Carbon dioxide and other greenhouse gases (GHGs) are responsible for global warming, the long-term worldwide average warming experienced since the industrial revolution. GHGs arise from human use of fossil fuels for energy. Major emitters of GHGs include both industrialized countries and, in recent decades, developing countries as well. Higher global temperatures cause the extremes of hot and cold, and wet and dry, weather of recent years. This blog examines global warming and its effects.
See the Tabbed Pages for links to video tutorials, and a linked list of post titles grouped by topic.
This blog is expressly directed to readers who do not have strong training or backgrounds in science, with the intent of helping them grasp the underpinnings of this important issue. I'm going to present an ongoing series of posts that will develop various aspects of the science of global warming, its causes and possible methods for minimizing its advance and overcoming at least partially its detrimental effects.
Each post will begin with a capsule summary. It will then proceed with captioned sections to amplify and justify the statements and conclusions of the summary. I'll present images and tables where helpful to develop a point, since "a picture is worth a thousand words".
Friday, December 14, 2012
Storm Surges and Sea Level Rise
Summary.Hurricane Sandy inflicted heavy damage on the northeastern U. S. states of New Jersey, New York and Connecticut on October 29, 2012.Much of the damage arose from the storm surge of unprecedented intensity
that accompanied the storm.
summarizes several recent scientific articles characterizing melting of polar
ice, historical sea level rise over recent decades, and model calculations
projecting future sea level rise.Melting of polar ice, higher sea levels, and stronger storm surges have
occurred in recent years, in conjunction with the long-term increase in global
average temperature.Model projections
incorporating various scenarios that continue to emit carbon dioxide predict
that sea levels will continue rising to high levels for the next 290 years.
The nations of the
world will continue paying the damages caused by extreme events such as
Hurricane Sandy, with expenses passed on as higher tax rates and higher
insurance premiums, among others.As an
alternative to spending resources on such remediation, humanity should
undertake investment in technologies that limit greenhouse gas emissions, and
indeed should deploy industrial scale technologies that deplete carbon dioxide
already emitted from the atmosphere.
Sandy struck the state of New Jersey and the New York metropolitan area on Monday
October 29, 2012.It caused damage estimated at upwards of
US$50 billion, much of it due to storm surges that impacted wide stretches of
shoreline in New
the heart of New
and eastward along the states of New York and Connecticut.
The ravages of the
storm are likely due to factors related to global warming, such as increases in
the moisture content of air over warm ocean waters, rising sea levels, and a
blocking high pressure system that forced the path of the storm westward toward
land instead of northeastward following the coastline.
U. S. President Obama is submitting a request
for about US$50 billion to the Congress for emergency funding to help recovery
efforts from the storm.This amount is
based on estimates of the physical damage suffered from the storm and costs for
new infrastructure to minimize future storm threats.It is less than the amount of US$80 billion
sought by the affected states, New Jersey, New York and Connecticut, which includes estimates for complete
restoration of property and lost economic activity.
Much of the damage
from Hurricane Sandy arose from an ocean storm surge.This was made worse by the documented
increase in sea levels in recent decades attributed to global warming.The world-wide average sea level rise is
shown in the graphic below.
Global average sea
level trend from 1870 to 2000, referenced to a zero value given as the average
for the period from 1961 to 1990, in mm (50 mm is approximately 2.0 in.).
Sea level rise has
not attracted as much of the public’s attention as have other phenomena related
to global warming, such as extreme weather events more generally.Purely by coincidence several articles in
scientific journals appeared in recent weeks related to sea level rise.This post reviews some of them.They were all submitted by their authors to
the respective journals some months before Hurricane Sandy hit, so they cannot
be considered to have been stimulated by this event.
Record of Sea Level Rise
Melting.A team of 47 climate scientists from 26 institutions
in eight countries, assembled as the Ice Sheet Mass Balance Exercise, reviewed
and collated existing data on loss of ice mass in Greenland and Antarctica.
