CLIMATE CHANGE AND OCEAN ACIDIFICATION - Marine Pollution: What Everyone Needs to Know - page 169

temperatures during the summer months at sites in California
have increased by almost 3.5 o C (6.3 o F) in the last 60 years,
causing the upper limits of the habitats to retreat 50 cm (about
20 inches) down the shore, while the location of predators
and the position of the lower limit have remained constant.
Additional effects on predator/prey interactions come from
ocean acidification, to be discussed later.
What effects can happen from sea level rise?
Sea level rise (SLR) is caused by thermal expansion of the
warmer ocean water and by melting glaciers and ice sheets that
contribute new water to the ocean. Although average global
sea level remained relatively constant for almost 3,000 years,
it increased by about 17 cm (7 inches) during the twentieth
century, and is projected to rise by 40-80 cm by 2100. Over
the twentieth century, global sea level increased at an average
rate of about 2 mm per year, substantially greater than the rate
of the previous three millennia. Measurements from 1993 to
2008 indicate that sea level is already rising twice as fast as in
previous decades and is already exceeding the rise predicted
by climate models. There are also differences in the amount of
SLR in different parts of the earth. Although there is consider-
able variability associated with these and other estimates, 25
to 50% of SLR since 1960 has been attributed to thermal expan-
sion. Small glaciers and ice caps shrunk considerably during
the twentieth century and freshwater runoff from melting
land-based ice will increase in the future. However, over the
past 20 years melting ice sheets have become the biggest con-
tributors to SLR, and will remain the dominant contributor in
the twenty-first century if current trends continue. Sea level
rise could be up to 1 m by 2100.
Studies indicate that we have already committed ourselves
to a SLR of 1.1 m (3.6 ft) by the year 3000 as a result of green-
house gas emissions up to now. This could be more severe,
depending on the how much mitigation will take place. If