temperature at various depths can be measured and recorded and the CO2 content of the bubbles of trapped gas, while subject to a little variation, is remarkably consistent. These samples have been dated, albeit with some possible small errors with regard to the decay rate in the isotopes measured, for up to 50 million years but over 500,000 years their accuracy becomes increasingly questionable. It is the general close parallel, the causal association between the rise in temperature and the rise in CO2 over the past 10,000 years that has led to the present persuasion that the temperature change is driven by atmospheric CO2. However, close examination of the samples from the Vostok Lake area of Antarctica over this period appears to show that in many instances the temperature increase occurred some 600 to 1,000 years before the increase in CO2. The same prior association with temperature is to be found in other instances e.g. the skewing of earth's trajectory around the sun (flattening of its slightly elliptical circuit) so that it comes closer to the source of the sun's heat - during these warm spells the CO2 in the atmosphere increases. It's evident that the rise in CO2 in these instances is a consequence of the warming during these cycles and not a cause. And we are at present coming to the end of a warm cycle that probably started at the end of the Little Ice Age.
There is a close correlation between solar activity and the atmospheric temperature in the Arctic between 1800 and 2000 - much closer than that between temperature and CO2 during the same period. And this is so despite the fact that the International Panel on Climate Change (IPCC) in 2001 using mathematical models predicted that without curbing the rate of CO2 production, the earth's temperature would increase by 1.4%C - 4.2%C in the next 100 years. Their assumptions in this included a continuously accelerating increase in population, no adaptive responses (e.g. a switch to alternative energy sources) and accelerating growth in energy demand per capita. This level of increase in temperature is little different from that experienced between those living in London and those in the surrounding countryside. Inevitably the coldest part of the day would be most effected by this rise in temperature rather than the warmest days getting much warmer - hardly cause for the end of the world.
Ultimately until there is clear confirmation of the causal relationship between CO2 and the earth's temperature, the IPCC case (which incidently has been disputed by over 33,000 American scientists - ref Oregon University Department of Science and Medicine petition - and by some 400 climate scientists and astrophysicists from around the world in 2007, some of whom were on the IPCC panels and who make up 4 times the number who drew up the IPCC report) remains unproven. Despite some rather improbable/implausible explanations/theories put forward by some (e.g. based on water-CO2 feedback mechanisms) it so far remains kinda impossible to explain how an increase in CO2 could be a cause of a rise in temperature that occurred hundreds of years earlier. And if this "follow on fact" were to be proven beyond any reasonable doubt in the case of any ice core sample (e.g. in the Vostok Lake area), it would appear to disprove the theory that the increase in temperature is the result of a rise in CO2.
The evidence that climate change is CO2 driven appears at best equivocal and it may be the better part of wisdom to approach the matter with a more open minded stance. Of course there is little doubt that the world has warmed up over the past 50 years and that the rate of warming has been a little greater than that seen previously, and although it is possible to explain this rise by cyclical changes that occur naturally, it's the rate of change that has led to the speculation that some, if not all, of this is due to the extra CO2 released by human/industrial activity.
In summary the evidence to date for this hypothesis boils down to
- a general correlation between temperature and CO2 levels in ice core samples going back
600,000 years;
- an increase in human activity, CO2 levels (up 0.008%) and temperature (up 0.6% - 0.8%) over
the past 100 years;
- the demonstration that CO2 is a greenhoue gas
(and the consequent reasonable belief that more CO2 in the atmosphere will result in
reducing the amount of earth's heat lost into space).
The evidence against comprises
- the correlation between CO2 and temperature demonstrated in ice core samples shows that
in some instances the rise in temperature occurs before the increase in CO2, often by about
600 - 1,000 years;
- the earth was believed to be at its coldest 600 million years ago ("Snowball Earth") when the
concentration of CO2 in the atmosphere was up to100 times higher than today;
- in the past 50 years, when the measurements are most reliable, the correlation between CO2
levels and temperature is not very good (the correlation between temperature and solar
activity is much better);
- neither the rise in temperature in the medieval period nor the fall in the 16th and 17th
centuries appear to have been associated with an abrupt change in CO2 levels (and the fall
between 1945 and 1970 occurred at a time of intense industrial activity);
- although CO2 levels in all areas are similar, the changes in temperatures have not been the
same all over the world;
- since 2007 we have seen some unusually cold weather in various parts of the world;
- the CO2 released by human activity comes from the carbon sequestrated from the
atmosphere many years ago and is merely recycled, not adding to the net level of CO2 on the planet;
- the amount of CO2 in the atmosphere is minute compared with the amount of water vapour
and droplets, and water is a much more potent greenhouse gas.
