Sea Level Rise: The Next Big Thing?

Climate Action

In the past 120 years, the world’s oceans have risen by between eight and nine inches.  This is due to global warming. Roughly half of this expansion is due to ice melt and half to thermal expansion.  The rate of ice melt is rapidly increasing so it is now becoming the dominant effect.

This graph shows the record of sea level rise since 1900.

Note that the slowdown in the rate of sea level rise between 1950 and 1970 shown in the graph is attributed to a spate of dam building that stopped water from reaching the oceans until the reservoirs filled up.  This has been followed by a steeper rate of rise over the past 40 years as the interruption in the flow of runoff to the oceans ended.

Using regression analysis, we can create a trendline based on the 1990 to 2020 record to project sea level rise to 2100 as shown in the following graph.

The trend line shows that by 2100, sea level will rise by five feet.  But with all the uncertainty, this estimate and five bucks will get you a coffee at Starbucks.  Here is how NOAA captures this uncertainty:

This graph shows three scenarios based on three Representative Concentration Pathways (RCPs) developed by the IPCC.  Each RCP is associated with different levels of carbon dioxide emissions as shown in the next graph.

  • In the Low Scenario (RCP 2.5) carbon dioxide emissions begin to drop immediately and reach zero around 2080.
  • In the Intermediate Scenario (RCP 4.5), carbon dioxide emissions rise slightly before beginning to decline in 2040, reaching 15 billion tons per year by 2080.
  • In the High Scenario (RCP 6.0), annual CO2 emissions climb to 55 billion tons by 2060 before beginning a gradual decline to 46 billion tons by 2100.

Each of these pathways will produce different levels of atmospheric carbon dioxide concentration as this next graph shows.

If we compare the temperature rise since 1880 with the change in the concentration of carbon dioxide, we find that each 1 ppm change in the concentration of carbon dioxide produced a 0.009974493-degree change in the temperature.  Assuming this ratio continues to hold, the low concentration pathway will produce no change in temperature, the intermediate concentration pathway will produce a 1.6-degree increase in temperature by 2100, bringing us to a 2.7-degree overall rise, and the high concentration pathway will produce at 2.9-degree increase in temperature, bringing us to a 4.0-degree overall rise.  These numbers are all in the ballpark of what is currently being discussed.

Back to sea level rise. How fast could sea levels rise?  Paleoclimate data has shown that for many centuries while the planet was emerging from the last ice age, sea levels rose by up to 14 feet per century, so substantial sea level rise within a matter of decades is possible.  And CO2 levels were considerably lower then than they are today.  This is why scientists are so worried.

It takes a long time to melt a huge block of ice. That’s why climate scientists did not think we would have to worry about Greenland and Antarctica this century. But that view changed over the past 20 years as both ice sheets are melting far faster than expected.  Will this acceleration continue? Unless we dramatically reduce greenhouse gas emissions, the answer is a definite yes.   Some scientists think that we have already passed tipping points that have doomed both ice sheets to radical melting. Others believe that if we reduce greenhouse gas emissions, we may still be able to hold the line.

So, what are our chances of reducing emissions? Although the Biden administration is turning the ship in the right direction, it will take time, and even then, without even more severe natural disasters, the prospect of motivating a public that has to be enticed into getting vaccinated doesn’t seem promising.  But a faint heart never won a fair woman, so let’s consider what we can do.  A little number crunching will lay out the situation.

Energy consumption in 2020 was down 7 percent due to COVID, so in order to avoid that anomaly, I use energy consumption for 2019 as a baseline.  That year the world consumed 184 quadrillion watts of energy. (That’s a one followed by 15 zeroes.)  Eighty percent of this – 146 quadrillion watts – came from burning fossil fuels. What is it going to take to get this down to zero?

The amount of energy we use depends on two things: 1. How many people there are and 2. Their per capita energy consumption.  This gives us three ways we can reduce our fossil fuel emissions: 1. Have fewer babies, 2. Reduce our personal use of energy, and 3. Get energy from clean energy sources.  Let’s consider each option.

Population Management:

Countries with more developed economies have reached reproductive rates at or below the replacement rate while some less developed countries still have extremely high fertility rates.  India and Africa are now on track to have the highest rates of population growth.   India is expected to add 300 million people by 2050 – close to the population of the United States.  And Africa’s population is expected to double by 2050, adding – incredible as it seems – another 1.25 billion people.

When all things are considered, the global population is expected to grow from just under 8 billion people today to about 10 billion by 2050.  If the impact of climate change in the next three decades is severe, these numbers could come down.  Considering the likelihood that the climate during the second half of the century will be worse still, I don’t think it’s a useful exercise to try to forecast the global population for 2100.  As a general rule, I think it is reasonable to assume that the global population will continue to grow until humanity is forced by circumstances to alter its behavior.

Reduce Per Capita Consumption:

Energy is a form of wealth, and like wealth, there are the haves and have nots.  And as is usually the case, there are only a few haves and lots of have nots.

Energy consumption is measured in terms of per capita carbon dioxide emissions produced by the energy consumed.  The US does not have the highest per capita carbon footprint; that distinction goes to Qatar, Kuwait, and the UAE.  But among the major powers, the US is off the charts with annual emissions of 16.6 tons of CO2 per capita. By comparison, the EU comes in at 6.7 tons, China is at 7 tons, India is at 1.9 tons, and sub-Saharan Africa gets by with less than one ton per capita.  The global average is 4.8 tons per capita.

The point is that there is not a lot of potential to reduce per capita consumption because only a relatively small percentage of the world can afford to do it, and most of those people are here in the U.S.  With 330 million people, we are less than 5% of the global population.  Let’s say that we reduced our per capita emissions to the level of the EU.  That’s a reduction of about 10 tons per person.  Ten tons times 330 million is 3.3 billion tons.  It’s not an inconsequential amount, but with global annual emissions running close to 40 billion tons, it’s less than a ten percent reduction.  And, except for Canada, Australia, and some Mideast countries – all of which add up to a fraction of the US potential for emissions reduction – what we have is pretty much a one trick pony.

Clean Energy:

That leaves us with replacing fossil fuels with clean energy.  To keep things simple, I’ll just focus on the 145 quadrillion watts of energy that was produced by fossil fuels in 2019.  Except for China, the world is backing away from nuclear energy.  (We can leave fusion off the table for now.  It has yet to demonstrate that it is feasible.  The ITER experiment won’t be done until 2035, so barring some miracle from a small developer, it can’t help now, and now is when we need the help.)

So, if we do this all with wind and PV solar, what does that look like?  It’s a simple math problem.  Let’s start with wind.  The most common type of wind turbine now being built has a capacity of 2 megawatts.  Wind turbines operate at an average efficiency of 35%, so a wind turbine rated at 2 megawatts can produce 6 billion watt-hours of energy per year.  If we divide this into 146 quadrillion watt-hours we get 24 million wind turbines.  Of course, that is nowhere close to the realm of possibility.  And it doesn’t include the enormous amount of energy storage capacity that will be required to make an intermittent source of energy feasible.


Human behavior – specifically the amount of fossil fuels we continue to burn – is the key to determining how high sea level will rise.  None of the three courses of action to significantly reduce emissions appears to be open to us, and so, it is likely that we will be facing something between RCP 4.5 and RCP 6.0 – or worse depending on when we hit tipping points in the melting of Greenland and Antarctica.