Showing papers by "Ian Harris published in 2006"

Uncertainty estimates in regional and global observed temperature changes: A new data set from 1850

Abstract: [1] The historical surface temperature data set HadCRUT provides a record of surface temperature trends and variability since 1850. A new version of this data set, HadCRUT3, has been produced, benefiting from recent improvements to the sea surface temperature data set which forms its marine component, and from improvements to the station records which provide the land data. A comprehensive set of uncertainty estimates has been derived to accompany the data: Estimates of measurement and sampling error, temperature bias effects, and the effect of limited observational coverage on large-scale averages have all been made. Since the mid twentieth century the uncertainties in global and hemispheric mean temperatures are small, and the temperature increase greatly exceeds its uncertainty. In earlier periods the uncertainties are larger, but the temperature increase over the twentieth century is still significantly larger than its uncertainty.

A framework for assessing uncertainties in climate change impacts: Low-flow scenarios for the River Thames, UK

Abstract: A probabilistic framework is presented for combining information from an ensemble of four general circulation models (GCMs), two greenhouse gas emission scenarios, two statistical downscaling techniques, two hydrological model structures, and two sets of hydrological model parameters. GCMs were weighted according to an index of reliability for downscaled effective rainfall, a key determinant of low flows in the River Thames. Hydrological model structures were weighted by performance at reproducing annual low-flow series. Weights were also assigned to sets of water resource model (CATCHMOD) parameters using the Nash-Sutcliffe efficiency criterion. Emission scenarios and downscaling methods were unweighted. A Monte Carlo approach was then used to explore components of uncertainty affecting projections for the River Thames by the 2080s. The resulting cumulative distribution functions (CDFs) of low flows were most sensitive to uncertainty in the climate change scenarios and downscaling of different GCMs. Uncertainties due to the hydrological model parameters and emission scenario increase with time but were less important. Abrupt changes in low-flow CDFs were attributed to uncertainties in statistically downscaled summer rainfall. This was linked to different behavior of atmospheric moisture among the chosen GCMs.

First cross-matched floating chronology from the marine fossil record: data from growth lines of the long-lived bivalve mollusc Arctica islandica

Abstract: Integrated understanding of phasings within the climate system over the last glacial cycle, and at higher frequencies, is inhibited because no absolute timescale for the marine environment currently exists. This precludes identification of forcings and feedbacks, accurate temporal calibration of the marine radiocarbon reservoir effect, and the application of radiocarbon as a proxy of short-timescale ocean ventilation. This has prompted a search for annually banded marine proxies in the hope of establishing an accurate marine chronometer. We present annual growth band series from dead-collected specimens of the long-lived bivalve mollusc Arctica islandica from the northern North Sea and demonstrate their successful cross-matching, with the general timescale context independently verified by radiocarbon dating. Though at present limited to only a few statistically cross-matched series, this has already generated the longest Arctica chronology, and the first 'floating' chronology constructed entirely from marine fossils. The record covers the period from c. AD 1000 to 1400 and integrates a 267-yr series from the longest-lived Arctica specimen yet recorded from the North Sea. This breakthrough in cross-matching demonstrates that Arctica islandica can fulfill its potential as the 'tree of the sea' to provide an absolute timescale for the marine environment.

Climate change and coastal hydrographic response along the Atlantic Iberian margin (Tagus Prodelta and Muros Ría) during the last two millennia

Abstract: The Tagus Prodelta (W Portugal) and the Muros Ro´a (NW Spain) are areas of high deposition rates registering high-resolution palaeoclimatic records for western Iberia. We compare the climatic conditions of the two areas over the last two millennia based on proxies of temperature (sea surface temperatures and oxygen isotopes), continental input (grain size, iron and magnetic susceptibility) and productivity (inorganic and organic carbon, carbon isotopes, benthic foraminifera and diatoms). Biogeochemical changes in the Tagus Prodelta reflect widely recognized North Atlantic climatic periods encompassing the Roman Period (AD 0 � 350), the Dark Ages (AD 400 � 700), the 'Mediaeval Warm Period' (MWP; AD 800 � 1200) and the 'Little Ice Age' (LIA; AD 1300 � 1750). The atmospheric North Atlantic Oscillation (NAO) drives the Tagus Prodelta multidecadal, long-term variability in precipitation-river input during cold periods (negative NAO) and marine upwelling during warmer periods (positive NAO), a scheme that is reversed in the Galician region. The Muros Ro ´a shows only local hydrodynamics until AD 1150, including a 'suboxic' event in the inner Ro ´a around AD 500 � 700. Since AD 1150 Atlantic warm upwelled waters have ventilated the outer Ro´a but only reach the inner Ro´a at AD 1750. The twentieth- century records are also interpreted as a reflex of the inverse NAO mode in both areas, resulting in amplification of the LIA biogeochemical water conditions. Centennial-scale solar activity appears to be another important forcing mechanism (or the only one, if solar activity drives the NAO and 'Bond-cycles') behind changes in the hydrography of the Tagus Prodelta, and primary production, bottom ventilation and organic carbon degradation in the Muros Ro ´a.

The effect of long-term trends in dampness on historic buildings

Abstract: Architects from Sir Christopher Wren onwards have worried about the impact of time, smoke and weather on their buildings. Over the last century climate has often seemed less important than air pollution as a determinant of damage. The reduction in acidic air pollutants in urban areas in recent years has meant that frost, rain or wind can become more dominant as weathering processes than in the recent past. Although the predicted changes in temperature or precipitation seem small they can be amplified in some mechanisms of damage. Britain has a damp climate. This has been a lament since Roman times, when Tacitus was able to write that the British Isles were cloudy with frequent rains, but never bitterly cold. Such meteorological characteristics have important implications for the interaction of our buildings with their environment. While being damp, the climate is more temperate than in the continental Europe, so frost damage or the weight of snow on roofs has never been quite as important as, for example, in the European interior. Frequently, floods (Lanza 2003) and changes in the water table (Sauer 2005) damage heritage and archaeological sites such as Blickling Hall in Norfolk (see Fig. 1), but this paper concentrates on the dampness in terms of water vapour and rainfall rather than flooding. It considers the impact of changes in dampness that is likely to have an effect on buildings and the way the fabric may be sensitive to damage. In particular, we concentrate on how humid conditions can promote the decay of wood and mobilisation of salts, in addition to the role that wet surfaces play in enhancing the deposition of pollutants. Dry conditions can also affect building fabric through excessive moisture loss from unfired building materials, or more structural problems that can arise when soils dry out.