Climate Modelling Flashcards
What is a climate model?
A digital representation of the climate system that describes the behaviour of the various components of the system.
Models can treat physical and chemical processes and interactions, and use numerical approximation.
What are key forcings to the typical climate model?
Solar radiation
Concentration of GHGs, volcanic gases and particles.
Why do we model climate?
- Better forecasting and prediction of climate change.
- Climate reconstruction and understanding past processes to better estimate the future
What factors need to be known to simulate a past climate?
- Earth’s orbit
- Solar irradiance
- Volcanic and anthropogenic aerosols
- GHGs
For before the modern instrumental period of observations, 2 or more of these must be estimated from proxy data.
Describe the long term solar variability derived from sunspots
A cycle of 11 - year sunspots have been noted, where higher numbers of sunspots emits more irradiance. We can also derive solar flux from cosmogenic isotopes (14C and 10Be).
How is solar flux derived from cosmogenic isotopes?
- intensity of solar wind and total solar irradiance are positively correlated.
- The magnetic field associated with solar wind deflects cosmic radiation.
- Cosmic radiation generates 14C and 10Be
- We associate a high total solar irradiance with low production rates of 14C and 10Be, and we obtain records of these from ice cores and trees.
What two ways do we reconstruct long term volcanic forcing with?
Via measurements of:
- Acidity, which relates to maxima in sulphate aerosols.
- Sulphate Ion content in seawater.
V. Aerosols cool the surface and warm the upper atmosphere, affecting circulation.
What are energy balance models?
These are the simplest models that consider the balance between incoming shortwave radiation and outgoing longwave radiation., a global EBM treats Earth as a single point, a 1D EBM divides Earth into discrete latitudinal bands.
Benefits of energy balance models?
- Quick to run
- Easy to understand
- used in studies of sensitivity of Earth system to major radiational changes.
- However, they leave out many processes.
What are global climate models (GCMs)?
These are full 3d representations of climate, comprising at least the atmosphere and oceans, and now commonly sea ice.
These are the most comprehensive models used routinely for climate simulations.
What are Earth System Models (ESMs)?
These are developments on GCMs that include more elements, such as land ice, icebergs, biosphere and the carbon-cycle.
These are more comprehensive than GCMs but have not been fully developed as of yet.
How does a GCM work?
Earth surface is divided into grid points, where conditions are specified for each point, at each atmospheric and oceanic layer (can be multiple).
Equations are solved at each grid box to give meteorological values (temp, pressure, flow velocity) along time steps.
What size processes can atmospheric GCMs predict?
They can only really resolve large processes, such as planetary waves, cyclones and cloud clusters.
Their resolution is too coarse to notice thunder storms, boundary layer turbulence or anything small (known as parameterisations).
Whats is the Palaeoclimate Modelling Intercomparison Project?
We cannot run GCMs for a long time due to computation requirements, so to reconstruct palaeo conditions most runs are made to obtain a snapshot of the past world.
The PMIP combined experiments from 18 modelling centres, to reconstruct mid-Holocene mean surface air temp and precipitation.
What are EMICS (Earth system models of intermediate complexity)?
These are models that sacrifice complexity of GCMs to provide long simulations to understand palaeoclimatic conditions, their simplicity allows them to be run up to 100,000 years.
