Week 9 Flashcards
If your model is unperturbed by human influence etc. what would you expect it to do and what would be a sign something is wrong?
you would want it to maintain a constant temperature
if it is gradually getting warmer - there may be too much energy not escaping at the toa
tweak parameters in the model to do with sub-grid scale processes like clouds to alter the behaviour of the model
what is a constraint?
using observable relationship to constrain the simulations
eg. southern hemisphere jet move with clamte change, high speeds south does that move closer to the poles as we get warmer
What are some general reasons for differences in climate model projections?
differences in atmosphere and ocean parameterisations (huge uncertainty- no one answer)
these differences affect the climate feedbacks especially cloud feedbacks
to assess the range of possible future outcomes, we perform large model inter-comparisons
What does CMIP stand for?
coupled model intercomparison project
what does CMIP do?
international collaboration of climate science
coupled modles = coupled ocean atmosphere models plus other components
several doznes of climate modelling groups around the world perform the same experiments and make the results available for free
all models have a slight geographic bias
For CMIP6 what is the core experiement features?
it is called DECk
pre-industrial historical
1% Co2 increase every year
4x Co2 instantaneous quadruple to see how much warmer the model gets over time
historical changes - same boundary conditions and simluate the 20th cent - how well can this be done
What is part of the CMIP experiements?
there are lot of potential experiements simple or advanced - run to test for a range of factors like potential geoengineering
what does SSP stand for?
shared socioeconomic pathways
What are SSPs?
a set of socioeconomic pathways that can be modulated by different levels of mitigation action
gives a matrix for possible forcing scenarios
smaller forcing = smaller temperature change
these give you boundary conditions
they have storylines narratives describing how the associated emissions might come about - they enable fixed comparison between climate models
What is the difference between SSP and RCPs?
SSp = AR6 and RCp = AR5
rcp = representative concentration pathways
the two scenario groups were chosen to sample the whole range of plausible forcing outcomes
RCP 8.5 and SSP 8.5 = burn everything - 8.5 is the amount of the atmospheric forcing - for every sq meter of the atmosphere you have 8.5 what’s coming in - earth heats up
SSP 5 - ff development scanrio
What is the climate sensativity in CMIP6?
on average 3.9k as opposed to 3.5k in CMIP5
this is due to more positive cloud feedback and changes in cloud phase = reducing potential for negative feedback associated with clouds
How is internal variability a source of uncertainty?
tested using an ENSEMBLE = a set of identical simulations except for slightly different initial conditions
each ensemble member experiences different weather and internal variability
eg. the stage of the quasi-random oscilation of el-nino are you in - uncertainty at which stage you will be in thus uncertainty for global mean variation
what is the likelihood of each of the potential future cliamtes in an ensemble?
they are all equally likely
Does it matter what the starting temperature is in models?
not really- they will all end up with different temperatures - however it is trend in temperatures that is important
they can look different due to starting conditions and internal variability
but ensembles help quantify the internal variability of a projections
how is the scenario that we are in an uncertainty?
dont know which trajectory we are in
this uncertainty drives divergence in time and future feedbacks
uncertainty as to what feedbacks have been triggered in each scenario have huge implications for future projections of climate and resulting global mean temperature ranges
