Midterm Flashcards
Climate Model
Numerical model that calculates budgets of mass, velocity, and energy in different parts of the earth system to develop understanding
What are the primary differences between climate models and weather forecasting models?
Scale (resolution and length of simulation), Climate forcings, Process representation (photosynthesis, ice melt)
CMIP
Major international multi-model research activity, considered foundational element of climate science
How does CMIP work?
Climate scientists from each climate modeling center use their climate model to run a set of coordinated/identical climate experiments
What is the objective of CMIP6?
Better understand past, present, and future climate change arising from natural, un-forced variability, or in response to changes in radiative forcings in a multi-model context
Pros of using multiple models:
Assess uncertainty in climate projections
identify robust climate response to difference climate forcings
Why might there be a spread in projections even though each model run is using the same boundary conditions?
Model Uncertainty
Internal Variability
Radiative Forcing
change in radiation balacne at the top of the atmo as a result of external drivers; leads to long-term changes in global temp
Climate sensitivity
response of global mean surface air temp to a radiative forcing
Equilibrium climate sensitivity (ECS)
response of long term global mean surface air temp to a doubling of the atmo CO2 after planetary budget is balanced
Transient Climate response (TCR)
global mean surface air warming at the time of CO2 doubling in an idealized 1% year CO2 increase experiment
Ways to estimate climate sensitivity:
Climate models
Recent Observations
Paleoclimate data
Why might the use of historical period to determine ECS be a problem?
A major issue is the assumption that the climate feedbacks experienced during observational period remain constant over time (too low ECS value)
Issues with Paleoclimate Records:
proxy record may be specific to that time period and not applicable to current/future climate
Proxies have large uncertainties
Best Estimate of ECS
3C
Likely range 2.5-4
Best Estimate of TCR
1.8 C
Likely range 1.4-2.2
Climate system feedbacks:
a response of the climate system to a climate forcing that amplifies or diminishes the intitial effect of climate forcing
TCRE
transient climate response to cumulative carbon emissions
0.8-2.5C per 1000 Gtc emitted
What does TCRE help with?
allows for a direct relationship between climate targets and emission reduction efforts
What does emergent constraints do?
technique to reduce “model response uncertainty”
Emergent constraint
Statistical relationship across a model ensemble between a measureable aspect of the present day climate and an aspect of future pojected climate change
Steps for identifying robust emergent constraints:
EC must have a plausible physical mechanism
-verify that this mechanism is at work in model ensemble
-assess whether the EC survives out-of-sample testing
Vapor Pressure
pressure exerted by water molecules
corresponds with mass of water vapor (specific humidity)
saturation vapor pressure
point at which the atmo becomes saturated
Hydrologic Sensitivity
change in global mean precip with global surface air temp
what does global increase in precip say about residence time of water vapor?
residence time of WV increases
Emergent constraint on precipitation
precip must change in such a way that the energy budget of the atmosphere continues to balance
How is change in LP balanced
change in radiative cooling
how is global mean precipitation controlled?
availability of energy
how is precipitation change controlled?
ability of the atmosphere to radiate away heat
How does rising temperatures effect radiation?
causes more radiation to leave atmosphere
How is losing radiative energy balanced?
there has to be a compensating increase in atmospheric latent heating associated with greater precipitation
Global mean atmospheric moisture increases more than global mean precip, what does this imply?
convective mass fluxes must decrease
Convective parameterization steps:
1.) assess environment state of grid cell
2.) scheme determines whether convection should happen in grid cell
3.) modifies environment state of grid cell if convection “happened”
Initial Condition Ensemble
Only difference between simulations is that they are intiialized from slightly different conditions
Attribution
Process of evaluating the relative contributions of multiple causal factors to a change or event with an assignment of statistical confidence
Detection
process of demonstrating that climate or a system affected by climate has changed in some defined statistical sense without providing a reason for that change
Attribution example:
Comparing simulated global temperature in two sets of climate model ensembles
1.) One includes observed greenhouse gas increase
2.) one does not
Probabilistic Event Attribution
Quantify the change in probability of an event between model simulations of the past compared to simulations of the world had humans not interfered with climate
Hindcast Attribution Method
uses highly conditioned simulations which provide strong constraints on the state of the climate so they closely match observations and then perform forecast-type simulations
Probabilistic Event Attribution Steps:
1.) Decide which charateristic of the event to analyze
2.) Observational trend analysis
3.) Climate model evaluation
4.)Climate model analysis
Groundwater Runoff
groundwater seeps into surface water
surface runoff
movement of water across the ground; comes from infiltration excess overland flow and saturation excess overland flow
Infiltration excess overland flow
from urban sources like roofs or pavements or when soil properties do not allow for infiltration to keep up with high rainfall rates
Saturation excess overland flow
from precipitation or melted snow that could not be absorbed into the ground; soil is saturated keeping water from infiltrating
