Robyn Williams: Well, spring is sprung. The 1st of September is conventionally taken as the start of the new season, but I’ve never known why. Maybe it’s just a handy date, rather than a solstice, a convenience on your calendar. But be warned, it could all soon change. Everything’s changing these days, so why not the seasons? Tim Entwisle, Director of the Royal Botanic Gardens in Melbourne, has a new book just out. It’s called Sprinter and Sprummer: Australia’s Changing Seasons. For reasons he’ll reveal right now:

Tim Entwisle: The first, or the twenty-first, day of September is the start of spring in some countries. But not, I think, in Australia. Australia is different. It has different seasons. Yet most Australians don’t acknowledge or even notice these differences.

That’s partly because minutes, hours, days and months are the way we organise our lives – sowing crops, attending job interviews, picking up kids from child care, playing footy, getting our hair cut and so on. Seasons are for noting, celebrating and tracking the changes in the world around us. If we get them wrong we don’t lose our crop, job or children. No-one has responsibility for approving the seasons, and they are not anchored by Greenwich Mean or International Atomic Time. But they are part of our inherited culture, part of the ritual of living on Planet Earth. Our responses to seasons – like the seasons themselves, vary from place to place.

The definition of a season seems simple enough but, as I argue in my new book Sprinter and Sprummer: Australia's Changing Seasons (published by CSIRO), it is misunderstood, misinterpreted and misused. Why should we have four seasons? Why must they each take up three months of the year? Indigenous communities have always known that Australia’s climate is more complex than a simple four-season arrangement suggests. Isn’t it time for all Australians to adopt a more realistic, home-grown system?

When I began the book in 2010, while Director of Sydney’s Royal Botanic Gardens and Domain, I wanted to make two somewhat contradictory points. First, there is a peak flowering period in most Australian gardens and bushland, and it happens before what we normally call spring. Second, plants flower all year round, not just in ‘spring’, and I thought I would use the opportunity to feature some of the quirky plants of my local town, and country, Australia.

Then, three years ago, I moved to England, where we get many of our cultural traditions including our idea of four neat seasons, each three months long. I gained first-hand experience of ‘true seasons’ and the plants that either define them or respond to them, depending on your perspective. I found that even in their homeland, the four seasons don’t always match the annual cycles of nature. So I expanded the scope of the book to address a more fundamental question about whether seasons are ever really ‘fit for purpose’ and to include seasonal stories of plants from all over the world. Perhaps it’s not only Australia that needs a thorough review of its seasons.

I don’t want to overstate the case for having a set of good, robust seasons. Seasons, like most natural phenomena, have been part of pagan rituals for millennia. Each season has been given characteristics much like the Signs of the Zodiac, and with as much value. For example, the Greek elements of air, fire, earth and water have been correlated with the seasons spring, summer, autumn and winter respectively. As have the so-called humours – blood, yellow bile, black bile and phlegm. In a modern twist I’ve seen the Myers-Briggs personality types mapped against seasons. While climate may affect our mood and behaviour, any seasonal classification is unlikely to assist in clinical diagnosis, life planning or recruitment.

But why not have seasons that suit Australia. Since 1788, we have laboured and partied under a set of four European seasons that make no sense in most parts of the country. We may like them for historical or cultural reasons, or because they are the same throughout the world, but they tell us nothing, and reflect less, of our natural environment. In time-honoured fashion I decided from the safe distance of London that it was time for Australia to reject these seasons, to adopt a system that brings Australians more in tune with their plants and animals; a system to help notice and respond to climate change. So the book took shape.

After two years abroad I returned to Australia to take up my current role as Director of Melbourne’s Royal Botanic Gardens in March 2013, to experience nine days in a row with temperatures over 30°C, a weather record for the city. This tallied nicely with my preference for a longer summer season in Australia. Living in Sydney, London and now Melbourne again (I had left Melbourne in 1998 to move to Sydney) I’m convinced that the four traditional seasons don’t make sense in Australia. My proposal is that we have instead five seasons based on the climatic and biological cycles we observe around us.

In the book Sprinter and Sprummer, I start with the origins and theory of the traditional seasonal system – which I’ve nicknamed the ‘Vivaldi Option’ – then review the Aboriginal seasonal classifications used across Australia, followed by my five-season proposal.

Seasons have been with us since early in recorded human history. In fact, we could argue that breeding and feeding seasons are part of the cycles of many animals and that our species, Homo sapiens, has merely extended this concept a little. The key element of human seasons is dividing the solar year into segments that start at a predefined time each year. In ancient Mesopotamia the year was divided into two: one half beginning with the sowing of the barley (autumn), the other with its harvesting (spring). The early Egyptians, living beside the Nile, added an extra season and brought in the concept of a cold season and a hot season. Their three seasons were more or less ‘flood’, winter and summer.

