Other stuff

Borehole thermometry

Drill a borehole (usually in the Earth, sometimes in ice): measure the temperatures down the hole; then invert this temperature record to get a history of surface temperature changes. Problem: the sfc changes can be only weakly determined by the measured values, which are subject to error.

Past Temperatures Directly from the Greenland Ice Sheet; D. Dahl-Jensen, K. Mosegaard, N. Gundestrup, G. D. Clow, S. J. Johnsen, A. W. Hansen, N. Balling; Science Volume 282, Number 5387 Issue of 9 Oct 1998, pp. 268 - 271

Abstract: "A Monte Carlo inverse method has been used on the temperature profiles measured down through the Greenland Ice Core Project (GRIP) borehole, at the summit of the Greenland Ice Sheet, and the Dye 3 borehole 865 kilometers farther south. The result is a 50,000-year-long temperature history at GRIP and a 7000-year history at Dye 3. The Last Glacial Maximum, the Climatic Optimum, the Medieval Warmth, the Little Ice Age, and a warm period at 1930 A.D. are resolved from the GRIP reconstruction with the amplitudes -23 kelvin, +2.5 kelvin, +1 kelvin, -1 kelvin, and +0.5 kelvin, respectively. The Dye 3 temperature is similar to the GRIP history but has an amplitude 1.5 times larger, indicating higher climatic variability there. The calculated terrestrial heat flow density from the GRIP inversion is 51.3 milliwatts per square meter."

Note: the amplitudes that they mention here are *local*: hence the difference between GRIP and Dye-3. The amplitudes in mid-latitudes would be expected to be smaller.

Climate Change Record in Subsurface Temperatures: A Global Perspective; Henry N. Pollack, Shaopeng Huang, Po-Yu Shen; Science Volume 282, Number 5387 Issue of 9 Oct 1998, pp. 279 - 281

Abstract: "Analyses of underground temperature measurements from 358 boreholes in eastern North America, central Europe, southern Africa, and Australia indicate that, in the 20th century, the average surface temperature of Earth has increased by about 0.5°C and that the 20th century has been the warmest of the past five centuries. The subsurface temperatures also indicate that Earth's mean surface temperature has increased by about 1.0°C over the past five centuries. The geothermal data offer an independent confirmation of the unusual character of 20th-century climate that has emerged from recent multiproxy studies."

Ice cores

Synchronous Climate Changes in Antarctica and the North Atlantic; E. J. Steig, * E. J. Brook, J. W. C. White, C. M. Sucher, M. L. Bender, S. J. Lehman, D. L. Morse, E. D. Waddington, G. D. Clow; Science 1998 October 2; 282: 92-95

Abstract: "Central Greenland ice cores provide evidence of abrupt changes in climate over the past 100,000 years. Many of these changes have also been identified in sedimentary and geochemical signatures in deep-sea sediment cores from the North Atlantic, confirming the link between millennial-scale climate variability and ocean thermohaline circulation. It is shown here that two of the most prominent North Atlantic events--the rapid warming that marks the end of the last glacial period and the Bølling/Allerød-Younger Dryas oscillation--are also recorded in an ice core from Taylor Dome, in the western Ross Sea sector of Antarctica. This result contrasts with evidence from ice cores in other regions of Antarctica, which show an asynchronous response between the Northern and Southern Hemispheres."

Some publications from the Taylor dome project.

GCM analysis of local infuences on ice core delta signals

Ice core delta-O18 and thermometry suggest different temperature histories. One way to resolve this is to use GCMs to investigate changes in the meteorology. GCM analysis of local infuences on ice core delta signals by Gerhard Krinner, Christophe Genthon and Jean Jouzel do this in GEOPHYSICAL RESEARCH LETTERS, VOL. 24, NO. 22, PAGES 2825-2828, NOVEMBER 15, 1997.

Jouzel J, Alley RB, Cuffey KM, Dansgaard W, Grootes P, Hoffmann G, Johnsen SJ, Koster RD, Peel D, Shuman CA, Stievenard M, Stuiver M, White J (1997) Validity Of The Temperature Reconstruction From Water Isotopes In Ice Cores. JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS, v102, #C12, 26471-26487

