Deck 3 - Lectures 11-18 - David

Question 1

The operation of the earth’s energy budget under climate change

how does it work and how does it change?

Answer 1

• incoming solar radiation from the sun hits the surface, some is reflected by clouds. earth recieves solar radiation and radiates it away.
• what earth radiates back to space is at much longer wavelengths. that radiation is caused by gases in the atmospere and clouds.
• with climate change due to changes with the composition in the atmosphere the budget doesn’t close. CC causes a net imbalance in the system becuase of the change in composition in the atmosphere.

Question 2

The greenhouse effect

Answer 2

• if the shortwave thermal radiation is more than the longwave thermal radiaiton then the incoming radiation passes easily to the surface heating it.
• but the outgoing radiation does not pass easily back out to space. the outgoing long wave radiation is absorbed and re-radiated in all directions including downwards.
• in our atmosphere this means that it is thin in the SW and opaque in the LW, generates a warmer surface than the no absorption case.

Question 3

Shortwave vs. longwave radiation

Answer 3

Shortwave: the incoming solar radiation, approx. 90% light gets through to the earth. Transmittance = high, absorption = low.

Longwave: from the surface going out - a large fraction is trapped and re-radiated.

because the earths atmosphere is more opaque, less transmitting and more absorbing in the longwave compared to the shortwave.

Question 4

Geographic pattern of SW and LW radiation

Answer 4

Absorbed solar radiation is high at the tropics where the sun shines vertically. The w/msq are high.

High amounts of longwave radiation leaving at the high latitudes, not so much at the tropics.

At the tropics the earth is absorbing more than it’s emitting. At the higher latitudes the earth is emitting more than it’s absorbing.

This creates an energy gradient. In response air starts moving - the winds in the atmosphere and the currents in the ocean - are ways of shallowing the energy gradient.

Question 5

How does the air shallow the energy gradient?

3 factors

Answer 5

• Hadley Cells trade winds at the surface. air rises (thunderstorms) and then it dries, cools and sinks - you get subtropical high pressure system with an area of convergence.
• Eddie behaviour In the mid latitudes you get eddies. where cold air in the polar region, warm air at the lower latitudes wobbles and this forms jet streams which are amplified by different forms of atmospheric instability - they turn into LOW and HIGH pressure systems.
• Density Driven Circulation in the ocean. Different winds blowing past each other to create gyres. These fast currents transport warm water to the poles and cold water to higher latitude regions.

Question 6

Thermodynamic contribution

Answer 6

• uniform wettening globally associated with the extreme rainfall events
• as you warm the atmosphere, the water vapour cna be sustained as vapour to a greater extent.
• for each increase by 1 degree the temp of the air parcel can sustain 7% more water as water vapour.
• for extreme rainfall for the wettest parcels of air when hit a mountain range/coastline and dump it out
• air parcels can contain more moisture than previously.
• Making the air warmer allows it to store more moisture and when conditions are right and the moisture all comes down at once you’ve got a bigger bucketful of water to dump on the ground.

Question 7

Dynamic contribution

Answer 7

• changes in pattern of circulation and changes in local enterology.
• For NZ - westerlies - in the winter you expect the westerlies to intensify, partly because of recovery of the ozone hole, so you get more storms per week.
• By contrast that means that the rainshadow effect on the east coast of NZ and dynamic contribution in NZ in winter is a drying in those eastern parts while its wettening in the western parts.
• ou get more atmospheric rivers coming out of the tropics which is how NZ gets extreme rain. Doesn’t come from the south because it’s not warm enough to storm the moisture. You get storm damage, surge and coastal damage from the south but you don’t get extreme rainfall from the south

Question 8

Tipping points

Answer 8

• part of a climate system where a small change pushed the system beyond a warming threshold.
• Some are minor feedbacks and some are carbon cycle feedbacks (major is how the amazon behaves). In our best models we don’t see tipping points at the global scale.
• To have a climate change tipping point that will lead to an existential risk, it would need to be a global thing - in the top circle. There is plenty of scope for smaller scale effects.
• existential/global = emissions, concentrations, temperature - socio-economic processes, carbon cycle, climate response.
• regional - impacts and damages.