The Vivaldi option of four neatly defined seasons appears to have originated in the Mediterranean region, perhaps also independently in China and in places with less well documented histories. The Sumerians and Babylonians were the first in the region to use equinoxes and solstices to define four evenly timed seasons. The four season system was taken up by the Greeks then by the Romans. It spread through Europe and eventually to colonial countries such as Australia. The seasons start regularly on the first day of a month, or sometimes the 21st or thereabouts, depending on local habits and quirks (which I document a little in the book).

Others before me have suggested a new set of seasons, but we seem reluctant to change – like the Union Jack in our flag or the monarch in England, perhaps we draw comfort from these anachronisms. In the 1990s, Allan Reid encouraged members of the Gould League of Victoria to record their seasonal observations as part of his Timelines Project, leading to a six-season proposal for Melbourne. Retired school teacher in Sydney, Rick Kemp, contacted me when I first started talking about my seasonal discontent. Rick has devised an eight-season system based on the relative position of the Earth and the Sun – the solar seasons as he calls them. He also, like me, wants to move Wattle Day from the 1st of September back to the 1st of August (more in the book on that one too).

But not all Australians have four seasons. Our Indigenous communities have watched the world around them over tens of thousands of years, and have two to seven seasons to suit their local area. I can find only one example of Aboriginal Australians using four seasons: six is the most common number.

We could embrace one of the Aboriginal seasonal systems but I fear this might be just too radical for most Australians (who, contrary to popular belief, are a rather conservative people). The fuzziness of the boundaries won’t topple the government but I suspect they may be too complex for the methodical non-Aboriginal mind, and just won’t get used. We could and should happily use Aboriginal seasonal names but unless the whole seasonal structure is the same as the one used by local Aboriginal elders it would be wrong to do this. That would be tokenism at best and cultural theft and misapplication at worst. Instead I propose a modified Vivaldi system for southern Australia, by which I mean south of about Brisbane. It’s a tweaking of the current system. The familiar anchors, summer and winter, are there but the bits in between and the duration of the seasons are adjusted for the southern Australian climate.

My seasonal year starts with sprinter (August and September), the early Australian spring. That’s when the bushland and our gardens burst into flower. That’s also when that quintessential Australian plant, the wattle, is in peak flowering across Australia.

Next is sprummer (October and November), the changeable season, bringing a second wave of flowering.

Summer (December to March) should be four months long, extending beyond February, when there are still plenty of fine warm days.

Autumn (April and May) barely registers in Sydney but further south we get good autumn colour on mostly exotic trees, as well as peak fungal fruiting.

Winter (June and July) is a short burst of cold weather and a time when the plant world is preparing for the sprinter ahead.

The 'first' season, sprinter, is an early spring and in my mind a no-brainer. It is easy to recognise and backed up by good observational data. The other four are perhaps more aspirational, concepts to test and probe a little further. Although difficult to define, they are the perfect launch pad for stories about the seasonal triggers and tribulations in the life of a plant (and plant-like creatures): how plants initiate flowers and leaves, why autumn leaves are coloured and what plants do at night. Seasonal things… Then there is climate change and the fact that seasons are changing whether we like it or not. Perhaps we need an evolving system of seasons. But we should at least get it right in the first place and try to reflect, if not our local region, then a broad sweep across the country, such as I’ve done for southern Australia.

There are no perfect or correct seasons. I am happy for my system to be rigorously debated and tested, and I will be thrilled if through more people observing and monitoring the natural world I have to totally redesign it. I’m sceptical by nature but I’ve happily included conjecture and perception alongside peer-reviewed evidence and analysis. That’s mainly because we have so little data on how our Australian plants and animals respond to our climate. That said, I’m pleased to see more research on this topic over recent years, mostly driven by the need to understand the impacts of accelerated climate change. I’m also a big supporter of ClimateWatch, a citizen-science program set up by Earthwatch and other partners such as botanic gardens, to help us track more accurately the seasonal and other changes around us.

For now though there is definitely some hand-waving and passionate persuasion in my arguments, but my approach and my conviction are scientific. I’m with Thomas Huxley on this: ‘Science is’, he said, ‘nothing but trained and organised common sense …’ That common sense, along with the training to observe and record things, convinces me that the first, or the 21st, of September is not the first day of spring. September is the second half of sprinter, the characteristically early flowering season of southern Australia.

Robyn Williams: Well, brave fellow. Tim Entwisle is Director of the Royal Botanic Gardens in Melbourne, and his book, published by CSIRO this week, is called Sprinter and Sprummer: Australia’s Changing Seasons. Next week we go farming pigs.