Post on 01-Jan-2016
transcript
Modelling of climate and climate change
Čedo Branković
Croatian Meteorological and Hydrological Service (DHMZ)Zagreb
cedo.brankovic@cirus.dhz.hr
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
Source: IPCC (Intergovernmental Panel on Climate Change) report (2007)
* From measurements
* Change relative to 1961-1990
Evidence of climate change - local
Source: Č. Branković, I. Güttler, M. Gajić-Čapka Climate Dynamics (2013)
* Trends in air temperature at the Croatian Adriatic stations (°C/10 yr)
1952-2010
1981-2010
Crikvenicasummer season
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 modelECHAM5/MPI-OM vs. CRUTotal precipitation over land during winter, 1961-1990Source: Č.Branković, L.Srnec, M.Patarčić Climatic Change (2010)
Source: Č.Branković, M.Patarčić, I.Güttler, L.Srnec Climate Research (2012)
RegCM vs. CRU (errors)Air temperature at 2 m, winter 1961-1990
global modelobservation
s
Climate models and climate modelling – human impact
* Human impact is most likely crucial for atmospheric warming (because of increased concentration of greenhouse gases)
Source: www.meted.ucar.edu
observed change
all factors: natural and human
only natural factors
Climate models and climate modelling – future projections
European average temperature anomaly:certainty (!?)
individual simulation
natural fluctuation
Source: Hawkins, Weather (2011)
* Certainty in climate trend* Possible development(s)* Variations can obscure trend
Source: IPCC (2013)
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
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).
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