Biodiversity is essential to ecosystem health, and climate change is negatively impacting most ecosystems around the globe. To fully understand these impacts, we will explore the various ways that ecosystems are affected by changing temperatures, precipitation, weather, migrations, extinctions and human activity.

Biodiversity is broadly defined as the variability of life on earth among species, genera and ecosystems (7). Conservation researchers Paul R. and Anne Ehrlich posited in the 1980s that species are to ecosystems what rivets are to a plane’s wing. Losing one might not be a disaster, but each loss adds to the likelihood of a serious problem (1). Human activity is the main cause of climate change, and loss of biodiversity. As cities grow and forests are cut down for lumber, green spaces paved over for grey infrastructure, we are witnessing biodiversity being wiped out.

Tropical rainforests have the highest biodiversity on Earth.

One major indicator of this accelerating change is overall temperature rise, i.e. global warming, which has been a pivotal topic in international debates and policies for over three decades. Yet, the destructive trend continues, concurrent with disruptions in ecosystems and the eradication of species on a monumental scale. Global temperatures have risen approximately 1.1C since the late 1880’s with a sharply accelerated warming trend in the last three decades; 2024 was the warmest year on record (8).  Previously, capping temperature rise at 1.5C by 2100 was deemed acceptable. However, current modelling shows that even if all nations meet their Paris Agreement commitments, 3 degrees C give or take a few tenths of a degree is a more likely scenario (9).

All organisms have a species-specific range of temperature in which they optimally thrive.  Towards the outer limits of that range their vital systems and very survival is stressed. Go too far from the median value in either direction and the organism dies. Think of this in human terms, which we can all relate to. Without clothing or heated/air-conditioned shelters, the viable range of human existence is 21-31C.  Unprotected humans cannot survive prolonged exposure to temperatures outside of that range.  What happens if this model is applied to plant and animal species?  Plants in particular are vulnerable, due to their sessile nature. We can see how climatic zones, represented by plant hardiness zones (PHZ’s) have shifted over the past several decades.   Natural Resources Canada updated the 2010 zone map in 2024, and most regions saw a jump of between one half (a to b) to two full zones,confirming warmer winters, longer frost-free periods and hotter summers are altering plant suitability across the country. This shift means some areas, like parts of British Columbia and southern Ontario, may now support plants like certain palms or cold-hardy citrus (11). 

Natural Resources Canada Plant Hardiness Zones - 2024

Warming causes widespread habitat degradation and forces plants and animals to migrate towards higher altitudes and latitudes. Species are shifting their geographic ranges to track suitable climate conditions. Animals dependent on cold and ice, such as polar bears and penguins, are losing their habitat altogether as polar ice caps melt. As ocean levels rise, lowland ecosystems are threatened by flooding and salinification. Oceans themselves absorb a lot of atmospheric heat, and rising water temperatures stress corals, causing them to expel symbiotic algae and turn white (bleaching). A 2C rise in ocean temperatures will effectively kill 99% of remaining coral reefs (6). It is no surprise that marine species are moving poleward faster than terrestrial species.

The displacement and migration of species into new areas disrupts existing ecosystems and creates new ecological interactions, while allowing invasive species to spread into new areas.  The mountain pine beetle, for example, once limited by cold winters, has been able to spread into new regions due to warmer winters, thus threatening pine species all across Canada (10).

In addition, most plants and animals rely on light and temperature cues to initiate functions or lifecycle stages. Climate change alters the timing and intensity of such events resulting in mismatched food availability and reduced reproduction and survival rates.

The current rate of species extinction varies from 10 to 100 times the natural rate, which has conservationists and ecologists justifiably and deeply concerned. News media as well as personal observation has made many people aware of insect and bee species decline in recent decades, but few realize just how catastrophic the loss of insects would be (12). For all organisms, loss of genetic diversity within a species reduces its ability to adapt to new conditions and diseases through natural selection.

Global plant biodiversity 20 years ago - a different story today. 

Every person alive today has witnessed or heard of extreme weather events and related natural disasters. Climate change has increased the frequency and intensity of droughts, wildfires, storms and floods. Such events are catastrophic and result in immediate habitat destruction and loss of life for flora, fauna and humans alike. Extreme heatwaves cause mass mortality for heat-sensitive species, and prolonged heat and drought cycles over multiple years, result in profound ecosystem and ecoregion disruption. In my area of the Pacific Northwestern coastal rainforest, characterized by the predominant western hemlock-redcedar ecosystem, redcedars (Thuja plicata) are dying everywhere, even in irrigated gardens and forests previously considered moist. The loss of this keystone species affects hundreds of others at multiple trophic levels in ecosystems where it previously thrived.

Ecosystems are comprised of various species that belong to different functional groups - a class of organisms that perform a certain job. Decomposers, nitrogen fixers, and carbohydrate manufacturers are different examples of functional groups. The more functional groups there are, the more stable and diverse the ecosystem is. The following diagram depicts different ecosystem types, ranging from the bottom of a cave to the heart of a lush tropical rainforest, and everything in between.  Where do you think biodiversity is highest? Having many different species perform the same job allows the ecosystem to continue to function even if one or two species decline since others are available to step in and fill the biological role. An ecosystem consisting of only a small number of species and therefore lacking in biodiversity would be seriously imperilled by the loss of one or two species and may even collapse. (This topic is covered more in depth in Week 2 of Gaia College’s Organic Master Gardener course.)

Ecosystem Functional groups. Image originally printed in The Soil Biology Primer

Biodiversity loss caused by climate change compromises essential ecosystem services that humans rely on including crop pollination, clean air and water, climate regulation and food security. There are also significant economic detriments to agriculture, fisheries and tourism industries. In addition to the spread of invasive species to new areas, there is the increased risk of disease spread through viruses and other pathogens, as ecosystems and populations shift.  Greenhouse gas (GHG) emitting industries aside, human activities such as land clearing for agriculture or grazing pastures, deforestation for the lumber industry, trawlers using dredge nets that empty oceans of fish species and paving over natural areas to expand cities and roadways, have all directly reduced areas of Nature and its ability to sustain life on Earth.

In the complex web of life, bolstered and nourished by biodiversity, all species are dependent on the wellbeing of others. It is a mistake to assume that as technologically advanced humans we do not need creatures like ground-nesting bees, earthworms, cyanobacteria, moths, berry shrubs or oak trees (a shout out to Dr. Douglas Tallamy here, author of Bringing Nature Home and Nature’sBest Hope). Our only viable way forward, as the sole species that has the ability to determine the life of the majority of all other species, is to rapidly and drastically reduce GHG’s, while undertaking widespread ecological restoration and ceasing further destruction. By adopting an attitude of stewardship and collaboration rather than dominance and competition, we can restore the wellbeing of all, and use our power for the greater good.

Temperate forest ecosystems can remain a reality if humans act meaningfully to conserve and restore natural areas. 

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Written by Laurie Smith.