Their report (A. Shepherd
and coworkers, Science, Vol. 338, pp. 1183-1189, 2012
) assessed previous data sets obtained over 19 years by satellite using the
methods of radar altimetry (elevation measurement), laser altimetry, radar
interferometry between two satellites and gravimetry (measuring changes in the
force of gravity due to lost ice mass), 32 years of model calculations of
surface mass balance, and other models of changes in glacier properties.There was a need for this because the earlier
reports from one technique or another were never considered together.It was not clear whether the results were or
were not consistent.
that the differing methods produced consistent results, Shepherd and coworkers obtained
results for Greenland as a whole, and for three different regions
in Antarctica, as summarized in the following table:
of the report by Shepherd and coworkers is emphasized in an accompanying news comment (R. A. Kerr,
Science, Vol. 338, p. 1138, 2012),
as providing a single set of results
that all agreed to.The report firmly
establishes the large and accelerating rate of loss of ice mass especially from
Greenland and West Antarctica.Kerr points out that the loss reported represents about 20% of the
contribution to sea level rise, the remainder originating from melting mountain
glaciers and the expansion of the water of the oceans as its temperature
increases.All these effects are due to
Polar Ice Melting.In a reviewI.
Joughin and coworkers (Science, Vol. 338, pp. 1172-1176, 2012)
discuss the present state of understanding of the factors involved in ice sheet
loss in Greenland and Antarctica.
principal source of melting is the heat content of ocean waters bathing the ice
shelf (Antarctica) or the outlet glacier (Greenland).The mechanisms involved are complex, and differ in the two cases.The Antarctic ice shelf floats extensively
over ocean waters, which circulate according to circumpolar ocean currents, with
changes in density arising as fresh water from melted ice enters the ocean, and
from tidal mixing at the surface interface with the ice.Recent warming of the underlying ocean
currents leads to more rapid melting of the ice shelf from its lower surface.
glaciers, on the other hand, migrate directly over land surfaces without
floating on the ocean, so the flow of currents differs greatly.These glaciers calve icebergs, and are bathed
in the North Atlantic Circulation.Surface melting occurs in Greenland,
but not in Antarctica, and the liquid descends through glacial crevices
to the ice-land interface, thus changing the salinity of the ocean at the
Over the past two
decades, Greenland glaciers have flowed 50% faster than
before, likely owing to the effect of global warming on providing warmer water
at the ice-ocean boundary.The authors
conclude that much still remains to learn about these phenomena.Incorporating the present knowledge into
general circulation models in order to predict future melting rates will be
successful if the models operate with high spatial resolution.It appears that such models for melting
“indicate the potential for far more extreme changes within this century than
had been anticipated”.
surges.A. Grinsted and coworkers (Proceedings of the (U. S.) National Academy of Sciences, Vol. 109, pp. 19601-19605, 2012),
based in China, Sweden, Finland and the United Kingdom, studied storm surges
along the Gulf of Mexico and the U. S. Atlantic coast over the period 1923 to
2008 by analyzing tide gauge readings from six locations along these
shorelines.(1923 was chosen for the start
because it is the year of a strong storm surge; active surges continued during
small number of locations is justified because surges extend large distances
from storm centers (their cutoff was 250 km (155 mi,)) and last several
days.The authors constructed a new
surge index which accounts for the potential energy contained in elevated water
levels, and adjusts the data by removing an annual background tidal level for
each location.The results are
correlated with whether an event falls in a cold year or a warm year, where
deviations from the median temperature for the interval studied here govern
whether an event is classified as a cold or warm year event.The temperature data are global average
annual temperatures.They cross from
being generally cold to being strikingly warm at about 1978; the years in the
period from 2000 on are generally 0.4-0.7ºC (0.7-1.3ºF) above the median.This temperature trend is already quite well
known.The authors then generate a graph
of the surge index for all surge events, plotted against the frequency of their
Surge events were segregated
according to whether they occurred in a cold year or a warm year.Strikingly, events with high surge indexes
(i.e., having the highest energy at landfall) occur twice as frequently in warm
years as in cold years.Additionally the
authors find that warm years generate more storm surge events than do cold
This suggests that
global warming leads to more intense storm surges, understandably since warmer
air can hold higher amounts of water vapor, leading to stronger winds.Wind strength is an important factor in
creating the energy contained in a storm surge.
