Earth’s radiative balance or, how I learned to stop worrying and love the greenhouse effect If the Earth had no atmosphere: T  T 4 = S / 4 (1 — A) T = 255 K -18 ˚C 0 ˚F Albedo (reflectivity) Solar constant (1370 W/m 2 ) Stefan-Boltzmann constant (5.67x10 -8 ) reflected Absorbed and re-radiated as heat

= 33 ˚ of ‘normal’ greenhouse warming Actual surface No atmosphere Sunlight Infra-red radiation Air

Temperature anomaly (˚C) Global Temperatures for the last 150 years (5-year running average; as of ~2005) Civil war Model T World War II Al Gore invents the internet

After Jones and Wigley, 1980 “... a global deterioration of climate, by order of magnitude larger than any hitherto experienced by civilized mankind, is a very real possibility and indeed may be due very soon.” Climate change in the age of Disco

The last ~10 years: another plateau resembling ~1950

Currently favored explanation of the plateaus is that these are periods when accumulated heat gets preferentially stored in ocean instead of atmosphere…

Warming has a strong geographic bias ( avg. vs mean) ±2.5 ˚C scale

A long-suspected driving force — rise in CO 2 Global average AD Mauna Loa AD

The CO 2 Greenhouse Effect What should physical principles lead me to expect of global warming? Complications Solar ‘constant’ is a variable Water-vapor feedback Albedo Ice Clouds Aerosols and dust Ground cover 33 ˚ of warming = 20˚ from H 2 O v + 10 ˚ from CO ˚ from other things CO 2 has risen 10’s of %, so T should have risen by a degree or more Arrhenius, 1896 Doubling CO 2 = 5-6 ˚C warming

Cylon invasion happens here

Reid, 1999; by way of Sunspots and early 20th century temperatures

So what factor is to blame for 20 th century T rise? Wrong question — lots of things are to ‘blame’ but some are more important than others, and at different times