Editing Environmental determinism (section)

=== Effects of climate on productivity ===
The impact that climate and water navigability have on economic growth and GDP per capita was studied by notable scholars including [[Paul Krugman]], [[Jared Diamond]], and [[Jeffrey Sachs]].<ref>{{Citation | mode=cs1 | last1=Mellinger | first1=Andrew D. | last2=Sachs | first2=Jeffrey D. | last3=Gallup | first3=John L. | date=1999 | title=Climate, water navigability, and economic development | type=Working paper | publisher=Harvard Institute for International Development}}</ref> By using variables to measure environmental determinism, such as climate, land composition, latitude, and the presence of infectious disease, they account for trends in worldwide economic development on local, regional and global scales. To do so, they measure economic growth with GDP per capita adjusted to purchasing power parity (PPP), while also taking into consideration population density and labor productivity.<ref name="Geography and Economic Development" />

Economic historians have found that societies in the [[Northern Hemisphere]] experience higher standards of living, and that as latitude increases north or south from the equator, levels of real GDP per capita also increases. Climate is closely correlated with agricultural production since without ideal weather conditions, agriculture alone will not produce the surplus supply needed to build and maintain economies. Locations with hot tropical climates often suffer underdevelopment due to low fertility of soils, excessive plant transpiration, ecological conditions favoring infectious diseases, and unreliable water supply. These factors can cause tropical zones to suffer a 30% to 50% decrease in productivity relative to temperate climate zones.<ref name="Geography and Economic Development" /><ref name="Easterly Levine 2003" /> Tropical infectious diseases that thrive in hot and moist equatorial climates cause thousands of deaths each year. They are also an economic drain on society due to high medical costs, and the unwillingness of foreign capital to invest in a sickly state. Because infectious diseases like malaria often need a warm ecology for growth, states in the mid to high latitudes are naturally protected from the devastating effects of those diseases.<ref name="Geography and Economic Development" />