Flashcards in 3.4 Sea Level Change Deck (18)
What are the two different types of sea level change?
What is eustatic sea level change?
caused by the change in the volume of water in the sea, or by a change in the shape of the ocean basins
Are the effects of eustatic change local or global?
What are the main causes of eustatic change?
1. changes in climate
increase in temperature causes melting of ice sheets, which increase sea level, water expands which increases sea level further
decrease in temperature causes more precipitation to fall as snow, the volume of water stored in glaciers and decreases the sea level
2. tectonic movements of the earth's crust that alter the shape of ocean basins, sea floor spreading increases the volume of the basin and so decreases the sea level
What is isostatic sea level change?
caused by vertical movements of land relative to the sea.
downward movement of the land causes sea level to rise locally
uplift of land causes sea level to fall
Are the effects of isostatic change global or local?
What are the main causes of isostatic change?
1. uplift or depression of the earths crust due to accumulation or melting of ice sheets, slow uplift of land can continue for thousands of years after the weight of a glacier has gone, accumulation of sediment can cause depression
2. subsidence of land due to shrinkage after abstraction of groundwater
3. tectonic processes, one plate is forced under another
Why does sea level vary on a short time scale?
due to tidal cycles, onshore winds, low atmospheric pressure systems
Describe the previous sea levels through time
1. last glacial period, water was stored in ice sheets so sea level was lower - 130m than present
2. temperatures started to increase, ice sheets melted and sea level rose
3. sea level has fluctuated since then
4. since 1930 sea level is rising
How long ago was the last glacial period?
110,000 - 12,000 years ago
What is the main cause of sea level rise?
What is global warming?
when global temperature increases
Why has the temperature increased rapidly over the last century?
due to human activities such as deforestation and during fossil fuels which cause climate change
Why do human activities cause climate change?
increase the concentration of greenhouse gases in the atmosphere
What do greenhouse gases do?
they absorb outgoing long-wave radiation so less is lost to space. as the concentration increases more energy is trapped and the plant warms up
Why does climate change increase sea levels?
causes an increase in sea level due to the melting of ice sheets and thermal expansion of water in oceans
How high is the global sea level rising per year?