A sudden and unexplained drop in the amount of water vapor present high in the atmosphere almost a decade ago has substantially slowed the rate of warming at Earth’s surface in recent years, scientists say.

In late 2000 and early 2001, concentrations of water vapor in a narrow slice of the lower stratosphere dropped by 0.5 parts per million, or about 10 percent, and have remained relatively stable since then. Because the decline was noted by several types of instruments, including some on satellites and others lofted on balloons, the sharp decrease is presumed to be real, says Karen Rosenlof, a meteorologist at NOAA’s Earth System Research Laboratory in Boulder, Colo.

And because water vapor is a powerful greenhouse gas, the decline has slowed the increase of global temperatures, Rosenlof, Susan Solomon, also of NOAA in Boulder, and their colleagues report online January 28 and in an upcoming Science.

“This is such a sudden decrease, we can’t explain what’s behind it,” Rosenlof says. One large source of water vapor in the stratosphere is the oxidation of methane, she notes. But the decline in concentration of that gas detected by the researchers seems to be limited to a layer 2 kilometers thick in the lower stratosphere, while methane is found throughout the stratosphere. And even though scientists have discerned a leveling off in atmospheric methane in recent years, that trend doesn’t seem to be directly linked to the drop in the concentrations of stratospheric water vapor, she says.

Regardless of the cause of the decline, the team’s modeling suggests that the decrease in water vapor concentrations in the lower stratosphere has slowed down average global warming. The rate of increase in the average global surface temperature from 2000 to 2009 was about 25 percent lower than it otherwise would have been, the researchers report. The team’s analyses using a climate model suggest that average global surface temperatures rose only 0.1 degrees Celsius during that period, rather than the 0.14 degree increase expected because of increases in other greenhouse gases.

The researchers speculate that the amount of water vapor gradually rising into the stratosphere at tropical latitudes has decreased, possibly due to a shift in global patterns of sea-surface temperatures that influence rates of evaporation and water vapor movement.

The new findings “are a nice demonstration of the sensitivity of the climate to water vapor concentrations in the lower stratosphere,” says Andrew Gettelman, an atmospheric scientist at the National Center for Atmospheric Research, also in Boulder.

Andrew Dessler, an atmospheric scientist at Texas A&M University in College Station says he thinks the team has identified a new source of short-term variability in climate, one different from long-term drivers such as anthropogenic greenhouse gases. And even though the effect seems to be substantial, the decrease in water vapor may be temporary.

What’s more, Dessler says, humans can’t depend on a continued decline in water vapor in the lower stratosphere to slow surface warming further in the long term. “Water vapor is scarce in the lower stratosphere already, and you can’t drop below zero,” he notes. “This is not going to save our bacon.”

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• Water Vapor Caused One-Third Of Global Warming In 1990s: Study (huffingtonpost.com)
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• Slowdown in warming may be due to water vapour: study (cbc.ca)
• Water vapour caused one-third of global warming in 1990s, study reveals (guardian.co.uk)

MechanicalUniverse_DerivativeNotes

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GeneralThoughts

Of course, the links for physics in the side bar are handy references for study — especially the kinematics and dynamics notes of Dr. Evans.

So the primary concepts which will appear on this midterm:

• The Calculus – derivatives and anti-derivatives as used to define position, velocity, and acceleration – as well as the relevant trigonometry and geometry;  and effective use of a general Problem Solving Format
• from Kinematics – study of the motion of point particles; constant acceleration situations including — one dimensional motion, projectile motion, circular motion, “effective gravity” — vector equation for motion in accelerating reference frames
• from Dynamics – study of the causes of motion of point particles; definition of force, Newton’s laws – and free body diagrams, numerical analysis using Euler’s method – especially for analysis of motion with resistive forces, Lorentz and Galilean transformations for the study of relative motion
• Definition of work, the development of the Work-Energy theorem and Power

Dialogue is paraphrased from quotes in Louisa Gilder’s _The Age of Entanglement_ and David Lindley’s _Uncertainy_, with one line taken from Graham Farmelo’s Dirac biography _The Strangest Man_. There are occasional interjections from my dog, Emmy, because she’s smart like that.

If you’d like a more detailed discussion of the physics involved, check out my book _How to Teach Physics to Your Dog_, which explains quantum physics through conversations with Emmy. It will be released 12/22/2009, and available wherever books are sold.

[New York, 3 October 1789]

By the President of the United States of America, a Proclamation.

Whereas it is the duty of all Nations to acknowledge the providence of Almighty God, to obey his will, to be grateful for his benefits, and humbly to implore his protection and favor– and whereas both Houses of Congress have by their joint Committee requested me to recommend to the People of the United States a day of public thanksgiving and prayer to be observed by acknowledging with grateful hearts the many signal favors of Almighty God especially by affording them an opportunity peaceably to establish a form of government for their safety and happiness.

Now therefore I do recommend and assign Thursday the 26th day of November next to be devoted by the People of these States to the service of that great and glorious Being, who is the beneficent Author of all the good that was, that is, or that will be– That we may then all unite in rendering unto him our sincere and humble thanks–for his kind care and protection of the People of this Country previous to their becoming a Nation–for the signal and manifold mercies, and the favorable interpositions of his Providence which we experienced in the course and conclusion of the late war–for the great degree of tranquility, union, and plenty, which we have since enjoyed–for the peaceable and rational manner, in which we have been enabled to establish constitutions of government for our safety and happiness, and particularly the national One now lately instituted–for the civil and religious liberty with which we are blessed; and the means we have of acquiring and diffusing useful knowledge; and in general for all the great and various favors which he hath been pleased to confer upon us.

and also that we may then unite in most humbly offering our prayers and supplications to the great Lord and Ruler of Nations and beseech him to pardon our national and other transgressions– to enable us all, whether in public or private stations, to perform our several and relative duties properly and punctually–to render our national government a blessing to all the people, by constantly being a Government of wise, just, and constitutional laws, discreetly and faithfully executed and obeyed–to protect and guide all Sovereigns and Nations (especially such as have shewn kindness unto us) and to bless them with good government, peace, and concord–To promote the knowledge and practice of true religion and virtue, and the encrease of science among them and us–and generally to grant unto all Mankind such a degree of temporal prosperity as he alone knows to be best.

Given under my hand at the City of New York the third day of October in the year of our Lord 1789.

Go: Washington

A simple spectrometer can be built from a CD and a box. Cut a slit on one side of the box. Place the CD on the other side with about 60 degree angle. Look down into the openning on the box. The slit should not be too wide, otherwise the spectrum lines will be blurred. It should not be too narrow either, otherwise the spectrum is too dim. I use a 0.2mm wide slit.

structure of the CD spectroscope

my cereal box spectroscope (arrow: the slit)
viewing the spectrum

Let’s look at the spectra of some common light sources. [I highly recommend that you follow the link to Jerry's site and check out the rest of his photos -- good stuff]
All photos by the authors with a Nikon coolpix 995 camera.

My students will make a version which can be calibrated and “scaled”.

Copy and paste the following if the link does not work:

http://ocw.mit.edu/OcwWeb/Physics/8-01Physics-IFall1999/VideoLectures/index.htm

Having rejoiced — we come down from the mountain top [the swing], and get to work by viewing and summarizing the first five lectures [yes, this is homework for my dear physheads-- Due October 5, 2009]