Ocean Warming

Around 93% of all heat trapped by greenhouse gases accumulate in the Earth’s oceans.

 

Ocean Warming

As man continues to overload the atmosphere with carbon dioxide, heat is trapped (greenhouse effect) which steadily increases the planet's temperature, and that of the oceans.

 

Ocean warming is causing sea levels to rise due to thermal expansion and the melting of glaciers and ice sheets in the Antarctica. A recent study suggests that up to 390 billion tons of ice and snow are melting away each year. The study adds that since 1961, the world has lost 10.6 trillion tons of ice and snow. Melted, that's enough to cover the lower 48 U.S. states in about 4 feet of water.

 

Ocean heat content is one of the main measures of climate change, with around 93% of all heat trapped by greenhouse gases in the atmosphere accumulating in the Earth’s oceans. 2018 was the hottest year ever recorded for our oceans, and they are warming even faster than previously thought.

A further study, also published in February 2019, shows that climate change will reverse the recovery of whales in the Southern Ocean by damaging the krill on which they feed. Models predict concerning declines, and even local extinctions by 2100, for Pacific populations of blue and fin whales, and Atlantic and Indian Ocean fin and humpback whales.

 

Models of ocean chemistry and biology predict that as the ocean surface warms in response to increasing atmospheric greenhouse gases, phytoplankton productivity will decline. Productivity is expected to drop because as the surface waters warm, the water column becomes increasingly stratified since there is less vertical mixing to recycle nutrients from deep waters back to the surface.

Also published in February 2019, the Environmental Defense Fund reported that hotter oceans lead to:

 

• rising sea levels when water molecules expand from increasing temperatures, and then erode coasts, threaten infrastructure and contaminate freshwater with intruding saltwater.
• heavier downpours and widespread flooding because more ocean water evaporates as temperatures increase, supplying the atmosphere with more moisture.
• more destructive hurricanes because of the increased moisture in the air and higher sea levels that worsen storm surges.
• dying coral reefs as the corals’ colorful algae, their main food source, leave the corals due to heat stress. This bleaches corals of their vivid colors, causing them to starve, while affecting the survival of thousands of species that live in the reefs.
• fish moving pole ward because their current habitats are becoming too warm, disrupting fisheries.

 

Today, three major sensitive areas to global warming are rapidly crumbling away: the Arctic, Antarctica and the northern hemisphere permafrost. A 2016 study reported in the journal Science found that for every ton of carbon dioxide emitted, around 32 square feet of ice disappears. The Arctic ecosystems are under threat, making polar bears homeless and driving away Antarctic krill and the many animals that feed on them. It also impacts the production of ice-dependent algae, which feeds Arctic cod.

 

Potential Release of Undersea Carbon Reservoirs

A further study published in February 2019, predicts that ocean warming could release undersea carbon reservoirs to the atmosphere. If undersea carbon reservoirs are upset again, they would emit a huge new source of greenhouse gases, exacerbating climate change. Temperature increases in the ocean are on pace to reach that tipping point by the end of the century. For example, a big carbon reservoir beneath the western Pacific near Taiwan is already within a few degrees Celsius of destabilising. Moreover, the phenomenon is a threat unaccounted for in climate model projections. Undersea carbon dioxide reservoirs are relatively recent discoveries and their characteristics and history are only beginning to be understood.

 

Falling Ocean Oxygen Levels

The ocean absorbs most of the heat held in the atmosphere, and as the ocean heats up, oxygen can't dissolve as well into the water. The warmer the water, the less oxygen it can take up. Fertiliser pollution can also cause phytoplankton to bloom, which makes the water chemically dense and oxygen depleted.

 

There are other factors that can cause oxygen loss but these are currently not fully understood. What is for sure is that previous models have significantly underestimated the observed oxygen loss, and ocean dead zones are much worse than previously thought.