Climate Attribution

Question 1

climate change attribution -> determine whether observed changes in weather = caused by cliamte change

Answer 1

more certainty into the impact of humans -> 1995 = humans had a discernable influence -> 2021 = human activity is the dominating cause from pre-industrial times

Question 2

modelling -> can be used when the observation record < 17 years (Trenberth, 2012)

Answer 2

attribution studies are conducted testing for causation between climate variables -> one of the greatest triumphs of the 21st century

Question 3

early anthropogenic research -> experiments

Answer 3

1856 - Foote = warmed glass cylinders -> found co2 was most impressionable
1861 - Tyndall = analysed impacts of temperatures changeson ghgs
1896 - Arrhenius = ghgh on the earth’s surface in the form of a model
1938 - Callendar = modelled anthropogenic impacts on temperature

Question 4

early climate models prior to the 1990s failed to represent water vapour

Answer 4

they were unstable and would get warmer as the ocean would be evaporated away

Question 5

climate models = simplification of the processes taking place across the earth

Answer 5

they are forced and a series of outputs in the form of a simulation or projection are created

Question 6

climate models = gridded = the information is processed across these grids at smaller scales -> often parameterisation takes place (McGuffie and Henderson-Sellers, 2014)

Answer 6

the models are then often forced with variables e.g. ghgs, aersols

Question 7

early attribution modelling -> model was forced (pre-industrial co2 and current cos etc…) and the output was compared to an unforced model

Answer 7

equilibrium models -> had a coarse resolution and were coupled = models were inaccurate

Question 8

Mitchell et al., 1995 -> HadCRUT (2.5x3.75 w/ 20 oceanic + 19 atmospheric layers) -> forced co2 and aerosol concentrations

Answer 8

took several years to run = forced the climate and a correlation was taken to see if it matched observation records -> aerosol component not depicted well in models as it assumed lower planetary albefo

Question 9

in the 1990s

Answer 9

we were able to model the natural variability of the climate

Question 10

1995 IPCC report -> low resolution modelling but had patterns which identified warming and cooling

Answer 10

transient models -> these were coupled models which had improved resolutions from the equilibrium models

Question 11

Santer et al., 1996 -> forced, aerosols, ozone and co2 concentrations to determine vertical atmospheric changes

Answer 11

assumed it was linear = did not account for interactions between the ghgs and how these would implicate the atmosphere and forcing only run once = 1 sample size

Question 12

hypothesis testing era -> realised that volcanic aerosols not as impactful across the midlatitudes due to the winds = more impactful across the tropics by nullifying the impacts of co2

Answer 12

ozone hole -> input into climate models and its effects on the atmosphere

Question 13

Tett et al., 1999 -> (HadCM2) did the same as Santer but did not assume linearity between the mechanisms = forced (ghg), (ghg + sulphates), (ghg + sulphates + ozone) -> first time that natural and anthropogenic variables were split

Answer 13

tested against the observed ‘fingerprint warming’ = atmospheric warming with cooling in the stratosphere, warming in the mid-upper troposphere, which is intensified most in the tropics, and warming but at a slower rate at the surface. Tett’s forced modelling = sulphates in the forcing led to a cooler stratosphere, ozone exacerbated this cooling and better represented the radiosonde observation record -> later halved the ozone concentration and had a better representation

Question 14

Stott et al., 2000 -> HadCM3 = different climate runs to highlight that the initial conditions were not producing the simulate climate

Answer 14

meant that human activity was the cause or that models are not proficient enough in simulations -> maybe deep sea current not being depicted

Question 15

Tett et al., 2000 -> forced variables to please model/climate deniers with solar radiation and volcanic aerosols

Answer 15

Tett et al., 2002 -> improved early research -> determine how much warming was attributable to human activity = 0.5degrees

Question 16

model uncertainty is determined

Answer 16

by running the model multiple times = analyse to see whether there is significant change = ensemble models produce the best results as the signal is clearer e.g. CMIP3 and 5 (McGuffie and Henderson-Sellers, 2014)

Question 17

improvements in modelling -> more data being incorporated e.g. soil moisture content in attributing the 2015 Ethiopian drought (Phillip et al., 2017)

Answer 17

increased computational power = higher resolution and more runs e.g. weather@home (Phillip et al., 2018)

Question 18

attribution of extreme events -> emerged from improvements in modelling

Answer 18

focuses on determining whether an extreme event was in line with weather patterns or was created due to climate change

Question 19

EEA -> Technique 1 (Risk-based approach) (Shepherd, 2016) -> models used to produce counterfactual simulations (weather forecasts based on lots of different initial conditions) and a factual data set (forecast based on the observed conditions)

Answer 19

statistical analysis to determine the likelihood of the extreme event = fractional attributable risk

