# [Climate Change Science Planning (CCSP) Workshop. Dec 3-5, 2002]{.underline}

## [A close look at temperature trends from surface stations and proxy data]{.underline}

Presentation by S. Fred Singer, panelist in Group 15 (\"Resolution in
Disparities in Temperature Records\") on Dec 4.

**A. Key question:**

**Is the climate currently warming**? The data are conflicting; some say
Yes, others say No. Settling this issue should have the **highest
priority** for the Climate Change Science Program. It could decide
whether current climate models can be relied on to project future
climate changes.

This is not an idle question. The National Academy/National Research
Council had set up a panel to try reconciling the disparities between
**surface** data from weather stations that show a global warming trend
since 1979 and data from **satellites** (MSU) and **radiosondes** (on
weather balloons) that show little if any warming of the troposphere.
The NAS/NRC report, issued on Jan. 2000, has not settled the matter
**\[1\]**.

I note that all of the three current observing systems were designed for
operational purposes; it is due to the skill and ingenuity of the
investigators that such data could be used to extract the long-term
temperature trends needed to study climate changes.

Others have scrutinized the satellite and balloon data. Let me discuss
here problems with the surface data that a well-designed
climate-research program must address.

### B. Surface Land Stations

1\. There is little dispute about the pre-1979 record **\[2,3\]**. The
surface data show a strong warming, with a peak around 1940, followed by
cooling till about 1975 At that time, there is a sudden jump to about
the 1940 value. The most widely accepted explanation is that natural
climate variability dominates over enhanced greenhouse effects; these
are likely much smaller than model calculations would suggest. Few would
assign a major human influence to the pre-1940 warming (like, e.g.,
Wigley et al **\[4\]**)

2\. There are distinct disparities arising from different schemes of
analysis of the sfc data from weather stations. The difference between
the GHCN (NCDC-NOAA) and Jones (Univ of East Anglia) has been as large
as 0.3C in recent years.

3\. As published by Hansen, Karl et al **\[5\]**, the various
corrections to the raw data for the Continental US add up to \~ 0.3C
since 1960. They include adjustments for urban effects.

4\. After correction, the US record shows no warming since 1940, in
contrast to the "global record" which shows a trend of \~ 0.15C per
decade since 1979 **\[6\]**. One should not assume automatically that
the global record is contaminated and would also show a 1940 peak if
corrected. But the global record has not been subjected to the same
careful scrutiny as the US record.

5\. Various difficulties with global weather station records have been
detailed by Gray and Daly **\[7,8\].** In the Arctic, the decade of
1930-40 appears to have been warmest, and warmer than the most recent
decade **\[9\];** but there is still substantial disagreement between
reported trends there and also with the results of climate models.

6\. Loss of weather stations: The Global Historical Climate Network
(GHCN) showed a peak of some 15,000 stations around 1970. The number now
is down to 5000 and still dropping, as stations not essential for
operational purposes are being closed down. The loss is primarily of
rural stations, with airport stations maintained or expanded for obvious
reasons. But airports are warming as they expand to meet increasing air
traffic and as urban areas reach and enclose airports. This gives rise
to local warming trends that are not easily removed from the global sfc
record.

### C. Sea Surface temperatures

1\. Sea surface temperatures (SST) are of special importance since the
oceans cover more than 70% of the globe, but measurements have been
mostly along shipping routes. Furthermore, methods for measuring SST
have changed drastically over time and this could have affected the
reported temperatures and trends: i) Wooden buckets, followed by canvas
buckets; ii) engine cooling water with temperatures measured at the
inlet (whose depth has varied with ship size); iii) fixed and drifting
buoys; iv) IR and microwave emission from the surface as measured by
satellites; v) air temperatures as measured at island stations; vi)
night-time marine air temperatures (NMAT) measured aboard ships.

2\. The reported NMAT -- SST discrepancy in trends **\[10\]** is still
unexplained

3\. Drifting buoys fill in much of the hitherto uncovered ocean areas.
Unfortunately, such buoys cannot be calibrated once released.
Intercomparison between drifting buoys shows deviations (i.e.,
uncertainties) that are of the order of the reported warming **\[11\]**.

