Sea level rises that could result from global warming

Climate change could lead to sea levels rising to a point where low-lying parts of the world would be devastated. Indeed, this is widely regarded as inevitable. But just how high are sea levels likely to reach – and when will this happen?

Global temperatures rising by two degrees Celsius

This measure of two degrees relates to the difference between average global temperatures now and what they were before the Industrial Revolution that began in Western Europe in the late 18th century. It is thought that restricting the rise to two degrees offers the best hope of preventing the disastrous consequences that many climate scientists predict. However, this will not be easy if action is not taken now to restrict the burning of fossil fuels.

The 2-degree temperature rise will in any case lead to a general sea level rise of 0.8 metres, simply from the effect of water expanding as it gets warmer. This effect is already taking place, the effects being noticed particularly in low-lying island nations.

Antarctic ice shelves are set to collapse

The polar ice caps are repositories of vast quantities of frozen water. One of the chief dangers of global warming is that enough of this ice will melt to cause significant sea-level rises.

Scientists at the University of Washington in Seattle have concluded that at least one vast ice shelf in Antarctica is bound to collapse, whatever steps are taken to limit global warming. This is because the processes leading to collapse are irreversible.

An ice shelf is a tongue of ice that is fed by glaciers and projects beyond the continent into the surrounding sea. The shelf that is causing concern is about two kilometres thick, but its base can be reached by relatively warm oceanic water that causes melting. There would be no problem if the rate of melting was matched by the supply of extra ice from above in the form of glaciers from off the land, but this is no longer the case because the glaciers are in retreat. As sea ice melts, more water will be able to reach the base of the shelf and cause further melting.

When the ice shelf collapses and all its ice turns to liquid water, the eventual result will be a global sea level rise of 3.3 metres. If other glacial melting is taken into account, as well as the 0.8 metres rise mentioned above, the total expected rise will be 4.5 metres.

Is that all?

Not necessarily! The hope that the global temperature rise will plateau at +2 degrees is just that – a hope. What would be the likely scenario if the rise was, say, 4 degrees?

The answer is – a great deal worse. For one thing, there are other ice shelves in Antarctica that would be vulnerable to collapse. For another, the Greenland ice cap is at risk and its point of no return could be reached within the next 50 years.

If all this happened, and all the at-risk ice melted, a 4.5 metre rise in global sea levels would be just the start. The overall rise could be as high as 19 metres! The lower figure would be enough to inundate places such as the Netherlands and Florida, but a rise four times as great would have consequences that are hard to imagine.

But when?

It could take one or two centuries for the +4.5 metre level to be reached, but it certainly will be reached at some future point because the processes currently in motion are irreversible.

The worst scenario – a 19 metre rise – could be thousands of years down the road.

However, a one metre rise – which would have very serious consequences for low-lying nations – could easily be something that many people alive today will see and have to contend with.

Can it be stopped?

That depends on what is meant by “it”. As mentioned above, some degree of sea level rise is inevitable, and even the predicted 4.5 metre rise will have severe repercussions for future generations. Plans for future human settlement need to bear this in mind, because there are many places in the world where this will  simply be impossible and there is absolutely nothing that can be done to rectify the situation.

However, it is still within the realm of human ingenuity to prevent the worst scenario – a 19 metre rise – from occurring a lot further down the line. Global warming can be slowed to a manageable level if humanity is sensible in the way it uses energy in the future – primarily by keeping fossil fuels in the ground and using every opportunity to exploit renewable energy sources.

There are plenty of examples already evident of how this can be done – in the UK there have been several days in recent months on which more electricity has been generated from renewables than from oil and coal. Developments in battery design are proceeding apace, which gives cause for hope that more energy produced by, for example, solar and wind can be stored and released when needed.

What is needed most is a universal belief that the problems can be solved and refusal by governments across the world to listen to the blandishments of fossil fuel producers whose only concern is immediate profit.

The relatively short-term prospect is not good for preventing major sea level rises. However, the longer-term prospects are much more hopeful, as long we take seriously our responsibility for future generations.

© John Welford