Resolution of Tropospheric Temperature Disparities

**December 4, 2002**

**Rapporteur -- David Goodrich**

**Karl** -- (Overview) Models project tropospheric surface temp.
increase, stratospheric decrease; troposphere warms more than surface.

Observations: surface warms more than troposphere.

Observation problems? Poor forcings? Inadequate model physics?

New analyses since NRC; radiosondes show little or no warming to 0.2C

Surface temperature increases of \> 0.15C since late 1970's

Models cannot simulate surface-troposphere difference

Disparity centered on tropics

Understanding causes of stratospheric temperature tied to troposphere

Size of satellite corrections larger than signal, because of
calibration, orbital drift

65% of total difference related to NOAA-9 satellite

Radiosondes have considerable time-dependent biases

Step increase before start of satellite record (1976-77)

Physical basis: Differences in spatial coverage (accounts for \~ 1/3 of
difference)

Other forcings: volcanic, ozone depletion

Bottom line: Accounting for coverage, volcanoes and ozone, internal
variability helps explain some, but not all of the differential warmings
(from UAH and radiosonde)

Moving forward:

Make GUAN into an Upper Air Climate Reference Network

Remote unmanned aircraft

Adhere to GCOS Satellite Monitoring Principles

Focus on NOAA-9, ancillary channels

High altitude surface network

GCOS Surface Network: adhere to principles

Ensure real-time delivery of global temperature datasets

Model simulation of NOAA satellite sampling; ensemble simulations; new
reanalysis

**Christy** -- Main difference between satellite and surface is in
tropics

Both RSS, UAH much smaller trend than Hadley model run

UAH corrections emphasize empirical corrections

All difference in trend between RSS and UAH occur after NOAA-9

Where do we go?

Retrospectively correct radiosonde data sets

Improve sonde information practices

Need to expand sondes in tropics

Need to fund "operational research"

Take care of satellite climate issues

Problem with NCEP 100 mbar reanalyses

# Wentz -- Orbital decay introduced 0.1C cooling; RSS 0.1C/decade; UAH 0.01C/decade; do not overlap

Differences between UAH and RSS appears to be on NOAA-9 (65%)

Differences between analyses not explained; have spatial patterns

Two MSU data sets agree better with each other than with radiosondes

Ways forward:

Groups exchange software and data

Intercomparisons with other observational sets

MSU 2 and 4

Radiosonde trend and diurnal signals

SST

Land Surface temperature from satellite microwave radiometers

Comparisons with climate models

**Singer** -- Is the climate warming?

Surface data needs to be scrutinized

Surface and radiosonde data disagree

Global temperatures rise, U.S. temperatures do not

Total corrections are 0.3C

Marine temperatures from buoys are uncalibrated

Most of land stations are from airports and are affected by urban heat
islands

Proxy data: Mann et al does not show recent warming; it is in fact
surface temperature record

Briffa et al does not show overall warming

No proxy data shows warming in recent decades: Jacoby

Ice cores show Greenland cooling

No substantial warming; climate sensitivity overstated by IPCC

**Santer** -- Why have sfc and troposphere warmed at different rates?

Strong surface warming, weak warming seen by satellites

Sampling satellite data at surface sites accounts for 1/3 of difference

Including El Nino and volcano effects gives satellite warming trend

Model: surface and troposphere warm at same rate

Removing El Nino and volcano effects removes some of model-satellite
differences

Modeled tropospheric temperature agrees with RSS data set, not with UAH

Other evidence: tropopause height agrees with model results

PCM: can only reproduce observed record with GHG's, not just natural
variability

Conclusions:

-   Without volcanoes, troposphere would have warmed

-   Eruptions cool troposphere more than surface

-   Models and obs surface temperature in good agreement

-   Obs uncertainty can explain some differences

-   Tropospheric height changes are consistent with a warming
    troposphere

**Trenberth** --

Surface temperature

Advantages: long record, independent analyses, coverage changes with
time

Trends robust

Radiosondes

Coverage marginal before 1964

Many changes in instrumentation, suspected biases

Few groups with instrumental analyses

Very spotty coverage, dozens of instruments

Satellites

Global coverage, since 1978

Satellite, orbit drift biases; 9+ different instruments

Advantage: Global, millions of observations

Disadvantages: Continuity

Glaciers

Tropical glaciers show melting, ablation during time of satellite record

Issues: inversions isolate troposphere

Chapter questions:

Need to simulate observed record within bounds of predictability

No reliable baseline with which to reference measurements

Radiosonde records can be improved using reanalysis feedback files

Key issues: Vertical structure of climate change in the atmosphere and
how well do models reproduce it?

Is trade inversion at the right level in models?

Is static stability in modles maintained correctly?

Forcings

It is not just GHG forcing expectations that should be compared with
observed

**Audience Questions**:

Anthes, NCAR: GPS measurements will be the best global thermometer,
could be compared with MSU; still short record

Revkin, New York Times: Wentz: No fundamental difference in methods;
need to exchange codes

Christy: Bias corrections are different between groups

Karl: In IPCC report, extensive intercomparison between surface records;
they are small. Still have to make major corrections

Bates, NCDC: Remote sensing is radiance data; comparisons should be in
radiances. Note that GPS does not measure temperature.

Need multiple checks and consistency in the system

Cayan, SIO: Snowmelt shows earlier springtime by several weeks over last
several decades; this is consistent with surface networks.

> Need to use unconventional measurements, e.g. biological measures
> (phenological). Western mountains could extend into troposphere

Singer: Cooling at Kilamajaro Trenberth: Thermometer shows warming at
base

Epstein, Harvard: Does lower troposphere heat faster than surface?
Trenberth: Not straightforward; dependent on trade wind inversion

Hardy, UMass -- High elevation measurements on Kilamangaro: large
diurnal cycle, trade wind inversion

Christy: Upper troposphere does show warming in tropics

Seidel, NOAA: Need for dedicated upper air network 60-70% reporting on
GUAN

Sundquist, USGS: If you are willing to accept calibration of proxy with
temperature, why do you reject the temperature record

Singer: Ice core data is published

Christy: Differences between

Ackerman, PNNL: Could deploy Raman lidar profiles at small number of
sites (10 sites globally)