WEDNESDAY was the warmest October day since 2011, but it didn’t feel like it in south Durham as I drove on the A68 which, just north of Darlington, was so shrouded in fog that the headlights turned themselves on.

But at Heighington, the sun burst through and backlit the mist so all around was a shimmery, silvery screen. Starring on that screen were the trees on the verge. Usually they are unremarkably anonymous, bare piles of twigs in winter or a dense screen of green in summer.

But on Wednesday, they were a riot by the roadside. A riot of colour – an ash was waving day-glo yellow leaves at drivers, while the sycamores were simply smouldering: scarlet and crimson turning to oranges and golds, burnished and burning.

A leaf's job is to catch the sunlight. It takes the energy from the light and uses it to convert the water rising up its trunk and the carbon dioxide it plucks from the air into a glucose. This sugary stuff then becomes the tree's food.

There are four pigments in a leaf to catch the sunlight: green chlorophyll, yellow xanthopyll, orange carotene and grey phaeophytin. The chlorophyll is where the food production occurs, so green becomes the dominant colour of the leaf.

But at this time of year, the tree senses that the days are getting shorter and the temperature is dropping. It realises winter is coming and soon there won't be enough light or heat to produce food. So it begins to shut down.

A layer of cells grows over the tubes which pump water into the leaf. The leaf is cut off; death awaits it – but it goes out in a blaze of glory.

Because the cholorophyll has been the most active, it is the first to die and disappear. The carotene and xanthopyll then grab the window of opportunity, and paint the leaves with their oranges and yellows.

The rich reds are created by the last of the sugar that has become trapped in the leaf when the tubes were sealed. With no way out, and heated by the last warmth of the year, the sugar turns into a beautiful bruise of purpley-red.

On Wednesday, I was on my way to have a preview climb up the new tower in Bishop Auckland Market Place. It gave me a bird’s eye view of the palace archaeology and the park dendrology – all the trees surrounding Auckland Castle were holding onto their mantle of green whereas, back in Darlington, every town centre tree had turned a hotch-potch of colour.

Perhaps Bishop has its own micro-climate, or perhaps the trees there have already adapted to global warming. Scientists in America – where the colours of the fall are big business among the leaf-peeping community – reckon that higher average temperatures have caused the date of the leaf-turn to laten by five days in the last 18 years.

But global warming may enhance the colour show. The extended warmth of late summer increases the sugar concentration in the leaves which creates that fiery redness – a fire that in previous times would have been extinguished by an early frost.

This may be why this year seems to be a good year for leaf-peepers: in Darlington’s South Park yesterday there was an ash that was as good as any firework: plumes of bright yellowy-greens at the bottom exploding into skybursts of reds and golds at the top.

But that was yesterday. Today comes Storm Callum and the fireworks and the roadside rioters will be blown down into the gutter.