This post is best read after viewing parts 1, 2 and 3 that set the scene for what is described here.
I noted in parts 1 and 2 that variability in global temperature is greatest between November and March when the globe is coolest. This is related to high variability in southern summer when global cloud cover peaks. I suggested that this variability is likely related to variation in cloud cover. In part 3 I outlined a mechanism related to the coupled circulation of the stratosphere and the troposphere in the Arctic and the Antarctic that induces a variation in cloud cover and described the spatial expression of that variation.
The manner in which the planet warms is surprising. If we look hard enough, it tells us how and why it warms. The value of a good theory is that it makes explicable what we see. It is much safer therefore to look at the manner in which the planet warms, as I have done in parts 1 and 2, before theorizing.
What follows is big picture analysis jumping from highlight to highlight. For data I rely on Kalnay, E. and Coauthors, 1996: The NCEP/NCAR Reanalysis 40-year Project. Bull. Amer. Meteor. Soc., 77, 437-471. accessible here: http://www.esrl.noaa.gov/psd/cgi-bin/data/timeseries/timeseries1.pl.
In this article we see that:
- Equatorial sea surface temperature varies with equatorial sea level pressure.
- Equatorial sea surface pressure varies with the solar wind.
- In respect of anomalous behavior that is superimposed on the seasonal cycle, the hemispheres heat alternately.
- The northern hemisphere suffers the widest swings in temperature but largely in winter.
- The evolution of temperature depends in large part upon what is happening in Antarctica.
- The planet tends to heat or cool most dramatically between November and March when cloud cover is most extensive.
- The mechanism responsible for climate variation that is described here can account for the diversity in our experience of climate change over the last sixty years and the cooling to come. It is a mechanism that allows one hemisphere to warm while the other cools.
The Sun and atmospheric pressure
The Southern Oscillation Index (SOI) tracks the ENSO phenomenon in the Pacific Ocean. It is based on the difference in sea level pressure between Darwin Australia (12°south 131°east) and Tahiti (18°south 150° west in French Polynesia).
Daily sea level pressure for Darwin and Tahiti is available at: http://www.longpaddock.qld.gov.au/seasonalclimateoutlook/southernoscillationindex/soidatafiles/DailySOI1933-1992Base.txt
Because the record is short, the average is lumpy. It is assumed that, were the record long enough, it would be smooth. To obtain a smooth line the data has been adjusted manually. That smooth line is shown against the actual 30 day moving average of Darwin sea level pressure for the period January 1999-July 2011 in figure 1.
Figure 1 Seasonal evolution of Darwin daily sea level pressure in mb.
An anomaly in sea level pressure is a departure from the average daily value for a selected period. In this case the period is January 1999 to July 2011.
Figure 2 charts the relationship between the daily anomaly in sea level pressure at Darwin and the Dst index which is an index of geomagnetic activity that relates to the strength of the ring current in the ionosphere.
Figure 2 Dst Index and SLP anomaly Darwin
Left axis: Daily Dst index in nanoteslas. Source: http://wdc.kugi.kyoto-u.ac.jp/dst_realtime/201108/index.html Note that a fall in the Dst index represents increased geomagnetic activity.
Right axis: Anomaly in daily sea level pressure at Darwin, Australia in millibars.
Note that the right axis is inverted
It is plain that Darwin sea level pressure is influenced by geomagnetic activity.
Similarly, sea level pressure in Antarctica is influenced by geomagnetic activity as we see in figure 3. There is no readily available index of daily sea level pressure in Antarctica but the Antarctic Oscillation Index (AAO) is a good substitute. It varies inversely with sea level pressure at the pole.
Figure 3 DST index and anomaly and the AAO index
Left axis: Daily Dst index in nanoteslas.
Right axis: Daily AAO index. This axis is inverted.
In figure 3 we see that as the Dst index plunges into the negative the AAO index increases in value indicating falling pressure over Antarctica.
It is apparent that under the influence of geomagnetic activity the atmosphere moves away from the Antarctica towards the equator.
The same phenomenon is demonstrated using the ap index and the AAO in figure 4
Figure 4 AP index of geomagnetic activity and the AAO
Left axis: Daily Ap index in nanoteslas
Right axis: Daily AAO index
The ap index and the AAO index increase together. An increase in the AAO index indicates falling atmospheric pressure at the pole. At times the relationship seems to be better than at other times. Other variables that will be described below influence the atmospheric response to the solar wind. In particular the level of solar irradiance is important in that it governs the plasma density within the neutral atmosphere. Plasma density determines the effect on neutrals (electrically balanced particles) as plasma responds to a change in the electromagnetic field by accelerating away and bumping the neutrals along as it goes.