Level Trends.A. Sallenger and coworkers (Nature Climate Change, Vol. 2, pp. 884–888, 2012)
report a hotspot in recent sea level rise along the northeast coast of the U. S. between Cape Hatteras, North Carolina, and Boston, a distance of about 1000 km (620 mi.).This includes the New Jersey-New York-Connecticut shoreline subjected to the storm surge of
This study analyzed
tide gauge data from 1894 to the present.Most analysis focused on time windows of 60 years, 50 years and 40 years
all ending in 2009.They find that as
the time window narrows and becomes weighted more to recent decades, this
hotspot becomes more intense.The 60
year window shows tide gauges in this region with annual rates of sea level
rise in the range (this writer interpreted color-coded data points) of about 1
to 3 mm per year, whereas the 40 year window shows that this rate has
increased to mm per year in most cases.In contrast to this hotspot, the gauge data
from further south than CapeHatteras and further north than Boston show mostly no sea level rise, indicating
that the regional nature of the hotspot appears to be real.The authors relate that their demonstration
of a sea level rise hotspot along the northeast coast is consistent with several
model predictions by other workers of such a hotspot.
S. Rahmstorf, one
of the coworkers with M. Schaeffer in work described in detail below, warned on Nov. 28, 2012
that sea levels have been increasing in recent decades even faster than
predicted earlier by the Intergovernmental Panel on Climate Change.
Large Future Sea
Level Rise Due to Further Planetary Warming.M. Schaeffer and
coworkers (Nature Climate Change, Vol. 2, pp. 867–870, 2012)
modeled sea level rise projected into the future based on a range of greenhouse
gas/temperature rise scenarios.
the United Nations Framework Convention on Climate Change annual conference
held in Cancun, Mexico in December 2010 the nations of the world pledged to restrain
further emissions of greenhouse gases (GHGs) such that the long-term global
average temperature increase would not be greater than 2ºC (3.6ºF) above the
level that prevailed before the industrial revolution began.This limit corresponds to an atmospheric concentration
for carbon dioxide or its equivalent GHGs of about 450 ppm (parts per million).Sea level rise model projections were
calibrated by correctly reproducing sea level data starting from the year 1000
up to 2006.Projections overlapped by
starting as early as 1860, extending to the year 2300.
Large sea level
rises are foreseen for 2100, continuing to even higher sea levels by 2300.In
the year 2100, an emissions scenario that maintains the 2ºC limit is predicted
to generate a sea level rise of 75-80 cm (29.5-31.5 in.) above the level of
2000, while a scenario with no abatement of emissions generates a rise of about
1 m (39.4 in.) and a radical scenario in which all emissions cease after 2016
provides a rise of about 60 cm (23.6 in.) by 2100.
The oceans contain
a great deal of thermal and climate inertia since the ability of liquid water
to store and release heat is about 1000 times greater than for air, and various
ocean depths circulate to exchange heat content only over very long time
frames.For these reasons sea level rise
trends that are apparent in projections at the year 2100 continue along similar
trajectories further into the future.Schaeffer and coworkers extended their projections to the year
2300.The scenario maintaining the 2ºC
limit is projected to generate a sea level rise of 2.7 m (8.9 ft.) above the
level of 2000.A relatively unconstrained
scenario (similar to no abatement) is predicted to produce a further sea level
rise of about 3.5 m (11.5 ft.).Even in
the third scenario, reducing emissions to zero in 2016, sea level is projected
to continue rising to 1.25 m (4.1 ft.) by 2300.
