January 21 , 2013: Climate Change Basics
difference between weather & climate is time & the way it is studied
o weather: day to day variation in the state of the atmosphere (temperature &
weather events) combination of temperature, humidity, cloudiness, etc.
what will it be like today?
how hot is it right now?
when will that storm hit out section of the country?
o climate: weather information & how the atmosphere “behaves” over long
periods of time (precipitation, fog) statistical information describing
variation of weather at given place for specified interval
on average, does it rain a lot during September?
what is the climate like over there?
differences between weather & climate alter climate change
James Hansen 1963 began to think about impacts of airborne particles
o as moon entered earth’s shadow it surprisingly completely disappeared
o Mount Agung, Indonesia erupted & injected gases/debris particles into
o particles scattered & absorbed incoming light, darkening earth’s surface
Milankovitch theory describes collective effects of changes in earth’s movements
o eccentricity period of 100 000 years
o axial tilt changes period of 41 000 years
o precession: change in orientation of earth’s orbit period of 26 000 years
National Centre for Atmospheric Research widely recognized for best weather
dataset in world
o problem: weather stations rather sparse
o Hansen knew weather fluctuations would introduce short-term temperature
anomalies into weather stations that aren’t same as climate change
o produced average temperature changes, not absolutel temperature changes
o temperature readings of weather stations within 1000 km of one another =
highly correlated so could map global temperate changes over time despite
fact weather stations widely spaced & located mainly on land
Hansen intrigued by humans forcing globe to warm
o simulated influence of all known greenhouse gases except CO to see if net
effect could be felt on global scale
o warming effect of all gases combined comparable to effect of 2O on its own
o demonstrated human & natural activities could force climate change BUT
knew natural forcings (volcanic eruptions, changes in sun activity) go up &
down but human forcing (greenhouse gases) steadily increasing
a simplified earth
o if you remove clouds, water vapour, greenhouse gases, dust, etc., will only
have N & O o there is a radiation balance of ea