UQx DENIAL101x 2.2.3.1 Sea Level Rise


One of the most concerning consequences, and
an indicator of global warming is sea level rise. Sea level rise has the potential to
displace coastal populations throughout the globe and consequently allows storm surges
from tropical storm systems to penetrate further inland, This causes damage to places previously
untouched by the sea. Sea level rise is not uniform and some areas will see significantly
more rise than others. One reason sea level is rising is from the
thermal expansion of seawater as the oceans warm. When water gets warmer, it expands.
As a result, warmer water takes up more space than colder water. This effect alone has been
responsible for a lot of of the sea level rise we have observed so far. Thermal expansion
is pretty straightforward, just basic physics. Another reason sea levels are rising is due
to the melting of ice that sits on land, such as glaciers and the two ice sheets: Greenland
and Antarctica. When sea ice melts, it doesn’t add to sea level rise – just like melting
ice cubes in a cup don’t make the water level go up. So as far as sea level rise is
concerned, it’s melting land ice that matters. We have some awesome satellite technology
and other observations to keep track of ice loss, but predicting future ice loss is what
gives our model projections of sea level rise the most uncertainty. This rate of melt of
glaciers and ice sheets is complex and change is happening quite quickly. What sea level rise have we observed in the
past? Well, by stitching together the tide gauge record with the recent satellite record,
we have found sea levels have already risen about 20 cm since 1880. We have also observed that the rate of sea
level rise is increasing. In other words, sea level is rising more quickly now than
we’ve seen over the past century. We expect global temperatures to continue
to warm, so we expect thermal expansion’s contribution to sea level rise to continue.
This also means we expect land ice to continue to melt. It’s very likely that the rate
of sea level rise will increase more and more over the 21st century, although how quickly
sea level rise speeds up depends on how much carbon dioxide we emit. For a middle of the road emissions scenario,
the IPCC report projects a rise of about a half a meter, or one and a half feet, by the
end of the century. Other studies predict as much sea level rise as twice that amount.
The answer will depend on how much ice melt takes place on the ice sheets. So that is what we know about sea level rise,
but some myths distort the observations of sea level risel. One myth related to sea level
rise is that sea level rise is exaggerated, and it is actually slowing down. This myth
uses the technique of cherry picking. This means it picks out a short term change in
sea level and exploits it while ignoring the long term trend. For example, look at this graph of sea level
rise. Notice the dip around 2010 when sea level actually went down temporarily. One
of the reasons for the dip was an incredible amount of rainfall and flooding that year
in Australia and South America. You might remember hearing about the devastating Queensland
flooding that year. If the water cycle produces flooding rains over land, and the water doesn’t
drain back into the ocean right away, this can temporarily affect sea levels. But eventually, the water did drain back into
the ocean. Sea level rebounded and continued increasing along the trend line as expected. So, in summary, we’ve seen that all scenarios
point to continued increasing sea level rise. We expect more sea level rise in the 21st
century than we did in the 20th century, despite the myth that distorts the science of sea
level rise.

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