Scaling and scenarios: the ghosts of data past, present and future

1. Scaling and scenarios: the ghosts of data past, present and future Tim Mitchell (CRU-past, TYN-present, ???-future)

2. ?? Monthly or Extremes ?? • The ‘data’ (past, present, future) here is exclusively monthly. • Is it relevant to extremes? • Yes! • monthly extremes are extremes too! • monthly data may sometimes be used to estimate daily extremes • experiences with monthly data help to plan our daily work • many techniques are similar for monthly and daily data • Of course, there are many contrasts between monthly and daily data too, hence the need for this slide!

3. Overview

4. Work: past … Data: past Monthly grids of observations (1901-2000) • work previously led by Mark New (now in Oxford) • climatology at 10 minutes, time-series at 0.5 degrees • global land only (excluding Antarctica) • tmp, pre, dtr, cld, vap, (wet, frs) • space-optimised

5. Work: past … Data: future The ATEAM scenarios (2001-2100) • ATEAM = EU 5th project on ecosystems • Europe (10 minute), global land (0.5 deg) • 16 scenarios: 4 GCMs * 4 SRES • tmp, pre, dtr, cld, vap

6. Overview

7. Work: present … Data: past Supplying users: sub-sample from March 2003

8. Work: present … Data: present Six-monthly updates to monthly grids • Many users are working with non-climate data-sets that are very short and very recent. • Many users also need up-to-date information to feed into the policy-making process. • Therefore we are currently implementing a regular (probably 6-monthly) update to the monthly grids. • Flow of information: • CLIMAT bulletins (Met Office)  CRU databases  grids

9. Work: present … Data: future Developing the pattern scaling technique devised ~1990, tested ~2000, extended ~now • from linear change to stabilisation • from changes in the mean to changes in variability • from changes in the ‘usual’ to changes in ‘extremes’

10. Overview

11. Work: future … Data: past Improving the grids • This is an endless task, but an important one, carried out largely in the background and without explicit funding. • Augment the station databases to improve coverage outside the West and early in the 20th century. • Check, re-check, and check again the temporal homogeneity of the station time-series. • A proposal to the EU (Clare G, Phil J) hopes to develop similar daily databases, and high-resolution grids for Europe.

12. Work: future … Data: future Dreaming… • Develop facility to produce user-specified scenarios on-demand [successor to Scengen,likely in 2003] • Eliminate the mismatch in spatial scales between past and future, by using RCMs. [awaits a large RCM sample] • Introduce scenarios with changes in variability statistics. [awaits the development of a robust theory] • Introduce scenarios with credible month-to-month variations derived from models, rather than observations. [requires RCMs, and errors not to exceed ‘no change’ hypothesis]

13. Overview

14. data past data present data future work past Monthly grids of observations (1901-2000) The ATEAM scenarios (2001-2100) work present Supplying users Six-monthly updates to monthly grids Developing the pattern scaling technique work future Improving the grids Dreaming… Overview