Out of sync: How climate change is messing with nature’s timing

For nature, timing is everything. The return of swallows and cuckoos marks the start of summer. These charismatic African migrants get all the attention; however, it is the appearance of the fuzzy, black, low and slow flying St Mark’s fly (Bibio marci) which gets my family excited.

The timing of the first emergence of adult St Mark’s flies is so reliable they are named after St Mark’s Day on April 25th. These are one of the few flies that you can easily catch with your hands – if you are quick enough. Small hands pull individual flies out of the mid-air swarm as we walk past hedgerows.

Phenology is the science of the timing of biological events. Our ancestors were attuned to the appearance of birds, flowers and insects and named them for their timing or co-occurrence with other species.

The start of the flowering season for the cuckoo flower (Cardamine pratensis) coincides with the return of the cuckoo to Ireland from its winter haunt in Africa. In turn, the orange-tip butterfly (Anthocharis cardamines) commonly uses the cuckoo flower as a foodplant for its caterpillars, so is reliant on the timing of the flower.

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While anthropogenic climate change does not change day length, which is the key determinant of our seasons, it alters the timing of frosts and rainfall events and increases temperature.

Some animals and plants are triggered to emerge or change their behaviour in response to spring and summer temperatures; a mild winter and early spring can cause trees to leaf out and flower earlier. In general, leaf-out and first flowering dates have advanced by around two to five days per decade over the past 30 to 40 years.

Earlier flowering

Japanese scientists compiled flowering dates for Japanese cherry back to the 9th century, with a clear trend of earlier flowering over the past decades coinciding with warmer spring temperatures. The timing of the ripening of wine grapes and their nutritional composition are affected by rainfall and temperature over the summer. Harvest dates for wine grapes are another incredible source of historical information on how the climate affects phenology. Harvest dates for the Burgundy region date back to 1354, and show that harvests over the past decades are around 13 days earlier than historical records.

Earlier harvesting is not the only problem that wine-makers have to deal with. Hotter temperatures during ripening change both the proportion of sugars in the grape and the chemicals in the grape skin that gives red wine its colour. Higher sugar content in the grape in turn alters the alcohol content. John Wilson writes about the consequences of climate change-induced changes in grape characteristics for Bordeaux wines. From this year, new grape varieties that are better adapted to hot climates will be allowed in Bordeaux wine.

The adaptation of the highly conservative French wine industry to hotter climates will lead to a shift in the varieties of grapes planted in the Bordeaux region and is an example of the type of adaptation that will be needed across many different industries as the reality of climate change starts to bite.

Warmer world

We are already locked into a certain amount of climate change, with the goal of the Paris climate agreement to limit global warming well below 2 degrees, preferably to 1.5 degrees, compared to pre-industrial levels. Our best-case scenario, if we meet the Paris climate goals, is still a warmer world. Higher temperatures, fewer frost days and changes in the timing and intensity of rainfall events will have serious consequences for the natural world too. In particular, the connections between the timings of animals and plants that rely on each other may be disrupted.

Blue tits rely on a steady supply of caterpillars on which to feed their young chicks in spring, this requires coordinated timing between the leafing-out of trees, the emergence of adult butterflies and moths, and optimal growing conditions for the caterpillars. An early spring and untimely frost can disrupt these connections and leave the blue tits unable to raise their young. The dates of wine harvest and cherry blossom are just simple indicators of much more complex disruptions of biological timings in natural ecosystems.

In future we may be catching St Mark’s flies on St Patrick’s day.

Yvonne Buckley is an ecologist, Irish Research Council laureate and professor of zoology at Trinity College Dublin