Question 9

Regional Tipping point example

Answer 9

• There is a lot of evidence that you can have hysteresis in systems at the regional scale.
• Desertification - once you have burned off the savannah you can get a feedback process where the moisture stored in the savannah - a local moisture source in the ecosystem, then you can have a little microclimate that sustains the thing, once you cut down the trees or burn off the grass and you take away that moisture and once its gone it can be very hard to get back.
• NZ - was covered in beech trees and once they were gone they didn’t come back easily. So there’s hysteresis in that system.
• desertification, forests to farmland, drying of inland lakes.

Question 10

What causes changes in sea level?

Answer 10

• moving the water around by tides or winds
• glaciation - Add and subtract water - done through ice. Trap rainfall on the continents to form glaciers. glacio-eustacy Biggest changes. Sea level is associated with changes with ice sheets. Storing of ice on land - called glacio eustasy.
• Thermal changes - water behaves differently at different temperatures. Changing the size of the basins. Make the basin narrower and sea level will rise and if you pull the basins apart the sea level will fall.

Question 11

causes to SLR: thermal expansion

Answer 11

• water has a loose crystal structure.
• water has its most compressed form at 4 degrees celcius
• if you melt ice you add volume to the ocean. adding warmth to the deep ocean water wont initially cause sea level rise because the water is sitting between 0-4 degrees C. once beyond 4 degrees the water tends to expand and become denser.

Question 12

regional changes to SLR: glacio-isostacy

Answer 12

• the process where the earths crust seeks to reach equilibrium following loading or unloading by ice.
• Around the coast of scotland sea level is falling in most locations - hwy? Because we used to have a thick ice cap sitting over scotland which disappeared 13-14 thousand years ago. So thick and heavy that is compressed the crust beneath it. Pressure of km of ice has depressed the crust and once the ice is released the area in the north of england has been going up. At the same time in the south of england there is no such effect. Not having a rebound effect, as a consequence those areas are seeing only the sea level change phenomena.
• So in scotland you have the decline in sea level that is driven by the globe but it is counterbalanced by more uplift than the sea elvel rise.
• The most extreme case of this is the baltic.

Question 13

local sea level rise changes: subsidence and tectonics

Answer 13

*If you have sediment pouring into an area coming in through the river systems, the weight will cause land levels to subside. Mississippi delta - subsidence rate, the maximum flow is coming down the mississippi and the maximum subsidence is where the mississippi is pouring sediment in. The weight of the sediment causes the crust to sink and that gives local subsidence. If you apply local subsidence and apply a global sea level rise you get a much faster speed of SL rise.
* new orleans
* uplift by tectonic activity

Question 14

SLR impact: retreat

Coastal response to Inundation and loss of land

Answer 14

• erosion occurs when the beach is out of equilibrium.
• In winter, after storms have gone through you have the temporary movement of material off the beach and the beaches flatten out. In summer the beaches steepen up as you’re building material on the beach. As long as there is enough sediment supply the beaches will return to their normal location.
  SL intersects at a fairly shallow angle, so sediments can move up and down the beach.
• When there is SL change, in the longer term the idea that the beach is too steep to support sediment accretion and the wave action will cause material to be washed off shore.

Question 15

Assumption of the Bruun Rule

definition, equation and issues.

Answer 15

• the bruun rule proposes shoreline retreat derived by assuming erosion in upper part of profile is balanced by deposition in the lower part.
• Is this applicable in real life? Doesn’t take into account other processes on the beach, assumption that it’s a closed system.
• That is not true - what happens out in the ocean is reflective of the filling in at the subaerial beach and then you can continue to translate but actually there is sediment being lost from the system all the time and its being lost by going beyond the width of the shore face and wave action breaking down the sediment, the consequences of that is that the bruun rule calculation is always a minimum.

Question 16

SLR retreat: barrier retrogrades

Answer 16

• barrier erosion - bruun rule
• barrier translation. the barriers can translate - means roll over and move shore wards. Once the SL comes up far enough and the waves are breaking the waves go over the top and push material over the top of the barrier - called a roll-over model.
• barrier overstepping.- happens when the energy in the coastal zone is to high and all the material in the barrier gets broken down but not eliminated but once broken down the waves carry the material further inland and will build a new barrier closer to the shore, so in a single storm with barrier overstepping in a drowned barrier setting, you can get a coastline retreating by 200m in one event.

