Are you as excited as I am about the prospect of foliage peeping this weekend? Years spent in the subtropics have made me truly appreciate the generous explosion of colours that nature in the more temperate parts of the world unveils this time of the year, just before shedding it all to succumb to austerity. I have been chasing the experience all over the northern hemisphere, from the bright reds of maple trees in New England to the yellow rain of ginkgo leaves in South Korea and all the shades in between. I simply cannot get enough of the gorgeous spectacle of autumn.
So, although I realise that aesthetics should probably be the last thing on my sustainability-preoccupied mind right now, I can’t ignore the alarming reports that climate change is interfering even with this rather innocent foliage obsession of mine.
It is not the timing of the annual show that I am concerned about. Although it might sound logical, and some observations confirm that climate change is pushing back the start of autumn colour shift to later in the year, the scientific evidence is not conclusive. There is nothing to be complacent about, of course. “If climate warming continues unabated, the situation is likely to change after about 2040, with senescence then starting earlier than it does now,” warns Susanne S. Renner, honorary professor of biology at Washington University in St. Louis.
No, what I find really upsetting is that, apparently, the milder autumns that we experience ever more frequently are affecting the quality of my beloved foliage. Warmer temperatures tend to reduce the production of anthocyanin (the red, purple, and blue pigments) in leaves. In layman’s terms, it means those autumn colours are en route to becoming less brilliantly red or purple. Even if colour brilliance is hard to quantify, the effect has been experimentally demonstrated in sugar maple trees.
Another disturbing trend picked up, for instance, by a well-placed rooftop camera at Columbia University’s Lamont-Doherty Earth Observatory, is that the period before trees shed their bright and colourful leaves is getting shorter. “Earlier, the peak fall colours would last for maybe a week and a half, and now it’s condensing into a shorter and shorter period,” observes Mukund Rao, a postdoctoral research scientist at Lamont, who helped to install the camera to study how trees are changing with the seasons and with the shifting climate.
Now, the fact that trees are in such a hurry to drop their leaves is really bad news, far beyond my aesthetic preferences. You see, once the trees are leafless, they are not just less attractive but also quite useless when it comes to sequestering carbon emissions. Susanne Renner, who, alongside other scientists, has been studying the earlier onset of abscission in temperate European forests, says the implications are “humongous”, amounting to gigatons of carbon dioxide every year that could remain in the atmosphere. A school example of the notorious climate feedback effect kicking in.
Seeing as my favourite autumn spectacle might be about to become both shorter and duller, there is hardly any time to waste. Let’s get out there and savour it while it lasts. And while at it, let’s think of ways to protect the vibrant autumn spectacle for those who will inherit the earth from us.
 In case you are not familiar with the term, leaf senescence is the gradual deterioration of leaves due to the degradation of chlorophyll (green pigment), which reveals the carotenoids (yellow, orange, and red pigments), the very cause of autumn leaf colour in deciduous trees.
 Another biology term for you, abscission is the process of shedding old or unwanted organs, such as leaves