Seven Meter Sea Rise: A Predictable, Worst-Case Scenario

The question of "Why Seven Meters" is a really good one. And there is a good answer for this. But the answer requires some preliminary work. Sea level changes every century as climate conditions change. After an ice age, sea level will rise as the glaciers shrink. As another ice age grows, sea level will fall as water is captured on the continents. Between ice ages, continents rise as well when released from the weight of thousands of feet of ice. Without human intervention, we would likely see the trend of slow sea level rise continue as it has for centuries. The rise of a couple feet in a century (like the last century) is barely noticeable on many shorelines.

Even without human intervention, there is evidence of prior occasions of a rapid sea-level rise of several meters within a century. Scientists are investigating the causes of these sudden changes in sea level. They suspect this is due to an equally rapid melting of an Antarctic, Greenland, and/or other continental ice source, but they do not know yet exactly what caused the melting of the ice. They also note that shelf ice can flow into oceans before it melts and still raise sea levels.

What they do know is that a sudden (in geological time) melting of one or more of these ice sources would result in a several meter rise of sea level (the melting of all the ice on the planet would result in a sea level rise of more than eighty meters). A significant, several-meter rise of sea level is fully predictable should one or more of these major continental ice sources melt. Such an event, if it happens within a short time span, would be considered by most climate scientists as one of the predictable scenarios for global climate change.

The Final report of the IPCC 4th Assessment says this about Greenland ice sheet vulnerability (November 16, 2007):
"Contraction of the Greenland ice sheet is projected to continue to contribute to sea level rise after 2100. Current models suggest virtually complete elimination of the Greenland ice sheet and a resulting contribution to sea level rise of about 7 m if global average warming were sustained for millennia in excess of 1.9 to 4.6 industrial values. The corresponding future temperatures in Greenland are comparable to those inferred for the last interglacial period 125,000 years ago, when paleoclimatic information suggests reductions of polar land ice extent and 4 to 6 m of sea level rise.

Current global model studies project that the Antarctic ice sheet will remain too cold for widespread surface melting and gain mass due to increased snowfall. However, net loss of ice mass could occur if dynamical ice discharge dominates the ice sheet mass balance.

Anthropogenic warming could lead to some impacts that are abrupt or irreversible, depending upon the rate and magnitude of the climate change.

Partial loss of ice sheets on polar land could imply meters of sea level rise, major changes in coastlines and inundation of low-lying areas, with greatest effects in river deltas and low-lying islands. Such changes are projected to occur over millennial time scales, but more rapid sea level rise on century time scales cannot be excluded. "

Other scientific bodies also report that the complete melting of the Greenland Ice Sheet would create about a seven-meter sea rise from the current level: "The onset of the long-term melting of the Greenland Ice Sheet is an example of a threshold that is likely to be crossed during this century. Climate models project that local warming in Greenland will exceed 3 degrees C during this century. Ice sheet models project that a warming of that magnitude would initiate the long-term melting of the Greenland Ice Sheet. Even if climatic conditions then stabilized, an increase of this magnitude is projected to lead eventually (over centuries) to a virtually complete melting of the Greenland Ice Sheet, resulting in a global sea level rise of about seven meters."

Source: ACIA, Impacts of a Warming Arctic: Arctic Climate Impact Assessment. 2004. Cambridge University Press. p.33
Available at: http://www.acia.uaf.edu. 

Would there actually be a sea level rise of six meters? Seven meters? Eight meters? And when? Both the timing and the amount of sea-level rise are important to know. Unfortunately, the precise amount and the timing of sea-level rise will only be knowable once the conditions that will create the ice melting are fully characterized. This means that while scientists can predict the potential range of sea level rise in advance, the actual amount will only be knowable once the conditions are already in place.

But by that time, it will be too late to affect the precursor conditions that led to the ice melting.

Now that human-induced (anthropogenic) climate changes are being measured, there is a concern that the human-induced warming of the surface temperature in the Polar Regions might trigger the rapid melting of one or more of these major ice sources. This is a predictable, worst-case scenario for human-induced climate change.

Unfortunately, the models for continental ice melting are not yet capable of capturing the complex features that NASA satellites are now discovering in these ice fields. Instead of melting slowly, like a giant ice cube, ice in Greenland and elsewhere seems capable of melting much more rapidly. Reports back from the field are noticing disturbing trends in this regard.

Rapid ice melt and consequent rapid sea level rise symbolizes one of the predictable futures we face in a time of climate change. A rise of seven meters is one of the actual predictions made by climate scientists for this scenario. This is why lightblueline  has chosen seven meters as its target.

None of us wants to see this scenario realized. The goal of lightblueline is to help raise the awareness of the potential for climate change to lead to a new climate that will destroy parts of our current landscape. We are fighting to keep the ocean down at the beach, and not in our neighborhoods and streets. We are looking to stop the human activities that would lead to such a future climate. We are choosing to be smart today instead of all-wet tomorrow.

Why pick seven meters? It is a worst-case scenario, not a best case. But then, we do not need to fear the best case. A seven-meter rise in sea level is a predictable outcome of a significant amount of Polar shelf ice melting. What would cause this to happen? Scientists are working on this problem but might not have the final answer until it is too late for us to stop the scenario from becoming our future. We need to act now to prevent what we know are human activities that are adding heat to the Polar atmosphere. The seven-meter level lightblueline  shows all of us who live near the ocean the extent to which human actions might destroy the lifestyles we cherish.