Archive for February 2011

The frozen tundra could heat the Earth

February 22nd, 2011 by Sarah Pryputniewicz

A new study from the University of Colorado suggests that 66% of Earth’s permafrost could disappear by the year 2200.  And this could be really bad for Earth’s temperature.

If the temperature increases, the permafrost melts.  Simple enough, right?  But it’s slightly more complicated.  Trapped in the permafrost is lots and lots of carbon–in the form of plant material trapped in the frozen soil.

When it’s frozen, bacteria and fungi don’t break it down quickly.  But when it’s thawed out, the plant material quickly decays.  As soil bacteria and fungi break down the organic matter, they release tons of carbon dioxide into the atmosphere. This leads to higher temperatures and more thawing permafrost.

“The amount we expect to be released by permafrost is equivalent to half of the amount of carbon released since the dawn of the Industrial Age,” said Kevin Schaefer, lead author on the study.

Greater reductions in fossil fuel emissions to account for carbon released by the permafrost will be a daunting global challenge, Schaefer said. “The problem is getting more and more difficult all the time,” he said. “It is hard enough to reduce the emissions in any case, but now we have to reduce emissions even more. We think it is important to get that message out now.”

http://www.sciencedaily.com/releases/2011/02/110216132100.htm

Explore the relationship between temperature and greenhouse gases in our activity, “What will Earth’s climate be in the future?

Going up?

February 17th, 2011 by Sarah Pryputniewicz
A new study from the University of Washington suggests that Earth’s temperature will keep increasing, even if all greenhouse gas emissions were stopped right now.
Why?  Because greenhouse gases will last longer in the atmosphere than particulate matter (aerosols) that reflect the sun’s light.  So, the solar radiation coming in will increase and the heat energy will be reflected by the greenhouse gases.  (Explore the relationship between temperature, greenhouse gases, and albedo in our activity, “What will Earth’s climate be in the future?“)
How much would the temperature rise if we were able to cut all greenhouse gas emissions right now?  In the best case scenario, global temperature will actually decline.  In the worst case scenario, the global temperature would rise by 3.5°F.
Why the big disparity?  Scientists don’t really know the overall effect of the aerosols, particles as disparate as soot from burning fossil fuels and sea salt.  But this doesn’t mean that their predictions are worthless:
“… uncertainties do not lessen the importance of the findings, he said. The scientists are confident, from the results of equations they used, that some warming would have to occur even if all emissions stopped now. But there are more uncertainties, and thus a lower confidence level, associated with larger temperature increases.”
Ending all greenhouse gas emissions immediately is not a realistic option.  So Earth’s temperature will likely increase further.  How much?  Scientists are still tweaking the models to determine that.
http://www.sciencedaily.com/releases/2011/02/110215150845.htm

Comparing convection and conduction using Energy2D

February 6th, 2011 by Charles Xie
The following are two Energy2D simulations that compare convection and conduction, which should run within this page if you have installed Java and Java applets are enabled with your browser. The first one shows the case of natural convection. The second one shows the case of forced convection.

Instruction: Click inside a simulation window. Press 'R' to  start or stop, 'T' to reset, 'L' to reload the initial configurations, and 'G' to open or close a graph. The virtual temperature sensors can be moved around, though most other pieces are locked to their positions. Right-click on the windows for more actions.

Natural convection (driven by thermal buoyancy):

Forced convection (driven by airflow):


A Von Kármán vortex street.
The following screenshot shows a typical Von Kármán vortex street produced from the second simulation. Energy2D is also capable of producing other interesting fluid patterns such as mushroom cloudsBernard's Cell, and the Kelvin–Helmholtz instability.

More generally, Energy2D is a Java application that allows users to create interactive, real-time simulations of heat and mass flow. A simulation you create can be easily placed on the Internet just like what you saw above.

On a separate note, below are two results for conduction simulations using Energy2D that illustrate the circuit analogy: Ohm's Law is the electrical analogy of Fourier's Law of Heat Conduction. It is interesting to note that Ohm actually drew considerable inspiration from Fourier's work on heat conduction in the theoretical explanation of his work (see Ohm's Law in Wikipedia). Ironically, today's students seem to be more familiar with Ohm's Law than Fourier's Law. So the circuit analogy is used in textbooks to help students understand heat conduction.

The analogy to a parallel circuit.
The analogy to a series circuit.