Climate Change And Extreme Weather Events
It is commonly said that weather and climate are entirely separate so that global temperature trends cannot be discerned from day to day weather.
Against that we all know that as soon as an exceptional event occurs there are those who cannot resist announcing that it is a sign of global warming. Indeed, it has been suggested that global warming results in more extremes of every kind including exceptional cold spells.
Starting with first principles it does seem likely that something as significant as a change in global temperature TREND really ought to be discernible somehow on a day to day basis. After all, weather continuing over time IS climate. The difficulty lies in deciding which weather indicators are useful and which are not.
Extremes are not particularly helpful. Whether the underlying temperature trend is up or down extremes will always occur and are, in fact, frequent events. Every day an extreme record is broken in many places and in part that is a consequence of the short history of weather recording and the sheer number of locations where humans are now available to observe weather events that would have gone unnoticed a few decades ago. Add to that the huge number of possible weather variables and their combinations together with the enhanced awareness arising from current climate concerns and it is hardly surprising that we are nowadays inundated with reports of extremes and exceptional events. However there is no ready comparator between the number and severity of extremes occurring now and those that occurred in the past.
The actual temperature at any given time is not much help either. When one considers the available temperature range between absolute zero and the boiling point of water the fact is that an average change of a couple of degrees centigrade is not physically noticeable and there is a possibility that of the upward temperature change observed in ground based recording sites at least a portion of that change could be attributable to changes in the site characteristics over time.
Increased building development and general urbanisation around and near sites is a prime candidate. That will be why the more recent satellite based recording systems do not fully reflect the observed ground based rise. Satellites are still not as accurate as we would like them to be though and even they require adjustment from time to time and sensible interpretation of their readings. However for present purposes I do not intend to dispute that there was some apparent warming during the 20th Century and especially from 1975 to 1998. So far there has been no warming in the 21st Century.
To link day to day weather to climate over time requires a less specific and more flexible indicator so to choose one it is necessary to ignore the obvious and look at basic principles.
If the globe as a whole is warming it seems logical that there should be some noticeable difference in weather patterns compared to times when the globe as a whole is cooling.
Generally, heat arrives from the sun and is, over time, radiated to space. Although radiation to space occurs over the whole planet there is a general movement of heat from equator to poles via the oceans and atmosphere. On average there is a net gain in heat in equatorial regions and a net loss at the poles.
Unfortunately we know too little about the flow of ocean currents and the thermal behaviour of the oceans to be able to draw any helpful conclusions from oceanic features. I have my own theory on that point which I’ve expressed in my earlier articles so that it may be possible to use the more recently discovered decadal oceanic oscillations as a diagnostic tool but this article is about weather so I will leave the oceans to one side in this article.
We have to look at the flow of air in the atmosphere to see if we can find anything that helps.
The most noticeable airflow phenomenon in the atmosphere is the jet stream. It guides the movement of mid latitude depressions and effectively marks an interface between warmer equatorial air and colder polar air. The intensity of the flow affects the depth and speed of the depressions and the speeds of the winds around them.
It is very important to be aware that coolness or warmth in themselves do NOT affect the severity and strength of weather systems overall. It is often said that global warming will result in greater extremes of storminess but that is in my opinion fear mongering nonsense. What matters in the creation of extremes of storminess is temperature differential not absolute temperature or amount of water vapour being carried by the air (warmer air can carry more water vapour). Warm humid air will not dump it’s load unless it is cooled down so if the globe warms evenly or cools evenly there will be no change in the frequency or severity of storms. In practice any temperature change either up or down will be increasing or decreasing differentials depending on the temperature regime at the commencement of a new trend. Neither warming nor cooling is any different in that respect. So, extremes of storminess are not a useful indicator either way. They just indicate that changes are occurring but are neutral as regards the direction of change.
