Terra Cotta (low temperature fired and somewhat porous) roof tiles in Tuscany exhibiting a fine growth of surface growing species due to the prevailing humidity and relatively low incidence of ultra violet light. In Australia this sort of luxuriant growth is more common on humid south facing slopes protected from direct sunlight.
Studies in Climate
Looked at from a farmers point of view the bulk of the Earth is actually cooler than is desirable. Plant growth is inhibited in winter. It is the very warm moist summer climates of south and east Asia that support the densest population on the planet. The bulk of the rest of the Earth could do with some warming, especially if it coincided with more rainfall.
Every place on Earth has experienced climate change over geological time. Fossils of shells that are native to tropical seas can be found in the mud of the estuary of the Swan River an environment too cool to support these life forms today.
On the scale of a single human lifetime parts of the Earth have cooled and warmed, in particular the high northern latitudes. After three decades of cooling winters up to 1978 there followed two decades of warming winters peaking with the big El Nino of 1998. That warming trend did not continue. Since 2008 we see a trend for cooling winters in the mid to high northern latitudes with winter cold of an extreme not experienced since the 1960’s and 1970’s. Cold air at times penetrates to Vietnam and the Gulf of Mexico. This pattern of change has long been recognised and is described as the ‘Arctic Oscillation’. It relates to the relative strength of cold winds emanating from the Arctic Circle versus warm winds heading north from the mid latitudes. This flux in the winds is related to air pressure variations at mid versus high latitudes. Change in air pressure is driven by changes in the ozone content of the stratosphere/ upper troposphere. At 50-60° of latitude the prevailing low pressure cells wax and wane in intensity directly according to the amount of ozone in the air. If ozone levels diminish the air cools, atmospheric pressure increases between 50-60° of latitude and the pole and weakens at 30-40° of latitude. This increases the equator-wards penetration of the cold polar easterlies while diminishing the pole-ward penetration of the warm westerly winds that emanate from the sub tropics.
Even a simpleton observes that surface temperature depends upon cloud cover and the direction of the prevailing wind. If we look at the rise and fall of air temperature from the surface to the tropopause and into the stratosphere we see that the dominant agent of change in surface air temperature is the changing density of cloud influenced by the incursions of ozone into the upper troposphere driven by change in the stratosphere. In the upper troposphere the level of moisture in the air is relatively invariable. When the air warms due to the ability of ozone to absorb outgoing radiation from the Earth, cloud density diminishes and more sunlight reaches the ground. The surface then warms. At the same time, the warm winds originating in the high pressure cells at 30-40° of latitude grow stronger while the cold easterlies of polar latitudes are diminished with the fall in polar air pressure.
Ozone levels in the stratosphere and upper troposphere peak in winter. It is in winter that the climate is seen to vary most markedly.
The role of ozone is easily illustrated. In the southern mid latitudes, near the surface, we see peak air temperature in summer as we would expect. But in the upper troposphere at 6-10km in elevation we see peak air temperatures in winter as the level of ozone in the stratosphere and upper troposphere increases. This is due to the diminishing levels of short wave energy from the sun as the angle of incidence changes; the sun sinks lower in the sky. Ozone as a molecule with three oxygen atoms is easily split by short wave radiation from the sun. Less short wave energy in winter means more ozone. Ozone warms by absorbing long wave energy given off by the Earth and the lower levels of the atmosphere. More ozone means warmer air, means less cloud and warmer surface temperature.
Ozone levels in the stratosphere rise and fall not only seasonally but also over decades and centuries, due the changing intensity of very short wave ionising radiation from the sun. It is the waxing and waning of ionising energy from the sun over solar cycles averaging 11 years, and longer cycles of 100 and 200 years that changes the composition of the upper atmosphere including its ozone content. This directly influences cloud cover and the direction and temperature of the winds that prevail at the surface.
As northern hemisphere winters become cooler we will see a recovery in ice in the Arctic in winter. Unlike Antarctica there is little ice in the Arctic in summer. There never has been. Ice in the Arctic is a seasonal affair and in winter it is very much dependent upon what is known as the ‘Arctic Oscillation’. This term simply refers to the strength of the cold polar easterlies versus the warm south westerlies. It is in the high northern latitudes that we see the most dramatic swings in temperature over time. This is not new. It is not due to the works of man. It is an entirely natural phenomenon driven by changes in the atmosphere wrought by solar energy that is responsible for the ionisation of the upper atmosphere.
Why do we see this change most markedly in the northern hemisphere? It’s because the Southern Hemisphere is ozone depleted all year round due to the strength of the night jet over the pole that brings ionised nitrogen into the stratosphere from the mesosphere. Ionised nitrogen is hungry for ionised oxygen and the combination product is NO2 and NO3. Less ionised oxygen means less ozone. An ozone starved atmosphere has less scope for inter-annual, decadal and longer interval variations. It is the relatively ozone rich northern hemisphere that the most dramatic changes occur, especially in winter. At some time in the future the Baltic ocean will freeze over and people will ice skate on the Thames just as they did in the little Ice Age that stretched between 1350 to about 1850.
When people are ice skating on the Thames they will wonder whether it might not be a good thing if the temperature were a little warmer like it was in the late twentieth Century.
The Vine and Climate
The bulk of Australia gets very hot in the months of February, March and April when vines mature their fruit. Few Australian viticultural environments have the protection from hot winds that the northern parts of Europe enjoy by the combination of the Mediterranean Sea, the Pyrenees and the European Alps. Albany at 35 degrees south is slightly closer to the equator than Gibraltar at 36 degrees north. On first sight therefore, one might expect the wines of the South West of WA to have more in common with those of Algeria rather than those of Montpellier, Avignon, Bordeaux or Dijon. However, the South West of Western Australia gets first use of Indian Ocean air as it moves west to East and is less troubled by damaging heat events than all points to the east. And the Southern hemisphere is much cooler at comparable latitudes than the northern hemisphere because the oceans slow down the warming of the hemisphere in summer. The southern hemisphere is two thirds ocean whereas the northern is two thirds land.
If one searches the Australian continent for the best climates to conserve flavour, it is the cloudy regions in the extreme south-west that offer the most favourable environments. The autumn months of March and April are fine and balmy, and the winds in the main gently off the sea, as the continent gradually cools. The low-pressure systems that bring the winter rain are still coursing the southern ocean well to the south. Any rain originating in cyclone activity of the tropics tends to sweep inland to the east leaving the vines of the south west corner free to mature their fruit free of misadventure.
In the south west the vine produces all its foliage by mid January. Growth then ceases and the fruit readily accumulates sugar to mature the fruit between March and April. A long growing season and an absence of heat in autumn yields favourable conditions to ripen equally the very early varieties and the very late i.e. Pinot Noir through to Cabernet Sauvignon and Mourvedre, with a fine chance of producing flavoursome wine across the board. This is highly unusual in the world of viticulture, in any continent. In higher latitudes one must match a variety to growing season and ripening time in order to escape unwanted heat while avoiding the onset of winter that will curtail sugar accumulation and promote disease. Inevitably, seasons are more variable at higher latitudes.
In the cloudy south, overnight humidity is 100%, falling to perhaps 55% at midday. It is rare for daytime temperatures to exceed 24 degrees Centigrade. The fruit slowly ripens while retaining in greater concentration the array of flavours possible in any given grape variety. In the context of Australian viticultural climates, this is unusual.