W4 Flashcards
What is special about ocean warming?
oceans have a high heat capacity and very slow mixing rate
What is the equation for climate sensativity? and what are the units
N= f - ^±T
teepee triangeT
F is whatts per meter squares
T is in kelvins
What is the equation for an equilibrium having been achieved? - i.e. what would n equal?
how would you solve for the 2xC02 Warming?
N is the imbalance therefore N= 0
at equilibrium 0 (n) = F(2xCo2)- λ∆T(2xco2)
change inT (∆T) = F2xCo2/λ
what does Lambdeh or λ in the equation tell you?
it is the climate feedback parameter - the climate feedback determines how much warming is needed to respond to the forcing
how much you need to warm in order to oppose the forcing of F
it essentially relates a change in temperature to a change in radiation
it is a big uncertainty - Co2 forcing is well understood, aerosols less so
radiative change per unit temperature change - measure efficiently the earths response to changes in radiative output to space per warming/cooling per degrees celsius
Why is climate sensitivity such an important metric?
- it is critical to projecting how the climate will respond to increases in Co2 emissions
- climate models give you very different models about the climate sensitivity - AR6 estimates that the best estimate is 3oC with a range of 2.5-4oc
How can climate sensitivity be estimated?
- climate model experiements with Co2 forcing
- the instrumental record
-Paleocliamte reconstructions - understanding of forcing and feedback processes
- a combination of these methods
but regardless of the method there is large uncertainties
What is an emergent constraint?
Physically explainable empirical relationships between the current climate and long term climate prediction that emerge in collections of climate model simulations
emergent constraints are indirect sources –> we know how clouds vary seasonally - if you find that climate models have a seasonal variation in clouds this would be an emergent constraint
- it is something observable that tells you something about the future
How has climate sensitivity estimates reduced their uncertainty?
- improved understandings of feedback processes - mainly clouds
- move away from climate models, focus on other lines of evidence - process understanding, instrumental record and paleoclimate etc. –> it was too difficult to get models to match up but this new combination provides a slightly better assessment
- idea of reducing the unknown unknowns
what is the transient cliamte response
DEF= the amount of global warming at the time of Co2 doubling, assuming a 1% increase per year - after 70yrs
TCR is more focused on shorter time scales like decadeds
Why is the TCR lower than the ECS
Calculated differently to climate sensitivity - sensitivity assumes that you reach an equilibrium but this requires long time periods - TCR is not assuming an equilibrium is reached and only measures the warming at the point where doubling of Co2 has been reached
What is the relationship between TCR and ECS in climate models and why?
- models with a high climate sensitivity tend to have a high TCR and vice versa therefore they are related
WHY?
they have the same feedbacks at play in the models
what distinguishes the models is whether they have feedbacks that amplify or dampen cc
What is a feedback?
a response to a forcing that can amplify or dampen the original forcing
Can you explain the albedo feedback?
Co2 forcing -> warming -> ice melts> lower albedo-> more abosrbed solar radiation -> more warming
postive feedback
lower albedo is darker and therefore has a greater absorption
Can you give some examples of feedbacks?
albedo
water vapour feedback
Cloud feedback
water vapour and cloud feedback are distinct - water vapour is a gas and clouds are a liquid therefore they have their own distinct impact on the climate
Can you expand on the water vapour feedback?
water vapour is a powerful ghg
water vapour content is tightly controlled by temperature vis the CLAUSIUS-CLAPEYRON RELATION
max vapour content goes up exponentially with temperature
relationships predicts 7% increase in water vapour content per degree of warming
water vapour feedback is positive
What is the Clausius-Clapeyron relation?
links the saturation of water vapour pressure to the max concentration of water vapour you can have at a temperature
it is an exponential relationship
predicts a 7% increase per degree of warming - max concentration
typically there is a little less than max concentration we tend to measure relative humidity
What is relative humidity?
how much is in the air compared to the max concentration in the air
we experience the relative humidity
what is absolute humidity?
the actual amount of water vapour in the air
this is what matters to the climate - but just from a warming it is difficult to say if there is going to be more or less water vapour - evaporation and evapotranspiration
Can you explain the two ways that clouds impact the radiation budget?
They impact the radiation budget in two ways
- they reflect solar radiation and have a cooling effect
- they absorb terrestrial radiation - like ghg and have a warming effect - the ice crystals in the clouds absorb long wave radiation
- on average, the cooling effect dominates - the climate is colder than if clouds didn’t exist
What are clouds feedback effects?
LONGWAVE
- the long wave ghg of clouds will increase under global warming - positive feedback associated with the rise of high clouds with warming
- the strength fo the GHG effect is proportional to cloud height - as the cloud rises it has a stronger ghg effect - it emits at a lower temperature and a bigger different between ground and cloud reduces the outflow of energy - positive feedback
SHORTWAVE
cooling by the cloud will probably decrease, mainly because of decreasing cloud cover in the tropcis - also a positive feedback
- however this is very uncertainty in climate sensitivity comes from
- fractional coverage (how much of earth is covered by clouds) reduces therefore more warming, stays the same you get less warming
Why do models struggle with clouds?
they are small scale features and the models are unable to simulat the cloud - would need to consider each ice crystal in the cloud for precipitation and evapotranspiration
climate models work on much bigger scales and make simplifying assumptions about how clouds will change into the future
What does AR6 think about clouds
the net effect of changes in clouds is to amplify human-induced warming - the net cloud feedback is positive with a high confidence
came to the conclusion that the cloud effect is going to amplify global warming