Logically a warming spell must be evidenced by more warmth coming in at the equator than is lost to space by radiation. A cooling spell must be evidenced by more heat being lost to space than is coming in at the equator. The question is whether those two scenarios produce different weather signals and I believe they do.
It only needs tiny differences either way to switch the globe from net cooling to net warming and as I’ve said in my previous articles my belief is that the influence of the sun combined with the heat storage capacity of the oceans is so large and overwhelming that the greenhouse effect would have little effect on the switches from net cooling to net warming or vice versa. The importance of the greenhouse effect lies in it’s contribution to overall temperature so that with it the world is warmer than it otherwise would have been but that cannot override the hugely greater effect of the sun and oceans in controlling the switches between warming and cooling trends. The only effect it could have would be to delay or bring forward the date of the changes between the two modes. In fact it may be that the oceans set the global atmospheric temperature and not the atmospheric greenhouse effect but I will deal with that in my next article.
So, what weather indicator might suggest we are in either a cooling mode or a warming mode?
Overall cloudiness globally could be a useful indicator but it’s so hard to measure reliably that I’m inclined not to use it. Whilst on the subject I should consider the apparent correlations between cloudiness and cosmic rays or cloudiness and geomagnetic changes. After consideration I believe they are secondary correlations of no predictive significance. I believe that what happens is that in periods of solar induced cooling the atmosphere in the process of cooling becomes unable to hold as much water vapour so that overall cloudiness increases. It is quite true that when the sun is less active there are more cosmic rays hitting the Earth and there are geomagnetic changes but I see no present need to include those processes in an explanation of any increased cloudiness.
As always one should start with the simplest explanation namely that the Earth gets cloudier when the atmosphere is cooling and less cloudy when the atmosphere is warming because warmer air holds more water in vapour form than does cooler air. All we need to explain cloudiness changes is temperature changes. It follows that more global precipitation is a sign of cooling whereas less global precipitation is a sign of warming but for the purposes of this article I am looking for a more consistent weather indicator of global temperature trend.
It is noteworthy that there do seem to have been more severe precipitation events since the global temperature trend started to turn downwards recently but I still see suggestions from committed alarmists that that is a consequence of warming rather than cooling. I strongly disagree with such people.
My submission is that one needs only to observe whether the net movement of air over the entire globe at the surface is either from poles to equator or vice versa.
If the net surface flow is towards the poles we are warming. If the net surface flow is towards the equator we are cooling. Naturally, air circulates so any net flow in one direction has to return to source from the opposite direction at a higher level in the atmosphere so the concept of a net flow in any particular direction can be confusing.
Perhaps better to regard it as similar to the difference between clockwise and counter clockwise movement and if one takes a lateral cross section of the atmosphere it is easier to envisage with the lower level winds effecting the primary warming or cooling process and returning back to source at higher levels. If one stands at 45 degrees latitude and faces West then a warming flow will be in the form of a counter clockwise rotation and clockwise for a cooling flow. It will never be that obvious of course because we are considering a net average effect over time but the mental image may be helpful.
The problem then lies in knowing how to tell the difference in a three dimensional mixture of gases such as the atmosphere which has many chaotic movements at all levels.
I like to keep things simple and to rely on real world observations. I have observed the cooling of the 60’s to mid 70’s, the subsequent warming, the stall in warming that followed and now possibly a move towards cooling.
There is a noticeable difference in day to day weather patterns which over time indicates one trend or the other but it is too rough and ready to diagnose the scale of either. For present purposes however we need only discern the trend. The scale of any trend will require other diagnostic methods.
Simply put, are areas around the 45 degree latitude getting winds mostly from a southerly point or mostly from a northerly point? Could it really be that simple?
When I refer to northerly or southerly winds I mean any flow of air with a component from one direction or the other, not just direct northerly or southerly flows.
To decide whether I am talking nonsense or not all one needs to do is consider the movement of the jet streams in conjunction with the main high pressure systems.
