Originally posted by Gabe Garfield
Three major problems with asserting that global warming is occurring:
1. There simply aren't enough measurements being taken.
Satellites actually provide an alternative data source - and they are not limited to only taking measurements over land. Where we don't have adequate measurements is in the deep oceans. Water is particularly handy at storing heat - and we only have a reasonable idea of the temeratures at the surface. Nevertheless, I don't think inadequate sampling is the problem - global warming is clearly happening - the real debate among atmospheric scientists is why this warming is occuring.
2. Microscale effects on thermometers.
You are absolutely correct on this - a typical thermometer is only exposed to a very small portion of air around it - and that measurement is used as representative of a very large region. However, for the global warming argument - it is more important to look at the long term trends at a given station, where microscale effects become a bias and do not impact the tendencies. An exception is when the area around the weather station has been altered over time, or if a station is moved, as they often are with urbanization moving too close to previously rural areas where weather instruments are located. When this is a factor, then special care must be taken. That said, urbanization alone is obviously increasing surface temperatures as well - we are all familiar with urban heat islands - and this is a contributor to global warming, but by how much is tough to tell.
As already stated, whether the globe is warming is not at issue - it is. Polar caps are melting, the oceans are warming, the thermohaline circulation is changing, the surface and upper atmosphere are warming. These things are all known. There are a number of factors that goes into understanding the cause of global warming - and let me offer just one to prevent and endless rant.
The deep ocean current conveyor belt is associated with water from the western Atlantic (Gulf Stream) meeting cold and less saline (mixed with ice melt from the north pole) water that then sinks in the north Atlantic to the deep ocean. This current of water flows down around the southern tip of Africa and then eventually upwells into the central Pacific ocean, and returns as a surface ocean current to the Atlantic.
http://www.poemsinc.org/oceano/world14.gif
This process takes ~ 500 years for the same water to make a cycle - so the water currently upwelling in the Pacific was last exposed to the atmosphere long before the anthropogenic issue came about. Like how water vapor is saturated in air above water surfaces, gases are also saturated into water - and this is kept in balance with the vapor pressure of the gases. Since the atmopheric constituency has changed since the last time this upwelling water was at the surface, then the ocean is subsaturated with respect to some gases (recall Dalton's law of partial pressures), it then absorbs additional gas (such as CO2) to regain balance. The exact rate at which this occurs is rather difficult to measure - as the local rates (for a small patch of ocean) are very small - but over large areas, such as the central Pacific, the integral effect can be quite substantial. Aside from the gas balance, there is also thermal balance, as if the temperature of the sinking water is slightly warmer, then eventually the water upwelling also becomes slightly warmer - but the effect is delayed for some time.
This is one of probably hundreds of processes that go into understanding global gas and the subsequent energy balance that make the problem overwhelming complicated - and is why scientists are having such a tough time providing a clear and concise before and after kind of picture.
Glen