coworkers show by their sea level projections that drastic extents of sea
level rise are locked in place already at this time, regardless of which
emissions policy is undertaken; only the degree of rise is subject to
vary.They conclude that sea level rise
can be constrained “within a few centuries” only by implementing worldwide
industrial scale processes to lower the concentration of atmospheric carbon
dioxide.This has not been commonly
discussed to date; Schaeffer and coworkers suggest such reductions, for example,
by combining a switch to bioenergy (which permits approaching zero net emissions)
coupled with use of technology for carbon dioxide capture and geological storage
in energy generating facilities.This
combination would result in a cumulative negative flux of carbon dioxide, lowering
its concentration in the atmosphere.
coworkers importantly conclude “A key aspect of [slowing sea level rise] …
is the long response time of sea level that is physically expected from the
slow response of large ice sheets and the deep ocean to climate change, [which
is] also found in [the geologic climate record]. This … means that about half
of the twenty-first century [sea level rise] is already committed from past
emissions. It further means that mitigation measures, even [radical reductions],
have practically no effect on sea level over the coming 50 years and only a
moderate effect on sea level by 2100.[Such measures, however, can have] … a major effect on magnitude of [sea
level rise] in the centuries thereafter.”
summarizes several recent scientific articles, most of which (except for the
Rahmstorf release) were transmitted to the respective journals several months
before Hurricane Sandy impacted the northeast U. S. coast.Thus their publication is not a response to
that event.Shepherd and coworkers, and
the comment by Kerr, documented the regions in Greenland and Antarctica that have undergone the most loss of ice
mass, generating liquid water that contributes to sea level rise.Joughin and coworkers review physical
mechanisms that come into play in providing the heat that results in melting of
ice mass.Grinsted and coworkers, and
the comment by Holland, traced historical tide gauge data, showing
that storm surge frequency and intensity have been increasing in recent years
and preferentially arise in years of warm global average temperatures.Sallenger and coworkers analyzed tide gauge
data along the northeast Atlantic coast of the U. S. and showed a recent trend of increased sea
level rise, and rate of rise, as a hotspot in this region, which is not present
along adjacent coastlines.
coworkers, projecting sea level rise trends into the future using several
different scenarios for the emission of heat-trapping greenhouse gases, predict
that pronounced increases in sea level will occur by 2100.Furthermore, the trends creating them will
continue beyond that time, generating even stronger sea level increases by
2300.They conclude that worldwide
efforts must be undertaken not only to slow the rate of new emissions, but in
fact to use combinations of technologies that result in a net depletion of
greenhouse gases from the atmosphere.
Hurricane Sandy struck the northeastern U. S. in October 2012, causing profound damage,
much of it due to Sandy’s ocean storm surge.This post summarizes that sea levels are
rising, and storm surges are becoming more intense, in correlation with
increased global warming.
US$50 billion request for unbudgeted emergency relief to help restore the
northeast is particularly difficult to consider now, in December 2012, coming
as it does during intense fiscal negotiations seeking to balance reducing
outlays and increasing revenues.It is
believed the request will not include compensating offsets to spending
elsewhere.This means that any emergency
aid passed into law is added to the U. S. national debt, requiring that it be paid
back at some later time by increasing taxes and/or cutting spending.Likewise, insurance companies have been hit
hard by anticipated claims arising from the storm.Their benefit payments will have to be made
up by increasing future premiums for weather-related claims.More generally, because of the high
probability that global warming contributes to the damage caused by storms such
as Hurricane Sandy, it is expected that future extreme weather events caused or
worsened by global warming will inflict continued large financial consequences
on the nations of the world for their remediation.
In recognition of
this clear understanding, Schaeffer and coworkers have called for large scale
remediation involving the deployment of new technologies for decarbonizing
energy production, including the implementation of carbon capture and
storage.This blog has taken a
comparable position many times over the past year or more.The consideration of the harms brought about
by intensifying sea level rise, summarized in this post, creates a clarion call
for robust action by all nations of the world to act as soon as possible.Investment in mitigating technologies will
reduce the need for emergency government expenditures as responses to extreme