The evidence of climate change
(Image: Barth Bailey)
Animals and plants are moving or dying: ‘phenological’ changes
- The study of cyclic and seasonal natural phenomena, especially in relation to climate and plant and animal life, is called phenology (video 1).
- Here in New Zealand, we’re familiar seasonal cycles: daffodils and migratory birds appearing in spring; the best times of year to plant seedlings and harvest food crops; falling leaves and shorter daylight hours signalling autumn.
- While changes in daylight hours follow a predictable cycle because of Earth’s orbit around the sun, each year, winter doesn’t seem to last as long because temperatures are higher. Some plants are blossoming sooner, crops are ripening sooner, and fishermen are catching warmer water species they’ve never seen before. These and other changes in plants and animals are perhaps the most obvious attributes of climate change, and one we cannot deny: Earth’s climate is warming and species are on the move.
“Climate change has caused shifts in species’ distributions, changes in cyclic and seasonal behaviour, and altered population dynamics. In addition, it has caused further disruptions from the genetic to the ecosystem level in marine, terrestrial and freshwater ecosystems.” – Department of Conservation
Ecosystems are composed of plants and animals—including humans—that depend on one another for different life supporting ecosystem services through biological interactions. Phenological changes are the clearest evidence of climate change because there is no ambiguity; rising temperatures are having undeniable and costly consequences.
Example 1: A bird species lays eggs based on the number of daylight hours, so that its chicks hatch just as caterpillars are at their fattest (Fig. 1). But as the climate warms the caterpillar eggs hatch sooner. The birds can’t find food, the chicks starve, and meanwhile without predators the caterpillars gorge themselves on plants and produce a lot more eggs that hatch the following season, eating yet more plants (Fig. 2).
While some species might adapt by changing their diets, that in turn has an impact on other species. The result is a ripple effect across the entire ecosystem.
Example 2 species on the move: As the climate warms, some plants and animals that evolved to live on cooler climates are migrating to either higher altitudes or latitudes. In many places they can’t move because there is nowhere for them to go, for example, cities and farms are in the way.
In the ocean more tropical fish are now being seen in the waters around New Zealand while some sea creatures are heading in the wrong direction:
“In the northwest Atlantic Ocean, slow-moving snails, sand dollars, mussels and other creatures with drifting larvae are spawning earlier, triggered by warmer seas. Unfortunately, that’s when winds and currents are aligned to drive them into even hotter waters. The result is that the ranges of once-abundant species are shrinking.” – Science, 2020
Example 3 losing pollinators: If a plant species flowers earlier because the days are warmer, but the migratory bird species that feeds and pollinates it migrates according to the length of the day, the bird won’t arrive in time to pollinate the flower or feed off its nectar. The plant won’t be pollinated and the bird also goes hungry, so both are at risk. If the plant is a food crop it may become scarce or even die out.
Example 4 too many boys and not enough girls: (Fig. 3).
Example 5 too hot for flowers (and fruit) to form:
Temperatures fluctuate all the time, so many plants that have adapted to flower in spring take their cue from long periods of cold weather followed by warm weather, ie, a cold winter rather than a few cold days or weeks. Having adapted to the cold, some are no longer flowering in Spring because the winter wasn’t cold enough. No flowers means they can’t be pollinated by bees, and they won’t produce seeds or fruit. If this happens every year, eventually the entire species will die out as it can’t reproduce.
Natural ecosystems are more resilient to change because they are composed of a high diversity of species that evolved by ‘survival of the fittest’. They don’t depend on endless amounts of artificial fertilisers or pesticides, so while some species will be lost, if they can migrate to cooler climates (either by going higher up mountains or further south), or in the case of coastal ecosystems by moving inland as sea levels rise, they will quickly adapt.
However, natural ecosystems in New Zealand are so fragmented that unless they can take to the air or swim the ocean, few species can move.
This also poses a problem for those restoring ecosystems: should they plant what used to be there by eco-sourcing local seeds and plants? Or should they also include natives plants from warmer climates, especially long lived plants like trees, which will have ti survive a warming world in the coming decades?
References and further reading
- DOC: New Zealand Reptiles
- New Zealand Ecological Society
- 2020: Zhao et al; Temperature-dependent growth contributes to long-term cold sensing, Nature 583 pp825–829
- 2020: Lida & Mahonen; Growth-mediated sensing of long-term cold in plants (Nature article explaining the above research)
- 2020: Fuchs et al; Wrong-way migrations of benthic species driven by ocean warming and larval transport, Nature Climate Change
- 2020: Stockstad, Ocean warming has seafloor species headed in the wrong direction (Science article explaining the above research paper)
- 2020: Christie et al; Department of Conservation climate change adaptation action plan Te Papa Atawhai hewhakamahereh tepeurutau m te huringa huarangi
- 2020: DOC; Te Mana o te Taiao – Aotearoa New Zealand Biodiversity Strategy 2020, Department of Conservation
- 2020: DOC; Biodiversity in Aotearoa: an overview of state, trends and pressures Department of Conservation
- 2020: Hu; Changing landscapes: Compositional and phenological shifts in New Zealand’s natural grassland (Thesis, Doctor of Philosophy). University of Otago.
- 2009: Peñuelas et al: Phenology Feedbacks on Climate Change Science 324/ 5929 pp887-888
- 1989: Atkins et al: Modelling the effects of possible climate change scenarios on the phenology of New Zealand fruit crops. SHS Acta Horticulturae 276: II International Symposium on Computer Modelling in Fruit Research and Orchard Management