Monthly Archives: March 2008

Tipping Points in the Earth’s Climate System

Modern climate science tells us that increased emissions of greenhouse gases, most notably carbon dioxide, will change the climate that we are used to and have consequences for ecosystems and societies worldwide. A rise of just several degrees can have large and widespread impacts that dramatically alter civilization, but there are worries aside from a slow and steady rise. Climatic records show that large, widespread, and abrupt climate changes have occurred repeatedly in the past. Dr. Richard Alley of Penn State University has lectured on this topic and has used an analogy of the climate being like a drunken college student– when you don’t do much to it then it will just sit there, but if you move it around a little bit then it will stagger about and maybe fall. The last ten thousand years or so (the Holocene) has been an unusual time of relative calmness, with little variation in the climate. However, for most of the last 100,000 years, and even before, this has not been the case. One of the potential threats that comes from altering the chemistry of the atmosphere, and changing the land around to suit or needs, is the ability to flip a “climate switch” and force it between different states. Other possibilities include crossing critical thresholds, such as melting the arctic sea ice, that will have large socio-economic and/or ecological consequences. Such events have been labeled “tipping points” and many scientists (notably James Hansen of NASA, Alley, and others) have started to issue many warmings that the Earth may not respond to a new climate is a nice and steady fashion.

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Follow up to lecture by Chris Walcek at HVCC

So Chris Colose says a few week ago that University of Albany’s professor and senior researcher Dr. Chris Walcek is to give a talk on global warming entitled “More Inconvenient and Convenient Aspects of Global Warming.” All went well, no one threw anything at Chris Walcek, although one irate chap did stand up in the Q&A and yell about the disservice he gave to the audience. That guy was a little strange, but what about Chris Walcek’s presentation??

I want to give justice to his points, so I can open up discussion to everyone. I also want to just bring up a lot of science so that even people who did not attend can discuss freely. According to Dr. Walcek, the “AGW consensus” vs. “skeptic” summary can be said as follows:

On Warming

Consensus– Yes it is

Skeptics– Yes, but trends very small compared to natural fluctuations

Causation

Consensus– Mostly anthropogenic (human-induced) factors in recent times

Skeptics– Possibly some anthropogenic, more solar variation, very low confidence for attribution

Is it bad ?

Consensus– Is bad

Skeptics– Maybe some bad, maybe some good

Can we slow it down?

Consensus– Can slow

Skeptics– Can’t stop global warming in any significant way

Additional points raised by Chris Walcek include– Sea level variability is not significant, cooling and ice accumulation in Antarctica interior, CO2 lagged (not led) temperature over the glacial-interglacial cycles, solar correlation to temperature is high over the 20th century, globe is warming but not outside the range of natural variation and within our understanding of the climate system, models not yet sufficient.

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Physics of the Greenhouse Effect Pt 2

In the preceding post, on the greenhouse effect, I investigated the role of the greenhouse effect and its play in radiative balance, and how the presence of an atmosphere acts to raise planetary temperatures. The take home points should be that for a planet with no infrared absorbing layer above the surface, the fourth power of the surface temperature always approximates a value determined by the incoming solar radiation. The only way the surface temperatures can exceed this value is if there is an atmosphere which acts to be a blanket to outgoing radiation. A planet can also be heated by internal processes such as radioactive decay or rigorous convections from the mantle, but these are rather negligible on the terrestrial planets. Adding greenhouse gases to an atmosphere whose temperature decreases with height must act to warm the surface by making the net downward emission greater than zero. In this post, I will elaborate on specific greenhouse gases, the runaway greenhouse effect, and an antigreenhouse effect.

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Physics of the Greenhouse Effect Pt 1

Jean Baptise-Fourier is generally credited with the discovery of a greenhouse effect, which involves the process by which the presence of an atmosphere acts to raise the surface temperature of a planet. This was extremely simplified at the time, and the term greenhouse never appears in his 1827 writing, but he did establish the effect that the atmosphere had on incoming light and outgoing infrared (heat) radiation, and that some heat was absorbed by the atmosphere which was opaque in the infrared but transparent to incoming solar energy. A copy of his essay, translated by R.T. Pierrehumbert can be found here. We’ve made a lot of progress since then, as Svante Arrhenius began to quantify the phenomenon nearly 75 years later, the work of Stefan and Boltzmann established the relationship between an object’s temperature and its outgoing radiation, the role of convection and water vapor and clouds turn out to be important in more complex models developed later, etc. The pionerring paper by Arrhenius, entitled On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground, which is the famous 1896 piece, began to investigate what the effects of doubling the atmospheric CO2 content would be. At this time, most of the interest in the subject was in solving the mystery of the coming and going of ice ages. Like most pioneering efforts, Fourier or Arrhenius did not have the last word, and we still have much to learn today, but they provided a big leap in how we understand planetary temperatures and the role of the atmosphere in radiative balance. Fourier was one of the first to speculate that human activities could influence climate, and such topics are rather important in modern times.

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