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Effects & Impacts: Animals & plants moving or dying (phenological changes)

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Phenological changes

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Summary

  • The study of the seasonal changes that plants and animals go through is called phenology (Video 1).
  • We’re all familiar with seasonal cycles: daffodils and migratory birds appearing in spring; the best times of year to plant and harvest food crops; falling leaves and shorter daylight hours signaling autumn. While changes in daylight hours follow a predictable cycle because Earth’s axis is tilted, 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 attributes of climate change: species are moving…or dying because there is nowhere for them to go. Heatwaves associated with climate warming have already caused catastrophic population declines and the reorganization of biological communities in certain places, in part because less overall water vapour in the air interferes with photosynthesis.

Combining the extreme thermal sensitivities with projected increases in maximum temperatures globally,we predict that moderate warming scenarios can increase heat failure rates by 774% (terrestrial) and 180% (aquatic) by 2100. This finding suggests that we are likely to underestimate the potential impact of even a modest global warming scenario. – Jørgensen et al, 2022

Approximately half of the species assessed globally have shifted polewards or, on land, also to higher elevations (very high confidence). Biological responses including changes in geographic placement and shifting seasonal timing are often not sufficient to cope with recent climate change (very high confidence). Hundreds of local losses of species have been driven by increases in the magnitude of heat extremes (high confidence) and mass mortality events on land and in the ocean (very high confidence). Impacts on some ecosystems are approaching irreversibility such as the impacts of hydrological changes resulting from the retreat of glaciers… – IPCC Synthesis Report 2023

Over one third of the world’s trees now face an extinction risk  – IUCN Redlist, October 2024

  Effects

Other sections

Home > Climate wiki > Effects > Phenology: species on the move

Summary

  • The study of the seasonal changes that plants and animals go through is called phenology (Video 1).
  • We’re all familiar with seasonal cycles: daffodils and migratory birds appearing in spring; the best times of year to plant and harvest food crops; falling leaves and shorter daylight hours signaling autumn. While changes in daylight hours follow a predictable cycle because Earth’s axis is tilted, 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 attributes of climate change: species are moving…or dying because there is nowhere for them to go. Heatwaves associated with climate warming have already caused catastrophic population declines and the reorganization of biological communities in certain places, in part because less overall water vapour in the air interferes with photosynthesis.

Combining the extreme thermal sensitivities with projected increases in maximum temperatures globally,we predict that moderate warming scenarios can increase heat failure rates by 774% (terrestrial) and 180% (aquatic) by 2100. This finding suggests that we are likely to underestimate the potential impact of even a modest global warming scenario. – Jørgensen et al, 2022

Approximately half of the species assessed globally have shifted polewards or, on land, also to higher elevations (very high confidence). Biological responses including changes in geographic placement and shifting seasonal timing are often not sufficient to cope with recent climate change (very high confidence). Hundreds of local losses of species have been driven by increases in the magnitude of heat extremes (high confidence) and mass mortality events on land and in the ocean (very high confidence). Impacts on some ecosystems are approaching irreversibility such as the impacts of hydrological changes resulting from the retreat of glaciers…– IPCC Synthesis Report 2023

Over one third of the world’s trees now face an extinction risk  – IUCN Redlist, October 2024

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: 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.

Fig. 1: Plants and animals evolved to behave in certain ways, like migrating or laying eggs, because of seasonal cues. Some species react to the length of the day; others to temperature. Before the climate began changing, the timing of events was in balance.
Fig. 1: Plants and animals evolved to behave in certain ways, like migrating or laying eggs, because of seasonal cues. Some species react to the length of the day; others to temperature. Before the climate began changing, the timing of events was in balance.
Fig. 2: Now that temperatures are rising, some but not all plants and animals are being cued to behave differently. This is called 'phenological mismatch', that is, the timing of events is 'mismatched'. Some species may starve, like the baby birds in Fig. 1, while others, like leaf-eating caterpillars grow into plague numbers and eat too much, killing plants. This is damaging for both natural environments and also farmers and gardeners.
Fig. 2: Now that temperatures are rising, some but not all plants and animals are being cued to behave differently. This is called ‘phenological mismatch’, that is, the timing of events is ‘mismatched’. Some species may starve, like the baby birds in Fig. 1, while others, like leaf-eating caterpillars grow into plague numbers and eat too much, killing plants. This is damaging for both natural environments and also farmers and gardeners.

Species on the move…but many unable to 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 including lakes and reservours, they can’t move because there is nowhere for them to go, for example, cities and farms are in the way or moving uphill to where lakes may be cooler is not possible.

“The fragmented distribution of standing waters in a landscape will restrict redistribution, even for species with high dispersal ability, so that the negative consequences of rapid warming for freshwater species are likely to be much greater than in terrestrial and marine realms..”  – Woolway & Maberly, Nature Climate Change, 2020

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

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.

Too many boys and not enough girls (Fig. 3).

Fig. 3: Tuatara eggs generally produce 50% male and 50% female hatchlings. An increase in temperatures of just 1°C means that 80% of the hatchlings are male. As the world has already warmed 1°2C, that has profound implications for the species unless it can move to cooler locations. (Image: Sid Mosdell / CC BY 2.0)
Fig. 3: Tuatara eggs generally produce 50% male and 50% female hatchlings. An increase in temperatures of just 1°C means that 80% of the hatchlings are male. As the world has already warmed 1°2C, that has profound implications for the species unless it can move to cooler locations. (Image: Sid Mosdell / CC BY 2.0)

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 (Fig. 4).

Fig. 4: Many plant species won't flower in the spring unless they have experienced a long period of cold weather. If the plant doesn't flower, it won't be fertilised so it won't produce seeds or fruit. (Image: Nature)
Fig. 4: Many plant species won’t flower in the spring unless they have experienced a long period of cold weather. If the plant doesn’t flower, it won’t be fertilised so it won’t produce seeds or fruit. (Image: Nature)

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 we plant what existed in a place  by eco-sourcing local seeds and plants? Or should we also include natives plants from warmer climates, especially long lived plants like trees, which will need to survive a warming world in the coming decades?

Diseases, including those affecting humans, wild species, and livestock are also on the move: see Pandemics, this website.

“Climate change is already boosting the spread of virus sharing among mammals, the animal group thought most likely to pass new diseases on to humans.This is because warming is forcing mammals to move to new habitats in search of cooler, more tolerable climates. As they move, they are more likely to encounter unfamiliar species – providing an opportunity for novel virus transmission. Scientists say this “ecological transition” has already begun – and will continue to worsen regardless of our efforts to rein in rising global emissions. .”  – Dunne, 2022

Fig. 5: From the IPCC report: Climate Change 2022: Impacts, Adaptation and Vulnerability. 'Australasia' includes New Zealand. The limited evidence in reference to freshwater ecosystems is indicative of limited data or a complete loss of ecosystems. For instance, 90% of all wetlands in New Zealand have been lost due to agriculture and development, and almost all braided rivers systems have been extensively modified.
Fig. 5: From the IPCC report: Climate Change 2022: Impacts, Adaptation and Vulnerability. ‘Australasia’ includes New Zealand. The limited evidence in reference to freshwater ecosystems is indicative of limited data or a complete loss of ecosystems. For instance, 90% of all wetlands in New Zealand have been lost due to agriculture and development, and almost all braided rivers systems have been extensively modified.

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