Az olajár gyengülő makrogazdasági hatásai. Két versengő elmélet szintézise = Weakening macroeconomic effects of the oil price. A synthesis of two competing theories

Az 1970-es évek olajválságait követő stagflációs periódusok óta gyakorlatilag minden nagyobb áremelkedés alkalmával felerősödnek a kedvezőtlen makrogazdasági hatásokkal kapcsolatos félelmek, miközben a tapasztalat azt mutatja, hogy az importőröket egyre kevésbé érinti az olaj reálárának alakulása. A gyengülő hatások okaként Blanchard-Galí [2007] a gazdaságok hatékonyabb és rugalmasabb működését jelölte meg, míg Kilian [2010] szerint a 2000 utáni áremelkedést a kedvező világgazdasági környezet fűtötte, ami ellensúlyozta a magasabb ár okozta negatív folyamatokat. A tanulmány Kilian [2009] modelljének kiterjesztésével, időben változó paraméterű ökonometriai eljárással vizsgálja a két megközelítés összeegyeztethetőségét. Az eredmények a hipotézisek egymást kiegészítő kapcsolatára engednek következtetni, azaz a makrogazdasági következmények szempontjából nem maga az ár, hanem annak kiváltó okai lényegesek, ugyanakkor e mögöttes tényezők hatása az elmúlt évtizedekben folyamatosan változott. _____ Many economists argue that the stagflation periods of the 1970s were related to the two main oil crises. However, experience shows that these effects were eliminated over the decades, e. g. oil-importing economies enjoyed solid growth and low inflation when oil prices surged in the 2000s. Blanchard and Galí (2007) found that economies became more effective and elastic in handling high energy prices, while Kilian (2010) took as the main reason for the weakening macroeconomic effects of oil-price shocks the structural differences behind the price changes. The article sets out to test the compatibility of the two rival theories, using time-varying parameter models. The results show that both hypotheses can be correct concurrently: the structure of the change in price matters, but the impulse responses varied over time.

Trends in research on the possible effects of climate change concerning aquatic ecosystems with special emphasis on the modelling approach

Knowledge on the expected effects of climate change on aquatic ecosystems is defined by three ways. On the one hand, long-term observation in the field serves as a basis for the possible changes; on the other hand, the experimental approach may bring valuable pieces of information to the research field. The expected effects of climate change cannot be studied by empirical approach; rather mathematical models are useful tools for this purpose. Within this study, the main findings of field observations and their implications for future were summarized; moreover, the modelling approaches were discussed in a more detailed way. Some models try to describe the variation of physical parameters in a given aquatic habitat, thus our knowledge on their biota is confined to the findings based on our present observations. Others are destined for answering special issues related to the given water body. Complex ecosystem models are the keys of our better understanding of the possible effects of climate change. Basically, these models were not created for testing the influence of global warming, rather focused on the description of a complex system (e. g. a lake) involving environmental variables, nutrients. However, such models are capable of studying climatic changes as well by taking into consideration a large set of environmental variables. Mostly, the outputs are consistent with the assumptions based on the findings in the field. Since synthetized models are rather difficult to handle and require quite large series of data, the authors proposed a more simple modelling approach, which is capable of examining the effects of global warming. This approach includes weather dependent simulation modelling of the seasonal dynamics of aquatic organisms within a simplified framework.