Reno, Nevada is a sportsman’s paradise. Twenty minutes from world class skiing, and thirty minutes from Lake Tahoe. It is hard to imagine a more convenient place to live for winter sports, summer sports, and almost all of the amenities of a city. And if more is needed, SF is a quick 3 hours away. But there is a fairly significant threat to this lifestyle – climate change. I have only lived in Reno for two winters, but it is pretty clear that the Sierra is starving for snow. I am hopeful that the coming El Nino will help end this miserable west coast drought. But even that will be a temporary event. It seems that drought and fire may become the new norm. In addition to the lack of snow, the lake is low and the Truckee River flow rates are falling.
And by climate change standards – these observations are not so bad. It gets worse as you get closer to the poles. The changes observed in Alaska, for example, are significantly more dramatic, with temperature increases far exceeding the average 1 degree observed globally. Is this surprising? Of course not! There is no debate. Burning fossil fuels makes carbon dioxide. Carbon dioxide absorbs IR radiation. The surface of the earth absorbs solar radiation and emits IR radiation. So if there is more stuff in the atmosphere that absorbs IR radiation, then the earth absorbs more energy than it emits, and its equilibrium temperature increases. Basic stuff.
Unfortunately, it gets more complicated. Along with carbon dioxide, burning fuel also increases the concentration of aerosols (small particles) in the atmosphere. These particles tend to scatter solar radiation back out into space before it is absorbed by the earth – thereby causing a cooling effect. This has reduced the actual global temperature increase from what was expected from the observed increase in CO2 concentrations. And even worse, it is impossible for scientists to quantitatively predict the effect of aerosols because 1) particles are not uniformly distributed around the globe, and 2) light scattering off of particles depends on their shape and chemical composition. Some particles even serve as “cloud condensation nuclei”. So increased particle concentration means more cloud droplets, which in turn means brighter clouds, smaller cloud droplets, and less precipitation.
Some particles – like soot – absorb solar radiation, increasing the rate of warming. Soot particles have been observed in Arctic and Greenland snow, causing the snow to melt faster. Decreased snow cover leads to increased absorption by the ground, which leads to increased warming. This increased melting also causes methane to be released from permafrost – which is an even more potent absorber of IR radiation – causing increased warming. These “feedback” effects are even more difficult to model because they are highly non-uniform.
Here are some more complicating effects. Increasing temperatures makes more water evaporate. Water itself absorbs IR radiation in the atmosphere, further increasing warming. Also, increased global temperature shifts the frequency of the radiation that the earth emits, which in turn will change how much is absorbed by atmospheric gases. Ocean patterns will change because melting ice changes local salinity levels, which effects ocean water density. These changes in ocean patterns lead to changing weather patterns. Some scientists predict a weakening of the jet stream – which would lead to increased penetration of Arctic air into the mid-latitudes (i.e. the famous polar vortex events in the US). And if a large volcano erupts, the earth cools temporarily for a year or two. Etc., etc., etc.
The bottom line is that global climate modeling is a very, very difficult thing to do. Scientists who do climate modeling make different assumptions and come up with different scenarios. This makes it easy to close your eyes and plug your ears, and say “blah blah blah, I can’t hear you, global warming is a liberal myth because I had to wear a jacket yesterday blah blah blah”.
All I know is that there is less snow in the Sierra, and it is seriously affecting my ability to ski.