Question 17

Coastal managment responses

4

Answer 17

1. do nothing - wait and see approach, allows destruction of coastal infrastructure - means abandoning peoples houses, avoids cost of construction and maintenence of hard engineering.
2. managed realignment - the coastal system is changing and anything down at the coast is at risk. Decide on the value of the assets and if of significant enough value then we will physically move it. involves the removal of coastal defence (pollution) and relocation of infrastructure. ecological benefits - ecosystems migrate landwards maintaining ecosystem function and services. however, cant always move inland due to no space.
3. hold the line - use hard engineering structures and soft engineering, aims to keep sea at current position. seawalls or groynes - trapping sediment to make a buffer along the coast. The waves coming in - they have a potential amount of work that they can do, that work will be expended in erosion on the ocean floor as it comes into shallow water and as waves break in erosion on the beaches. beach nourishment. Seawalls are good at resisting waves but enhances erosion at the base of the wall and overtime the shoreline will be excavated at the base of the sea wall, long term if there is SL rise or strong coastal systems there is a tendency for the walls to be undermined.
4. limited intervention - allows continued occupation of coastal land by modification of buildings. could involve ecosystem engineering to increase coastal elevation or absorb storm impact. Protect structures as much as possible without hard engineering and without interfering with the system.

Question 18

rising groundwater impacts

SLR impact

Answer 18

• The rising groundwater causes the following:
• Deformation of roads
• Leakage into storm water systems which can cause pollution into the water table
• Impact on buried services - don’t want pipes below the water table.
• Rising damp with houses and cold damp floors.
• Building damage
• Health impacts from damp and mould
• Reduced storm water sinkage
• Damage and restricted access to gardens and yards - your trees will die because root system needs to breathe.

Question 19

saltwater intrusion

Answer 19

Saltwater intrusion is where marine water penetrates into the water table and makes the water saline. Problematic. Relatively high rainfall environment where there is recharge of your freshwater, it is not normally a huge problem. All of the global aquifers are held in position by sea level so you have freshwater on the land and curves down to the sea and you have rivers on the surface, you have freshwater going down below at differing amounts of distance depending on the local setting, even if you have saltwater coming in you very rarely get saltwater coming to the surface without human miss-intervention because what you end up with is a lense of saltwater. One of the biggest problems with SL rise is freshwater flooding because as the SL rises the freshwater lenses being held in by the sea effectively also rise in response so you get a vertical rise in the level of the water and inundation of groundwater.

The worst effect is saline intrusion into the groundwater. Wont get that in canterbury. We get 5-10 m of rain at the top fo the southern alps and enormous hydrostatic pressure in our water systems going down from the alps to the coast. With the exception of draw down from some of the shallow aquifers.

In countries that are drier the sea level goes up but you also get more saline incursion, the saltwater migrates into the freshwater lens. We wont have this due to the freshwater from the southern alps. Turns drinking water to salt water.

Question 20

tropical cyclone formation

Answer 20

1. Fairly warm and clam surface water, warming air rises above and creates a pressure deficit in the middle (relative pressure drops at the surface) and local winds want to infill that gap (flow down a pressure gradient).
2. Then you get the warm moist air rises and condenses and the clouds go very high near the top of the troposphere and a pattern of alternate rising and sinking motions - warm moist air is rising and forms big thunder clouds and precipitates out rain and releases latent heat in the upper troposphere and bands of downdrafts in between the cells of rising air and then condensation releases latent heat
3. The horizontal surface winds want to infill the gap but winds don’t flow on a rotating planet. At the equator you can’t get a rotational motion going, the rotational motion rises because of the coriolis force which is a function of latitude. The air wants to flow in the gap in the middle but gets deflected by the gap in the middle and flow around and around. That is the characteristic shape - eye in the middle - of a tropical cyclone as the winds spiral around the centre.

Since coriolis is a function of latitude, at 0 degrees you can’t get that rotational motion going.

