ABSTRACT
In climate change science the term 'Arctic amplification' has become synonymous with an estimation of the ratio of a change in Arctic temperatures compared with a broader reference change under the same period, usually in global temperatures. Here, it is shown that this definition of Arctic amplification comes with a suite of difficulties related to the statistical properties of the ratio estimator itself. Most problematic is the complexity of categorizing uncertainty in Arctic amplification when the global, or reference, change in temperature is close to 0 over a period of interest, in which case it may be impossible to set bounds on this uncertainty. An important conceptual distinction is made between the 'Ratio of Means' and 'Mean Ratio' approaches to defining a ratio estimate of Arctic amplification, as they do not only possess different uncertainty properties regarding the amplification factor, but are also demonstrated to ask different scientific questions. Uncertainty in the estimated range of the Arctic amplification factor using the latest global climate models and climate forcing scenarios is expanded upon and shown to be greater than previously demonstrated for future climate projections, particularly using forcing scenarios with lower concentrations of greenhouse gases.
ABSTRACT
Accurate modelling and prediction of the local to continental-scale hydroclimate response to global warming is essential given the strong impact of hydroclimate on ecosystem functioning, crop yields, water resources, and economic security. However, uncertainty in hydroclimate projections remains large, in part due to the short length of instrumental measurements available with which to assess climate models. Here we present a spatial reconstruction of hydroclimate variability over the past twelve centuries across the Northern Hemisphere derived from a network of 196 at least millennium-long proxy records. We use this reconstruction to place recent hydrological changes and future precipitation scenarios in a long-term context of spatially resolved and temporally persistent hydroclimate patterns. We find a larger percentage of land area with relatively wetter conditions in the ninth to eleventh and the twentieth centuries, whereas drier conditions are more widespread between the twelfth and nineteenth centuries. Our reconstruction reveals that prominent seesaw patterns of alternating moisture regimes observed in instrumental data across the Mediterranean, western USA, and China have operated consistently over the past twelve centuries. Using an updated compilation of 128 temperature proxy records, we assess the relationship between the reconstructed centennial-scale Northern Hemisphere hydroclimate and temperature variability. Even though dry and wet conditions occurred over extensive areas under both warm and cold climate regimes, a statistically significant co-variability of hydroclimate and temperature is evident for particular regions. We compare the reconstructed hydroclimate anomalies with coupled atmosphere-ocean general circulation model simulations and find reasonable agreement during pre-industrial times. However, the intensification of the twentieth-century-mean hydroclimate anomalies in the simulations, as compared to previous centuries, is not supported by our new multi-proxy reconstruction. This finding suggests that much work remains before we can model hydroclimate variability accurately, and highlights the importance of using palaeoclimate data to place recent and predicted hydroclimate changes in a millennium-long context.
Subject(s)
Climate Change/statistics & numerical data , Climate , Rain , Atmosphere , China , Ecosystem , Geographic Mapping , Geologic Sediments/chemistry , History, 15th Century , History, 16th Century , History, 17th Century , History, 18th Century , History, 19th Century , History, 20th Century , History, 21st Century , History, Medieval , Hydrology , Ice/analysis , Mediterranean Region , Models, Theoretical , Soil/chemistry , Spatio-Temporal Analysis , Temperature , Trees/anatomy & histology , Trees/growth & development , Uncertainty , United StatesABSTRACT
The prognostic impact of different anatomical sites in patients with cutaneous malignant melanoma (CMM) has been widely debated and requires further elucidation. Therefore, we developed EssDoll, a new computerized method to address the question of site in relation to prognosis. A population-based cohort of 1891 patients, diagnosed between 1976 and 1987 with invasive CMM without evidence of metastasis, was identified. The body surface was divided into 24 areas. Hazard ratios (HRs) for CMM death were calculated and areas were compared in both the whole model and in pairs. Cox's proportional hazard regression model was used and adjustments were made for established prognostic factors. Furthermore, the overall effect of site was calculated using the likelihood ratio test. Overall, the tumour site was of prognostic importance (P=0.0036). There was a significantly increased risk of CMM-specific death in patients with a primary tumour site in the middle and lower back (HR=1.8, P=0.04) and in the supramammary and mammary area (HR=1.8, P=0.05). When all areas were analysed in pairs, the dorsal shoulder, superior back and clavicular area also showed a worse prognosis. CMM diagnosed in other anatomical regions, including the calves, Achilles, upper arms, forehead, temples, cheeks and face, seemed to be related to a better prognosis. It can be concluded that the tumour site is of prognostic importance, and that the middle and lower back and supramammary and mammary areas are independent factors related to a poor prognosis.
