1. Observations of climate change
Help!
Kevin E Trenberth
NCAR

2. Global Warming is unequivocal
Since 1970, rise in: Decrease in:
Global surface temperatures NH Snow extent
Tropospheric temperatures Arctic sea ice
Global SSTs, ocean Ts Glaciers
Global sea level Cold temperatures
Water vapor
Rainfall intensity
Precipitation extratropics
Hurricane intensity
Drought
Extreme high temperatures
Heat waves
IPCC 2007

3. Global Warming The climate is changing.
We can and should take mitigating actions that will slow and eventually stop climate change.
Meanwhile we must adapt to climate change.
But adapt to what?
We do not have predictions.
We do not have adequate reliable observations.
We do not have the needed
information system!

4. Global mean temperatures are rising faster with time Warmest 12 years:
1998,2005,2003,2002,2004,2006, 2001,1997,1995,1999,1990,2000
0.052
0.026
0.018
0.012
Period Rate
Years /decade
IPCC 2007

5. Heat waves are increasing: an example
Trend plus variability?
Extreme Heat Wave
Summer 2003
Europe
30,000 deaths
IPCC 2007

6. It has not warmed uniformly: More warming over land
Surface
Temperature
It has not warmed uniformly:
More warming over land
Why no warming over SE USA?
Or N Atlantic
IPCC 2007

7. Drought is increasing most places
Mainly decrease in rain over land in tropics and subtropics, but enhanced by increased atmospheric demand with warming
The most important spatial pattern (top) of the monthly Palmer Drought Severity Index (PDSI) for 1900 to 2002.
The time series (below) accounts for most of the trend in PDSI.
IPCC 2007

8. Extremes of temperature are changing!
Observed trends (days) per decade for 1951 to 2003:
5th or 95th percentiles
From Alexander et al. (2006)
IPCC 2007

9. Increases in rainfall and cloud counter warming
Drought
Absence of warming by day coincides with wetter and cloudier conditions
Trend in Warm Days
IPCC 2007

10. Regional climate change
Hypothesis: It is impossible to address regional climate change without fully addressing how patterns of climate variability (modes) change, and thus how:
ENSO: El Niño Southern Oscillation
NAO/NAM: North Atlantic Oscillation/Northern Annular Mode
SAM: Southern Annular Mode
PDO: Pacific Decadal Oscillation
AMO: Atlantic Multidecadal Oscillation
change!

11. El Niño - Southern Oscillation
Cooler
Wetter
SLP Surface temperature
Precipitation
IPCC 2007

12. Pacific Decadal Oscillation
1976/77 climate shift
Pacific Decadal Oscillation
SST pattern (above) and time series (lower right) of 1st EOF of N Pacific SSTs.
NPI index of Aleutian Low
Indian Ocean SST (tropics)
IPCC 2007

13. Many observed climate anomalies can be simulated in models with specified SSTs
Sahel drought: Hurrell et al 2004, Giannini et al 2003, Hoerling,
US Dust Bowl: Schubert et al. 2004, Seager et al. 2005
Drought (US, Europe, Asia): Hoerling and Kumar 2003
But we can not (yet) simulate the observed SSTs.

14. Global increases in SST are not uniform. Why?
Coupling with atmosphere
Tropical Indian Ocean has warmed to be competitive as warmest part of global ocean.
Tropical Pacific gets relief owing to ENSO?
Deeper mixing in Atlantic, THC.
This pattern is NOT well simulated by coupled models!
Relates to ocean uptake of heat, heat content & transport.
IPCC 2007

15. IPCC experience on observations
Sorting out the climate signal from the noise in inadequate observations from a changing observing system is an ongoing continual challenge
Space-based observations are a particular challenge

16. Temperatures
IPCC 2007
Annual anomalies of maximum and minimum temperatures and diurnal temperature range (DTR) (°C) averaged for the 71% of global land areas for 1950 to 2004.
DTR
Issues:
Missing data and treatment
Quality control
Max and Min T much more
sensitive to inhomogeneities
4. Urban heat island
5. Need to continue to pressure
countries to provide high
frequency data (hourly and daily)

17. Precipitation: not a continuous variable
Large differences in amounts. Inability to analyze characteristics: intensity, frequency, duration, type, as well as amount. Need hourly data!
IPCC 2007

18. Tropical rainfall 30N-30S
Land Total
Ocean
Issues:
Need much more complete and better data on all hydrological variables set in a holistic framework:
Precipitation: hourly (intensity, frequency, duration, type, amount); streamflow, runoff, evaporation, drought indices, soil moisture (incl ice), snow cover depth…
Land: systematic offset 3%
Ocean: no relationship
Total: dominated by ocean

19. North Atlantic hurricanes have increased with SSTs
Marked increase after 1994
N. Atlantic hurricane record best after 1944 with aircraft surveillance.
Global number and percentage of intense hurricanes
is increasing
( )
SST

20. Some issues:
Partial reprocessing of ISCCP data has occurred for tropical storms (Kossin)
Records are far from homogeneous, even for satellite era
Records/practices are not comparable in different regions, even now.
We desperately need an internationally coordinated reprocessing of all satellite data for hurricanes, to get many parameters of interest, such as size, intensity, rainfall, integrated variables (0-100 km; km) etc.
Ivan 2004

21. Main Issues The in situ data are not global and have problems
Satellites drift in orbit and instruments degrade: the data generally do not provide a climate record. They could.
The satellite record is in jeopardy, especially from demanifesting several climate instruments from NPOESS.
A baseline transfer standard is essential: in situ super sites (reference radiosonde plus network).
Regional climate requires attention to modes of variability and model initialization

22. Why do we need an integrated Earth System Analysis?
We have a lot of observations: from satellites and other remote sensing.
The volumes are huge
We use but a small fraction
Most are not climate quality
Inconsistencies exist across variables
They do not make a climate observing system
Reprocessing and reanalysis must be part of system
Goal: Climate Data Records

23. There is a need to better come to grips with the continually changing observing system.
There is no baseline network to anchor the analyses or space observations.
The radiosonde network is not it!
The challenge is to improve continuity and be able to relate a current set of observations to those taken 20 years ago (or in the future).
There is a need for more attention to data synthesis, reprocessing, analysis and re-analysis of existing data sets; and
5. There must be a baseline set of measurements:
 Sparse network (30-40) of “reference sondes” for satellite calibration and climate monitoring, UT water vapor; co-located with regular sonde sites to replace them at appropriate times; integrated with ozone sondes and/or GAW and BSRN = GRUAN?
 GPS Radio Occultation.

24. Information System The challenge is to better determine:
how the climate system is changing
how the forcings are changing
how these relate to each other (incl. feedbacks)
attribution of anomalies to causes
what they mean for the immediate and more distant future (assessment)
Validate and improve models
seamless predictions on multiple time scales
how to use this information for informed planning and decision making
how to manage the data and reanalyze it routinely
how to disseminate products around the world
how to interact with users and stakeholders and add regional value
From Trenberth et al 2002
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Information System