Temperature and Latitude: What Causes the Uneven Warming Across the Globe?

[Mk]

http://data.giss.nasa.gov/gistemp/2005/2005cal_fig3.gif
Why does the latitude-temperture graph look the way it does?

 

[Bystander]

"Why" do you ask? About the annual changes in its appearance? About the variations in general?

You're looking at fifty years of observations/measurements taken daily for every 10-20 thousand km², some at established sites, some at transient sites, of a dynamic system. The temperature is not constant. The measurement method has not been conserved. The site locations have not been conserved.

 

[bugon]

If I understand correctly, your question is why do the higher latitudes have a higher temperature increase? And why is the northern hemisphere warming larger? If so, then here's the answer.

Irrespective of the source of warming (whether anthropogenic or not...), the climate variations at higher latitudes are always expected to be larger. This is because the temperature at low latitudes is mainly the result of the energy balance between energy emitted and absorbed at low latitudes, whereas at high latitudes, the story is different.

The temperature of high latitudes is governed not by the radiative energy reaching those latitudes but instead energy reaching low latitudes and then advected northwards through water vapor (and also oceanic currents). Basically, water evaporates (takes latent heat) at low latitudes, moves northward, condenses and releases the latent heat. Thus, the temperature at high latitudes depends on the efficiency of this conveyer belt.

When the climate warms, there is much more water vapor in the atmosphere. This implies that high latitudes can very warmed very efficiently, and the temperature difference between tropical and polar regions becomes relatively small. If the atmosphere cools, it also dries out, and the efficiency of this heat transfer is substantially diminished. The bottom line, the high latitudes are much more affected from any climate change.

The reason that the northern hemisphere changes more is because it has less heat capacity (the oceans) and can thus thermally adjust more easily.

– NJS
(http://www.sciencebits.com/" )