The data for the year 2008 shows the relationship during a protracted solar minimum when the atmosphere is least inflated because solar irradiance is weak. It can be observed that the relationship between these variables (although still imperfect) is better at solar minimum. At that time, the response of the atmosphere to the solar wind is amplified. Solar irradiance and geomagnetic activity do not vary together. Under high levels of irradiance the response of the atmosphere to geomagnetic activity is much reduced and harder to discern. At solar maximum the atmosphere can return to the pole regardless of the level of geomagnetic activity. High atmospheric pressure at the southern pole is associated with a cooling planet because night jet activity varies directly with pressure at the pole. The night jet brings nitrogen oxides into the stratosphere reducing ozone formation. This weakens the coupled circulation of the stratosphere and the troposphere resulting in rising surface pressure at 60-70° south (and over Antarctica generally), increased cloud and weakened westerly winds. This is a self reinforcing process.
Aspects of ENSO
The anomaly in daily sea level pressure at Tahiti has been calculated in the same way as for Darwin. Figure 5 looks at the relationship between the margin between these two pressure anomalies on the one hand and the Southern Oscillation Index on the other.
Figure 5 Tahiti less Darwin SLP compared to the SOI
Left axis Southern Oscillation Index
Right axis: Pressure anomaly in Tahiti less the anomaly in Darwin.
The difference in the sea level pressure anomaly between the Tahiti and Darwin tracks the Southern Oscillation Index. A fall in the index relates to El Nino warming. This is associated with a slackening of the trade winds due to a loss of the pressure differential between Tahiti and Darwin.
A slackening of the trade winds is associated with an even greater slackening of the north westerlies in the southern hemisphere.
The slackening of the north westerlies in the southern hemisphere is due to a rise in surface pressure at 60-70° south (and over Antarctica generally). This is associated with a fall in surface pressure in the Arctic ( a simple exchange of atmosphere between the hemispheres driven by change in the coupled circulation over Antarctica).
The fall in surface pressure in the Arctic is associated with an increase in the temperature of the polar stratosphere as night jet activity falls away enabling an increase in the ozone concentration of the stratosphere. Under the influence of the coupled circulation in the Arctic this affects sea surface temperature throughout the northern hemisphere but most energetically at 50-60° north. This is a winter phenomenon.
Low surface pressure in the Arctic is the expression of the warm phase of the Northern Annular Mode (also called the Arctic Oscillation) wherein the domain of the warm humid south westerlies extends to the North Pole to the exclusion of the frigid polar easterlies. Accordingly Arctic air temperature increases and the area occupied by sea ice falls away. The dominance of warm over cool episodes marked the period 1978 through to 2007. A cool mode commenced in 2007 and the northern hemisphere is currently experiencing winter temperatures not seen since the cool mode of the 1960′s and 1970′s.
The warm mode is marked by El Nino dominance in the Pacific whereas the cool mode relates to La Nina dominance. Dominance can be assessed in terms of the length of time that the index has one sign or the other or by simply accumulating index values over time. Neither the Arctic Oscillation or ENSO is ever climate neutral.
The initiating influence in this activity is the solar wind, but the effect of the solar wind is amplified by the activity of a strengthened coupling of the stratosphere and the troposphere over Antarctica.
As will be demonstrated below, the pattern of inverse pressure relations between the hemispheres dictates how the planet warms. But first, lets look at the relationship between sea level pressure and temperature at the equator.
Figure 6 Monthly anomalies in sea level pressure at Darwin and Tahiti
Figure 6 shows that although there are times when sea level pressure anomalies in Darwin and Tahiti move in the same direction at the same time, a period of intense warming like that which occurred in early 2010 is associated with positive anomalies in sea surface pressure for Darwin and negative anomalies for Tahiti (weak trades). Conversely, the period of strong cooling that commenced in mid 2010 is associated with negative pressure anomalies in Darwin and positive anomalies in Tahiti (strong trades).
The upshot is that sea surface temperature at the equator moves directly with sea level pressure in Darwin. Since the sea surface temperature response is associated with geomagnetic activity and is a global phenomenon one would expect that Darwin pressure would move in concert with equatorial sea surface pressure around the entire globe and this is indeed the case as we see in figure 7. The range of variation in Darwin is about twice the variation in near equatorial latitudes. The Pacific is a theater of extremes. Darwin sea level pressure increases when the zone of convection moves from Indonesia to the mid Pacific during warming events.
