The American Geophysical Union (AGU) have released this statement on Climate Change:
The Earth's climate is now clearly out of balance and is warming. Many components of the climate system - including the temperatures of the atmosphere, land and ocean, the extent of sea ice and mountain glaciers, the sea level, the distribution of precipitation, and the length of seasons - are now changing at rates and in patterns that are not natural and are best explained by the increased atmospheric abundances of greenhouse gases and aerosols generated by human activity during the 20th century. Global average surface temperatures increased on average by about 0.6°C over the period 1956-2006. As of 2006, eleven of the previous twelve years were warmer than any others since 1850. The observed rapid retreat of Arctic sea ice is expected to continue and lead to the disappearance of summertime ice within this century. Evidence from most oceans and all continents except Antarctica shows warming attributable to human activities. Recent changes in many physical and biological systems are linked with this regional climate change. A sustained research effort, involving many AGU members and summarized in the 2007 assessments of the Intergovernmental Panel on Climate Change, continues to improve our scientific understanding of the climate.
During recent millennia of relatively stable climate, civilization became established and populations have grown rapidly. In the next 50 years, even the lower limit of impending climate change - an additional global mean warming of 1°C above the last decade - is far beyond the range of climate variability experienced during the past thousand years and poses global problems in planning for and adapting to it. Warming greater than 2°C above 19th century levels is projected to be disruptive, reducing global agricultural productivity, causing widespread loss of biodiversity, and-if sustained over centuries-melting much of the Greenland ice sheet with ensuing rise in sea level of several meters. If this 2°C warming is to be avoided, then our net annual emissions of CO2 must be reduced by more than 50 percent within this century. With such projections, there are many sources of scientific uncertainty, but none are known that could make the impact of climate change inconsequential. Given the uncertainty in climate projections, there can be surprises that may cause more dramatic disruptions than anticipated from the most probable model projections.
With climate change, as with ozone depletion, the human footprint on Earth is apparent. The cause of disruptive climate change, unlike ozone depletion, is tied to energy use and runs through modern society. Solutions will necessarily involve all aspects of society. Mitigation strategies and adaptation responses will call for collaborations across science, technology, industry, and government. Members of the AGU, as part of the scientific community, collectively have special responsibilities: to pursue research needed to understand it; to educate the public on the causes, risks, and hazards; and to communicate clearly and objectively with those who can implement policies to shape future climate.
Human Impacts on ClimateAdopted by Council December 2003
Revised and Reaffirmed December 2007
Marc Morano's response:
“The AGU Board issued a statement on climate change without putting it to a vote of the group's more than 50,000 members. Its sweeping claims, drafted by nine committee members, rely heavily on long term computer model projections, cherry-picking of data and a one-sided view of recent research. As with the recent statements by the AMS and the NAS, this is the product of a small circle of scientists who all share the same point of view, and who failed to put their statement to a vote of the AGU members on whose behalf they now claim to speak. As such it amounts to nothing more than a restatement of the opinion of a small group, rather than a consensus document.”
Marc Morano
Communications Director
Senate Environment and Public Works Committee (EPW) Inhofe Staff
Temperature of the Earth
Similarly we can calculate the effective temperature of the Earth TE by equating the energy received from the Sun and the energy transmitted by the Earth, under the black-body approximation:
T_E \, = T_S \sqrt{r_S\over 2 a_0 } \;
= 5780 \; {\rm K} \times \sqrt{696 \times 10^{6} \; {\rm m} \over 2 \times 149.598 \times 10^{9} \; {\rm m} }
\approx 279 \; {\rm K} \; ,
where TS is the temperature of the Sun, rS the radius of the Sun, and a0 is the distance between the Earth and the Sun. Thus resulting in an effective temperature of 6°C on the surface of the Earth.
In summary, the surface of the Sun is 21 times as hot as that of the Earth taken as a blackbody, and therefore it emits 190,000 times as much energy per square meter. The distance from the Sun to the Earth is 215 times the radius of the Sun, reducing the energy per square meter by a factor 46,000. Taking into account that the cross-section of a sphere is one fourth of its surface area, we see that there is equilibrium of approximately 342 W per m2 surface area, or 1,370 W per m2 cross-sectional area.
