|Results To Date:
This report summarises progress so far in the second year (of three) in the two sections of the project, according to the section layout of the proposal.
A. CLIMATE DATA AND ANALYSIS
The last complete year (2005) was the second warmest year on record, with a preliminary value of 0.50 degC above the 1961 90 base period. Ten of the last eleven years (1995-2005) in the series are now the warmest in the series (HadCRUT2v). Only 1996 is not in the list of top eleven warmest years, replaced by 1990. Data from HadCRUT2v are available on the CRU web site.
A new version of the basic dataset (HadCRUT3v) has been developed (Brohan et al., 2006) and now extends back a further six years to 1850. This dataset includes a comprehensive set of uncertainty estimates to accompany the data: estimates of measurement and sampling error, temperature bias effects, and the effect of limited observational coverage on large-scale averages. Since the mid-20th century, uncertainties in global and hemispheric average temperatures are small and the temperature increase greatly exceeds the uncertainties. For earlier periods, the uncertainties are larger, but the rise is still significantly larger. All the historic gridded data for this new version will be put onto the CRU web site, beginning with the January 2006 value. Data from HadCRUT2v will stop being updated when the December 2005 value is ready, but the page will be kept live for at least a year.
Higher resolution (0.5 by 0.5 degree latitude/longitude grid boxes) datasets for temperature and other variables (precipitation, rainday counts, diurnal temperature range, cloudiness, vapour pressure) developed a few years ago by New et al. (2000) have been extended and updated by Mitchell and Jones (2005). This dataset development has significantly benefited from Dept. of Energy support over the last 20 years and uses the improved temperature database (Jones and Moberg, 2003) and other CRU databases. These high-resolution datasets are also available from the CRU web site. During 2006, this dataset will be updated from 2002 to 2005 and be further updated in near-real time.
Analyses of temperature data
The Third Assessment Report of the IPCC noted that there were differences between the three major analyses of surface temperature (those discussed here, HadCRUT2v and those produced by GHCN and GISS). To determine whether these were due to differing station input or gridding techniques, an intercomparsion was performed (Vose et al., 2005). For the land regions, the CRU data were used with the GHCN method of spatial averaging. The results showed that for trends at the hemispheric scale the effect of the different gridding methods is negligible. Most of the differences relate to the definition of the global average. CRU has always assumed this to be the average of the two hemispheres, whereas GHCN use the weighted average of all available areas. As most of the missing regions are in the SH, this slightly biases the global average to the NH. Monthly-scale variability is similar between the CRU and GHCN datasets, but is reduced for GISS, due to their gridding technique of 80 equal-area boxes, rather than using 5 by 5 degree latitude-longitude grid boxes.
Other temperature analyses
Two papers have extended instrumental records. The first extended the temperature record for southwest Greenland (Vinther et al., 2006) back to 1784, a considerable extension before 1873, when records were previously thought to have begun. The record is particularly important during the winter season, as it provides almost a 100 more years for calibration of oxygen isotope measures in several southern Greenland ice cores. The second extends Japanese temperature and pressure records back before the official start of records in the country in the late-1870s. Fragmentary records now exist for three sites (Nagasaki, Tokyo and Osaka) back to the 1820s, potentially enabling a direct calibration with Japanese diary information, which is available from the early 1600s to about 1860.
We have also been involved in an extensive reassessment of the global upper-air temperature record (called HadAT2) from 1958-2002 (Thorne et al., 2005). This paper has been extensively used in the upcoming CCSP report on vertical temperature trends.
Finally, in this section, we have revisited the reasons for the changing correlations between the winter NAO and average NH temperatures north of 20 degrees N over the period 1870 to 2003. This work is currently being written up for a paper (Haylock and Jones, 2006). The changes are not due to poorer data quality in earlier years. Instead, the relationships are stronger early and late in the record, but weaker during the period from 1910-1960. Our working hypothesis for the changes is that the North Pacific region has marked changes in variability, while they are remarkably constant in the North Atlantic. The influence of the NAO on temperature weakens when the North Pacific becomes more variable.
B. GCM EVALUATION
B1. Low-frequency climate variability
The millennial temperature record has also been addressed by Rutherford et al. (2005), where comparisons have been made using almost totally independent networks of proxy climatic data. Results clearly show a similar course of change over the millennium and unprecedented warmth in the late-20th century, in accord with our earlier extensive review (Jones and Mann, 2004). Several new studies have addressed the topical issue of temperature change over the millennium since our review paper appeared, but although they often highlight different aspects of the course of change, none dispute that post-1975 warmth is unprecedented in a millennial context.
