By Paul Homewood

Repost from Erl Happ’s site:

The author is a grape farmer and wine maker, and a close observer of climate.

It is widely asserted that grape vintages are nowadays earlier, due to hotter summers. I reject that assertion.  Winters are warmer than in the past. Not summers. The earlier start to a longer growing season and enhanced availability of CO2 enhances photosynthetic capacity. It improves efficiency in the use of scarce water by the grape vine. This very likely accounts for the earlier time of ripening. In addition, when the ripening month has been in February, the warmest month, and it occurs in January, the maturation period is cooler than hitherto, an advantage.

The Australian Bureau of Meteorology’s maintains that Australia’s climate has warmed on average by 1.44 ± 0.24 °C since national records began in 1910.  But this statistic is the result of averaging monthly data that gives equal weight to autumn, winter, spring, and summer months. The inference is that temperature is rising in summer, in daytime when the sun is shining and this is considered a dangerous development.

To establish whether there has been warming in summer we should examine the average daily maximum temperature in locations that are already, or likely to become, unsuitably warm from the plant productivity/fruit quality point of view.

The bulk of the continent, including the major fruit growing and cropping areas, is described as hot dry summer, cold winter. Surprisingly, only a few towns in this zone have temperature records for a century or more. But, this is indeed the case for Mildura, Kalgoorlie, Adelaide, Alice Springs and Bourke. Their locations are indicated on the map below.

Data above and below from:

Mildura is close to the junction of the Murray and the Darling Rivers, where most of Australia’s grapes, citrus, almonds, pistachios, olives, carrots, and asparagus are grown. Mildura prides itself on four hundred more sunlight hours per annum than the Queensland’s Gold Coast where people go in their retirement, to live out their remaining years in a warm environment close to the sea. Mildura has rich red, energy absorbing soils that radiate strongly.

We have data for the post office up to 1950 and for the airport, that is about 4Km away, after that date.

First let us look at the monthly average daily minimum temperature in February, the warmest month.

The minimum, both prior to and after 1950, is close to 16.5C. No change. Contrary to expectations based on greenhouse theory, all the energy that is picked up during the day is dissipated overnight. There is no inhibition of the cooling process in the eight hours of darkness in mid-summer. Quick and complete. There is no ‘greenhouse effect’ in Mildura.

The average daily maximum in February is shown below.

In the 70 years prior to 1950 the average maximum reached or exceeded 35C on ten occasions. In the seventy years post 1950 it reached 35C on two occasions and exceeded it once. In the most recent seventy years the mean maximum is cooler by about a degree. If we rule out the data for the years prior to 1910, as being perhaps inflated due to the use of ‘non standard equipment’, no change.

Periods of sustained heat occurred between 1890 and 1905 and more recently, between 2011 and 2019. In these years there were wide fluctuations in temperature over short intervals. What can account for these gyrations?

Even the drovers dog knows that the temperature of the air is driven by the origin of the travelling airmass arriving from different points of the compass every day of the year. That is what a weather map shows. The direction of flow depends on the distribution of surface pressure. The sustained heat of the odd warm year and the early decades is plainly due to something other than trace gas composition. It is fair to suggest that the recent warmth is likely due to the same influences that brought warmer air in the earlier years.

Full post here.


February 25, 2021 at 05:24AM