Our planet’s climate is significantly influenced by the world’s oceans. Let’s break down their role and discover how climate change is affecting them.
- Oceans play a major part in controlling the climate by taking in carbon dioxide (CO2) and heat.
- In recent decades, they have stored more than a quarter of the CO2 produced by human activities and about 90% of the extra heat.
- They are the largest carbon storage space on Earth, holding nearly 38,000 billion tons of carbon.
- Billions of people rely on oceans as a source of food and income.
Unfortunately, the stability of these benefits is in danger due to climate change.
- Climate change is making the oceans warmer and more acidic.
- These changes could alter how the oceans take in and store carbon.
- As human-made CO2 emissions go on, some processes of carbon storage in the ocean might flip from capturing to releasing carbon in the future.
Ocean Warming, Melting Ice And Sea Level Rise
Since 1970, the oceans have absorbed excess heat, resulting in a steady increase in their average temperature by about 0.11°C per decade. As the oceans redistribute this heat towards the poles, it contributes to the melting of ice sheets and glaciers, ultimately leading to a rise in the mean sea level. Currently, the estimated increase stands at 0.19m between 1901 and 2010.
Sea Level Rise Causes And Effects
- Melting ice sheets in Antarctica and Greenland potentially cause sea level rise.
- Thermal expansion, where warming seawater expands, is a major driver of sea level rise.
Impact Of Sea Ice Meltdown
- Sea ice meltdown, while not directly affecting sea levels, reduces sunlight-reflecting surfaces on Earth.
- The resulting absorption of more solar energy at the surface leads to more ocean warming.
- Changes to sea ice disrupt normal ocean circulation, potentially weakening the Atlantic Meridional Overturning Circulation.
Projections For Sea Level Rise
- Even with rapid greenhouse gas emission reductions, sea level is expected to rise 29-59cm above 1986-2005 levels by 2100.
- If emissions continue unabated, and ice sheets respond as expected, sea level rise could reach 1m by 2100 relative to 1986-2005 levels.
- This increase in sea level presents significant risks to global coastal regions and can lead to more destructive coastal flooding during storms.
Ocean Warming, Weather And Climatic Impacts
Ocean warming affects our atmosphere and climate in profound ways, leading to extreme weather events, altered rainfall patterns, and changing weather systems. Here’s a concise breakdown:
Impact On Extreme Weather Events
- Ocean temperature increase fuels extreme weather events, such as storms and hurricanes.
- This warmth provides increased atmospheric energy, contributing to the intensity of these events.
- Areas beyond typical hurricane zones are seeing increased impact due to atmospheric changes.
Effect On Weather Patterns And Rainfall
- Elevated ocean surface temperatures modify global weather patterns.
- There’s a redistribution of rainfall – some regions endure flooding, while others face drought and wildfire risk.
- The oceans’ role in driving the evaporation and precipitation cycles is intensified with warmer surface temperatures.
Interaction With Drought And Wildfire Risk
- An increase in evaporation leads to more water vapour, feeding into rainstorms and blizzards.
- ‘Landfalling droughts,’ which begin over oceans and slowly migrate to land, have been linked to these changing weather patterns.
The Impact Of Warming And Acidification On Marine Life And Food Security
Climate change, characterised by warming and acidification, is wreaking havoc on marine life. These changes aren’t just threatening biodiversity, but also impact human livelihoods and food security.
Effect On Coral Reefs And Marine Species
- Global warming is contributing to the widespread bleaching of coral reefs. Even if emissions decrease to limit warming to 1.5°C, only 10-30% of global coral reefs may survive. This figure falls to just 1% if warming hits 2°C.
- Acidification, resulting from increased carbon dioxide absorption, reduces carbonate ions, crucial for shell building in marine species.
- Warming temperatures have also prompted many species to migrate towards cooler waters.
Impact On Ocean Fisheries
- Ocean fisheries, already weakened by poor governance, overfishing, and habitat destruction, are further threatened by warming and acidification.
- Over 3 billion people worldwide, especially those in coastal, low-income regions, rely on these fisheries for nutrition.
Threat To Food Security
- In certain communities in West Africa, Southeast Asia, and small island developing states, marine fisheries provide over half of the dietary animal protein and essential micronutrients.
- Warming also escalates microbial respiration, causing oxygen-depleted zones in the ocean, threatening the survival of marine life.
Ocean Carbon Sequestration And Twilight Zone
The increasing carbon emissions are altering the ocean’s biological processes, impacting the carbon sequestration rate and potentially making it a carbon source. However, our understanding remains limited, particularly concerning the ‘twilight zone’ and its interaction with climate change.
The Carbon Sequestration Mechanism
- Emissions are rising, leading to the oceans sequestering more carbon through biogeochemical processes.
- Latest findings indicate a decrease in the net production of micro-plants and the amount sinking from the surface by the century’s end.
- There’s a potential scenario where an increased amount of organic carbon, in the form of sinking particulate organic matter, reaches the deep ocean.
- At the same time, the production of new micro-plants is decreasing.
- If this happens, it is theoretically possible for the carbon sequestration mechanism to stall.
- A stalling mechanism means the rate of carbon leaving the deep ocean and returning to the atmosphere would exceed the rate of carbon reaching it, resulting in a negative sequestration rate.
Uncertainties And The Twilight Zone
- We have limited knowledge about the ocean’s ‘twilight zone’ (200-1000m below the surface) and its carbon sequestration processes.
- This lack of understanding extends to the zone’s interaction with climate change and its impact on higher food chain levels.
Impact On Fisheries
- The twilight zone sustains significant fishery stocks globally.
- The potential effects of fishing in this zone on the overall oceanic system and carbon biogeochemistry are unknown.