Climate Change

How climate change affects sharks & rays

By releasing greenhouse gases into the atmosphere, humans are changing the global climate in ways that are affecting the marine environment in terms of weather patterns, water temperature, sea level, ocean chemistry, currents, coastal erosion and the frequency of storms. We have already observed many of these effects, but scientists are expecting them to become more severe as climate change continues. Changes such as these to the foundations of the marine environment are likely to affect marine creatures’ food supply, migration patterns, distribution, reproduction and relationships with other parts of the food web. These changes could also affect the way animals behave. Sharks are no exception. Scientists recently made predictions that two shark species in Australia, for example, may move southwards – away from the equator – at a rate of 40 miles (65 kilometres) per decade to escape warming waters. And scientists are already finding evidence that fish are moving polewards in this way, so their predators – like sharks and rays, seabirds and marine mammals, among others – will have to follow them. Sharks are slow to evolve – they generally grow slowly, mature late in life and have long generation times – so it is difficult for them to adapt to the new conditions brought about by the rapid climate change that we are inducing. Climate change is happening now; it is ongoing and it is going to get worse before it gets better. Even in the midst of this change, we don’t know for sure what to expect. Nevertheless, scientists conduct experiments day by day and observe how the earth’s climate and environment are changing, giving us more information about what’s happening and what to expect. This is particularly important when it comes to species that are already endangered and are exposed to a multitude of threats – and sharks and rays qualify in both respects. As we gain more knowledge, we are able to make informed decisions about how to mitigate the threats and manage our behaviour for the benefit of the planet – and, by extension, ourselves.

Frequently asked questions about climate change:

What is climate and how does it work?

To really understand climate change and its effects, it’s important to first understand what our climate is and how it works. The word ‘climate’ describes the average weather conditions for a particular location over a certain time period. If we are talking about local climate, we are looking at the weather conditions in a specific area or region; global climate is the average across the entire globe. Scientists usually use a number of different properties to assess the climate, including surface temperature, precipitation (e.g. rainfall) and wind.

Our global climate is the product of five main components, which are all interlinked – almost like the parts of a machine. These are collectively known as the climate system and consist of 1) the air around us (atmosphere), 2) the oceans (hydrosphere), 3) frozen water (cryosphere), 4) the earth’s rocky outer layer (lithosphere) and 5) the parts of the earth where life exists (biosphere). These components interact in many different ways across space and time to create our delicately balanced climate. For example, the way that heat and water exchange between the atmosphere and hydrosphere generates our ocean currents, which play a vital role in stabilising the global climate. Changes in one component can affect the whole system and throw the whole climate off balance.

What is climate change?

It’s normal for our weather to change over relatively short timeframes. For example, a particular season may be wetter and colder than the previous season, and then warmer and drier the following year. Climate change refers to something much bigger and more sustained – long-term shifts in average conditions at a global scale, which differ from the norm [1, 4, 5]. Climate change has been occurring since the earth formed billions of years ago. Over the course of the planet’s history there has been a series of ice ages and warmer periods that cycle roughly once every 100,000 years.

Planet earth is experiencing climate change right now. You may have heard of global warming – the gradual rise of the average global surface temperature over the past several decades. But we’re not just getting warmer. Scientists have lots of ‘indicators’ they use to measure global climate change and monitor the key components in the climate system. The World Meteorological Organization (WMO) measures global ocean heat content, ocean acidification, the extent of Arctic and Antarctic sea ice, global sea level and concentrations of greenhouse gases in the atmosphere. The latest reports indicate that the sea levels are rising, sea ice is retreating and extreme weather events, such as hurricanes and heat waves, are occurring more frequently all around the world.

What are the causes of climate change?

Many factors can cause the climate to change. Until relatively recently, natural causes have been influencing these changes, including the way the earth orbits the sun (which contributed to the ice ages) and volcanic eruptions. But the overwhelming majority of scientists agree that the changes we are experiencing now are driven by our own actions.