Question 20

for extreme event attribution there needs to be a strict definition e.g. temporal and spatial boundaries

Answer 20

e.g. overflow rates for flooding or peak days of precipitation e.g. England and Wales wettest periods 2000 (Pall et al., 2011)

Question 21

extreme event attribution -> first paper -> Stott et al., 2004 = human contribution to the European heatwave of 2003

Answer 21

paper produced a grid box over c. Eur -> average temperature threshold under the current record but above the previous record
modelled the different simulations to determine that human activity did contribute
modelling inaccuracies -> some issues with land and atmospheric feedbacks e.g. vegetation dying would have exacerbated the drought through albedo induced shifts

Question 22

EEA -> Technique 2 (Storyline Approach) -> analyse the atmospheric conditions which led to the climate event -> see if these were anthropogenically driven or not -> known as partial attribution as dynamical processes not all considered

Answer 22

first used -> 2013 to analyse the 2011 Texan drought (Hoerling et al., 2013)

Question 23

climate attribution = observational record compared to forced variable shifts to determine human contribution to planetary change

Answer 23

event attribution = observations used to define the event to determine the degree of human influence in its formation

Question 24

Phillip et al., 2018 -> 3-day May floods in France 2016

Answer 24

data and models validated for the extreme event (5 climate models were used to simulate the precipitation over the River Seine and Loire from April-June in the form of analysing rates for 3 days which could then be used to determine the return period) -> return period for precipitation rates was produced (GEV distribution and multiplicative bias correction), trend produced = risk ratio (likelihood of a similar event occurring in a climate without human influence), and an attribution of the trend was conducted -> anthropogenic activity increased the precipitation rates over the River Seine 2.2x and over the River Loire 1.9x.

Question 25

Philip et al., 2018 -> criticsms

Answer 25

different paper was published 10 days after the event -> similar conclusions -> rejected since it was too soon published -> wanted a more rigorous analysis of the data.
wanted to determine the contribution of human influence to the floods -> study was criticised as it failed to incorporate topography, land-use change and ground saturation rates.

Question 26

Jones et al., 2008 -> NH summertime temperatures

Answer 26

HadGEM1 and CRUTEM3v -> analyse how anthropogenic climate change impacting NH summertime temperatures = made possible through better simulations of the NH and therefore could determine how human activity contributed to the warm periods (Jones et al., 2008).
Focus on using observed data -> simulated an All run, a ANTHRO run and a NATURAL run for the NH -> comparisons with the real-time data then compared to the models = ALL run aligned best with the observed data with multidecadal variability -> NATURAL aligned most poorly -> correlations used to determine this = ALL simulation 0.84 could explain 70% of variability.
Applied Stott’s method across 14 regions in the NH -> optima detection to analyse the role of each of the greenhouse gases on the observed and simulated temperatures.
ANTHRO = observed temperatures and therefore warmer NH summers.

Question 27

Otto et al., 2018 -> 2010 Thailand Flooding (monsoon + TS) -> 10-20th October

Answer 27

observational data in the form of precipitation is influenced too heavily by seasonal variability and spatial coverage low for the 0.5x0.5 gridded precipitation data set (1979-present) = did calculate a 2.5 year return period for the precipitation rates > pre-industrial (nonanthropogenic warming) = 4.8x increase in risk.

Question 28

models struggle to capture convection -> convective parameters have only started being used more recently e.g. 25km coarse model within the Pall et al. (2019) paper

Answer 28

overcome this by analysing the weather patterns which produce these precipitation rates e.g. low pressure – note can only really be used over the midlatitudes due to the relationship of low pressure and precipitation rates -> at the same time over the tropics MCCs are too small-scale to be detected by models (McGuffie and Henderson-Sellers, 2014).

Question 29

models struggle to depict mountains and ocean ->

Answer 29

HadCM3 model in Stott et al. (2000)’s research -> unable to simulate over the N.A. as it could not incorporate the NAO + (McGuffie and Henderson-Seller, 2014)

Question 30

improvements in the resolution quality of modelling

Answer 30

number of rows and boxes in gridding has improved e.g. 1970s models have a grid of around 500km and there were 10 vertical layers while more current research has a spatial resolution of around 100km and 50-60 layers (McGuffie and Henderson-Sellers, 2014).

Question 31

World Attribution Service

Answer 31

real-time modern-day attribution research -> apply the techniques of attribution as an event takes place to determine the impact of climate change on the real-time occurrence of the event e.g. politicisation of extreme attribution in science.

Question 32

Teleconnections -> ENSO exacerbating climatic conditions

Answer 32

La Niña 2011 -> increased atmospheric water vapour around China, Indian and Pakistan (Trenberth, 2012).