B2. High-frequency climatic variability
Work in this area is reassessing earlier analyses with monthly-mean pressure data over the Southern Hemisphere undertaken under DoE support over 15 years ago (Jones and Wigley, 1988 and Jones, 1991). All the necessary station sea-level pressure data have been assembled and the same regression equations re-used to develop gridded series for the period from the mid-1980s to the end of 2004. In the nest few weeks, these grids will be compared with sea-level pressure data from the ERA-40 Reanalyses.
Sixteen AOGCMs were used, together with an upwelling-diffusion energy balance model (UDEBM) to assess the effect of climate sensitivity on the response to volcanic forcing. The maximum cooling for any given eruption was shown to depend approximately on the climate sensitivity raised to the power 0.37. After the maximum cooling for low-latitude eruptions, the temperature relaxes back towards the initial state with an e-folding time of 29-43 months. The cooling associated with Pinatubo appears to require a climate sensitivity above the IPCC lower bound of 1.5 degrees C, but sensitivities above the upper range cannot be ruled out. In short, volcanic-induced cooling cannot reduce the potential range of climate sensitivity.
Brohan, P., Kennedy, J., Harris, I., Tett, S.F.B. and Jones, P.D., 2006: Uncertainty estimates in regional and global observed temperature changes: a new dataset from 1850. J. Geophys. Res. (in press).
Haylock, M.R. and Jones, P.D., 2006: Interdecadal changes in the 1870-2003 Northern Hemisphere winter sea level pressure variability and relationships with temperature. J. Geophys. Res. (to be submitted).
Jones, P.D., 1991: Southern Hemisphere sea level pressure data: an analysis and reconstructions back to 1951 and 1911. International Journal of Climatology 11, 585-607.
Jones, P.D. and Mann, M.E., 2004: Climate over past millennia. Reviews of Geophysics, 42, doi:10.1029/2003RG000143.
Jones, P.D. and Moberg, A., 2003: Hemispheric and large-scale surface air temperature variations: An extensive revision and update to 2001. J. Climate 16, 206-223.
Jones, P.D. and Wigley, T.M.L., 1988: Antarctic gridded sea level pressure data: An analysis and reconstruction back to 1957. Journal of Climate 1, 1199-1220.
Mitchell, T.D. and Jones, P.D., 2005: An improved method of constructing a database of monthly climate observations and associated high-resolution grids. Int. J. Climatol. 25, 693-712.
New, M., Hulme, M. and Jones, P.D., 2000: Representing twentieth century space-time climate variability, II: Development of 1901-96 monthly grids of terrestrial surface climate. J. Climate 13, 2217-2238.
Rutherford, S., Mann, M.E., Osborn, T.J., Bradley, R.S., Briffa. K.R., Hughes, M.K. and Jones, P.D., 2005: Proxy-based Northern Hemisphere surface temperature reconstructions: Sensitivity to methodology, predictor network, target season and target domain, J. Climate 18, 2308-2329.
Thorne, P.W., Parker, D.E., Tett, S.F.B., Jones, P.D., McCarthy, M., Coleman, H. and Brohan, P., 2005: Revisiting radiosonde upper air temperatures from 1958-2002. J. Geophys. Res. 110, D18105, doi:10.1029/2004/JD005753.
Vinther, B. M., Andersen, K.K., Jones, P.D., Briffa, K.R. and Cappelen, J., 2006: Extending Greenland temperature records into the late 18th Century. J. Geophys. Res. (accepted).
Vose, R.S., Wuertz, D., Peterson, T.C. and Jones, P.D., 2005: An intercomparison of trends in surface air temperature analyses at the global, hemispheric and grid-box scale. Geophys. Res. Letts. 32, L18718, doi:10.1029/200GL023502.
Wigley, T.M.L., Ammann, C.M., Santer, B.D. and Raper, S.C.B., 2005: The effect of climate sensitivity on the response to volcanic forcing. J. Geophys. Res. 110, D09107, doi:10.1029/2004JD005557.
Zaiki, M., Konnen, G.P., Tsukahara, T., Jones, P.D., Mikami, T. and Matsumoto, K., 2005: Recovery of 19th century Tokyo/Osaka meteorological data in Japan. Int. J. Climatol. 25 (in press).
All the above acknowledge support from the current grant, with the exception of those before 2004, which acknowledge earlier Department of Energy support.