Modelling of climate and climate change Čedo Branković Croatian Meteorological and Hydrological Service (DHMZ) Zagreb

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

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) Crikvenica summer 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 model ECHAM5/MPI-OM vs. CRU Total precipitation over land during winter, Source: Č.Branković, L.Srnec, M.Patarčić Climatic Change (2010) Source: Č.Branković, M.Patarčić, I.G ü ttler, L.Srnec Climate Research (2012) RegCM vs. CRU (errors) Air temperature at 2 m, winter global model observations

Climate models and climate modelling – human impact * Human impact is most likely crucial for atmospheric warming (because of increased concentration of greenhouse gases) Source: observed change all factors: natural and human only natural factors

Climate models and climate modelling – future projections European average temperature anomaly: certainty (!?) individual simulationnatural 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:

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 (control period) and future projections for (near future) and (distant future). ~30~15

Climate change and forest fire risk – future projections Change: minus Change: minus