Figure 7 Sea level pressure in Darwin compared to that at 15°north to 15° south latitude.
Left axis: Monthly anomalies in sea level pressure 15°North to 15°south latitude, mb.
Right axis: Monthly anomalies in sea level pressure at Darwin, mb
How much of the change in sea surface temperature at the equator is associated with the variation in pressure in near equatorial latitudes?
Figure 8 Anomalies in sea surface temperature (10°N-10°S) and sea level pressure (15°N-15°S) with respect to the average for the period 1948 to July 2011
Left axis: Sea surface pressure in mb. Twelve month moving average of raw data centered on seventh month.
Right axis: Sea surface temperature in °C. Twelve month moving average of raw data centered on seventh month.
The closeness of the relationship that is seen in figure 8, and the fact that the curves start and finish together suggest that phenomena responsible for warming, that is allied with the rise and fall in sea level pressure at the equator is consistent with the change in sea surface temperature between 1948 and the present time. This is not the whole story however. In the short-term volcanic influences can influential. Notice the depression of temperature following the eruption of Pinatubo in 1991.
The relationship between surface pressure and geomagnetic activity
The relationship between the Dst index (or the ap index) of geomagnetic activity and sea level atmospheric pressure is non linear. From episode to episode other influences condition the surface pressure response. These influences could include:
Two factors modify the sea level pressure from day-to-day, month to month and year to year and these work in a bottom up fashion:
- Pressure changes on a daily basis with the passage of high and low pressure cells around the globe and the wetting and drying of the air.
- In near equatorial latitudes in the Pacific sphere sea level pressure is affected by the migration of the zone of convection between Indonesia and the central Pacific.
Conditions in the stratosphere and mesosphere are the strongest influence on the evolution of surface pressure. The shift of the atmosphere from high to mid and low latitudes that is monitored as the Arctic Oscillation and the Antarctic Oscillation index depends upon:
- The plasma density where plasma interacts with neutral atmospheric molecules under the influence of the changing electromagnetic field.
- The state of ionization of the atmosphere as it depends upon the changing incidence of very short wave radiation from the sun.
- The changing electromagnetic field within the solid Earth.
- The changing spatio-temporal expression of the Northern Annular Mode and the Southern Annular Mode. The mode results from the coupling of the stratosphere and the troposphere that introduces ozone from the stratosphere into the troposphere causing the troposphere to warm, lowering surface atmospheric pressure in a ring like pattern at 60-70°south latitude and also 50-60° north latitude. But the expression of the mode changes over time, for instance, a migration of zones of ozone descent affects the relativity of sea level pressure between New Zealand and the Pacific Ocean west of Chile. This is possibly involved in the El Nino ‘Modoki’ phenomenon.
- The rate of introduction of nitrogen oxides from the mesosphere into the stratosphere over the poles affects the population of free oxygen atoms capable of forming ozone, and therefore the ozone content of the polar stratosphere. This in turn bears upon the concentration of ozone in the air that descends within the coupled circulation and the strength of the surface pressure and temperature response.
The relationship between the NAM and the SAM and sea surface temperature
The northern and southern annular modes of inter-annual climate variability influence sea surface temperature. The flow of ozone towards the equator via the high altitude counter westerlies (see part 3) warms and dries the air reducing cloud cover. Accordingly a pattern of positive sea surface temperature anomalies is generated that stretches from high southern hemisphere latitudes towards the equator in a north-westerly direction and from high northern latitudes towards the equator in a south-westerly direction. This pattern of sea surface temperature anomalies can be seen to originate from zones of increased geopotential heights at 200hPa that identify the locations of ozone descent in the coupled circulation of the stratosphere and the troposphere. This is the fingerprint of climate change as it is written in sea surface temperature.
The seasonal evolution of ENSO
Figure 9 shows the evolution of sea level pressure in Darwin and Tahiti over a year.
Figure 9 The seasonal evolution of the pressure relativity between Tahiti and Darwin
Left axis: Sea level pressure, mb. Right axis: Difference between blue and red curves, mb
The green curve represents the difference between the red and the blue curves. It shows the pressure differential driving the trade winds between Tahiti and Darwin as it evolves in an ‘average year’. It is positive in all months, builds strongly from July onwards and peaks just after the turn of the year. The Trades are weakest in mid year.
Figure 10 Variability in the raw data pressure differential between Tahiti and Darwin since 1999, mb
Figure 10 shows that in the last decade, variability in ENSO is least in mid year and greatest at the end of the year.
