EFFECTIVE TEMPERATURE OF THE EARTH SYSTEM First the Sun : 1. The spectrum of solar radiation measured outside the Earth’s atmosphere matches closely that of a blackbody at 5800 K. 2. The Sun’s radiation peaks in the visible range of wavelengths (l = nm). 3. The total radiation E S emitted by the Sun (temperature T S = 5800 K) per unit time is given by the radiation flux multiplied by the area of the Sun: where R S = 7x10 5 km is the Sun’s radius and is the Stefan-Boltzmann constant [ 5.67x10 -8 W m -2 K -4 ] Lecture 1. The “Greenhouse” Effect

Now for the Earth, a distance d = 1.5x10 8 km from the Sun. The solar radiation flux F S distributed uniformly over the sphere centered at the Sun and of radius d is: Substituting numerical values we obtain F S = 1370 W m -2, which we also called the solar constant. The mean solar radiation flux absorbed per unit area of the Earth’s surface is F S (1-A)/4, where A (albedo = 0.28) is the fraction reflected back to space. The energy balance equation for the Earth is then given by which yields an effective temperature for the Earth, T E = 255 K. T E is the temperature at which the Earth System must radiate to be in energy balance with the Sun.

Why are we not a frozen block of Ice? Answer: “greenhouse” gases 1. What do “greenhouse” gases do? They absorb radiation in the IR ( ,000nm) 2. How does this help? If then which gives as the effective radiating temperature. This is for a simple isothermal uniform absorption model. [extracted from “Atmospheric Chemistry” by Daniel Jacob]

Faq 1.1 from IPCC (2007) Energy Flows in the Atmosphere

Impact of Increasing CO 2

GREENHOUSE GAS CANDIDATES 1. What is the number 1 natural “greenhouse” gas? Hint, it is responsible for much of the albedo 2. What is the number 2 natural “greenhouse” gas? Hint, it has also been around as long as number What is the number 3 natural “greenhouse” gas. Hint, early bacteria ate it up.

Total Column Water Vapor Anomalies ( ) Held and Soden J.Clim We have high confidence in the model projections of increased water vapor.

Change in Low Cloud Amount (%/K) for Doubled CO 2 GFDL and NCAR/CAM models Courtesy of Brian Soden

Jouzel, Lorius et al-- Vostok late 70’s-80’s Etheridge, et al -- Law Dome 1990’s Ice cores + direct measurements provide a beautiful record of the history of atmospheric carbon dioxide www globalwarmingart.com.

from IPCC (2007) Red lines are atmospheric samples. Other colors show ice cores.

Carbon dioxide methane Nitrous oxide CFCs RECENT HISTORY

IPCC 2007 Non-Technical Definition Radiative forcing is a measure of how the energy balance of the Earth-atmosphere system is influenced when factors that affect climate, such as atmospheric composition or surface reflectivity, are altered. When radiative forcing is positive, the energy of the Earth- atmosphere system will ultimately increase, leading to a warming of the system. In contrast, for a negative radiative forcing, the energy will ultimately decrease, leading to a cooling of the system.

Radiative forcing of climate (1750 to present): Important contributions from air pollutants IPCC, 2007

Carbon dioxide methane Nitrous oxide CFCs other

Global ocean heat content Energy is going into ocean => More energy is entering the atmosphere from space than is going out Almost all parts of the Earth’s surface have warmed over the past 100 years IPCC 4th Assessment Report.

From IPCC (2007) For sea level, tide gauges in blue. Satellites in red. Circles for individual years. Uncertainty range shaded.