How Does Climate Change Affect Biodiversity?

We often consider climate change in terms of how it will directly affect the human population – for example, greater extremes of temperature, more frequent droughts and flooding, and sea level rise impacting on our cities, homes and the global economy.

But arguably the most significant effects of a warming planet and changing weather patterns will be on other living species; plants, animals, birds and marine life. Biodiversity – the number and range of living species – is expected to suffer a significant decline as the climate warms, resulting in negative impacts on global ecosystems and, ultimately, on humankind.

Impacts of climate change on biodiversity

#1 Effects of rising temperature

Current international efforts to restrict climate change to less than 2 degrees Celsius might suggest that the expected temperature change is not huge, and therefore little damage will be done. There are two important factors, however, that mean that even a modest rise in the average global temperature will result in irreversible harm to living organisms and ecosystems.

First, the effects of global warming are not uniform across the planet’s surface.

Some areas have already begun to experience abnormal weather patterns, such as extended periods of extreme temperatures or lower precipitation, resulting in the expansion of desert areas, shrinkage of glaciers, and death of coral reefs.

Changes to global weather patterns and ocean currents mean that the effects will be localized, often disproportionately affecting the most sensitive habitats.

The Arctic, Antarctic and high latitudes have experienced the highest rates of warming, a trend that is projected to continue [1].

Second, the increase in temperature is happening more quickly than the rate at which most living species can adapt.

Many living organisms are exceptionally good at adapting to new environments, and have done so as the Earth’s climate has changed in past millennia; for most, however, the speed of anthropogenic climate change is simply too fast for evolution to keep up.

Those that cannot adapt quickly enough are at risk of extinction.

#2 Changes in the population and distribution of species

One of the recurring images used to illustrate climate change is that of the polar bear. Although it has become a cliché, it does demonstrate one of the major effects of climate change for large mammals; loss of habitat.

Like many other species that have adapted to live on or under the ice, animals such as polar bears rely on low temperatures to maintain the sea ice they need to travel, hunt and breed successfully.

Ice-free summers in the Arctic would mean the loss of the polar bears’ entire habitat and the destruction of a biome that supports an entire food chain including algae, invertebrates, birds, fish and marine mammals. As the top predator, polar bears eat seals, which in turn eat Arctic cod. The cod feed on zooplankton, which themselves consume algae, which inhabit ice pockets.

However, if rising temperatures cause ice to melt, then the algae will lose their habitat, leaving the zooplankton short of their preferred food and with the ripple effect running all the way up to the polar bears. So, rapidly shrinking icecaps will leave insufficient habitat for these populations to survive, resulting in large scale loss of biodiversity.

In other regions, species have begun to alter or expand the territories they cover in response to increasing temperatures. This has resulted in a shift to cooler and moister regions, to higher elevations in mountainous areas, and towards the poles, in order to stay within a similar climate range.

For example, 37 species of dragonfly have moved 30 kilometers northwards per decade in the UK, while several species of small mammal have shifted 50 meters per decade upwards in Yosemite National Park.

For mammals, birds, insects and invertebrates, this shift is not simply because they prefer a cooler temperature. As the plants and smaller animals they rely on for food change their pattern of distribution, so the entire food chain must follow. When these interdependent species get ‘out of sync’, the whole ecosystem may begin to collapse.

Furthermore, although population shifts may be beneficial in the short term, they are unsustainable over time as species reach geographical limits such as oceans or deserts, or manmade boundaries such as cities, or as the available habitat shrinks.

#3 Changing seasons, migration and breeding cycles

Most species depend on seasonal cues to begin activities such as hibernation, migration, germination, flowering, nest-making and mating. As weather patterns change and the climate warms, the seasons may begin and end at different times, affecting the habits of some species.

When these natural cycles – known as phenology – are altered, the ecosystem can begin to malfunction. If the changes to different species of plants, insects, birds and mammals no longer match, then the food sources they rely on may not be available at crucial times, such as when chicks hatch.

To take a simple example, many birds time their nesting, mating and egg-laying so that the chicks will hatch at a time of maximum abundance, when there are plentiful caterpillars and others food sources available to feed them.

In turn, the moths and butterflies have timed their egg-laying and hatching so the young caterpillars can eat the new, tender leaves of their favorite food source.

Most plant species germinate and grow most vigorously when the weather is both warm and wet enough to sustain it: If changes to the weather pattern mean that a specific plant species germinates and completes its lifecycle too early, or grows poorly due to excessive heat or lack of rainfall, the caterpillars that depend on it will starve and the young birds may fail to thrive.

In ecosystems around the world, there are many thousands of interdependent species – from microbes in the soil to top predators such as wolves and bears – that have evolved together and rely entirely on the presence of other species in order to survive. If any one of these is unable to adapt to the effects of climate change, the consequences could be catastrophic.

