Saturday, November 4, 2017

If Polar Ice Melts How Much Will Sea Level Rise?





Probably no single item brings the scientific-political argument over climate change more into focus than sea level rise and its consequences. Here are the facts to counter the “alternative facts” that have been floated in national political discourse. See also the earlier article (http://askageologist.blogspot.com/2013/07/climate-change-is-it-real.html) on “Climate Change – is it Real?” Curiously, only in America is the science of climate change being questioned. However, only in America (and Myanmar) do we still use feet, pounds, and gallons.



In all fairness, this is not an easy scientific problem to address. Non-linear behaviors (something changing much faster than the variable forcing it is changing), and extremely complex interlocking feedback between physics and chemistry related to Earth’s weather systems, makes any modeling truly daunting. Nevertheless, scientists have developed a number of predictive models, and they are beginning to agree ever more closely.

Q: What if all the ice caps melt how bad will it flood the nearby continents, and would it change the tides of the world? How fast would the world have to react.

- Stephen L

A: There are about 21 million cubic kilometers (5 million cubic miles) of ice on the Earth’s surface. If all of this melted, it would raise sea levels by about 65 meters (215 feet). An image compiled by National Geographic magazine (http://www.nationalgeographic.com/magazine/2013/09/rising-seas-ice-melt-new-shoreline-maps/) gives a breath-taking sense of what this would mean for humanity. Florida would disappear – Washington, DC, also. This isn’t going to happen immediately, of course. For all this ice to melt would require the average global temperature to rise from a current 14C (58F) to 27C (80F). This is not impossible, especially if carbon continues to be extracted and burned at current rates or higher. 


However, there are many issues beyond polar ice involved with sea level rise:


1. Tectonic changes

2. Thermal expansion of the oceans

3. Melting ice

4. Local weather events (e.g., hurricanes)

5. Ocean albedo change

6. Methane clathrates

7. How fast will it rise?



1. Tectonic changes are an issue because, all things being equal, sea level is an equilibrium by definition and should rise everywhere at the same rate. Nevertheless, the east coast of North America is seeing a greater sea level rise than the west coast. This is because of tectonic changes, related to mid-Atlantic sea floor spreading, that are causing steady sinking along the east coast of the United States.



2. Thermal expansion is important because if you heat water it will expand. With climate change well underway (and isotopic studies indicate that it is largely man-made), we can expect all the world's oceans to expand... and therefore rise. Water is at its most dense at 4 degrees Celsius. Freeze water and it will expand (this explains why frozen water pipes burst). Warm it above 4 degrees Celsius and it will steadily expand.



3. Antarctica is covered with ice an average of 2,100 meters (7,000 feet) thick. If all of the Antarctic ice melted, sea levels around the world would rise about 60 meters (200 feet). Arctic ice is not nearly as thick, but Greenland by itself, if all its ice melted, would increase sea level rise an additional 7 meters (20 feet).



4. Local weather events are the most immediately attention-getting, and there are at least two different aspects to this. Warmer ocean water translates into more heat energy going into a hurricane - the storms become bigger and the destructive wind velocities become stronger. The recent Atlantic hurricane Irma is a case in point: it is the largest and strongest Atlantic hurricane ever recorded since measurements were first acquired. When its eye reached the southern tip of the Florida peninsula, it's outer rain bands were already into Georgia - and that was just half of this monster. However, hurricanes push seawater before them and drag at their cores a huge low-pressure zone, and this gives rise to what is called a "storm surge." The storm surge for hurricane Katrina, which devastated New Orleans in 2005, caused over $100 Billion in damage largely because its storm-surge was an additional 5 meters (16 feet) above the normal tidal differences. Add a "king tide" (when Earth and Moon are aligned and the high tide is greatest) to a 5 meter storm surge and you have a very destructive combination. It's like a giant, slow tsunami.



5. If ice disappears from the poles and from Greenland, then the albedo of the Earth will change. Albedo is the percentage of the incident light or radiation that is reflected by a surface, and is typically used for a planet or moon. In this case, ice-covered polar regions are very strong (though not perfect) reflectors of sunlight. If the ice were to disappear, the energy absorption of the polar regions would increase dramatically. Like ocean warming, this is another contributor to the non-linear character of sea level rise: a simple increase in a certain value causes secondary effects that dramatically increase the effect disproportionately in a non-linear fashion.



6. Methane clathrates (methane hydrates, "fire ice", etc.) are methane-ice held in a suspended quasi-stable crystal state found in the world’s cold deep ocean sediments (below at least 200 meters or 600 feet depth). This methane is a product of carbon being sequestered over time by CO2 capture (decayed materials falling to the ocean floor). The amount of carbon sequestered in this form beneath the world’s oceans is between 500 and 2,500 gigatons, comparable with all known sources of hydrocarbons on land. There is evidence now that ocean temperatures as deep as 500 meters are rising. Methane, being a far stronger greenhouse gas than carbon dioxide, if released in these numbers, will cause a dramatic rise in global temperatures. This is another contributor to the non-linear character of sea level rise, and helps explain why estimating climate change consequences is so difficult.



7. How fast will sea level rise happen? That is the million-dollar question for our age. The Intergovernmental Panel on Climate Change issued a report in 1995 containing various projections of the sea level change by the year 2100. They estimated that average sea levels worldwide will rise 50 centimeters (20 inches), and their +/- range went up to 95 centimeters (over 3 feet). The rise will come in part from thermal expansion of the ocean and in part from melting glaciers and ice sheets. Fifty centimeters is no small amount – this could have an enormous, disproportionate effect on coastal cities, especially during storms like Katrina, Sandy, or Irma.  Keep in mind that this estimate is over 20 years old, and more recent sea level rise estimates vary widely but are not small. Since that 1995 report there have been gigantic ice sheet calving events in the Antarctic. The most recent (Summer of 2017) on the Ross Ice Shelf is an “iceberg” the size of Delaware, that ranges from 15 to 50 meters (up to 165 feet) high... and it will all melt as it drifts northward. 



About 80% of the human population now lives within 100 km of an ocean, and the most expensive and sought-after kinds of land are ocean-front properties.  You don't have to be a rocket scientist to realize that ocean-front property investment might not be a good idea. Miami "dodged the bullet" from hurricane Irma in September 2017, but it's just a matter of time before a larger, even more destructive hurricane will hit it dead center. The loss of life and property to just Miami alone are unimaginable. The entire eastern United States is at risk, and hurricane Sandy (2012) made it clear that low-lying cities like Washington DC and New York are at terrible risk due to climate change. Giant typhoons in the subtropical Pacific are causing huge damage every year to east and southeast Asia. 

We should be have been reacting to these scenarios long ago. Places like The Netherlands and the City of Venice have certainly been taking steps to mitigate the consequences of sea level rise for decades now. However, the world needs to address the reason for it. Choosing myth over climate science is not the way to go. That approach didn't work for Big Tobacco, either.
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