3.2.1 Economic Development
On the regional scale, the PUE of 70 out of 113 countries had a
significant linear or quadratic relationship with GDP per capita. Among
these countries, 47 of them suggest the expected U shape relationship
between PUE and GDP per capita (Table 4), though the turning points and
slopes vary. These 47 countries accounted for over half of the global
harvested area and total P in crop production, and over 80% of P
fertilizer consumption at cropland in 2010 (61%, 70%, and 84%,
respectively). They include major crop-producing and
fertilizer-consuming countries such as the U.S., Brazil, China, and
India.
EKC hypothesis was not rejected across the 113 countries when the
independent variables only include the linear and quadratic terms of GDP
per capita (Table S10). After considering country and time effects and
adding more variables to the regression model, only the linear term has
a significantly positive relationship with PUE (Table 4, Table S10, and
Table S14). These results indicate synergy between global economic
development and PUE (the second half of the EKC curve) between 1961-2014
in these 113 countries.
Note that the EKC hypothesis does not tell the future of a country or
define the pathway that all countries should follow. Instead, EKC
suggests potential reasons behind PUE patterns and informs political
strategies to improve PUE. China has been experiencing an increasing GDP
per capita and decreasing PUE (Fig. S3). According to the EKC
hypothesis, this tradeoff may no longer continue, as China’s PUE is
approaching a lower asymptote between 30% and 40% (Table 3). However,
China’s PUE would not inevitably reach a turning point and then increase
without any technological innovation or political interventions.
Improved technologies and proper policies can help a country like China
turn the corner on the EKC and reach a sustainable PUE in an even
shorter time.