Climatic Change: Scientific Issues

Transcription

1 Climate Change: Scientific Issues Anno Accademico, 2011/12 Valter Maggi Lab. di Glaciologia, Dip. Scienze dell Ambiente e del Territorio.

2 What is climate change? Climate is the average weather (its mean and variability) over some certain time span and certain area. Broader definition in terms of the state of the Earth System Climate change (IPCC) is the change in climate with time due to natural variability or human activity Climate change (FCCC) is the change of climate that is due directly or indirectly to human activity 2

3 Questions to be addressed Is climate changing? Is this change due to our activities? How well can we quantify these changes? Will climate continue to change? Do we understand the implications of these changes? NB. Common misuse: Anthropogenic = caused by humans (actually human-producing!) 3

4 Learning Objectives To appreciate how climate has changed in the past and to put modern changes in context To understand the physical and chemical processes (and feedbacks between them) involved in determining the past, present and future climates Understand the difficulties associated with detection and attribution of climate change Appreciate that scientific understanding is not set in stone Understand the consequences of climate change for the planet. 4

5 Skills you will hone Ability to assemble information from diverse sources Basic quantitative understanding of climate regulation and forcing Form a cogent argument on a complex topic where there is no obvious yes/no answer To clearly separate fact: knowns expectation: most likely outcome based on current knowledge speculation: one possible outcome of many, but often worth exploring opinion: differing interpretations of the same facts nonsense: unfounded opinion 5

6 Known unknowns We know the processes but have difficulty quantifying them or understanding the implications of uncertainty (aerosol effect on climate) Unknown unknowns Genuine surprises. Out of our hands. Need ability to react after the surprise. Often from coupled nonlinear processes 6

7 Indice del corso 1. INTRODUCTION OBSERVED CLIMATE VARIABILITY AND CHANGE 2. Recent Centuries 3. Climate reconstruction 4. The last 100 Myears CLIMATE SCIENCE 5. Energy balance 6. Heat fluxes 7. Physical climate interactions 8. Natural modes and coupled systems 9. The carbon cycle 10. Chemistry-, biogeochemistry- and biosphere-climate interactions HUMAN PERTURBATION OF CLIMATE 11. Climate forcing agents 12. Aerosol forcing of climate 13. Climate models and simulation of current climate 14. Climate change detection and attribution FUTURE CLIMATE 15. Climate predictions 16. Effects of climate change 7

8 OBSERVED CLIMATE VARIABILITY AND CHANGE 2. Climate of recent centuries Last 150 years, Medieval warm period, The Little Ice Age, Variations in greenhouse gases. The Anthropocene? 3. Climate reconstruction Proxy records, oxygen isotopes, ice cores, tree rings, sediments, written records 4. Climate of the last 100 thousand years Glaciation, Younger Dryas event, rapid climate change, Milankovitch theory, variations in greenhouse gases 8

9 CLIMATE SCIENCE 5. Energy balance Radiation streams, natural greenhouse effect, simple balance models, radiative forcing 6. Heat fluxes Heat redistribution due to atmospheric circulation, Monsoons, etc., the hydrological cycle 7. Physical climate interactions Feedback cycles involving the cryosphere, ocean, land surface, water vapour, clouds 9

10 CLIMATE SCIENCE, cont Natural modes and coupled systems El Nino, North Atlantic Oscillation, climate stability and rapid climate change, chaos 9. The carbon cycle Carbon reservoirs and exchanges (limestone, fossil fuels, biomass, atmosphere, perturbations) 10. Chemistry, biogeochemsitry and biosphere-climate interactions Ozone depletion/climate change, GHG lifetime, DMS CLAW hypothesis, biotic responses and the C-cycle, dust deposition and algal blooms 10

11 HUMAN PERTURBATION OF CLIMATE 11. Climate forcing agents Contributions to radiative forcing, changes in GHGs, aerosols, solar, etc; global warming potential; forcing- response relationships and climate sensitivity 12. Aerosol forcing of climate Greatest uncertainty in current climate change, reasons for uncertainty, observations, models 13. Climate models and simulation of current climate What is a climate model and what is simulated? Climate sensitivity, response to forcings, coupling of ocean-biospherecryosphere-atmsophere, testing understanding, prediction 11

12 HUMAN PERTURBATION OF CLIMATE, cont Climate change detection and attribution Has climate change occurred? How much of the change can be attributed to human activities? How certain are we? 12

13 FUTURE CLIMATE 15. Future emissions Energy demand, emissions scenarios, model predictions of temperature, rainfall, sea ice, etc. 16. Effects of future climate change Melting ice, shifting agriculture, cloudiness, storminess, disease, sea levels 13

14 How to do well on this module Key is background reading and synthesis High exam marks will favour: Evidence for background reading A critical analysis synthesis Exam will not forgive Repetition of unfounded opinions, hear-say etc. 15

15 The observational record 17 IPCC 07

16 Changes in greenhouse gases 18 IPCC 07

17

18

19

20

21 Climate of the last 1000 years 19

22 Climate reconstruction 20

23 Glacial-interglacial variability 21

24 Earth s natural greenhouse 22

25 The inter-tropical convergence zone (ITCZ) 23