What is SLR?
A trend in the increase of the height of global mean sea level, linked to GW.
Over the last century à Rate of increase accelerated.
Moving from what was thought to be a stable equilibrium à 3.1 mm yr-1 (due to anthropogenic forcing).
Over the 20th century a rise of 17cm was seen à and is projected to increase a further 18–59 cm by 2100 relative to 1990.
At a rate 3-5 times faster than previously seen.
Information can be obtained through core samples, tide gauges and, more recently satellite imagery.
Why is it occurring?
Eustatic variations à mean sea level/measure of the height of the ocean surface, caused by:
-As water heats (due to increased atm. temp.) it expands, occupies a larger volume à causes SLR. -IPCC 3rd report – contribute 110-430m between 1990-2100 (70-75% total rise).
-Leads to changes in volume of ocean water. -Ice sheets floating on the surface of ocean do not cause change in ocean volume à have already displaced water. -But it is ice situated above sea level/on land that causes the problem and increases the volume of water. -IPCC 3rd report – contribute 10-230mm between 1990-2100.
-Post-glacial rebound- rising land that was previously compressed by the weight of glacier (some can be 3km thick). -Viscoelastic mantle displaced underneath. -Around edges of former glacier- bulging of land masses à land now sinking (subsidence) à experiencing elevated SLR than other areas.
Ocean circulation changes:
-Regional rather than global effects. -Circulation caused by differences in density, temperature and salinity of ocean water. -E.g. weakening/shut down of Atlantic over-turning circulation à 1m increase in SL. -Compared to other factors à contribute more rapidly. -Ocean isn’t flat (series of hills and depressions due to Coriolis force and geostrophic flows) à Atlantic associated with a particularly low level of water. Circulation weakened = depression could rise rapidly.
How can we mitigate against it?
-Have to address the issue causing it à anthropogenic GW and CC à
-Unnatural increase in the amount GHGs in atmopshere à resulted in warming of the climate à intensified radiative formcing. -To tackle GHG emissions: -Decreases sources. -Increase sinks. -Address the sectors that are largest contributors for emissions: -Electricity generation – invest in renewables (wind/solar/hydro)/reduce dependence on non-renewables (decreasing sources). -Transportation – invest in PT, awareness campaigns, cleaner fuels (decreasing sources). -Deforestation – E.g. REDD+ scheme – decrease deforestation and degradation (decrease sources of emissions)/reforestation and afforestation (increase sinks).
Delaying reduction in emissions = increase change of more severe CC impacts (higher and fast rise in SL).
Earlier mitigation processes are started and implemented on a large scale, sooner the benefits will be felt à less need to invest in extreme-adaptation strategies.
Delay in the response of the C System àbenefits in place now wont be felt until later.
Emissions stabilised now = still gradual increase in temp. for next few centuries.
-Thermal expansion will continue. -Glaciers will continue to melt.
IPCC 3rd Report Emissions Scenarios
No matter what emissions scenario the world develops for itself, sea level will continue to rise regardless.
Situation made worse:
-There is unwillingness to change – as well as climate inertia, there is also political inertia. -Means that global economy so reliant on GHG polluting, it does not want to make large-scale changes to greener technologies (major drawbacks in ST economics).
If the warming observed now is a consequence of past actions, then pollution today will mean warming continues into the far future.
Means SLR will continue.
Means that mitigation alone is not effective. And in a world that is unwilling to mitigate, adaptation may be the best way forward.