This article focuses on entrepreneurship in economic geography and aims at a systematic investigation of regional variation in knowledge-based entrepreneurial activity. We develop and test a three-phase structural model for regional systems of entrepreneurship after introducing a systems approach to entrepreneurship. The model is built upon the absorptive capacity theory of knowledge spillover entrepreneurship that identifies new knowledge as one source of entrepreneurial opportunities and human capital as the major source of entrepreneurial absorptive capacity. Based on data of US metropolitan areas, we find that entrepreneurial absorptive capacity is a critical driving force for knowledge-based entrepreneurial activity. We also find that high technology and cultural diversity contribute to the vibrancy of regional systems of entrepreneurship.

The ongoing and projected warming in the northern high latitudes (NHL; poleward of 601N) may lead to dramatic changes in the terrestrial carbon cycle. On the one hand, warming and increasing atmospheric CO 2 concentration stimulate vegetation productivity, taking up CO 2 . On the other hand, warming accelerates the decomposition of soil organic matter (SOM), releasing carbon into the atmosphere. Here, the NHL terrestrial carbon storage is investigated based on 10 models from the Coupled Carbon Cycle Climate Model Intercomparison Project. Our analysis suggests that the NHL will be a carbon sink of 0.3 AE 0.3 Pg C yr À1 by 2100. The cumulative land organic carbon storage is modeled to increase by 38 AE 20 Pg C over 1901 levels, of which 17 AE 8 Pg C comes from vegetation (43%) and 21 AE 16 Pg C from the soil (8%). Both CO 2 fertilization and warming enhance vegetation growth in the NHL. Although the intense warming there enhances SOM decomposition, soil organic carbon (SOC) storage continues to increase in the 21st century. This is because higher vegetation productivity leads to more turnover (litterfall) into the soil, a process that has received relatively little attention. However, the projected growth rate of SOC begins to level off after 2060 when SOM decomposition accelerates at high temperature and then catches up with the increasing input from vegetation turnover. Such competing mechanisms may lead to a switch of the NHL SOC pool from a sink to a source after 2100 under more intense warming, but large uncertainty exists due to our incomplete understanding of processes such as the strength of the CO 2 fertilization effect, permafrost, and the role of soil moisture. Unlike the CO 2 fertilization effect that enhances vegetation productivity across the world, global warming increases the productivity at high latitudes but tends to reduce it in the tropics and mid-latitudes. These effects are further enhanced as a result of positive carbon cycle-climate feedbacks due to additional CO 2 and warming.

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[1] The behavior of the coupled carbon cycle and physical climate system in a global warming scenario is studied using an Earth system model including the atmosphere, land, ocean, and the carbon cycle embedded in these components. A fully coupled carbon-climate simulation and several sensitivity runs were conducted for the period of 1860 -2100 with prescribed IPCC-SRES-A1B emission scenario. Results indicate a positive feedback to global warming from the interactive carbon cycle, with an additional increase of 90 ppmv in the atmospheric CO 2 , and 0.6 degree additional warming, thus confirming recent results from the Hadley Centre and IPSL. However, the changes in various carbon pools are more modest, largely due to the multiple limiting factors constraining terrestrial productivity and carbon loss. The large differences among the three models are manifestations of some of the poorly constrained processes such as the global strength of the CO 2 fertilization effect and the turnover time and rates of soil decomposition.

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A rare drought occurred from 1998 to 2002 across much of the Northern Hemisphere midlatitude regions. Using observational data and numerical models, we analyze the impact of this event on terrestrial ecosystem and the global carbon cycle. The biological productivity in these regions was found to decrease by 0.9 PgC yr(-1) or 5% compared to the average of the previous two decades, in conjunction with significantly reduced vegetation greenness. The drought led to a land carbon release that is large enough to significantly modify the canonical tropically dominated ENSO response. An atmospheric inversion reveals that during the 1998 - 2002 drought period, Northern Hemisphere midlatitude changed from a 1980 1998 average of 0.7 PgC yr(-1) carbon sink to nearly neutral to the atmosphere, while a forward model suggests a change of 1.3 PgC yr(-1) in the same direction. This large CO₂ source may explain the consecutive large increase in atmospheric CO₂ growth rate of about 2 ppmv yr(-1) in recent years, as well as the anomalous timing of events. This Northern Hemisphere CO₂ anomaly was largely caused by reduced vegetation growth due to less precipitation, but also with significant contribution from higher temperature that directly increases respiration loss and indirectly further reduces soil moisture. Since the Northern Hemisphere midlatitude landscape has been significantly modified by agriculture, grazing, irrigation and fire suppression, the strong signature in the global carbon cycle of a drought initiated by changes in tropical oceanic temperatures is a remarkable manifestation of climate variability, with implications for carbon cycle response and feedback to future climate change. [References: 14

Popularised by the work of Richard Florida, the role of tolerance, openness and social or cultural diversity in urban development has gained much attention. Recent literature on urban and regional economics has found associations between these social factors and technology, entrepreneurship, innovation, housing and economic performance. In most of these studies, the terms tolerance, openness and diversity are generally conflated or interchangeably used. This article argues that diversity’s impacts on innovation and entrepreneurship are notably different from tolerance and openness and that diversity should be defined and measured differently from tolerance and openness. This article uses data of US metropolitan areas to examine the statistical difference between diversity and tolerance, and compares the effect of each on innovation and entrepreneurship in multivariate analysis. Diversity is measured using the Herfindahl–Hirschman index based on countries of birth, while tolerance is measured using the composite gay and bohemian index.

O30, P25, R12,