The above derivation is a rough approximation only, as it assumes the Earth is a perfect blackbody. The same equilibrium planetary temperature would result if the planet's emissivity and absorptivity were reduced by some constant fraction at all wavelengths, since the incoming and outgoing powers would still match at the same temperature (this equilibrium temperature would no longer fit the definition of effective temperature, however).
The real Earth does not have this "gray-body" property. The terrestrial albedo is such that about 30% of incident solar radiation is reflected back into space; taking the reduced energy from the sun into account and computing the temperature of a black-body radiator that would emit that much energy back into space yields an "effective temperature", consistent with the definition of that concept, of about 255 K.[3] However, compared to the 30% reflection of the Sun's energy, a much larger fraction of long-wave radiation from the surface of the earth is absorbed or reflected in the atmosphere instead of being radiated away, by greenhouse gases, namely water vapor, carbon dioxide and methane.[4][5] Since the emissivity (weighted more in the longer wavelengths where the Earth radiates), is reduced more than than the absorptivity (weighted more in the shorter wavelengths of the Sun's radiation), the equilibrium temperature is higher than the simple black-body calculation estimates, not lower. The Earth's actual average surface temperature is about 288 K, rather than 279 K, as a result; global warming is an increase in this equilibrium temperature due to human-caused additions to the greenhouse gasses.
"It is not a question of whether CO2 traps the heat but how long."
If you look at that diagram again, it doesn't matter if a lot of that heat is then sent back to the earth, to be re-radiated again, which is what happens.
SJT
"Lets see if I can get this right."
Not even relevant Luke was creating a little row about Stefan Boltzmann in that derivation I showed that is actually cancels out. It's really standard textbook stuff that I've known for about 42 years not rocket science. It leads to an equilibrium temperature of avout 279K or ~6C the so called measured temperature is around 288 (it has changed little the past century) and the difference is due to the fact that the earth is not in thermodynamic equilibrium because it does not behave like a black body rendering Stefan-Boltzmann constant irrelevant because it only applies to black bodies.
The fact that the atmosphere absorbs IR at certain wavelengths means it is not a black body either and once again Stephan-
Boltzmann is broken.
Do you get that?
SJT
"That effectively 'traps' heat within the area of the earths atmosphere."
It is not a question of whether CO2 traps the heat but how long. Once a CO2 absorbs some IR in the 15m micron band that energy gets smeared within the order of nano-seconds to the other atmospheric species which will radiate that through inelastic collision at other wave lengths. Most of this will get blocked by water vapour but the energy gets lifted due to the thermal expansion eventually to the troposphere where it can radiate quite happily at those wavelengths through to space due to general lack of water in the stratosphere. This is perhaps an over simplified model but we know simply from diurnal lag of around 30 degrees of temperature to insolation that the time constant is only a few hours.
But N2 and O2 aren't very effective GHGs, due to their molecular shape, so they don't really enter into consideration.
The pressure does cause the troposphere to rise, but that also makes the 'trapdoor' thicker.
If you look at that diagram you like,
http://www.climateaudit.org/wp-content/uploads/2008/01/balanc3.jpg
Convection does not appear to be much of a factor compared to radiation.
SJT
"That effectively 'traps' heat within the area of the earths atmosphere."
The real question is how long it "traps" it for and given that there is about a 30 degree lag in the diurnal variation in temperature the atmosphere has a relaxation time constant of only a few hours. Real fact of the matter is that if you have even a smattering of quantum mechanics is you would know that even if the CO2 would emit or relax it's excitation slowly the quenching by other atmospheric species occurs in time spans in the order of nano seconds thus warming the the atmosphere more than it would be by conduction and convection alone. The warmed air rises taking the heat to the tropopause where it is happily radiated through a wider window. It's wider owing to the general lack of water vapour in the stratosphere. (N2 an O2 radiate at wave lengths far above that of the CO2 "trap" right down to extreme high radio frequency).
"It's a simple matter of observable fact that temperature difference not available energy drives observed heat transport. That is what the second law is all about."
Lets see if I can get this right. The atmosphere makes things not so simple, since it effectively acts in a way similar to a trap door. The atmosphere is transparent to short wave radiation, not long wave radiation. That effectively 'traps' heat within the area of the earths atmosphere.
I say 'traps', but it does leak out eventually. The effect is to slow down the radiation of heat coming in and then leaving the earth. The end result is that the temperature of the earth will rise.