What is Ocean Warming and Why Does It Matter?

The oceans and atmosphere work together to form Earth's climate. However, Earth’s climate is changing. This is partly because of global warming. Global warming affects everything on Earth, including its oceans. When ocean temperatures rise, this causes problems across the planet. Let’s look at some of the ways the ocean is important to global temperature. Then let’s look at why rising ocean temperatures are something to worry about.

How does the ocean help control Earth’s temperature?

Energy from the Sun is called solar radiation. Earth absorbs solar radiation and converts it to thermal energy, or heat. As solar radiation travels through Earth’s atmosphere, some of the energy is reflected. The rest of it is absorbed. 
 
About half of the solar radiation that enters Earth’s atmosphere is absorbed by the Earth’s surface. The surface includes the land and oceans. The other half is scattered, reflected, or absorbed elsewhere. For example, it might be absorbed by Earth’s atmosphere, or by clouds in the atmosphere.

Oceans absorb the greatest amount of solar radiation that reaches the Earth’s surface. That's because oceans cover 70% of the Earth’s surface! Not only is the ocean good at absorbing solar radiation, it’s also good at doing it while “keeping its cool.” It has to be good at this, because it takes much more energy to change the temperature of the ocean than of the air. This is because of heat capacity.

Heat capacity is the amount of thermal energy it takes to raise the temperature of one gram of a substance by one degree Celsius. The heat capacity of water is 4.186 Joules/gram °C. That is about four times more than the heat capacity of air. This means that ocean water can absorb four times more solar radiation than air before its temperature will rise by one degree.

Did you know?

In order for Earth’s temperature to remain constant, the same amount of solar energy that enters Earth’s atmosphere must leave it. This is called Earth’s energy budget. 

How is climate change impacting ocean temperatures?

Global temperatures are rising because of climate change. This is partly due to the greenhouse effect caused by greenhouse gas emissions. The greenhouse effect causes more solar radiation to be trapped in the Earth's atmosphere. The atmosphere would be much warmer if it weren't for the oceans. But as global temperatures rise, it becomes more difficult for the oceans to help keep the atmosphere cool.

Since 1955, the oceans have absorbed about 90% of the excess heat in the atmosphere. The US National Oceanic and Atmospheric Administration (NOAA) states that the average ocean surface temperature has risen by 0.07 degrees Celsius every decade for the past 100 years. But it has risen twice as fast since 1985.

What are the implications of rising ocean temperatures?

As ocean temperatures rise, the glaciers that make up the polar ice caps are melting faster. The polar ice caps are located in the Arctic and in Antarctica. In fact, scientists believe that polar ice has melted faster in the last 20 years than it has in the last 10 000. 

Because of this rapid melting, sea levels rise as the melt water runs into the ocean. Rising sea levels cause problems for coastal ecosystems. Some examples of problems include:

• erosion
• flooding
• habitat loss
• saltwater contamination of freshwater sources 

This is a problem for humans as well. As sea levels rise, cities on coasts will experience these problems too!

Since 1992, global sea levels have risen by about 11 millimetres. That might not seem like much. But if the speed of melting continues to increase, sea levels will rise much more quickly! 

Did you know?

Satellite imagery is used to track shrinking glaciers in places like Antarctica and Greenland. 

Another impact of rising ocean temperatures is ocean acidification. As the amount of carbon dioxide in the atmosphere increases, a chemical reaction occurs between carbon dioxide (CO₂) and ocean water (H₂O). This chemical reaction creates carbonic acid (H₂CO₃). 

On the 14-point pH scale, ocean pH has been at around a slightly basic 8.2 for the past 300 million years. But in the late 18th century, the Industrial Revolution began. Since then, ocean pH has dropped to 8.1. A pH drop of 0.1 may not seem like much. But it represents a 25% increase in ocean acidity over the past 200 years.

Rising ocean temperatures have an impact on many types of marine organisms. For example, carbonic acid can prevent shell growth in animals such as clams, oysters, and snails. 

Higher ocean temperatures have also been blamed for lowering the level of oxygen in the water. This process is called deoxygenation. There are several reasons this might be happening. Warmer water cannot hold as much oxygen. Warming also changes the way oxygen-rich surface water mixes with deeper, oxygen-poor water. 

Rising ocean temperatures directly affect corals. Corals have a symbiotic relationship with a type of algae called zooxanthellae. Zooxanthellae provide corals with nutrients to help them survive. Warmer ocean temperatures cause the corals to expel their algae. This results in a bleaching event. Corals can survive without their algae. But their stress levels go up, which makes them more vulnerable. 

The ocean is important for keeping the Earth’s temperature in check. But it can only help so much. We need to understand how climate change is impacting our planet. This includes how greenhouse gases impact the ocean, not just the atmosphere. We have to take care of our planet if we want it to help take care of us!