detection, attribution and projections Climate Change: detection, attribution and projections Alessio Bellucci Centro Euro-Mediterraneo sui Cambiamenti Climatici

IPCC WG1 AR5 Climate Change 2013: The Physical Science Basis The IPCC has released its WG1 AR5 Climate Change 2013: The Physical Science Basis on 27 Sept 2013 in Stockholm, Sweden. The Summary for Policymakers (SPM) can be downloaded from the IPCC website: http://www.ipcc.ch

The observations (Phenomenology of Climate Change)

The main indicator: Global Mean Surface T (GMST)

The main indicator: Global Mean Surface T (GMST)

1901 – 2012: Observed change in surface temperature

Warming of the climate system is unequivocal Snow cover (declining) Since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased. (declining) Arctic sea-ice Oceans (warming) Sea level (rising)

GHG Concentrations: 800,000 years BP-present The atmospheric concentrations of CO2, methane and nitrous oxide have increased to levels unprecedented in the last 800,000 years. N2O 380 CO2 CH4 GHG Concentrations: 800,000 years BP-present

The atmospheric concentrations of CO2, methane and nitrous oxide have increased to levels unprecedented in at least the last 800,000 years.

Impact of climate change on extreme events

Impact of climate change on extreme events

Understanding the causes (Beyond detection)

Climate Models Climate models are a very powerful tool to understand the causes behind climate change

Climate Change Attribution Observations Models (Anthropogenic +Natural forcing) The consistency between models and observations is obtained only after both anthropogenic (GHG+Aerosols) and natural (volcanoes, solar irradiance) forcings are considered Observations Models (Only natural forcing included)

The observed warming 1951−2010 is approximately 0.6°C to 0.7°C.

The observed warming 1951−2010 is approximately 0.6°C to 0.7°C. It is extremely likely that human influence has been the dominant cause of observed warming since the mid-20th century

Human influence on the climate system is clear. The observed warming 1951−2010 is approximately 0.6°C to 0.7°C. Human influence on the climate system is clear.

The future

Future Climate Projections For future climate projections, climate models requires Emission Scenarios. Models in AR5 use Representative Concentration Pathway (RCP) very high GHG emissions stabilization mitigation (peak and decline) RCPs represent a range of 21st Century climate policy scenarios

Projected Global Average Temperature Change by end of 21st Century The temperature increase during the last 100 years was only about 0.8oC. Global surface temperature change for the end of the 21st century is likely to exceed 1.5°C relative to 1850−1900 for all scenarios except RCP2.6.

Uncertainty in projected climate change Even only 1oC increase will be a serious change ? ?

Global mean sea level will continue to rise during the 21st century and virtually certain beyond 2100 RCP2.6 (2081-2100): likely range: 26 to 55 cm RCP8.5 (2081-2100): likely range: 45 to 82 cm

2100: surface temperature (2 scenarios) 1 – 1,5 oC Increase 4 – 7 oC Increase

Expected changes for precipitations over Europe (2080-2100 vs 1986-2005) SUMMER (JJA) drier climate in summer over the Med region WINTER (DJF) Small changes are expected over the Central and Northern Europe but a notable reduction (dry conditions) over the Mediterranean region

2100: moving towards a warmer and drier climate 10% Decrease 10-20% Decrease 1 – 1,5 oC Increase 4 – 7 oC Increase

MITIGATION: Limiting climate change will require substantial and sustained reductions of GHG emissions RCP2.6 would be the Emission Scenario to follow if we were to cap warming at 2oC To limit warming to likely less than 2oC as in RCP2.6, requires total emissions since preindustrial to be limited to less than about 790 PgC. 515 PgC were emitted by 2011.

Summarizing…. Climate Change is unequivocal. Even if policies and efforts to reduce emissions prove effective, some climate change is inevitable. Therefore, strategies and actions to adapt to its impacts are needed.

Summarizing…. THANK YOU Climate Change is unequivocal. Even if policies and efforts to reduce emissions prove effective, some climate change is inevitable. Therefore, strategies and actions to adapt to its impacts are needed. THANK YOU

Additional Slides

2100: mean precipitation (2 scenarios) 10% Decrease 10-20% Decrease

Cumulative emissions of CO2 largely determine global mean surface warming by the late 21st century and beyond Warming is largely independent of the emission profile. Only the total matters. More emissions early imply stronger reductions later. Every ton of CO2 causes about the same amount of warming, no matter when and where it is emitted Any temperature target implies a maximum in cumulative CO2 emissions. This is purely a physical and carbon cycle problem. Allocation over time is a economic and policy question. Overshooting the budget will overshoot the target.

1. Causes of climate change, In 1988 IPCC was established under WMO and UNEP to provide independent, objective, fair and transparent assessment of the state of global climate system. IPCC provides such assessment and is the source of information particularly to policy makers and UNFCCC on 1. Causes of climate change, 2. Potential impacts on built and natural systems and socio-economic, 3. Possible response options. IPCC had published 5 assessment reports and various other reports.

IPCC Reports:

The four Elements of the Fifth WGI Assessment Report 14 Chapters Atlas: Regional Projections ca. 2000 Pages, 1250 Figures und Diagrams, Timeseries und Maps for 35 Regions of the World, 2 Milion Gbytes. Summary for Policymakers 22 Pages, 10 Figures 4. Technical Summary ca. 90 Pages

Observed climate trends over Europe: surface temperature Recent 1981-2012 trends in annual mean temperature exceed the global mean land trend [IPCC AR5 Chapter 14]

The double challenge: CHALLENGE 1: In order to stabilize GHGs concentrations in the atmosphere, emissions would need to peak and decline thereafter. Mitigation efforts over the next decade will have a large impact on opportunities to achieve lower stabilization levels. CHALLENGE 2: Even if policies and efforts to reduce emissions prove effective, some climate change is inevitable; therefore, strategies and actions to adapt to its impacts are also needed.

Uncertainties in projections Internal variability – an important source of climate variability Future climate change is a sum of: an externally forced response, due to changes in radiative forcing arising from human activity, variations in the sun and major volcanic eruptions Internal variability, e.g. the El Niño-Southern Oscillation (ENSO) and other patterns, and year-to-year and decade-to-decade fluctuations in winds, precipitation, temperature, …

Impact of climate change on extreme events over Europe Very likely increase of the number of warm days and nights and decrease of the number of cold days and nights, since 1950 in Europe. Heat waves can be amplified by drier soil conditions resulting from warming General increases in the intensity and frequency of extreme precipitation especially in winter