So the variation in cloud cover is greatest in the midst of southern summer when the globe is coolest. It is at this time that global cloud cover peaks with three percent more cloud than in July-August. In mid year cloud cover is reduced due to the direct heating of the atmosphere by the land masses of the northern hemisphere. But at the turn of the year the northern continents are least illuminated and this cloud degrading influence, a product of the distribution of land and sea, is minimal.
The influence of the coupled circulation of the stratosphere and the troposphere in the Arctic between November and March explains the strong variation in cloud cover and sea surface temperature between November and March. It is at this time that the Earth is closest to the sun, irradiance is most intense, global cloud cover is greatest and most susceptible to alteration.
Surface temperature is determined not by variations in solar irradiance (very small) but by variation in cloud cover (very large). Cloud cover relates directly to the influence of the coupled circulation between the stratosphere and the troposphere over the poles. The main driver of long term change is the coupled circulation over Antarctica but in terms of the short term jerks the Arctic circulation is important and by and large it is a mirror image of that in the south. It is the rise and fall in pressure in Antarctica that determines surface pressure in the Arctic. The Arctic is more influential in determining the evolution of cloud cover in part because cloud cover is maximal at the time that the coupled circulation in the Arctic is most active.
But, the influence of the Arctic is also supercharged due to the relatively high concentration of ozone in the northern stratosphere. Ozone levels are high precisely because the coupled circulation is intermittent and the night jet less active than it is over Antarctica. In fact when Arctic pressure is weak, a situation that has persisted for thirty year intervals (e.g. 1978-1997) , ozone depletion via night jet activity is rarely seen. The temperature of the northern stratosphere is then anomalously high.
When cloud cover is curtailed the surface begins to warm. Then the land masses of both hemispheres provide a feedback by swiftly warming the atmosphere enhancing the loss of cloud cover. Add to this the fact that wind speed is generally much lower in the northern hemisphere and we can see why gyrations in sea surface temperature that are experienced in the north Pacific and north Atlantic are about twice the amplitude of those in the southern hemisphere. Increased evaporation due to high wind speed mutes the response of surface temperature in the southern hemisphere.
Southern waters do warm as ozone is introduced to the troposphere lowering surface pressure and speeding the flow of the westerlies. But the coupled circulation is perennial in the south and stratospheric ozone levels are consequently much less than in the northern hemisphere.
When sea surface pressure is depressed in the southern hemisphere high pressure in the Arctic enhances the flow of the polar easterlies that sweep across the northern continents towards tropical latitudes. But this is largely a winter phenomenon. It is high variability in winter that marks climate in the northern hemisphere. This is most evident in the Arctic as seen here: http://ocean.dmi.dk/arctic/meant80n.uk.php
The evolution of sea surface temperature by latitude
Figure 11 The evolution of sea surface temperature at 40-55°north and 40-55° south. Anomalies with respect to the 1948-2011 average, °C.
So far as the mid latitudes are concerned, we see the sea cooling in the southern hemisphere as it warms in the northern hemisphere. Don’t be confused by the apparently consistent pattern of warming in the southern hemisphere in summer. It’s not consistent at all. Look at 2001. Similarly one notes marked warming of northern seas in winter in 2002 and 2003. The hemispheres warm and cool alternately, a pattern that is inconsistent with the notion that a greenhouse effect is responsible for temperature change. This pattern of anomalies is an expression of atmospheric circumstances post the climate shift of 1976-8. It represents the current expression of atmospheric balances that are always changing. There is not one climate system but many. If you don’t appreciate the change in its parameters, you can’t model the climate system. It’s the assumptions behind the models that give them away.
It’s a system that is open to external influences.
Figure 12 The evolution of sea surface temperature at 40-55°north and 40-55° south. Anomalies with respect to the 1948-2011 average, °C.
Left axis: Northern hemisphere
Right axis: Southern hemisphere. The right axis inverted.
In figure 12 (a restatement of the data in figure 11) we see that the cooling of the southern mid latitudes, (inverted and re-scaled) has a lot of symmetry with the warming of the northern mid latitudes. Make no mistake, sea surface temperature responds to a global stimulus with mirror image effects between the northern and southern hemisphere. This must be so, because the pattern of pressure variation at all latitudes is dictated by the evolution of surface pressure over Antarctica. If pressure is falling in Antarctica it will be rising in the Arctic and vice-versa. The variation in surface pressure is directly related to the influx of ozone into the troposphere on the margins of the Arctic and the Antarctic via the coupling of the circulation of the stratosphere and troposphere that occurs at high latitudes. The strength of the coupling varies through the year. However if one takes notice of geopotential heights at 200hPa the circulation is active to some extent in influencing surface pressure and cloud cover in both hemispheres all year round.