Based on this degree of evidence it is reasonable to conclude that the world has warmed in the past 100 years and that this has accelerated slightly between 1970 and 1998 after a cold spell in the 1940s and 1950s. This acceleration has now flattened off and there has been no significant warming since the El Nino peak of 1997 nor increase in world temperatures since 1998. It's impossible to say at present whether this will remain within the limits of previous warm periods or whether it presages an exceptional period of global warming that will threaten mankind at some point in the future.
The evidence to date does not unequivically support the contention that manmade CO2 is the cause of present global warming. Prophesies of future trends in global temperatures have been exclusively based on computer models, which are essentially self confirming expressions of the original input dogma. To accept a theory without good evidence because it is presented as a "consensus view" is bad science. At the end of the day we just do not know what overall effect the CO2 released by man's efforts will have on the world's climate - it may take many years to obtain the necessary evidence. On the present evidence, however, it does not appear to be a cause for panic and the risk of waiting until there is more certainty seems much less than some would have us believe.
Here an additional word of caution may be in order. The precautionary principle is today championed by all sorts of people in all sorts of situations (what we might call the security disease) and it is often used to urge much stronger interventionist action to deal with the perceived threat of global warming. Even if some of the science is uncertain it is argued that the balance of risk requires acting as though the gloomiest predictions were the most accurate, because getting it wrong is seen as less dangerous than acting (or not) on the basis of more sanguine predictions and getting that wrong. This is the sort of thinking on say Tony Blair's part that led to the current war against Iraq, and we do now know the quite disastrous (at least short to mid term) results of that action.
Ironically, given the association in the Irish public mind (and that of various other jurisdictions) of "the left" with the man made global warming hyopothesis and "the right" with the sceptical opposing view, it seems the only current really practical alternative to our fossil fuel energy base is that of the nuclear option - paradoxically mostly opposed by "the left" and proposed by "the right" - go figure (as the Yanks might say). On balance the wisest (or perhaps I should say the least unwise) course of action at this point may be to take a deliberate decision to sit tight and not take any action. Of course this will not sit easy with the "proactive" mindset of many which informs their view of the progress of science and human development. However, as the good book says man does not live by bread alone and that God looks out for the birds of the air despite their "non planning".......in other words basic trust in something greater than me is surprisingly aligned with our spiritual welfare. Indeed it might be said that a substantial easing of obsessive attachment to our own egotistic endeavours may be an essential next step in our great evolutionary journey - only time and the Buddha will tell.
Sean.
Dean of Quareness.
February 2011.
Postscript (on the global ice caps): -
It is the assertions of a large rise in sea levels (from 7.9 inches by the IPCC in 2001 to 20 feet by 2100 suggested by Al Gore in his 2007 film An Inconvenient Truth) and the fear of flooding of low lying lands and islands which have caused most alarm. Any rise in the sea level would depend on global warming causing the melting of large amounts of land based ice and dumping it into the seas at a rate greater than that at which it evaporates.
The Arctic ice now covers much of what was once green land which was "lost" in the last great Ice Age thousands of years ago. It extends from the North Pole down towards Siberia in the east and Canada in the west and in winter it extends down to cover much of Greenland. However, the presence of oil under the Arctic, which was announced to the world by Russia claiming the landmass under the ice cap in August 2007 as an extension of the Siberian landmass which has enormous oil deposits, demonstrates how geographically new this ice cap probably is. Oil of course is a biofuel which comes from the degradation of plant life. Originally it came from the carbon dioxide in the atmosphere and the water and minerals in the soil. If oil is there today, the land must have been covered by plant life millions of years ago.