Abstract: "Well-documented present-day distributions of stable water isotopes (HDO and (H2O)-O-18) show the existence, in middle and high latitudes, of a linear relationship between the mean annual isotope content of precipitation (delta D and delta(18)O) and the mean annual temperature at the precipitation site. Paleoclimatologists have used this relationship, which is particularly well obeyed over Greenland and Antarctica, to infer paleotemperatures from ice core data. There is, however, growing evidence that spatial and temporal isotope/ surface temperature slopes differ, thus complicating the use of stable water isotopes as paleothermometers. In this paper we review empirical estimates of temporal slopes in polar regions and relevant information that can be inferred from isotope models: simple, Rayleigh-type distillation models and (particularly over Greenland) general circulation models (GCMs) fitted with isotope tracer diagnostics. Empirical estimates of temporal slopes appear consistently lower than present-day spatial slopes and are dependent on the timescale considered. This difference is most probably due to changes in the evaporative origins of moisture, changes in the seasonality of the precipitation, changes in the strength of the inversion layer, or some combination of these changes. Isotope models have not yet been used to evaluate the relative influences of these different factors. The apparent disagreement in the temporal and spatial slopes clearly makes calibrating the isotope paleothermometer difficult. Nevertheless, the use of a (calibrated) isotope paleothermometer appears justified; empirical estimates and most (though not all) GCM results support the practice of interpreting ice core isotope records in terms of local temperature changes."

CO2 variations

PALEOZOIC ATMOSPHERIC CO2 - IMPORTANCE OF SOLAR-RADIATION AND PLANT EVOLUTION; BERNER_RA; SCIENCE, 1993, Vol.261, No.5117, pp.68-70

Abstract: "Changes in solar radiation, as it affects the rate of weathering of silicates on the continents, and other changes involving weathering and the degassing of carbon dioxide (CO2) have been included in a long-term carbon-cycle model. These additions to the model show that the major controls on CO2 concentrations during the Paleozoic era were solar and biological, and not tectonic, in origin. The model predictions agree with independent estimates of a large mid-Paleozoic (400 to 320 million years ago) drop in CO2 concentrations, which led to large-scale glaciation. This agreement indicates that variations in the atmospheric greenhouse effect were important in global climate change during the distant geologic past."

A geochemical model to reconstruct CO2 variations of the past 570 Myr (Phanerozoic). In order to reconstruct weathering, etc, assumes

	T(t) - T(0) = G*ln(RCO2(t)) - W*t/570

where T is temperature, t is time (going backwards), G==6 oC (empirical) and W==12.9 oC (empirical). Note that that mdoel predicts that T increases by 6*ln(2) ~ 4 oC if CO2 is doubled in present conditions. The "W" factor includes the effect of the early cool sun.

The model predicts (from remembering the figure) that CO2 was up to 14 times present levels about 500 M yr ago; within 2 times current levels for the last 70-odd M yr.

MSU stuff

Prabhakara C, Iacovazzi R, Yoo JM, Dalu G (1998) Global Warming Deduced From Msu. GEOPHYSICAL RESEARCH LETTERS, v25, #11, 1927-1930

Microwave Sounding Unit (MSU) radiometer observations in Channel 2 (53.74 GHz) made from sequential, sun-synchronous, polar-orbiting NOAA operational satellites have been used to derive global temperature trend for the period 1980 to 1996. Christy et al. (1998) emphasize that they find a tropospheric cooling trend (-0.046 K decade(-1)) from 1979 to 1997 with these MSU data, although their analysis of near nadir measurements yields a near zero trend (0.003 K decade(-1)). Using an independent method to analyze the MSU Ch 2 nadir data separately over global ocean and land, we infer that the temperature trends over both these regions are about 0.11 K decade(- 1), during the period 1980 to 1996. This result is in better agreement with trend analyses based on conventional surface data.

Wentz FJ, Schabel M (1998) Effects of orbital decay on satellite-derived lower-tropospheric temperature trends, Nature v394 #6694 p661-664

The 17-year lower-tropospheric temperature record derived from the satellite Microwave Sounding Unit (MSU)(1-3) shows a global cooling trend, from 1979 to 1995, of -0.05 K per decade at an altitude of about 3.5 km (refs 4, 5). Air temperatures measured at the Earth's surface, in contrast, have risen by approximately 0.13 K per decade over the same period(4,6). The two temperature records are derived from measurements of different physical parameters, and thus are not directly comparable. In fact, the lower stratosphere is cooling substantially (by about -0.5 K per decade)(5), so the warming trend seen at the surface is expected to diminish with altitude and change into a cooling trend at some point in the troposphere. Even so, it has been suggested that the cooling trend seen in the satellite data is excessive(4,7,8). The difficulty in reconciling the information from these different sources has sparked a debate in the climate community about possible instrumental problems and the existence of global warming(4,7,9). Here we identify an artificial cooling trend in the satellite-derived temperature series caused by previously neglected orbital-decay effects. We find a new, corrected estimate of 0.07 K per decade for the MSU-based temperature trend, which is in closer agreement with surface temperatures. We also find that the reported(7) cooling of the lower troposphere, relative to the middle troposphere, is another artefact caused by uncorrected orbital-decay effects.