OPINION
Gillian Burke
“The ability to respond to change is baked into Earth’s systems”
“SPRING IS HERE! BUT WHEN DOES it start exactly? Meteorological seasons change every three calendar months, while astronomical seasons are marked by the quarterly points along what some might imagine is always a perfectly regular, circular orbit around the sun. If only it were that simple. In truth, spring arrives not as a single moment but rather a gradual fade-up that begins way back in the first dark days of January. The Earth may have “rounded the corner” at December’s winter solstice, but in the northern hemisphere it takes another two weeks for mornings to start getting brighter, earlier.
The sun seems to languish behind a slow and reluctant dawn because our path around the sun currently follows a slightly egg-shaped, or elliptical, orbital path with the sun positioned slightly off-centre. As the Earth reaches its furthest point from the sun, sunrise times in the northern hemisphere lag before creeping back up the clock once more.
At first the change is imperceptible, but those in tune will notice the earliest signs of the light making a slow return. It often coincides with the first song thrushes ringing out as the first woodpeckers drum to break the wintry silence. This year I heard both just a few days after the new year, within minutes of each other while out on a walk, and it was beautiful. Even in the deep mid-winter, I could sense that spring was in the air. Perhaps that’s because spring never really left at all.
Last year, summer heatwaves and an unseasonably mild autumn saw brambles simultaneously in fruit and in flower in mid-October. As if this wasn’t unnerving enough, I spotted a young cherry tree in full bloom just as Christmas decorations were going up in early December. With most flying insects long gone for the season, and little chance of being pollinated, the tree looked like a sorry case of “all dressed up and nowhere to go”.
Cherry blossom at Christmas is enough to give most people the heebie-jeebies but there is another perspective: deep in the genomes of all living things, and waiting to be used, is a library of possible solutions to the age-old question of staying alive. Seasonal anomalies needn’t always spell disaster for individual species, or indeed entire ecosystems, because within the ability to blossom in the winter lies the chance that genetic variation will leave enough wriggleroom for life to bend and flex and adapt its way out of an evolutionary tight spot.
Multiple pressures, from pollution to habitat and biodiversity loss to name a few, can make the task difficult or even impossible, however.
The ability to respond to cycles of seasonal and climate change is baked into Earth’s systems, thanks to a complicated cosmic dance with the sun. But this is not to be confused with anthropogenic, or humaninduced climate change, and to understand the difference requires us to understand natural cycles of climate change.
A dizzying array of astronomical variables affects the seasons and shape of the Earth’s climate over cycles that range from one year to hundreds of thousands of years.
The passing seasons can be marked by solar, or tropical, years that chart the sun’s path through the sky over time, while sidereal time is a measure of the Earth’s orbit against distant stars and constellations.
But even this fails to offer secure anchor points in a constantly changing solar system. The precession of the Earth (how much it wobbles on its axis); the eccentricity of the Earth (changes in the shape of Earth’s orbit from round to egg-shaped) and the changing orbital plane of the Earth around the sun (imagine the sun and Earth on an unsteady spinning plate and you’re halfway there) all combine to give us a perfectly imperfect wobbly journey around our little star. Worth a ponder as we enjoy this spring.
Catch up on all the episodes from last year’s Winterwatch on BBC iPlayer
Gillian Burke is a biologist, writer and presenter.
You can visit gillianburkevoice.com to read her blog and latest news.