How climate change is disrupting nature’s timing
For nature, timing is essential. The return of the swallows and cuckoos marks the beginning of summer. These charismatic African migrants are getting all the attention; however, it is the appearance of the fuzzy, black, low, slow Saint Mark’s fly (Bibio marci) that excites my family.
The timing of the first emergence of adult St. Mark’s flies is so reliable that they are named St. Mark’s Day on April 25. These are one of the few flies that you can easily catch with your hands – if you’re quick enough. Small hands pull individual flies out of the mid-flight swarm as we pass the hedges.
Phenology is the science of the moment of biological events. Our ancestors listened to the appearance of birds, flowers and insects and named them for their time or co-occurrence with other species.
The start of the cuckoo flower (Cardamine pratensis) flowering season coincides with the cuckoo’s return to Ireland from its winter haunt in Africa. In turn, the orange-tipped butterfly (Anthocharis cardamines) commonly uses the cuckoo flower as a food plant for its caterpillars, so depends on the timing of the flower.
While anthropogenic climate change does not alter the length of the day, which is the key determinant of our seasons, it alters the timing of frosts and precipitation and increases temperature.
Some animals and plants are required to emerge or change their behavior in response to spring and summer temperatures; a mild winter and early spring can cause trees to leaf and flower earlier. In general, flowering and first flowering dates have advanced about two to five days per decade over the past 30 to 40 years.
Japanese scientists have compiled the flowering dates of Japanese cherry trees in the 9th century, with a clear trend for earlier flowering in recent decades coinciding with warmer spring temperatures. The time of ripening of wine grapes and their nutritional composition are affected by precipitation and temperature during the summer. Wine grape harvest dates are another incredible source of historical information on how climate affects phenology. Harvest dates for the Burgundy region go back to 1354 and show that the harvests of the last few decades are about 13 days earlier than historical records.
The early harvest is not the only problem that winegrowers have to face. The higher temperatures during ripening change both the proportion of sugars in the grape and the chemicals in the grape skin that give red wine its color. A higher sugar content in grapes in turn changes the alcohol content. John Wilson writes on the consequences of changes induced by climate change in grape characteristics for Bordeaux wines. From this year, new grape varieties better suited to hot climates will be authorized in Bordeaux wines.
The adaptation of the very conservative French wine industry to warmer climates will lead to a change in the varieties of grapes planted in the Bordeaux region and is an example of the type of adaptation that will be required in many different industries due to climate change. begins to bite.
We are already locked into some climate change, with the Paris climate agreement aiming to limit global warming to well below 2 degrees, preferably 1.5 degrees, from pre-industrial levels. Our best case scenario, if we meet the Paris climate goals, remains a warmer world. Higher temperatures, fewer freezing days, and changes in the timing and intensity of rainfall events will also have serious consequences for the natural world. In particular, the connections between the schedules of animals and plants that depend on each other can be disrupted.
Blue tits depend on a constant supply of caterpillars to feed their young chicks in the spring, which requires coordinated timing between tree foliage, 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 blue tits unable to raise their young. The harvest and cherry blossom dates are only simple indicators of much more complex disturbances of biological times in natural ecosystems.
In the future, we may catch some St. Mark’s Flies on St. Patrick’s Day.
Yvonne Buckley is an environmentalist, Irish Research Council Fellow and Professor of Zoology at Trinity College Dublin