The sea is crucial. Like us humans, the body of the Earth is mostly made up of water; to say it keeps things ticking over would be an understatement.
We’ve talked before about the significance of clean marine water, but what about ocean temperatures? Like every other natural habitat, a fine balance is needed to maintain a healthy ecosystem. And when the planet’s water is relied upon for so much, the effects are deeply felt when that balance is knocked out of whack.
Here, we wanted to tackle a key part of that balance in the form of sea water temperature. Are sea temperatures going up? What’s global warming got to do with it? And, crucially, what impact does this have on the planet and on us?
How is global warming affecting water temperature?
The beginning of the Industrial Revolution a few hundred years ago marked the start of our excessive use of fossil fuels. Along with industrialisation came deforestation and the annihilation of many natural carbon-capturing environments.
All of this amounts to a huge increase in greenhouse gas (carbon dioxide, methane, etc) emissions and heat being pumped into the Earth’s atmosphere. In 2019, for example, CO2 levels in the atmosphere were higher than at any time in at least 2 million years.
Greenhouse gases form something of a blanket around the planet, trapping extra heat nearer the Earth’s surface, causing temperatures to rise. This is known as the greenhouse effect.
Of course, not all of the heat we have ever produced stays within the atmosphere, but it does have a huge impact – and that heat has to go somewhere. In fact, much of this heat is absorbed into the planet’s oceans.
Climate change as a natural phenomenon
Climate change in and of itself is, indeed, a ‘natural phenomenon’ – but we want to make some definitions very clear here. In its natural form, climate change describes long-term shifts in temperatures and weather patterns. The Ice Age, which came on incredibly slowly, can be described as a period of climate change.
Research shows that for the last 2.6 million years, the earth has been alternating between long ice ages and shorter interglacial periods. These generally happen around every 100,000 years – so typically, that’s 90,000 years of ice age and then a 10,000-year interglacial (warmer) period.
We’re currently in an interglacial period known as the Holocene and, for the last 2,000 years, the earth’s climate has been relatively mild and stable.
The Intergovernmental Panel on Climate Change has stated that, “Since systematic scientific assessments began in the 1970s, the influence of human activity on the warming of the climate system has evolved from theory to established fact.”
The impacts of sea surface temperature
So we know the causes of sea temperature warming. But what does it matter? A few degrees here and there would make for more comfortable swimming, right?
Unfortunately, like many phenomena caused by global warming, there’s more nuance to it than that. These degrees of warming can have devastating impacts on marine life, weather patterns, and land etemperatures – all of which affect us humans, so let’s take a closer look.
Weather patterns
There is evidence to show that rising sea temperatures have an impact on weather patterns around the globe.
For one, this general trend has been shown to result in an increase in the speed and intensity of storms. A study by Bhatia et al states: “Specifically, areas with the largest increase in sea surface temperatures (SSTs) and potential intensities appear to be collocated with the largest positive changes in intensification rates.”
The ocean, in its enormity, powers weather patterns by driving evaporation and precipitation cycles. As temperatures on the water’s surface increase, so too does the rate of evaporation, adding additional moisture to the atmosphere. As we learned in school, evaporation leads to precipitation i.e. rain! And lots of it.
Wetter areas will experience yet more precipitation, and already-dry regions become drier. As a result, these areas are set to experience more prolonged droughts and are at higher risk of wildfires.
Not only this, but the saltiness and temperature of the ocean drive ocean currents, which are then disrupted by melting ice and rising temperatures. This leads to yet more intense weather, like hurricanes, flooding (more on this in a moment), and tropical storms.
Land temperatures & sea levels
It’s strange to think about, but when water heats up, it expands. You might’ve heard that the cause of cracks in roads in winter is not the ice that settles there, but the thawing process that causes the ice to expand and put pressure on the tarmac. This process is known as thermal expansion.
Effectively the same thing is happening on the oceanic scale. In fact, about 40% of global sea level rise over the past few decades has been put down to thermal expansion – not simply melting polar ice caps.
As perhaps one of the most severe impacts of climate change, sea level rise (SLR) threatens to swallow up small-island nations and erode coastal regions. It’s already doing so, destroying not only communities but habitats for fish, birds, and plants. Not only does SLR strip areas away over time, but contributes to more powerful storm surges, floods, and hurricanes that do so overnight.
Furthermore, as sea water rises, salt contaminates agricultural soil and underground aquifers that we rely on for drinking water.