1. Climate Change in the Atmosphere: Forcings and Feedbacks
David Stevenson
NERC/Environment Agency Advanced Research Fellow (Lecturer in Atmospheric Modelling from 1st April)

2. What has caused recent climate change?
In what ways has climate changed?
What has caused recent climate change?

3. And what will be the causes of future climate change?
Surface temperature projections (IPCC, 2001)

4. Climate forcings Changes in atmospheric composition
Future changes in these likely to be most important forcing
Changes in atmospheric composition
Greenhouse gases
Aerosols
Changes in land-use (planetary albedo)
Deforestation/afforestation
External forcings
Solar variability
Large volcanic eruptions
Changes in Earth’s orbit etc. (>104 yrs)

5. Land-use change: e.g. forests to pasture – increases
albedo
Warming from increases in GHGs  +3 W m-2
General cooling from increases in aerosols – but high uncertainty
Solar forcing

6. Climate Feedbacks
Forcings have knock-on effects in the climate system, e.g.,  Temperature 
 water vapour; H2O is a GHG, +ve feedback
 sea ice; ocean is darker than ice, +ve feedback
ΔClouds, ? Feedback
ΔEcosystem sources/sinks of GHGs & aerosols, +ve feedbacks
ΔChemistry… ΔO3, Δoxidising capacity, generally –ve feedbacks
Models simulate feedbacks differently – leads to a range of model climate sensitivities
Big question: What is the real climate sensitivity?

7. Why the big range in predicted temperature?
Partly uncertainty in future emissions; partly uncertainty in climate sensitivity

8. What do we need?
Better observations of climate, past and present (can we derive climate sensitivity from observations?)
Better estimates of emissions and atmospheric budgets, and hence concentrations of GHGs and aerosols (forcings)
Better representation of climate feedbacks in models, and hence better constrained estimates of climate sensitivity (feedbacks)

9. Some examples of current atmospheric/oceanic global change research at Edinburgh

10. Observing and Modelling the surface Ocean
Chris Merchant
Chris Old
Helen Kettle
Owen Embury
Stephan Matthieson

12. Improved cloud screening algorithms for SST retrievals
Currently used operationally
New version – better coverage

13. Improved modelling of diurnal ocean-atmosphere coupling
Arabian Sea
0.17 m
5.0 m
LOTUS
Model
0.6 m
5.0 m
Obs
Old model New model
Root mean square error in diurnal amplitude / K
Location (mean)
Old model
New model
Arabian (1.09 K)
0.51
0.25
LOTUS (1.25 K)
0.62
0.17

14. Saharan Dust, 48 hours of data from August 2005
Dust is an important correction for satellite SSTs; also an important climate forcing.

15. Data retrieval and analysis from NASA’s Earth Observing System
Microwave Limb Sounder
on board the AURA satellite
Bob Harwood
Hugh Pumphrey
Ian
MacKenzie
Mark Filipiak
Cory Davis
Carlos Jimenez
Liang Feng

16. Stratospheric ozone 2005

17. Observed/simulated H2O vapour

18. CO from fires in S. America 2005

19. Modelling Global and Regional Atmospheric Composition
Keith Weston
David Stevenson
Ruth Doherty
Richard Damoah
Massimo Vieno

20. Year 2000 tropospheric NO2 columns
Model (ensemble mean)
Observed (GOME) (mean of 3 methods)
(10:30am local sampling in both cases)
Courtesy Twan van Noije, Henke Eskes

21. ‘Likely’ ‘Optimistic’ ‘Pessimistic’
Change in tropospheric O under 3 scenarios
Annual Zonal Mean
ΔO3 / ppbv
Annual
Tropo- spheric Column
ΔO3 / DU
‘Likely’
IIASA CLE
SRES B2 economy +
Current AQ Legislation
‘Optimistic’
IIASA MFR
SRES B2 economy +
Maximum Feasible Reductions
‘Pessimistic’
IPCC SRES A2 High economic growth + Little AQ legislation

22. Climate impact of aircraft NOx emissions
NB negative scale expanded
ΔO3
Short-term warming from ozone
Plus minor ozone long-term cooling
NB negative scale expanded
ΔOH
Long-term cooling from methane
ΔCH4
Decay with e-folding timescale of 11.1 years

23. Climate statistics and Phenology
Roy Thompson

24. More to Global Change than just Climate Change
When this oak tree was a sapling, maybe 200 years ago, the climate was perhaps 1K cooler.
Its main ‘food’ is CO2 – over its life, ambient levels have increased from 280 ppbv to 370 ppbv
Deposition of nitrogen – an essential nutrient – may have increased 10-fold or more
Exposure to ozone – a damaging pollutant – may have increased 3-fold or more

25. What do we need?
Better observations of climate, past and present (can we derive climate sensitivity from observations?)
Better estimates of emissions and atmospheric budgets, and hence concentrations of GHGs and aerosols (forcings)
Better representation of climate feedbacks in models, and hence better constrained estimates of climate sensitivity (feedbacks)