# **D. Recent Temperatures from Proxy Data**

Proxy (non-instrumental) data have advantages and disadvantages. They
provide additional evidence to confirm or deny instrumented surface data
and they are the only means we have to get paleo-temperatures. They all
require calibration and have peculiarities that limit their use.
Tree-ring data are limited to land areas, while ocean sediments, corals,
ice cores have other limitations.

1\. The IPCC-TAR report of 2001 used the multi-proxy record by Mann et
al to trace NH temperatures of the past 1000 years **\[2\]**. This
record agrees well with the instrumental record from 1850 to 1980; it
was also calibrated over that range. Unfortunately, the Mann record does
not extend beyond 1980 and therefore does not shed light on the
disparity since 1979; it backs neither sfc nor satellite temperatures.

2\. Other proxy records based mainly on tree ring data disagree with
Mann (and IPCC) in the centuries before 1850 **\[12\]**. They all
support the instrumental record, but only up to 1980; those that extend
beyond 1980 show no subsequent warming and thus disagree with the GHCN
global record: These include tree-ring data **\[13\]** as well as
ice-core data from Greenland **\[14\]** and the tropics **\[15\]**.
\[Since the increased levels of CO~2~ in the last decades can only
stimulate the growth of tree rings, the published data showing no
temperature rise may actually hide a drop in temperature.\]

3\. [To sum up]{.underline}: We have been examining some dozen published
proxy records that show temperatures beyond 1980. So far none show a
warming since 1980.

4\. Contrary evidence is often cited: shrinking of mountain glaciers and
of Arctic sea ice; warming of the deep ocean; rise in sea level during
the 20^th^ century. All of these observations can be accounted for in
terms of the delayed effects of a previous natural warming and thus not
necessarily due to any human influence **\[16\]**.

**E. Recommendations for research:**

**1. Surface records:**

The careful corrections applied to the US record should be extended to
the global record.

**2. SST records:**

The trends of SST should be determined separately from each of the
different data sources BEFORE they are combined \-\-- in an effort to
determine whether the recent (post -1980) reported warming is genuine.

**3. Proxy records:**

Extend current work to other proxy records: corals. lake sediments etc

## F. References

1\. NRC 2000 National Research Council. \"*Reconciling Observations of
Global Temperature Change.\"* National Academy Press. Washington, DC.
January 2000; see also G.C. Hegerl and J.M. Wallace. *J Climate*,
**15**, 2412-2428, 2002

2\. IPCC 2001 Houghton, J.T., Ding, Y., Griggs, D.J., Noguer, M., van
der Linden, P.J., Xiaosu, D., Maskell, K. and Johnson, C.A. (Eds.). 
2001.  *Climate Change 2001: The Scientific Basis*.  Cambridge
University Press, Cambridge, UK.

3\. S.F. Singer 1999. Hot Talk Cold Science: Global Warming's Unfinished
Debate (Independent Institute, Oakland, CA)

4\. T.M.L. Wigley, Smith, R. L., and Santer, B. D. Anthropogenic
influence on the auto-correlation structure of hemispheric-mean
temperatures. *Science* **282**, 1676-1679, 1998.

5\. J. Hansen, T.R. Karl et al. *JGR* **106**, 23947-23963, Oct 27, 2001

6\. NCDC web site; see also figure in ref 5

7\. V. Gray, on \< www.john-daly.com\>

8\. J. Daly on \< www.john-daly.com\>

9\. I. Polyakov et al. Trends and Variations in Arctic Climate Systems.
*EOS, Transactions, American Geophysical Union*, **83**, 547-548, Nov
19, 2002.

10\. J. Christy et al. *GRL* **28**,183-186,2001; C.K. Folland and T.R.
Karl. *Eos* **82**, 453-459, Oct 2, 2001.

11\. W.J. Emery et al. *JGR* **106**, 2387-2405, Feb 15, 2001

12\. Esper, J., Cook, E.R. and Schweingruber, F.H.  2002.  Low-frequency
signals in long tree-ring chronologies for reconstructing past
temperature variability.  *Science* **295**: 2250-2253.

13\. G.C. Jacoby et al. *Science* **273**, 771-773, 1996

14\. D. Dahl-Jensen et al. *Science* **254**, 698-700, 1999.

15\. L.C. Thompson et al. *Science* **289**, 1916, 2000

16\. S.F. Singer (to be published)