Lecture Material Flashcards
WMO’s classical period for climate observations
30 years
How temperature observations are made
- Weather huts (problems: environment)
- Weather balloons (problems: drift)
- Ships (problems: size of hull)
- Satellites (necessary to make some assumptions to measure surface temperature)
The 2 common methods for interpolating climate data
- Inverse Distance Weighting
- Kriging
Explain the Kriging technique
- Uses how similar temperatures are over current satellite data to estimate previous temperatures.
- Uses covariance information about spatial patterns.
- Always done using anomalies rather than actual temperatures. Advantages of this: anomalies have larger spatial correlation. Smaller impact if one station is temporarily unavailable.
The role of the ocean in the warming hiatus
- Land surface temperature hasn’t increased since 1998, but the ocean has kept warming faster than ever.
- During periods of rapid warming at the surface, the ocean is cooling and vice versa.
- We don’t know what causes this.
Define climate feedbacks
A collection of processes that either:
- reinforce or amplify the effect of an initial forcing
- suppress the effect of an initial forcing
List some climate feedbacks
- water vapour feedback (positive)
- ice-albedo feedback (positive)
- cloud feedback (either)
- ocean-carbon uptake (negative)
- soil moisture feedback in heatwaves (positive)
When and by whom was the IPCC established
by the
- World Meteorological Organisation (WMO)
- UN Environment Programme (UNEP)
in 1988.
What information does the IPCC review and assess
The most recent - scientific - technical - socio-economic information produced relevant to climate change
Differentiate between IPCC & UNFCCC
- IPCC are the scientists
- UNFCCC are the diplomats
In which years were the first two World Climate Conferences?
1st: 1979
2nd: 1990
There have been annual COPs since which year?
1995
What are the 3 IPCC working groups?
WG1: Scientific basis
WG2: Impacts, vulnerability, adaptation
WG3: Mitigation
Outline Planck’s radiation law
- Hotter objects emit more radiation
- The peak wavelength at which objects emit decreases with increasing temperature
- Frequency = 2pi / wavelength
Mean global surface temperature
- without atmosphere
- with atmosphere
with: -19 celsius
without: +15 celsius
In which spectrum are ghgs visible?
The infrared spectrum
The canonical value for albedo
30%
The Latent Heat Cycle
Some of the solar radiation absorbed by the surface is used to drive evaporation
The evaporation-heatwave feedback
- evaporation of water at the surface is a cooling term
- if there is no more water to evaporate, energy goes into warming surface
The positive cloud feedback
more clouds > more downward emission of infrared radiation > warming at the surface > more evaporation > more clouds
The negative cloud feedback
more clouds > more reflection of incoming solar radiation > cooling at the surface > less evaporation > less clouds
What is the solar radiation imbalance figure (net absorbed)?
And how is it measured
0.9 wm^-2
- Too small to be measure directly
- Can be computed from the change in mean temperature or from climate models
Outline GWP
Global Warming Potential
- defined as warming of a certain mass of ghgs relative to that same mass of CO2 over the next 100 years
- is used to compare the relative warming effects of different ghgs
Outline Radiative Forcing
- the amount of energy re-emitted back to earth from ghgs expressed in units of wm^-2
- a method of quantifying the greenhouse effect
Outline ECS
Equilibrium Climate Sensitivity
- the increase in the global mean temperature for doubling of CO2 concentrations.
- climate sensitivity in most models is 3 celsius.
Outline TCR
Transient Climate Response
- change in temperature due to a doubling of CO2 in the next 100 years
3 roles of the ozone layer
- it’s a ghg
- it filters out harmful UV radiation
- it plays a key role in smog near the surface
Define the 5 spheres
- Cryosphere: ice etc
- Lithosphere: tectonics & volcanism
- Biosphere: food web
- Hydrosphere: hydro cycle
- Atmosphere: climate
Total amount of energy added to the climate system
250 Zj
The amount of solar energy reaching the surface is dependent on
- albedo
- angle of the sun
Outline the Coriolis effect
- the velocity with which the earth’s surface rotates varies with latitude.
- this has implications for the ocean circulation and is what causes hurricanes and storms
Where has the extra CO2 gone?
- 25% into ocean
- 25% into land
- 50% into atmosphere
large inter-annual variability in the fraction between land and atmosphere
The 2 ocean pumps (CO2 uptake)
The biological pump
algae take up CO2 as they grow, then deposit it on the sea floor as they die and sink
The solubility pump
Co2 directly taken up by seawater. Colder temperatures mean better solubility.
The Classius-Clapeyron relation
For every degree of warming, the atmosphere holds 7.5% more moisture.
But: the link with precipitation is much weaker.