Figure 13 Evolution of sea surface temperature between 25 and 40° of latitude, °C.
Between 25° and 40° of latitude we see the same mirror image effect of alternate advance in sea surface temperature anomalies.
Figure 14 Evolution of sea surface temperature in near equatorial waters at 10-25° latitude. °C
In subtropical latitudes the tendency for the hemispheres to warm alternately is still apparent even though these latitudes are blessed with less cloud than higher latitudes. These latitudes are a long way away from the latitudes where the coupled circulation brings ozone into the troposphere.
Figure 15 Influence of high northern latitudes on the evolution of sea surface temperature. °C
In figure 15 we see the influence of the mid latitudes of the northern hemisphere in providing the spikes in sea surface temperature that can be seen in the evolution of sea surface temperature between 50°north and 50°south latitudes. It is not just the tropics or indeed the Pacific Ocean that is responsible for the evolution of temperature where the sun shines brightest.
Summary for policy makers
The Earth system, under the influence of solar emanations, modulates the reception of solar radiation at the surface by varying the extent of reflective cloud. The solar wind initiates this process via its influence on the distribution of the atmosphere between high and low latitudes. The effect of the coupled circulation of stratosphere and troposphere over Antarctica is to amplify these variations.
The day-to-day and year to year gyrations in cloud cover are associated with what we observe as ENSO. ENSO is a complex phenomenon that arises in part from dynamics in the Pacific including a shift in the main zone of convective activity. But the evolution of ENSO is also driven by change in surface pressure that affects deep ocean upwelling. It depends upon change in pressure at high latitudes where the stratosphere can behave like an extension of the troposphere. It does so because in winter, temperature falls away with altitude in the polar atmosphere from the surface all the way to 5hPa, encompassing both the troposphere and the stratosphere. When a convectional circulation is established the coolest parts of the stratosphere descend to elevations that we think of as the domain of the troposphere. This results in what has come to be known as the Annular Modes of inter-annual climate variation, zones of lower pressure that, as they establish reinforce the coupled circulation. These ‘annular modes’ are also involved in the evolution of climate on decadal and centennial time scales via their association with change in cloud cover. It can be shown that change in sea surface temperature and sea surface pressure in higher latitudes heralds change in the tropics.
If we were more observant we would note that gyrations in the climate are closely associated with a strong variation in the temperature in winter in the northern hemisphere. These variations are monitored as the Arctic Oscillation. This phenomenon is part of the rich texture of climate change of equal importance to ENSO. Both are dependent on Antarctic processes.
The role of trace amounts of ozone in the troposphere is critical to an understanding of cloud dynamics. It is the change in cloud cover that results in changing surface temperature.
Current understanding of what determines the ozone content and the temperature of the stratosphere is deficient. We need to understand the role of the night jet and the coupled circulations in modulating ozone concentration and therefore stratospheric temperature.
Geomagnetic activity and surface pressure variations evolve over long periods of time according to plasma dynamics that is seldom observed and little appreciated.
The dynamic described here provides a plausible explanation for the change in surface temperature that is observed. The pattern of temperature change is complex, varying by latitude and hemisphere. The fingerprint of change is inconsistent with the notion that the increase in so-called greenhouse gases in the troposphere is responsible for change.
The important thing to note is that the change is reversible and there is nothing that man can do but adapt. The temperature of the southern stratosphere has been gradually declining since 1978. A less active sun will see further falls in the temperature of the Antarctic stratosphere. This will gradually reverse the erosion of atmospheric pressure in high southern latitudes that has been influential in the warming process.
When we are dealing with complex systems like climate the idea that we can project an outcome and then qualify that projection with a statement about our degree of certainty in relation to the likelihood that we are correct, is inappropriate. Time and again we discover that our assumptions do not reflect the real world.
Those who refuse to acknowledge that their projections are inaccurate, and in any case variable from one soothsayer to the next, are not practicing science at all. They should be able to explain the variations that we see from day to day and year to year, and that includes ENSO and the Arctic Oscillation. They are in fact doing something other than ‘science’. On no account should they be suggesting that they understand the system or that their models are a source of truth.
We can not pretend that we understand the climate system unless we can explain ENSO, the Arctic Oscillation, put the Antarctic Oscillation in its context of evolving pressure relations as the Southern Annular Mode and explain the PDO and the NAO. When that is accomplished we might ask around as to whether people think the science is settled.
When we understand what determines the emanations from the sun we might hazard a forecast as to the weather to be expected in six months time.