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).

~30 ~15

Climate change and forest fire risk – future projections

Change: 2021-2050 minus 1961-1990

Change: 2071-2100 minus 1961-1990

+35 +15

+15 +5