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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