#4 Introduction of new diseases, pathogens and parasites

As species move to take advantage of new habitats, the risk of diseases, pathogens and parasites spreading also increases and this can have serious ramifications for human health, fisheries and agriculture.

For example, the oyster parasite, Perkinsus marinus, can cause serious die-offs in oysters. As a result of climate change, the parasite has extended its range by around 483 kilometers (300 miles), from Chesapeake Bay to Maine, creating problems for local fisheries which rely on oysters for their livelihoods.

#5 The rise of invasive species

Of course, climate change is beneficial for some species of plants and animals. When conditions begin to change, the species that can adapt most quickly may begin to dominate an ecosystem, further threatening other, weaker species that respond more slowly, or replacing those that fall prey to an increase in pests or diseases.

Alien invasive species – those that did not evolve alongside native plants and animals but were introduced from elsewhere, deliberately or accidentally – are, by nature, highly adaptable and opportunistic. As climate change leads to extended growing seasons in some areas, invasive plants take advantage by flowering earlier and crowding out less adaptable indigenous species.

Since the native plants are much more likely to provide food, shelter and nesting material for native wildlife, dominant invasive species can quickly threaten an entire ecosystem and its biodiversity.

#6 Ocean warming and acidification

Most of the warming that’s happening right now is not on the earth’s surface or in the atmosphere; it’s in the oceans [2], and that’s where many ecosystem changes are also occurring.

Changing ocean temperatures, acidification, and circulation currents – all caused by greenhouse gas emissions – are likely to lead to irreversible ecological damage including extinctions and habitat loss.

As the concentration of carbon dioxide (CO2) in the atmosphere increases, more CO2 is absorbed by the ocean, which makes it more acidic. The higher level of acidity prevents marine organisms from making shells and skeletons from calcium carbonate, and can even dissolve shells that have already been formed.  Many of the affected species play a vital role in the food chain and in ecosystem biodiversity.

Coral reefs, for example, contain around one third of the world’s entire marine biodiversity and provide a range of ecosystem functions, but they are severely threatened by coral bleaching due to increased sea surface temperatures and acidification.

Researchers estimate that most coral reefs will suffer long-term degradation by 2030 even if we limit global warming to 2 degrees Celsius [3].

The consequences of biodiversity loss

The most obvious consequence of biodiversity loss is large scale extinction of species, meaning that we would no longer have the great variety of wildlife and landscapes that we see and enjoy today. It is sad to think that in only a few generations’ time, our descendants may not be able to see living examples of plants, animals and marine life we regard as commonplace.

Although we know that, over the history of the planet, many species have become extinct, nature is able to compensate for the loss of a small number of species over a long period of time, as other species evolve.

Just as importantly, this rate of extinction and declining biodiversity will lead to the loss of a range of ecosystem services such as purification of air and water, climate stabilization, the generation of soil and natural vegetation and stable climatic conditions.

How will climate change and biodiversity loss affect us?

Human civilization relies on ecosystem functions to deliver a wide range of goods and services that are vital to support the continuation of human existence.

Loss of biodiversity affects the ability of ecosystems to provide us with food, clean air and fresh water, as well as medicines and genetic material – including many we may not even have discovered yet.

Because the many species that make up any ecosystem are interdependent, it’s hard to predict exactly what the effects of reduced biodiversity in any one area might be.

One of the major global threats to human existence, however, is a decline in pollinating insects. Because different types of pollinator prefer different plant species, biodiversity ensures we can continue to enjoy many types of food. Loss of biodiversity means we may no longer be able to produce affordable honey, berries, nuts, coffee or chocolate, and if all pollinators disappeared we may lose up to one third of all crops worldwide [5], resulting in widespread food shortages and famine.

Even coral reefs provide vital services, helping protect coastlines from the damaging effects of waves and storms, as well as providing food sources (including around 25 percent of the fish caught by developing nations [6]) and generating tourism. It has been estimated that the global value of coral reef ecosystem services is more than US$30 billion every year [7].

Ultimately, we rely on the biodiversity of the many different ecosystems around us to make the planet habitable, provide for our most basic human needs and enhance our quality of life.

How can you help to protect biodiversity?

As well as climate change, biodiversity is under threat from a number of human activities including pollution, over-exploitation of resources, urbanization and population growth.

Climate change, however, is something we can all help tackle every day.

Start now by aiming to:

• Cut your personal consumption of energy, water and other resources – at home, at school or at work.
• Reduce the amount of waste you produce, avoid disposable products, and recycle and compost your waste when possible.
• Buy locally made products, produced by people and organisations that you know are environmentally responsible.
• Walk, cycle or use public transport (or an electric vehicle, if you must drive).
• Learn more about your carbon footprint, and how you can minimize your climate change impact to help preserve biodiversity.