Outline the Milankovitch cycles
Obliquity of the earth
- 41,000 years
- tilt of earth’s axis
- can determine temperature’s seasonal variability
Eccentricity of the earth
- 100,000 years
- determines strength of ellipse of earth’s orbit around the sun
Precession of the Equinoxes:
- 19 & 23 ky
- Northern hemisphere tilted away/ towards the sun at aphelion.
Temperature vs CO2 lag
- For the last 400,000 years temperature has changed first, and CO2 followed.
- Milankovitch cycles change the temperature via solar radiation > warmer oceans release more CO2.
Outline PETM
Palaeocene- Eocene Thermal Maximum
- 55 million years ago
- Sea surface temperatures rose by 5 celsius in the tropics and 9 celsius near the poles.
Examples of paleoproxies
- tree rings
- isotopes of oxygen & carbon
- fossilised pollen & plankton
- animal bones
- charcoal
- landscape features
Outline ENSO
El Nino: warm ocean conditions off the coast of western Australia
Southern Oscillation: a change in pressure difference across the tropical Pacific
- More rain than normal in the Americas
- Australia & Indonesia suffer drought
- Because upwelling slows: get coral bleaching
Outline PDO
Pacific Decadal Oscillation
- Cool & warm phase in Northern Pacific
- 40-year time scales
Outline NAO
North Atlantic Oscillation
- Variation int he path of the jetsream
- Varies on decadal time series
- No clear timescale of the variation
Outline hysteresis in climate change
Phenomena lag behind
e. g. the amount of sea ice as a function of temperature
- it takes quite a lot of warming to melt ice
- Once the ice has gone, it takes very cold temperatures to form sea ice again
Passing a tipping point can happen when
- The control parameter is changed
- due to internal variations in the system feature itself
Differentiate between weather and climate models
Similarities:
- Core physics is very similar
- Weather modelling is an initial value problem
- Climate modelling is a boundary value problem
Outline parameters & variables of the simplest climate model and the variable required for the 2-layer model
parameters:
S(0): the solar constant
a: the albedo
epsilon: the emissivity
variables:
T(S): temperature at the surface
R: radiation
T(a): temperature of the atmosphere
sigma: the Boltzmann constant
The equations of the simplest model
- Incoming Solar Radiation
- Outgoing Solar Radiation
> Net (incoming) Solar radiation at surface - Outgoing longwave radiation
> Balance of radiation at surface
The dynamical core of a climate model
- Wind
- Ice
- Heat
…how they move elements around
The surface processes core of a climate model
- heat
- water
…how they get transferred between the different spheres
The chemistry core of a climate model
- gases
…how they interact with each other and the sphere
The radiation core of a climate model
- sunlight
- infrared light
…how they interact with atmospheric gases
The boundary conditions of climate models
- the topography of the continents and oceans
- the eruption of volcanoes
- the amount of incoming solar radiation
- the anthropogenic emission of ghgs
Advantages of only running one component of a climate model
- allows for increased resolution
- easier to control resemblance to reality
- useful for process studies
3 tiers of CMIP 5 experiments
Coupled Model Intercomparison Project
- Climate projections
- model evaluation
- understanding of processes
List RCPs in order of Radiative forcing
Highest to lowest:
- 5
- 0
- 5
- 6
Outline the theory behind ensembles of runs for CMIP5
- run a dozen or so runs with the same model, but slightly different initial conditions
- gives a good spread of internal variability
- the real world can be viewed as just one ensemble member, the so-called ‘replicate earth paradigm’
Is comparing climate models to model means a good validation method?
No
- we can’t expect models to get the internal variability right
- all models have slightly different phases of ENSO etc
- the multi model mean smoothes these differences out
- rather, skilful models and observations should be indistinguishable realisations of the Earth’s climate
Outline 4 methods of validating climate models
- postage stamp maps
- mean an orange comparison with time series
- Taylor diagrams
- angle is correlation
- radius is relative variability
- circle is RMSE
- slipping & hatching
- show where models agree on the sign of the change and where they don’t
- stippling: 90% of models agree on the sign of the change
- hatching: the models don’t agree
- CMIP5 models don’t agree on change in precipitation for RCP 2.6 (mostly hatching), but do slightly more for RCP 8.5 (more stippling).
Why the IPCC publishes simple, unweighted multi-model means
- doesn’t want to be political
- there is no evidence that models correctly replicating past climate change means they will correctly predict future climate change
Outline detection & attribution
- re-run models without anthropogenic forcing
- combine with Bayesian statistics to obtain a probability how much more likely event x is due to climate change
- WG1: GW since 1970s can only be explained by incorporating anthropogenic forcing.
Outline evidence from carbon isotopes for human impact on concentration of ghgs
- fossil fuels have relatively little carbon-13 isotopes
- volcanoes etc have relatively little carbon-12 isotopes
- the concentration of carbon-13 isotopes is decreasing