Question 21

Necessary conditions for the origin of cyclones:

Answer 21

• Warm water - needs a lot of energy, with a deep column, that’s why it has to be calm - with turbulence you don’t get the stratification of warm temperature throughout. If it’s all windy it gets mixed up.
• Atmospheric instability - conditions are right for the air to rise - in contact with the ocean surface.
• Then create a pressure deficit in the middle of the cyclone high.
• Enough coriolis force to sustain the low pressure centre - at least 5 degrees away from the equator.
• Pre Existing low level focus or disturbance - in the atmosphere there is always these wobbles in pressure and a situation where you have some sort of disturbance in the atmosphere.
• Low vertical wind shear - without it you wouldn’t be able to get the rising motion directly above the cyclone. You need rising and sinking motion. Won’t be able to build a self sustaining shape.
  Tend to form late summer - heating the surface waters all summer and then it’s quite a calm period. The atmospheric variations allow you to brew these things up.

Question 22

storm surge

Answer 22

• a rise above the normal water level along a shore resulting from reduced atmopsheric pressure and strong onshore winds, associated with a storm.
• important components: atmospheric pressure and wind.
• A shift in atmospheric pressure - high and low pressure. High → you push down on the water and low pressure - creating somewhere for the water to bunch up.

Question 23

extratropical cyclone formation

Answer 23

stationary front between cold and warm air. wind shear established. Two high pressure systems. One near cold polar air and another near the warm equatorial air, and a middle form between them. Winds opposing each other which create a vortex - create a trigger, upper level of divergence causing the formation of a low pressure zone along the front, warm and cold fronts begin to form and a low pressure system forms in the intersection between the low and high pressure systems

Low pressure deepens and you get a well defined front - cold front moves faster,

The cold front begins to catch up and forms an occluded front:

Then you get a very intense low pressure system with an occluded front near the centre of low pressure. It’s the frontal system doing the damage.

Question 24

difference between tropical and extratropical cyclones

Answer 24

• TCs are non-frontal and ECs are frontal.
• ECs are higher magnitude and duration.
• EC’s are assymetric and TCs are symmetrical

Question 25

How the European heatwave developed.

Answer 25

• A high pressure system parked over the north-west of the continent. There had been an extended dry period for all of 2003 meaning soil moisture was suppressed on the normal level that you would have. Soil moisture was lower than normal - soil moisture can play a role in breaking up big chunks of warm dry air becasue ltos of soil moisture = convection. Evaporate the water out of the soil and then you get big thunder clouds building up and then disrupt - they can act ot weaken the high pressure system over the top of it. If you lack soil moisture you cant get evaporation or convection going. The extended dry period and soil moisture played a role in preventing the disruption of the high pressure system.
• Warm sea surface temperature anomalies. Around western europe the sea was warmer than usual therefore sea breezes coming up due to the thermal contrast of the land and the ocean. Because of the warm SST anomalies meant that the thermal contrast between the land and the sea which prevented the air mixing. Pre condition the system by having the extended dry period with soil moisture suppressed, warm SST anomalies and then park a high pressure system over the top and together these made the heatwave possible.
• The reduced ability of the earth to cool at night because you are doing a more intense job of trapping outgoing longwave radiation - greenhouse gases trapping radiation is particularly pronounced at night when you haven’t got energy coming in at night but a good time to lose energy to space - only getting energy in daylight but losing energy in the day and the night. Because you’ve produced greenhouse gases you’ve reduced the ability of the earth to cool itself at night. One consequence is higher night time temps during the heatwave also meant that people couldn’t get away from the heatwave.
• heatwave blocking caused the heatwave

Question 26

heat wave: blocking systems

2 types

Answer 26

1. omega blocking - a high in the middle of two low pressure systems.
2. diffluent blocking - You get a high pressure system and a lower pressure system parked up together and the atmospheric stream flows around both. Gradually exchange some air.

Question 27

impacts of heat waves

Answer 27

• physcial - low river and lake levels (stresses potable and waste water resources, damages ecosystems), forest fires, rapid glacier melt.
• human effects - heat stroke, dehydration, drowning
• environmental and social effects - water supplies, food production, transport energy, algal blooms, ecosystem stress, food production - crop production drops.

