In London, I see autumn leaves on a scale you don’t get in Australia. In some places, I walk shin deep in red, orange and brown leaves.
London’s neighbourhoods are beautiful right now. However, I do feel sorry for the street sweepers. During the rest of the year, they’re clearing up litter, dog poop, pavement pizzas and cigarette butts. Now, on top of their usual duties, they fight an unwinnable battle with leaf litter.
The sweepers fill their rubbish carts with red, orange and brown, and the next day, the trees have re-layered the roads and footpaths.
The sweepers’ only respite is winter, when the branches of deciduous trees are exhausted and bare.
There is one other thing about the leaves that makes me worry.
You see, when leaves fall and naturally decay, the nutrients go back into the earth. At the same time, carbon dioxide is released. This doesn’t contribute to climate change because when leaves grow back in spring, the tree re-absorbs the carbon dioxide from the atmosphere.
What I worry about is that all those leaves collected by all those street sweepers will go to the rubbish tip. This must happen because the sweepers are still picking up litter. No one is going to separate the leaves from the litter.
In a rubbish tip, the rubbish is stacked in layers and capped every night so that the rats and pigeons don’t make a mess. This means that organic material like leaves have no oxygen. Instead of decaying (aerobically) and releasing carbon dioxide, the leaves will decay (anaerobically) and release methane.
Methane is a more powerful greenhouse gas than carbon dioxide. Over the next two decades, this methane released will trap 72 times more heat than carbon dioxide. Even after a hundred years, methane is still 25 times more potent than the same amount of carbon dioxide.
I wonder if anyone else has been thinking about this.