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Modelling of climate and climate change
Čedo Branković
Croatian Meteorological and Hydrological Service (DHMZ)
Zagreb
[email protected]
Outline
1. What is climate and what is climate change
2. Evidence of existing climate change
3. Climate models and climate modelling
- validation
- climate change and human impact
- future projections
- uncertainties
4. Climate change and forest fire risk
What is climate?
* Climate of an area is an aggregate of expected values of meteorological
parameters
* It is based on measurements and observations over long periods
(minimum 30 years)
* Climate is influenced by dynamics and interactions of the components of
climate system – atmosphere, hydrosphere, cryosphere (ice cover), soil,
biosphere (vegetation)
* “External” manifestation of complex and non-linear processes
* Elements of climate: solar insolation, air temperature, atmospheric
pressure, speed and direction of wind, moisture, cloudiness, precipitation,
evaporation, snow cover, …
What is climate change?
* Significant and permanent changes in statistical distribution of weather
phenomena (on time scales of decades to millions of years)
* Variation (of weather phenomena) at shorter time scales is not climate
change; they are inherent to climate system and are the consequence of
atmosphere’s chaotic nature
* Climate change occurs because of the change in Earth’s energy balance
- natural -
variations in Earth’s orbit (Milanković cycles),
volcanic eruptions (aerosols),
variations in solar radiation, tectonics (!)
- anthropogenic - deforestation, land use, burning of fossil fuels, …
- they can cause an increase in the level of the
greenhouse gases, aerosols, damage ozone layer
Evidence of climate change - global
* From measurements
* Change relative to 1961-1990
Source: IPCC (Intergovernmental Panel on
Climate Change) report (2007)
Evidence of climate change - local
* Trends in air temperature at the
Croatian Adriatic stations (°C/10 yr)
Source: Č. Branković, I. Güttler, M. Gajić-Čapka
Climate Dynamics (2013)
Crikvenica
summer season
1952-2010 1981-2010
Climate models and climate modelling
* Atmosphere is fluid governed by laws of physics (hydrodynamics and
thermodynamics) but also chemistry; they can be described in the form of
mathematical nonlinear partial differential equations
* When adapted for computational purposes (computers), the system of
equations is called (numerical) atmospheric or climate model
* Climate models are essential for estimates of climate change; only models
can “predict” future state of the atmosphere and climate; however ...
* Climate models are only approximations of real climate system because of
- lack of knowledge of all the processes involved
- discretisation of analytical equations
* Complex climate models require huge computational resources and their
development depends greatly on development of computer technology
(super-computers)
* Climate models can be broadly divided to
- global models – cover the whole globe, relatively coarse resolution
- regional models – cover a region, much finer resolution
Climate models and climate modelling - validation
* Climate simulations for periods with available observational data
* Estimates of model systematic errors influence our confidence in a model
ECHAM5/MPI-OM vs. CRU
Total precipitation over land
during winter, 1961-1990
global model
Source: Č.Branković, L.Srnec, M.Patarčić
Climatic Change (2010)
observations
RegCM vs. CRU (errors)
Air temperature at 2 m,
winter 1961-1990
Source: Č.Branković, M.Patarčić, I.Güttler, L.Srnec
Climate Research (2012)
Climate models and climate modelling – human impact
* Human impact is most likely crucial for atmospheric warming (because of
increased concentration of greenhouse gases)
all factors: natural
and human
observed change
only natural factors
Source: www.meted.ucar.edu
Climate models and climate modelling – future projections
European average temperature anomaly:
certainty (!?)
natural fluctuation
individual simulation
* Certainty in climate trend
* Possible development(s)
* Variations can obscure trend
Source: Hawkins, Weather (2011)
Climate models and climate modelling – what scenario?
* We do not know future concentrations of GHGs
* Depend on socio-economic development
strong forcing
weak forcing
Changes are not
uniformly distributed
Source: IPCC (2013)
Climate models and climate modelling - uncertainties
* Various uncertainties related to modelling of climate and climate change
Main sources of uncertainties:
* Natural: internal variability of climate system (unpredictable!)
- natural fluctuation can mask future (weak) climate changes
* Scientific and technical: imperfections in climate modelling
- our limited knowledge of climate system
- inadequacies of computer models (approximations)
- parameterisation of unresolved processes - turbulence, cloud
microphysics ... (various models may give different “answers” to the
same forcing)
* Socio-economic: scenario uncertainty
- lack of knowledge of future concentrations of greenhouse gases
- depends on Earth’s population, industrial & technological development...
Source: Hawkins and Sutton,
Bull.Amer.Meteor.Soc. (2009)
Cartoon movie on: www.climrun.eu
Climate change and forest fire risk – current climate
Data provided by Dr. Christos Giannakopoulos from
National Observatory of Athens (FP7 project Clim-Run)
* Forest Fire Weather Index (FWI): temperature, air relative humidity,
10m wind speed and 24-h accumulated precipitation
* Divided into fire danger classes: low 0–7, medium 8–16, high 17–31,
extreme > 32
* Daily output data from three RCMs from ENSEMBLES project at a
25 km x 25 km resolution
* Present day simulations 1961-1990 (control period) and future projections
for 2021-2050 (near future) and 2071-2100 (distant future).
~30
~15
Climate change and forest fire risk – future projections
Change: 2021-2050 minus 1961-1990
+15
+5
Change: 2071-2100 minus 1961-1990
+35
+15