Using the past to constrain the future: how the palaeorecord can improve estimates of global warming

Climate sensitivity is defined as the change in global mean equilibrium temperature after a doubling of atmospheric CO2 concentration and provides a simple measure of global warming. An early estimate of climate sensitivity, 1.5-4.5{\deg}C, has changed little subsequently, including the latest assessment by the Intergovernmental Panel on Climate Change. The persistence of such large uncertainties in this simple measure casts doubt on our understanding of the mechanisms of climate change and our ability to predict the response of the climate system to future perturbations. This has motivated continued attempts to constrain the range with climate data, alone or in conjunction with models. The majority of studies use data from the instrumental period (post-1850) but recent work has made use of information about the large climate changes experienced in the geological past. In this review, we first outline approaches that estimate climate sensitivity using instrumental climate observations and then summarise attempts to use the record of climate change on geological timescales. We examine the limitations of these studies and suggest ways in which the power of the palaeoclimate record could be better used to reduce uncertainties in our predictions of climate sensitivity.Comment: The final, definitive version of this paper has been published in Progress in Physical Geography, 31(5), 2007 by SAGE Publications Ltd, All rights reserved. \c{opyright} 2007 Edwards, Crucifix and Harriso

Review article: MHD wave propagation near coronal null points of magnetic fields

We present a comprehensive review of MHD wave behaviour in the neighbourhood of coronal null points: locations where the magnetic field, and hence the local Alfven speed, is zero. The behaviour of all three MHD wave modes, i.e. the Alfven wave and the fast and slow magnetoacoustic waves, has been investigated in the neighbourhood of 2D, 2.5D and (to a certain extent) 3D magnetic null points, for a variety of assumptions, configurations and geometries. In general, it is found that the fast magnetoacoustic wave behaviour is dictated by the Alfven-speed profile. In a $\beta=0$ plasma, the fast wave is focused towards the null point by a refraction effect and all the wave energy, and thus current density, accumulates close to the null point. Thus, null points will be locations for preferential heating by fast waves. Independently, the Alfven wave is found to propagate along magnetic fieldlines and is confined to the fieldlines it is generated on. As the wave approaches the null point, it spreads out due to the diverging fieldlines. Eventually, the Alfven wave accumulates along the separatrices (in 2D) or along the spine or fan-plane (in 3D). Hence, Alfven wave energy will be preferentially dissipated at these locations. It is clear that the magnetic field plays a fundamental role in the propagation and properties of MHD waves in the neighbourhood of coronal null points. This topic is a fundamental plasma process and results so far have also lead to critical insights into reconnection, mode-coupling, quasi-periodic pulsations and phase-mixing.Comment: 34 pages, 5 figures, invited review in Space Science Reviews => Note this is a 2011 paper, not a 2010 pape

Solute accumulation and osmotic adjustment in leaves of Brassica oilseeds in response to soil water deficit

To establish methods for improving drought tolerance in Brassica oilseeds, we examined the influence of soil water deficit on solute accumulation in expanded and expanding leaves. We assessed the contribution of individual solutes to osmotic adjustment (OA) and determined the effect of homozygosity on the variation of the expression of OA. Juvenile plants of canola (Brassica napus cvv. Karoo and Monty) and Indian mustard (B. juncea line PI-81792) were grown under glasshouse conditions. The 3 genotypes expressed similar magnitudes of OA in response to drought, compared with a 2-fold higher OA in expanding leaves than in fully expanded leaves. Drought-induced changes in OA of expanded leaves of all genotypes were largely due to the accumulation of nitrate (42-47%), soluble sugars (31-38%), and proline (11-14%). In expanding leaves, K + accumulation was significant (23-27%) as was proline (17-22%), whereas nitrate and soluble sugars were less important than in expanded leaves. By comparison, ions of Na+, Cl-, and water-soluble Mg 2+ and Ca2+ did not contribute significantly to OA. Proline was hardly detected in well watered plants, but sharply increased in leaves of droughted plants in direct proportion to the magnitude of OA (80 ± 7 mmol/MPa, r2 = 0.94). A comparison between doubled haploid (DH) and commercial seed sources of 2 B. napus cultivars showed similar mean values in OA. The DH lines had a 33% lower coefficient of variation in OA than cv. Karoo and 48% lower than cv. Monty among replicate plants. Proline may be a suitable 'marker' for OA in juvenile Brassica plants because of all the solutes measured, its concentration was directly proportional to the magnitude of OA across cultivars and leaf types. The use of DH lines will improve the precision in selection of genotypes that have the capacity to osmotically adjust under soil water deficit

Osmotic adjustment in leaves of Brassica oilseeds in response to water deficit

The influence of water deficit on water content (WC), total soluble solids (TSS), osmotic potential (OP), sugar content and osmotic adjustment (OA) of expanded and partly expanded leaves of Brassica oilseeds was examined. Nine canola (B. napus) cultivars (Karoo, Monty, Pinnacle, Hyden, Mystic, Rainbow, Surpass 300, Surpass 400, Surpass 501), two doubled haploids, one from Karoo (KDH) and the other from Monty (MDH) and one line of Indian mustard (B. juncea, PI-81792) were grown under glasshouse and net-house conditions. Expanded wilted leaves of Karoo and Monty absorbed excessive amounts of water per dry weight upon in vitro rehydration compared with control non-stressed leaves, resulting in underestimation of OA calculated on the basis of the relative water content (RWC). Hence, estimation of OA based on water weight per leaf dry weight (WC) was preferred. Young expanding leaves maintained visual turgor for 6-7 d after withholding irrigation, while expanded leaves on the same plants ceased to regain turgor overnight. The young expanding leaves exhibited greater accumulation of TSS and, consequently, more negative OPs compared with expanded leaves. Maintenance of OA after irrigation and turgor recovery was evident in both expanded and expanding leaves. Although OA under drought and upon turgor recovery varied within cultivars in different experiments, outstanding OA capacity, in terms of both magnitude and stability, was identified in the cultivar Hyden and in the doubled haploid of Monty, indicating the potential to select for this trait as well as to exploit variability for OA through haploidization