Melting ice is not the known cause of any reduction in the polar bear (or for that matter penguin) numbers. The threat to wildlife comes from man's encroachment on their environment, not from changes in temperature of less than 1 degree in 100 years. The actual reduction in the size of the Arctic ice depends less on absolute temperature changes than on the relative lengths of winter and summer and on the amount of rain that falls in the winter. The effect of global warming has tended to reduce the duration of the winters rather than to warm up the summers. Evidence available from satellite photographs indicated that in the past decade or so ice has often been more rapidly lost in summer than it has been replaced in winter (a process which reversed in 2005 - 2008, when the ice cap increased in size). Nevertheless the absolute significance of any change in the Arctic temperature will be known only after 50 - 100 years. Having said as much there does seem to have been some decrease in the overall size of the Arctic ice cap in the past 100 years. Because 4/5ths of this ice is under water, the melting has not produced a noticeable rise in sea level. Indeed if the ice melted entirely it would not cause more than a few millimetres rise as all but its visible surface is already under water.
A more real potential problem would arise if cold water from the melting Arctic ice cap and Greenland were to push the Gulf Stream further south causing much colder dryer weather in Northern Europe. Currently though, the Gulf Stream appears if anything to be getting warmer without any change in strength or direction, as indicated by buoys in the Atlantic. Although neither the land nor the sea temperature has changed dramatically in the past 100 years and the land based ice covering most of Greenland is probably slowly increasing, there is some evidence of a loss of ice from the edges of this landmass and an increase in the rate at which the ice melt from glaciers is being added to the seas around the coast. The two most likely explanations for this are
- the effect of water seeping through cracks in the glaciers, called moulins, and acting as a
lubricating slide under large masses of ice, easing their passage downhill towards the sea;
- the landmass under the ice is being warmed by geophysical heat from below the earth's thin
crust in this region, heat that cannot easily be dissipated due to the insulating effect of the
overlying ice.
Ultimately the significance of this melting effect will depend upon the balance between new ice formation and the rate at which the ice is lost into the sea. Present evidence suggests there is nothing new here and that it's not specifically linked to anthropogenic global warming.
Unlike the Arctic, the Antarctic ice is mainly heaped up on land and frozen sea surrounds its landmass. The extent of this frozen sea depends on the seasons. Like any iceberg, this ice ledge is vulnerable to an increase in sea temperature and there is some evidence that the sea in this region is getting slightly warmer which has over the past 100 years caused some gigantic icebergs jutting out from the peninsula to progressively erode and partially collapse (e.g. Larsen B and Wilkins shelves). Not being land based these ice shelves were always in danger of disintegrating during warmer years as they extended further north from the coldest region around the South Pole, not to mention the impact of the strong currents eroding their underwater base. And like all icebergs, they did not cause any recordable change in sea level when they collapsed and melted.
While it is difficult to be certain of the balance between new ice formation during the Antarctic winter and its loss during the warmer summer months, satellite observations suggest that much of the Antarctic ice is getting more extensive, especially that covering mountains in the eastern region where the ice is now up to 2 miles thick. This is probably due more to an increase in rainfall than to any change in temperature. In the western Antarctic, on the other hand, coastal ice appears to be subject to the same sliding motion as in Greenland. It's thought that this is an effect of the formation of rivers and lakes under the ice. The loss of ice from these coastal areas is slightly greater than the formation of new surface ice further inland, resulting in a small reduction in the total amount of ice in this region. Evidence from fossils found in ice bore samples in the region suggests that much of Western Antarctica is geologically less than 500,000 years old, compared with the 20 - 30 million year history of the rest of the Antarctic. More studies are needed before we can be certain as to what is happening, but it would seem that the net effect of the changes in the Antarctic ice cap on the global sea level is minimal. Indeed at present most scientists would agree that the Antarctic is not warming significantly.
All in all there is currently little to support the view that a rise in man made CO2 is causing any of the changes seen at the ice caps, many of which started long before the present rise in CO2 levels. Although changes are happening around the fringes of the ice caps, all the evidence suggests that they have been occurring for many hundreds of years. Whatever is happening we probably can safely say at this stage that the changes involved are unlikely to cause the alarming rise in sea levels some have predicted.