Launch 25 th May 2007, Royal Society of Edinburgh

1. SAGES Scottish Alliance for Geoscience, Environment & Society Launch25th May 2007, Royal Society of Edinburgh Centre For Earth System Dynamics My Vision for the CESD in SAGES Prof. Simon Tett, Chair of Earth System Dynamics: University of Edinburgh

2. Why did I join SAGES? • Exciting possibility of helping set up major new initiative • Knew that there were several good researchers in climate change and carbon cycle active in Scotland • Attracted by idea of multi-institution, multi-disciplinary collaboration rather than competition and focus on particular disciplines. • Earth system is broad problem. Needs multiple skills to make progress • Liked idea of broad hinterland. (“Society”, Glaciology, paleo-climate, land processes, land-carbon, satellite observations etc) • Felt it was time to do something different from current job at Met Office & Edinburgh a good city, for me and my family, to live in.

3. Models • Encapsulate our knowledge of the processes and physics that drive the Earth System. • Are uncertain • Basic equations are well known but large scale modelling of various processes such as convection is uncertain. • Can be used to predict the future and understand/interpret the past • Are chaotic. (Sensitive to initial conditions) • Need to be tested. • Are they fit for purpose?

4. Emergent Phenomenon • Interested in “Emergent Phenomenon” • Not interested in detailed, and unpredictable, evolution of state. • How much warming will there be? • How will hydrological cycle change? • Will the number of severe storms change? • Etc….

5. Proxy Temperatures suggest late 20th century very unusual

6. Instrumental temperatures show a warming of about 0.7K since 1900

7. Strong evidence that observed temperature changes over the last century are due to human effects

8. Estimates of Climate Sensitivity using models and observations From IPCC CH9, after Hegerl et al., nature 2006

9. What does the future hold? IPCC multi-model ensemble Ensemble of “perturbed physics” models showing large uncertainty range of future warming. Which are right? From IPCC. Ranges are broad and overlap one another (scenario “choice” vs understanding of the natural world.)

10. Carbon cycle How to constrain this? Have measurements of CO2 concentration and know about observed climate change/variability. Can we use this to estimate carbon feedbacks. BUT don’t know sources well… From Friedlingstein et al, 2006. Plots shows additional CO2 from feedbacks between climate change and carbon cycle. Values vary between 25 and 225 ppm at 2100 mostly due to land-carbon cycle feedbacks.

11. What leads to uncertainty in Future Change • Future emissions of CO2 & other trace gases and aerosols • Feedbacks • Physical: Clouds, water vapour, ice, snow. • Biosphere: Will the earth system continue to be a sink for CO2 or will it be a source? • Ocean – sets the timescale. • First order effect (will world warm by 1 or 10 K) by end of 21st Century. Both seem very unlikely. 10K would be “catastrophic climate change” and requires very strong physical & biological feedbacks. • My personal research aim is see to what extent, if any, observations can rule out strong physical & biological feedbacks leading to warming greater than about 4-5 K.

12. TOA fluxes from ERBE vs models Changes in Top of Atmospheric fluxes are related to (fast) feedbacks. See Forster and Gregory. Suggests low feedback and thus that models are too sensitive. (Could be issues with data as well…)

13. Last 1000 years Are uncertainties in reconstructions so large as to preclude any significant constraints?

14. My Challenge • Bring observations together with models to: • Test models (been done). • Quantify uncertainties. • Constrain the future. • Improve models (very hard).

15. Regional changes & modes of variability. • Thermohaline circulation • Lots of resources in this mainly due to concerns about its rapid shutdown. Impacts global (NH cooling, SH warming) with largest impact in Nth. Atlantic. • North Atlantic Oscillation. • Huge impact on European climate. Warm/wet winter vs cold/dry winters. Some work shows it can be affected by tropical volcanic eruptions. • El Nino/Southern Oscillation • Huge source of climate variability in the tropics and extra-tropics. Predictable up to about a year ahead. May have an influence on European climate. Coupled atmosphere/ocean mode. • General question. How will these modes change in a different climate? What is the reason, in the models, for the changes? Are they robust/realistic? How will their impacts change? • Warmer climate, in models, leads to, on average, drier summers and wetter winters. +NAO (dry winter) could then cause serious water shortages in the UK. Summer 2006 as example.

16. Impacts & Extremes • Policy relevant & what society needs to know. • How to link to users/stake holders? • Meteorology -> society and society->meteorology (what are the important changes that generate impacts?). • Need good metrics of natural variability in these so that can decide if possible future climate changes important. • My personal view is that impacts work needs more exploration, range of models (“traceable hierarchy”) and disciplines to provide good and robust answers.

17. Extremes • Extreme events are, by definition, rare • What is natural variability in extreme events? • Will GHG driven response overwhelm natural variability? • Depends on type of event. Hot summers vs severe storms Number of UK severe storms per year. (1/3 storm = 1 severe storm in a region). Multi-decadal variability. Preliminary results from Rob Allan

18. Assessing Recent Change Obs trend (K/dec) X where outside max abs 50-year trend from Natural. + where outside max trend. Recent changes outside nat var over large parts of world. Suggest possible impacts on natural systems

19. Earth System Modelling Strategy for SAGES • Run HadCM3 on a cluster. Allows community to develop experience and explore a variety of problems. • HadCM3 no longer “state-of-the-art” but still a good model and on a cluster will allow us to explore 1000 year timescales. • Move to SAGES/HadGEM3 ESM (being developed now) when it is ready. • For work on a cluster will need a “fast” version. • Start using HadGEM/HiGEM on Hector (new national super-computer facility).

20. Earth System Modelling Strategy for SAGES • Need to link with Hadley Centre and NCAS. • We need to be part of, and contribute, to a UK community. • How to use/organise community to coherently improve models. Particularly an issue for a distributed community like SAGES. • How do we build on each others work?

21. Final thought • The scientific challenge is great and society needs answers soon…. • Reasonable models today are better than excellent models in 50 years.