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TellUs: A Planet Committed To Sea Level Rise

Why sea levels will naturally rise regardless of our actions (do not take this as we don’t need to act urgently)

This blog will address why the sea levels are rising naturally, because yes they are rising naturally and until now I had no idea why myself! However it will also address how human activity is exacerbating this natural occurrence. What I also want to come across is how past actions still alter the Earth for hundreds and thousands of years to come. So we may assume that destructive Earth practices happening today won’t be an issue in the future because they’ll just “go away”, however this certainly is not the case. The past builds on and creates the present and in turn the future. 

Palaeography of the British Isles 18,000 years ago in the glacial stage
(Source: British Geological Survey)
During the last glacial period, known as the ‘glacial stage’, thick ice sheets covered much of North America, Asia and northern Europe. These ice sheets depressed the Earth’s surface and even though they retreated around 11,500 years ago the land is still rising due to a process titled isostatic rebound. 

This means land that was covered in ice sheets rises and the connecting land that didn’t tilts down, causing a relative rise in sea level at an approximate rate of 0.15 of a metre per century. This is a factor for coastal erosion in certain areas. Therefore past events thousands of years ago have consequences in the present. Landscapes are still changing due to natural climate change. 
As we know human activity warms the Earth through the release of greenhouse gases. The increased concentration of greenhouses gases in the atmosphere leads to the Earth retaining more solar radiation than it otherwise would. 

This warmth causes sea levels to rise for two reasons:
  1. Glaciers and terrestrial ice sheets start to melt, with this water then running into oceans
  2. The water in the oceans increase in volume as it warms, due to a process named thermal expansion

Thermal expansion is an increase in the volume of a liquid or matter in response to an increase in temperature. 

So even if greenhouse gas levels were stabilised at present levels, the atmospheric temperature would continue to increase for a number of years, in turn the oceans would warm and expand. 

Water also has a higher thermal inertia than the air. Thermal inertia is a measure of the rate of change at which a material approaches the temperature of its surroundings. This means water takes longer to warm or cool than air. So finally when the atmospheric temperature is stabilised the oceans would continue to absorb heat for decades. 

This diagram shows how much global warming goes to the ocean via thermal inertia
(Source: Pär Holmgren)

The planet is committed to sea level rises in the future and although natural processes contribute to this, human activity is a catalyst for these rises. Scientists from the Intergovernmental Panel on Climate Change indicated a rise from 18cm to 59cm sea level rise over the course of the twenty-first century. By the end of the century it could rise as much as one metre.

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Check out my previous blog: https://www.tellusabouttheenvironment.com/2019/10/tellus-99-of-carbon-lies-beneath-our.html
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