An unusual sight in the backyard this week – the leaves of ornamental pear trees, planted a few years ago for summer shade, are turning into striking autumn colours… in mid- summer. Could this be due to South Australia experiencing a cooler-than-average January?
In ‘why leaves turn brown in autumn’ one theory says that leaves change colour due to decreasing light availability and lower temperatures. Despite a few very hot days early in the month, January turned out to be the coolest in a decade for most of South Australia. Temperatures were about three degrees below average for more than a fortnight – Adelaide has mildest January in more than 10 years.
How is this possible given global warming trends? Part of the confusion comes down to our understanding of weather and climate and the difference between the two. Weather is what we see on a day-to-day basis. It is unpredictable and explains changes in the atmosphere over short periods of time. Climate, on the other hand, describes the behaviour of the atmosphere over long periods of time. Rainfall patterns are another example of how weather and climate differ.
“We expect that extreme rainfall events across the nation are likely to become more intense, even where annual-average rainfall is projected to decline.” Kevin Hennessy, Research Scientist, CSIRO, January 2015
Last month, in its most comprehensive analysis yet of the impacts of climate change, the Commonwealth Scientific and Industrial Research Organisation (CSIRO) painted a worst-case scenario of a rise of up to 5.1 degrees Celsius by 2090 in Australia if there are no actions taken to cut greenhouse emissions – see Australia getting hotter, faster than climate change rate.
I wonder if deciduous trees are putting on their autumn coat in summer elsewhere. How will the trees progress now that this cool run is ending and the forecast is for temperatures in the mid-thirties and low forties over the next few days? There is one thing I am fairly confident about. I doubt the gorgeous reds, oranges and yellows will revert to green before next spring.