Showing papers by "Mike Hulme published in 2001"

African climate change: 1900-2100

Abstract: This paper reviews observed (1900-2000) and possible future (2000-2100) continent- wide changes in temperature and rainfall for Africa. For the historic period we draw upon a new observed global climate data set which allows us to explore aspects of regional climate change related to diurnal temperature range and rainfall variability. The latter includes an investigation of regions where seasonal rainfall is sensitive to El Nino climate variability. This review of past climate change provides the context for our scenarios of future greenhouse gas-induced climate change in Africa. These scenarios draw upon the draft emissions scenarios prepared for the Intergovernmental Panel on Climate Change's Third Assessment Report, a suite of recent global climate model experi- ments, and a simple climate model to link these 2 sets of analyses. We present a range of 4 climate futures for Africa, focusing on changes in both continental and regional seasonal-mean temperature and rainfall. Estimates of associated changes in global CO2 concentration and global-mean sea-level change are also supplied. These scenarios draw upon some of the most recent climate modelling work. We also identify some fundamental limitations to knowledge with regard to future African cli- mate. These include the often poor representation of El Nino climate variability in global climate models, and the absence in these models of any representation of regional changes in land cover and dust and biomass aerosol loadings. These omitted processes may well have important consequences for future African climates, especially at regional scales. We conclude by discussing the value of the sort of climate change scenarios presented here and how best they should be used in national and regional vulnerability and adaptation assessments.

Regional Climate Information—Evaluation and Projections

Abstract: Contributing Authors R. Arritt, B. Bates, R. Benestad, G. Boer, A. Buishand, M. Castro, D. Chen, W. Cramer, R. Crane, J. F. Crossley, M. Dehn, K. Dethloff, J. Dippner, S. Emori, R. Francisco, J. Fyfe, F.W. Gerstengarbe, W. Gutowski, D. Gyalistras, I. Hanssen-Bauer, M. Hantel, D.C. Hassell, D. Heimann, C. Jack, J. Jacobeit, H. Kato, R. Katz, F. Kauker, T. Knutson, M. Lal, C. Landsea, R. Laprise, L.R. Leung, A.H. Lynch, W. May, J.L. McGregor, N.L. Miller, J. Murphy, J. Ribalaygua, A. Rinke, M. Rummukainen, F. Semazzi, K. Walsh, P. Werner, M. Widmann, R. Wilby, M. Wild, Y. Xue

Precipitation measurements and trends in the twentieth century

Abstract: Concern about anthropogenic climate change has heightened the need for accurate information about spatial and temporal variations in precipitation at the Earth’s surface. Large-scale precipitation estimates can be derived from either surface gauge measurements or by satellite remote sensing, both of which have shortcomings. Gauge measurements provide information about trends and variability of monthly precipitation throughout the entire twentieth century, but because of the lack of data from most ocean regions, this information is representative of only about 25–30% of the Earth’s surface. In contrast, satellite (especially multi-platform) measurements provide spatially complete coverage at monthly to subdaily resolution, but do not extend back beyond 1974. Merged gauge–satellite datasets maximize (and minimize) the relative benefits (and shortcomings) of each source type. While these merged products only extend back to 1979, their importance will grow as we move into the new century. Precipitation gauge data indicate that global land precipitation (excluding Antarctica) has increased by about 9 mm over the twentieth century (a trend of 0.89 mm/decade), which is relatively small compared with interannual and multi-decadal variability. Within this century-long trend, global precipitation exhibits considerable variability on decadal time-scales, with departures of up to 40 mm from the century mean of about 950 mm. Regionally, precipitation has increased over most land areas, with the exception of tropical North Africa, and parts of southern Africa, Amazonia and western South America. The dominant mode of interannual variability in global and

Climatic perspectives on Sahelian desiccation: 1973–1998

Abstract: The African Sahel provides the most dramatic example of multi-decadal climate variability that has been quantitatively and directly measured. Annual rainfall across this region fell by between 20 and 30 per cent between the decades leading up to political independence for the Sahelian nations (1930s to 1950s) and the decades since (1970s to 1990s). Climatic perspectives on the nature and causes of this period of desiccation have changed and, in some cases, matured as the years — and the drought — continued. This paper reviews these changing perspectives and reflects on three central questions: How unique an occurrence has been this desiccation in the recent human history of the Sahel? Can we find an adequate explanation for this desiccation in the natural forces that shape the climate system, or do we have to implicate human interventions in the system? Is our understanding of climate variability sufficient to allow us to develop seasonal rainfall forecasting capabilities for the region?

