Demography
Demography (from prefix demo- from Ancient Greek δῆμος dēmos meaning "the people", and -graphy from γράφω graphō, implies "writing, description or measurement") is the statistical study of populations, especially human beings. As a very general science, it can analyze any kind of dynamic living population, i.e., one that changes over time or space (see population dynamics). Demography encompasses the study of the size, structure, and distribution of these populations, and spatial or temporal changes in them in response to birth, migration, aging, and death. Based on the demographic research of the earth, earth's population up to the year 2050 and 2100 can be estimated by demographers. Demographics are quantifiable characteristics of a given population.
Economics
The blunt truth about the politics of climate change is that no country will want to sacrifice its economy in order to meet this challenge.
Tony Blair, address to the 2005 G8 climate change summit in London, as reported by David Adam, "Blair signals shift over climate change", The Guardian, 1 November 2005.
Economics
Economics is a subject that really relates to core aspects of human well-being, and there’s a methodology for thinking about these things. This was a very appealing combination to me. Market systems are capable of massive breakdowns that can result in long, devastating periods of high unemployment. And I felt that economists had really learned something about how to address that.
Janet Yellen, in "The Hand on the Lever" in The New Yorker (July 21, 2014) by Nicholas Lemann