“We have a clear signal that our climate is changing, and when you look at the evidence it’s because of human activities. The evidence is so strong I don’t know why we are arguing any more”.

So said Don Wuebbles of the University of Illinois. He pointed out that the world has just had the hottest year for 1,700 years, very probably for 5,000 years.

Thirteen of the fifteen warmest years ever recorded in Britain have been since 2000: the others were just before then. 2014 had the hottest summer for 350 years (when local records began). There is no doubt that we are experiencing climate change in these islands.

Around the world, the pattern is as clear as crystal: rapid, global warming, especially strong in the furthest northern climes, as in Alaska. There, the warming is drastic. Permafrost, which stores enormous reserves of carbon locked away in frozen peat, is melting: and the fossilized plant material, exposed to the air for the first time in millennia, is starting to oxidize. There is nothing to stop all the rest of it melting away.

Actually, the story up in the far north is more frightening than that. The warmer it becomes, the more three different positive feedback cycles collaborate to speed up global warming even more.

• First, as mentioned, the permafrost is melting. That releases carbon to the air, as the greenhouse gas carbon dioxide, which accelerates the warming and melting.
• Second, as the ice vanishes, the albedo (reflectivity) of the once-frozen north goes down dramatically, from icy white (reflecting most of the sunlight that hits it) to muddy brown or black (hardly reflecting anything). The ground absorbs more sunlight, so it becomes warmer, accelerating the melting and oxidation of carbon; and it directly contributes to having a warmer planet.
• Thirdly, as the lakes and pools lose their ice cover, enormous amounts of methane hydrates, chilly masses of carbon-rich material in the icy mud, collapse and release streams of bubbles of methane gas, a far more potent greenhouse gas than carbon dioxide. If it were to be burnt, carbon dioxide would be released; unburnt, it accelerates global warming still more rapidly.

Back in Britain, everyone noticed that the weather in late 2014 was exceptionally warm. October and November in my childhood were leafless windy months with what seemed to be incessant grey skies and driving rain that churned football pitches into cold greasy mud. This time around, it was possible to work outside in shirtsleeves to the end of November. The change? Out of all recognition. It was a wholly new climate.

But the weather is not the climate. Britain is now in winter’s grip. Scotland shivers down to -15 Celsius. Here, under clear blue skies, the Birch trees glitter in the nearly horizontal sunlight. A greater spotted woodpecker, calling “Chik!” loudly, flies into the canopy of a Birch, clings to the elegant white trunk, the few remaining triangular leaves shining a rich yellow. The woodpecker bounds off, its wings whirring in short bursts.

The cold weather, like the increasingly violent storms that brought down two trees in the reserve last week, is part of the warming pattern too. The atmosphere has more energy than before: warmer air masses meet cold ones with a higher difference in temperature, releasing more powerful storms than we ever used to see. Winters can be colder, wetter, and windier as a result: more trees fall; more valleys flood. It may not feel warmer, but this is a direct consequence of climate change. Feel like denying it? Look at the evidence. It’s all around you.