Climatic implications of revised IPCC emissions scenarios, the Kyoto Protocol and quantification of uncertainties

Abstract: In December 1997, the United Nations Framework Convention on Climate Change (FCCC) adopted the Kyoto Protocol. This paper describes a framework that models the climatic implications of this international agreement, using Monte Carlo simulations and the preliminary Intergovernmental Panel on Climate Change emissions scenarios (SRES). Emissions scenarios (including intervention scenarios), climate sensitivity, and terrestrial carbon sink are the key sampled model parameters. This framework gives prior probability distributions to these parameters and, using a simple climate model, posterior distributions of global temperature change are determined for the future.

An exploration of regional climate change scenarios for Scotland

Abstract: Based on a high resolution regional climate model (RCM) experiment, a climate change scenario for Scotland for the end of this century is constructed with the aim of exploring the added value of utilising a regional rather than a global model (GCM) for climate change scenario construction. Spatial variations in regional seasonal average temperature and precipitation change are analysed and the local response of ‘extreme’ weather events to climate warming is assessed using daily model output. The analyses suggest that in comparison with the GCM, the RCM does not provide fundamentally different patterns of seasonal climate change and daily weather response over Scotland, although it does capture more subtle spatial variations in these changes. The RCM also simulates more realistic daily weather events than the GCM, although the relative changes in the frequencies of daily extremes are not greatly different. However, with the limited length of the single model simulation analysed here, it is not eas...

The Effect of Increasing the Mean on the Percentage of Extreme Values in Gaussian and Skew Distributions. Response to X. Zhang et al.

Abstract: Changes in extremes are important indicators of climate change. Zhang et al. (2001) show that a change in the mean of a Gaussian distribution results in an increase in the total number of extremes. So if there is an increase in the total of extreme values, such as values more extreme than the 1st and 99th percentiles, then it does not necessarily follow that the standard deviation of the distribution has changed. We support Zhang et al.’s hypothesis for Gaussian distributions, but show, in addition, that a change in the mean of a skewed distribution can either increase or decrease the total number of extremes. For a Gaussian distribution the total percentage of values classed as extreme increases continuously as the mean is increased. This is because the Gaussian distribution is symmetrical about p = 50%. For any value of p, f( p)= f( 100 − p). On increasing the mean of the sample by q, the frequency of low values decreases by

Environment Group Research Programme Research Findings No.11 An Exploration of Regional Climate Change Scenarios for Scotland

Abstract: The University of East Anglia was contracted by the Scottish Executive to undertake research that would lead to elements of a regional climate change scenario for Scotland. This was to be consistent with the national UKCIP98 climate change scenarios, but utilising the latest results from experiments conducted with the Hadley Centre regional climate model (HadRM2). The main aim of this research was to explore the added value of using a regional rather than a global climate model for climate change scenario construction. The work focused on changes in mean seasonal climate and changes in the magnitude-frequency distribution of daily mean temperature, precipitation and wind speed.

Classics in physical geography revisited

Abstract: It is over a quarter of a century since Syukuro Manabe and Richard Wetherald published in the Journal of the Atmospheric Sciences their study of the effects of elevated CO2 concentrations on global climate calculated using, for the first time, a general circulation model (GCM). Over these 26 years, atmospheric CO2 concentration has increased by nearly 12% from about 331 ppmv to nearly 370 ppmv, the mean planetary surface air temperature has increased by about 0.3°C and global climate models have developed to such an extent that their demand for computing power now represents one of the biggest applications of the new generation of massively parallel supercomputers . . . and, of course, global warming has become one of the environmental icons of our time. Things were very different in 1975 when Manabe and Wetherald (henceforth MW) published the results of their pioneering experiment. Although anthropogenic CO2 emissions continued their twentieth-century rise, the planetary surface air temperature had been stable for 20 years or more – it was actually falling in the Northern Hemisphere, there was widespread public concern about global cooling (e.g., Calder, 1974), and state-of-the-art mainframe computers had less power than a 2001 laptop. Yet, looking back from the perspective of our artificially warmed Earth at the turn of the century, MW’s study represents a significant achievement and notable milestone in the scientific study of anthropogenic climate change. By the mid-1970s it was well established that atmospheric CO2 concentrations were rising. The Mauna Loa Observatory record in the north-central Pacific established by Charles Keeling had shown an increase in concentrations from 314 ppmv in 1957 to about 331 ppmv in 1975. The radiation physics of the greenhouse effect was also well established, as indeed it had been for many decades previously (see Fleming (1998) for an excellent account of its early scientific history). Arrhenius (1896), for example, had made an early calculation that doubling atmospheric CO2 concentration would lead to a global-mean surface air warming of about 3°C, while calculations made using onedimensional radiative-convective models in the 1960s and early 1970s had suggested that this so-called ‘climate sensitivity’ may be in the range 1.9°C to as much as 10°C. This wide range of published values reflected different modelling approaches and, in particular, different representations of the feedback processes associated with an enhanced greenhouse effect, most notably that of water vapour. In 1967, Manabe and Wetherald had themselves undertaken one such calculation that suggested a climate Progress in Physical Geography 25,3 (2001) pp. 385–387