If jet streams, on average, are further south then the high pressure systems to the north of them predominate and the globe is cooling. If, on average, they are further north then high pressure to the south of them predominates and the globe is warming.
I’ll leave it to others to check it out but I’ll just give an illustration.
I well remember the very cold winter of 1962/63. The UK persistently had high pressure over Greenland and Northern Europe giving a primary flow of air from the north. That feature was not just for the duration of that winter. Throughout the cooling trend up to 1975 or thereabouts winds with a northerly component were much more common than they were during the subsequent warming trend.
During the warming trend from 1975 to 1998 there were very few northerly flows of air in Western Europe. The hot summer of 1976 had the main area of high pressure over Southern Europe bringing a steady flow of hot equatorial air northwards. From 1998 to date there has been a shift away from the more frequent southerly flows and since 2007 the tendency for a polar component to wind flows at 45 degrees latitude in both hemispheres has increased further. In the spring and early summer of 2008 North America has been plagued by regular incursions of air from the north and Western Europe has been cooler than average due to many days of winds with a northerly component.
It is not a clear and tidy situation because the weather patterns change greatly from year to year and season to season despite the underlying warming or cooling trend and local variations can hide the underlying trend unless one looks at the whole hemisphere. Cold plunges over North America in winter give warm plumes over Europe which is what happened last winter (2007/2008) so despite a global cooling tendency Europe was anomalously warm.
My conclusion is that a careful observation of weather patterns over the entire globe and, in particular, ascertaining whether there is a net average surface movement of air towards the poles or towards the equator should reveal whether there is an overall global warming or cooling trend at any particular time. The best place to make the observation would be at 45 degrees latitude in each hemisphere because the halfway point between equator and pole is likely to be the point of balance if the global temperature were to be steady (which never actually happens).
In relation to CO2 the question is whether the influence of CO2 is strong enough to completely disrupt the operation of the switch from warming to cooling and vice versa in the face of what would have happened anyway due to other (probably Solar and Oceanic) influences or whether it just has a minor modulating effect. That is a matter that is the subject of much debate but it seems to me that if that were possible it would have happened many times in the past at times of much higher CO2 levels than the present day so that the risk would be readily apparent in the historical record but it is not. CO2 levels always seem to have followed warming and never to have caused it.
I have heard it said that periods of severe volcanic activity in the geological past increased global temperatures by emitting substantial volumes of greenhouse gases. That may be so but is not necessarily an indication that CO2 caused the warming. Volcanic activity puts a great number of gaseous materials into the atmosphere so any warming as a result of severe volcanic events would be more likely a result of increasing overall atmospheric density rather than just being attributable to CO2 emissions. As Venus shows us, a denser atmosphere results in a stronger greenhouse phenomenon. The thinner atmosphere of Mars shows the opposite scenario.
In fact, atmospheric density is far more important than the proportion of CO2 in dictating the strength of a planet’s atmospheric greenhouse effect.
It hardly matters if CO2 creates a warming influence during a natural cooling period. If anything it is helpful to planetary life by mitigating the adverse effects of the natural cooling.
If CO2 adds to a natural warming trend then it is only going to have a significant effect at or around the peak of the natural trend and so will only be a temporary phenomenon and highly unlikely to cross any ‘tipping’ point.
Additionally a serious cooling period from natural causes is likely to increase oceanic CO2 absorption and so dampen down any CO2 effect in the subsequent natural upturn although the length of lag is uncertain and may be as long as 800 years.
So, climate shifts of as broad a type as a shift from overall warming to overall cooling should be capable of being spotted at a very early stage by careful observation of global weather systems.
Climate is only weather that continues over time. A change in the general pattern can be discerned over and above the daily chaos.
In fact the weather change (which could either be sudden or gradual) is the first available indication that a climate change is under way provided it is observed globally in the way I suggest rather than locally or regionally. No doubt false alarms are likely but over time a new pattern becomes gradually clearer.
Published by Stephen Wilde April 23, 2011