changes to the water and carbon cycle by time scale Flashcards
(9 cards)
diurnal changes in the water cycle
-temperatures fall overnight–> reduced evapotranspiration
-rainfall in the afternoon–> intense heating of ground surface creates strong convection currents releasing precipitation–> sun rises and sets
diurnal changes in the carbon cycle
more carbon absorbed in the day (net absorption) –> more photosynthesis as sunlight
more carbon released in the night (net release) –> due to absence of photosynthesis from no sunlight and respiration occurrs
seasonal changes in the water cycle
-more sunlight in summer
–> high rates of evapotranspiration in summer –> high flows of water from underground/soil to the atmosphere
—> less stores of water and dish charge in late summer
-more snowmelt in summer (more river dish charge) –> permafrost thaws due to sun
seasonal changes in the carbon cycle
-trees are full of foliage in the summer, decreased CO2 –> northern hemisphere summer and more photosynthesis
-end of summer, trees lose leaves, CO2 released –> less photosynthesis and decomposition
changes in CO2 concentrations and temps over the past 400000 years
-over the past 400000 years there have been 4 major glacial cycles followed by the same number of inter- glacial cycles which each lasted 100000 years
-at the height of the last glacial 20000 years ago temps in the UK were 5* lower than today and much of Scotland, Wales, N England and Ireland were covered by 1km thick ice. During the interglacial period temps were similar to now
long term changes to the water cycle
-as ice sheets advance towards the equator they destroy extensive tracts of forest and grassland so that the area covered by vegetation shrinks. This also means there is a reduction in the water stored in the biosphere. This reduction in water means that the climate in the tropics becomes drier and deserts and grasslands displace areas of rainforest
-during glacial periods the biggest change to the water cycle is that there is a net transfer of water from the ocean reservoir to storage in ice sheets, glaciers, and permafrost. this causes sea levels to fall by 100-130m and ice –> sheets and glaciers expand to cover 1/3 of the land mass
-there are also reduced rates of ET during glacial periods due to less water being available as it is stored as ice. This reduces the exchange of water between the atmosphere, oceans , biosphere and soil. This combined with increased storage of water as ice slows down the water cycle
impact of long term climate change on the water cycle
-water vapour also releases latent heat on condensation which provides a source of energy in the atmosphere. This increased energy increases the occurrence of extreme weather events such as hurricanes and mid latitude storms becom more powerful
-global warming has increased evaporation which increases the water vapour conc. in the atmosphere. This starts a positive feedback effect as water vapour is a greenhouse gas and so evaporation and precipitation increases further. This leads to higher run off and a greater flood risk
-global warming accelerates the melting of glaciers, ice sheets such as Greenland and permafrost in the Arctic Tundra. Water storage in the cryosphere therefore shrinks as water is transferred to the oceans and atmosphere
long term changes to the carbon cycle
-during glacial periods the carbon pool in vegetation shrinks as ice sheets advance and occupy larger areas. & carbon is unable to be exchanged between soils and the atmosphere where soil is covered by ice. With less vegetation cover, fewer forests, lower temps and lower precipitation, NPP and the total volume of carbon fixed in photosynthesis will decline. This means that there is an overall slowing of the carbon flux and less decomposition occurring.
-the phytoplankton eventually die and sink to the bottom of the ocean where they are converted into sedimentary rocks and carbon is stored. During glacial periods the ocean temp is lower which makes CO2 more soluble
-as the graph shows there is a close correlation between temp and atmospheric CO2 conc.s. During glacial periods CO2 concs. fell to 180 ppm, while during warmer inter glacial periods they are 100ppm higher
-although there is no clear explanation for the drop in CO2 conc. during glacials, one idea is that excess CO2 is transferred from the atmosphere to the oceans because changes in ocean circulation bring more nutrients to the surface which encourages phytoplankton growth. This in turn increases sequestration of CO2 from the atmosphere to the ocean
-during glacial periods areas of tundra expand and replace temperate forests. This means that huge amounts of carbon are stored in the permafrost
impact of long term climate change on the carbon cycle
-generally higher global temps will increase the rate of decomposition so that more carbon is transferred more quickly to the atmosphere
-however in the humid tropics climate change may increase aridity and threaten the extent of forests. As forests are replaced by grasslands the amount of carbon stored in tropical biomes will decrease
-as temp rises above freezing carbon frozen in the permafrost is being released into the atmosphere through oxidation and decomposition
-long term climate change will see an increase in the carbon stored in the atmosphere a decrease in the carbon stored in the biosphere and a similar decrease in ocean carbon stores
-by contrast in high latitudes global warming will increase the extent of boreal forests of Siberia, Canada and Alaska northwards, increasing the amount of PS and sequestration of carbon compared to the previous tundra vegetation
-by contrast increasing acidification of the oceans due to greater absorption of CO2 means that PS by phytoplankton is reduced so the capacity of the oceans to store carbon is reduced
-there will be regional variations in the movement of carbon in and out of the atmosphere depending on the rates of PS decomposition and respiration