Question 28

Droughts

definitions

Answer 28

• drought is a sustained period of below-normal water availibility. it is a recurring worldwide phenomenon with spatial and temporal characteristics that vary significantly from one region to another.

Question 29

meteorological drought

Answer 29

refers to a precipitation deficiency, possibly combined with increase potential evapotranspiration, extendingover a large are and spanning an extensive period of time.

esentially dry weather patterns

Water deficiency in the flux of water from the atmosphere landing on the ground, time integrated. Potential evapotranspiration - flux of moisture to the land surface from the air is deficient, the other way of achieving those conditions is if the flux of moisture from the land to the air is anomalously high. Its an anomalous flux which has a drying effect on the ground which you are most interested in.

Question 30

Hydrological drought

Answer 30

Lack of water in the hydrological systems - liquid forms on the surface, rivers, ponds lakes etc.

can cover extensive areas and can last for months to years with devastating impacts on the ecological system and many economic sectors.
* drinking water supply
* crop production
* waterborne transportation
* electricity production
* recreation

Question 31

agricultural/soil moisture drought

Answer 31

deficiency of soil moisture, reducing the supply of moisture to vegetation. impacts on natural ecosystems and infrastructure.

Rather than water in its liquid form it is water embedded in soil, in the ground. Closely related to ecosystem drought - about plants not getting enough moisture from the earth - will also affect ecological systems as well as agriculture.

Question 32

Socioeconomic drought

Answer 32

the impacts of the meteorlogical, hydrological and agricultural drought. refers to a failure of water resource systems to meet water demands and to ecological or health-related impacts. Drought conditions are affecting things that we as a society value.

Question 33

contributions to droughts

draw diagram and explain

Answer 33

Contributions to drought - anomalies in precipitation (hydrological event) and anomalies in temperature (heat event). Meteorological drought is a precipitation deficiency.

Soil moisture drought can be characterised by both, by either or.

Hydrological drought - can be a function of both - low discharge - catchment and a soil moisture deficit therefore less water flowing into the river. Low ground-water storage because evaporated a lot of water - temperature.

Socio-economic drought is integrated across the entire thing.

Question 34

collection of anomalies of droughts overtime.

Answer 34

Propagation overtime of the anomalies in precipitation. Precipitation anomaly occurs before year 1 and 3. There’s a small lag and surface runoff into rivers. Lower rainfall and an anomalously low runoff that follows that precipitation event. The runoff event leads to a soil moisture deficiency which is more spread overtime but lags slightly. The stream flow is decreased in response to the anomalies,

Groundwater is depleted as a result of the anomalies. Takes time because for the precipitation anomaly at the top to percolate into the groundwater at depth you’re integrating a signal and a time quantity - takes a certain amount of time for the water to pass through into the groundwater.

Lag can be different for different events.

A flux coming out of the atmosphere propagates through a series of systems overtime.

Question 35

signal propagation

definitions

Answer 35

1. pooling - meteorological droughts are combined into a prolonged hydrological drought. Pooling - you have a series across a few years you have a normal mode, an ENSO feature which are more droughty than normal, hydrological system that is integrating the precipitation coming out of the atmosphere - lake is an integrator, the rainfalls on a catchment, the rain drains into a river, the river into a lake, the lake is integrating the precipitation coming down. If you have a series of meteorological droughts associated with something like a normal mode like enso then the hydrological drought is created by pooling.
2. attenuation - meteorological droughts are attenuated in the stores, causing a smoothing of the maximum negative anomaly. Attenuation - integration - a drought in y1 and y3, on one hand they combine but because you integrate as you go down the chain of rainfall to soil moisture to runoff to rivers and lake there’s an integration overtime smoothing out the peaks of the meteorological drought for the downstream systems.
3. lag - the onset is later when moving through the hydrological cycle. A lag in the system response, attenuation in the peak effects of the surface water are attenuated in groundwater. All these effects as you move in play.
4. lengthening - droughts last longer when moving from different types of droughts. Lengthening - characterised by longer time scales.