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This study presents a global scale analysis of cropping intensity, crop duration and fallow land extent computed by using the global dataset on monthly irrigated and rainfed crop areas MIRCA2000. MIRCA2000 was mainly derived from census data and crop calendars from literature. Global cropland extent was 16 million km2 around the year 2000 of which 4.4 million km2 (28%) was fallow, resulting in an average cropping intensity of 0.82 for total cropland extent and of 1.13 when excluding fallow land. The lowest cropping intensities related to total cropland extent were found for Southern Africa (0.45), Central America (0.49) and Middle Africa (0.54), while highest cropping intensities were computed for Eastern Asia (1.04) and Southern Asia (1.0). In remote or arid regions where shifting cultivation is practiced, fallow periods last 3-10 years or even longer. In contrast, crops are harvested two or more times per year in highly populated, often irrigated tropical or subtropical lowlands where multi-cropping systems are common. This indicates that intensification of agricultural land use is a strategy that may be able to significantly improve global food security. There exist large uncertainties regarding extent of cropland, harvested crop area and therefore cropping intensity at larger scales. Satellite imagery and remote sensing techniques provide opportunities for decreasing these uncertainties and to improve the MIRCA2000 inventory. [ABSTRACT FROM AUTHOR]

The Gulf Stream, as part of the Atlantic Meridional Overturning Circulation (AMOC), is known as a major driver of latitudinal energy transport in the North Atlantic presently causing mild winters over northwestern Eurasia. The intensity of the AMOC throughout the Neogene, prior to the final closure of the Central American Seaway (CAS) in the early Pliocene, is still poorly known, but most authors assume that the circulation was considerably weaker than present. Here we address this issue from a continental point of view. We studied the past AMOC intensity by analyzing Neogene continental climate patterns along North American and Western Eurasian transects. Based on a total of 317 palaeofloras thermal latitudinal gradients are reconstructed for three Neogene time slices, namely the middle Miocene, late Miocene, and late Pliocene using the Coexistence Approach to obtain quantitative climate data. The obtained proxy-based, continental temperature gradients are evaluated against data from a selection of published General Circulation Model (GCM) simulations for the three time slices studied. Our study suggests that shallow thermal latitudinal gradients existed in North America and Western Eurasia throughout the Miocene but became strongly steepened in the late Pliocene. In both Miocene time slices studied, the higher latitudes were by up to 30 °C warmer than present (cold month mean), also at times with presumed pre-industrial CO 2 such as the late Miocene. In the late Pliocene high-latitude, the temperature difference with respect to the present had decreased by up to 10 °C (cold month mean). Both mean annual temperatures and cold month means of the lower mid and low latitudes were at the present-day level throughout all three time slices, or even slightly below. In both Miocene time slices, zonal temperature means at both continental transects were similar in the mid and higher latitudes. However, several northwest European sites reveal very mild winter condition suggesting the early existence of a probably less intense Palaeo-Gulf Stream. The distinct thermal anomaly (annual and cold month means) today existing between North America and Western Eurasia appeared for the first time in the late Pliocene, attaining about 50% of the present-day magnitude. This supports the assumption that the AMOC intensified after the final closure of the CAS during the early Pliocene. The results obtained from the palaeobotanical proxies are in line with data from coeval marine archives, particularly with North Atlantic sea surface temperatures (SSTs) inferred from oxygen isotopes. However, the proxy-based thermal gradients are not well reproduced by a selection of GCM simulations, due to a well-known systematic underestimation of high latitude warming by GCMs for the Miocene and Pliocene time slices. [ABSTRACT FROM AUTHOR]

Water scarcity severely impairs food security and economic prosperity in many countries today. Expected future population changes will, in many countries as well as globally, increase the pressure on available water resources. On the supply side, renewable water resources will be affected by projected changes in precipitation patterns, temperature, and other climate variables. Here we use a large ensemble of global hydrological models (GHMs) forced by five global climate models and the latest greenhouse-gas concentration scenarios (Representative Concentration Pathways) to synthesize the current knowledge about climate change impacts on water resources. We show that climate change is likely to exacerbate regional and global water scarcity considerably. In particular, the ensemble average projects that a global warming of 2 °C above present (approximately 2.7 °C above preindustrial) will confront an additional approximate 15%of the global population with a severe decrease in water resources and will increase the number of people living under absolute water scarcity (<500m³ per capita per year) by another 40% (according to some models, more than 100%) compared with the effect of population growth alone. For some indicators of moderate impacts, the steepest increase is seen between the present day and 2 °C, whereas indicators of very severe impacts increase unabated beyond 2 °C. At the same time, the study highlights large uncertainties associated with these estimates, with both global climate models and GHMs contributing to the spread. GHM uncertainty is particularly dominant in many regions affected by declining water resources, suggesting a high potential for improved water resource projections through hydrological model development. [ABSTRACT FROM AUTHOR]