It’s interesting to see the blossoms on my plum tree getting an early start this year. I can’t remember what time they came out last year, but this feels early.

Is my fruit tree old and confused, or is this climate change finally arriving? Or did it touch down with $2 bananas? Or the 2003 razing of the high country? With global warming now firmly on the agenda, you just can’t help looking for it.

But anecdotal evidence is tricky at the best of times. It’s probably most useful in parts of the world where long-term changes in the nature or timing of really visible features – like annual migrations, freezing and break-up of high latitude rivers and oceans, and changes in glacial extent – can and have been observed.

Without those cues in Australia, it sometimes seems like one guess is as good as the next. It’s difficult enough, given the iconic variability of the continent’s weather, its ‘droughts and flooding rains’ – largely driven by the El Nino Southern Oscillation (ENSO) – to discern a climate change signal in historical climate records.

Detecting a signal in biological systems is one step further removed, made complicated by the fact that our ecosystems are well adapted to these quasi-decadal patterns of variability and the pointed climatic extremes they bring. We also lack the historical data sets detailing responses of species to these changes.

And yet, there is a highly probable climate change signal emerging from our climate records, and a myriad of anecdotal evidence in our biological systems mounting simultaneously. How much of this is careful observation and how much a matter of finding things simply because we’re looking for them?

If nothing else, it seems difficult to dismiss the sheer weight of evidence coming in. And treated carefully, such evidence could be extremely valuable. One of global warming’s fatal PR drawbacks is that it is so invisible. Perhaps the more that we see these patterns emerging among our flora and fauna, the less we will drag our feet on a problem that our environment minister recently conceded is a threat to civilisation. Unfortunately, those of us who live in cities may be the last to notice.

In any case, I hope I get a bumper plum crop this year. I really miss bananas.