During the Industrial Revolution, humans began to extract and burn vast amounts of fossil fuels – coal, oil and gas – to support the shift from manual labour to machine-based manufacturing. As technology has advanced and the human population has boomed, demand for fossil fuels has only risen. The problem is, although fossil fuels provide energy to support our modern lifestyles, they also release certain gases into the atmosphere, including carbon dioxide (CO2). These gases contribute to what is called the ‘greenhouse effect’.

We use greenhouses in our gardens to trap heat from the sun, allowing plants to thrive where it would otherwise be too cold for them to grow. The earth’s atmosphere is the same. It naturally contains a mixture of gases (including CO2 and methane), some of which trap the sun’s energy and keep it close to the earth. Without it, it would be too cold on the earth for us to survive. However, the extra man-made gases we are producing are adding to the greenhouse effect, trapping more energy and making our planet hotter than it was. According to a 2018 report by the Intergovernmental Panel on Climate Change (IPCC), human activities have caused our planet to get warmer than pre-industrial levels by about 1°C. The past three decades have probably been the warmest of the past 1,400 years, a trend that will only continue unless drastic action is taken.

Why does this matter?

A difference of 1°C might not sound that bad – in fact, it might sound quite pleasant, especially if you live in a chillier part of the world! But our global climate is a finely tuned system; seemingly small changes can have big knock-on effects. We are already seeing severe impacts on ecosystem and public health, food security, poverty and human safety. For example, the warmer temperatures are causing sea ice in the polar regions to melt and thus sea levels to rise, and placing coastal communities in danger [9]. Climate change effects are not the same everywhere, but extreme conditions are becoming more common. In other words, wetter places are getting wetter and drier places are getting drier, creating difficulties for agriculture and exposing people to more frequent natural disasters.

How does climate change affect sharks and rays?

Climate change has already had a significant – and potentially irreversible – impact on our oceans, which already shield us from the worst of the greenhouse effect, absorbing excess CO2 from the atmosphere and an incredible 93% of the extra energy arising from our man-made emissions. This means that our oceans have not only warmed, but they have become more acidic. Ocean acidification greatly impacts the amount of calcium available for corals to grow and will lead to fewer and smaller things with shells or calcium skeletons which can drastically disrupt the ecosystem. Further, the melting of sea ice has knock-on effects for our ocean currents. All these factors represent severe threats to marine life, affecting the composition, structure and function of marine ecosystems and food webs.

Sharks and rays are affected in a number of ways. Firstly, the warmer waters are affecting shark behaviour, causing them to migrate to areas they have never been seen before. As many sharks are apex predators, these changes in their movements can have huge effects on oceanic ecosystems. This is also true for their prey; many other marine species are moving about in response to changes in environmental conditions, meaning sharks that migrate back to certain areas to feed may find their food source has disappeared. For example, many species of plankton are demonstrating northward shifts in their distribution, which could carry implications for filter-feeding elasmobranchs like the basking shark.

Important habitats for sharks are also negatively impacted by climate change. Coral reefs, for instance, are at risk from ocean acidification and severe weather events. Many shark and ray species rely on coral reefs and are therefore vulnerable to such changes. The same can be said for mangrove forests, which are vital nursery grounds for sharks.

A major issue is that climate change, driven by human activity, is accelerating at an alarming rate. This means that the changes in our oceans are occurring too fast for marine life to sufficiently adapt. This is especially true of slow-to-evolve animals like sharks and rays, which have been around for millennia and tend to grow and reproduce gradually.

How can we stop climate change?

Experts believe that we have already gone too far to stop climate change completely, but we can slow it down if drastic, and immediate, action is taken. This will require world leaders to step up to the plate – but there are also lots of small actions we can take individually that all add up and make a huge difference! One way is to lessen your carbon footprint, which means taking steps to reduce the amount of greenhouse gas emissions we produce. This can include things like cycling to work instead of using a car, flying less and choosing food that has come from local sources (and so hasn’t been transported as far). You can also use your voice to ask your government to commit to global targets and to gently educate friends and family on making more sustainable choices. WWF have some great tips here.