Climate change (Class of 2019)

"Can climate be changed?" "Is climate changeable?" ... various meanings

• (1) Has climate changed in geological past (time scale 10000 years or longer)? ... Yes. (I will come back some day.)
  • 1820s: Discovery of "ice ages" <- study of geology + study of present glaciers
  • Present terminology of "ice ages" and "glacial periods"
    • An "ice age" can refer to an era of 10⁶ - 10⁸ years which may contain "glacial" cycles
    • "glacial" and "interglacial" periods ... cyclic in 10⁴ - 10⁵ years
    • "Little Ice Age" ... an event smaller than a glacial period, around CE (=AD) 1250-1850 (no consensus on the beginning)
• (2) Has climate changed in historical past (time scale 100s and 1000s of years)? ... Probably yes, but not sure whether "globally".
  • ... so much as to be crucial to human history? ... An open question.
• (3) Will climate change significantly in a century? ... Yes, globally, but it is because of anthropogenic forcing (present understanding)
  • 1920s-1940s: many (though not all) experts thought "No", so, once climate statistics of a place is established, it would be used permanently.
  • 1960s-: some changes are detected. Question: trend or interdecadal variation?
• (4) Do human beings (collectively) have enough power to cause changes to climate? ... Yes (present understanding).
  • Notion that peoplle are changing natural environment (not exactly "climate") has become popular.
    • 1950s-: detection of radioactivity caused by experimental nuclear detonation
    • 1960s-: knowledge of chemical pollution and its effect on ecosystems
    • 1970s-: knowledge of "desertification", deforestation etc.
  • 1970s: "Yes" in theory. (experts' consensus, not shared by the public yet)
  • 2000s: "Yes, we have already changed" by combination of observations and theory-based models.
• (5) Will human beings be able to control climate as they like? ... No (my understanding).
  • People often confuse (4) and (5).
  • 1940s-1950s: some leading scientists hoped developing technology to control climate.
  • 1960s-1970s: full control seems impossible. (theory of chaos; troubles in rain making experiments)
  • 2000s- : some scientists consider intentional climate modification (partial control of climate)