I will state from the outset that I have always been a keen proponent of minimising human effects on the environment. I first began worrying about the effects of increases in atmospheric carbon dioxide in the early 1970's, when I read about predictions that sea-levels could rise up to 10 metres by the year 2000. Since then I have (with good reason don't you think) become a little more sceptical. However, just because some predictions have failed to eventuate does not mean that we can ignore them all forever more; after all the boy who cried wolf was proven right in the end.
I also come from a scientific background and have the utmost respect for scientists. However, scientists are human, and are subject to the foibles that we all have. History has shown that accepted science is not always correct and that scientists are often not as rational and unbiassed as they would have us believe.
This is a fairly large topic so I have split it according to my four A's, that is:
accuracy - how accurate are the measurements and predictions
avoidance - assuming the predictions are accurate how easily can we avoid the consequences
adaptation - assuming we can't avoid some or all of consequences how can we adapt
acceptance - finally how can we accept what we can't avoid or adapt to
Accuracy
There are two aspects to accuracy. First, there are reports that the effects of global warming have already been measured, such as rising global temperatures. Second, there is the accuracy of the predictions to consider.
Temperatures
It is commonly stated that global temperatures have risen by about one degrees Celsius since the start of the industrial revolution based on millions of readings mainly from weather stations. Any one of these readings could easily be inaccurate for any number of reasons but the hope is that the inaccuracies will average out. However, there are systematic errors that could mean that the perceived trend of rising temperatures is not real.
One problem is that the thermometers that were used till the middle of the last century tended to give higher readings as they aged. I believe this means that global temperatures were perceived to have risen until about 1950 after which they were perceived to have fallen for a while, when in fact no such changes took place.
Another problem that I think would have a larger, though difficult to quantify, effect is human activity on local climate. Most weather stations are *not* located in isolated locations. I believe human activity in the immediate vicinity of many weather stations means that local temperatures would rise over time. However, this does not mean temperatures in remote locations have risen or even that global temperatures have risen very much.
For example, in the country town where I went to high school the weather station was located at the airport which was far from the town. Since then the land around the airport has been cleared (eg for a golf course), there is probably more air traffic at the airport, and there is also a new taxi-way not far from the weather station. All these factors mean that the air temperature is warmer in the immediate area.
Glacier Retreat
Most of the worlds glaciers are currently retreating. However, this is mainly due to the fact that the glaciers built up during the "mini ice age" about 200 years ago.
The mini ice age is generally not considered to be caused by any sort of human activity. I believe it was due to increased volcanic activity at the time.
Due to time-lags most glaciers are still retreating to their natural size for the current global temperature.
There is some evidence that glacier retreat has accelerated in the last few decades.
Sea Level
Rises in the level of the oceans will be the biggest repercussion of global warming. It is due to reduction in the size of glaciers (see above) and to thermal expansion of water. Some studies seem to indicate that man-made global warming is causing a rise in sea-levels.
Personally, I think it is very difficult to accurately measure changes in the sea-level except by satellite, since you don't know if your reference point is itself moving.
It is generally accepted that sea-levels have been rising by about 1 mm per year for hundreds of years but this is not due to human-induced global warming. The best studies indicate that there is little or no acceleration in this trend.
Climate Models
Most predictions of the effect of increased carbon dioxide in the atmosphere are based on very sophisticated computer models. I believe these models are getting better as computer processing power increases and climatologists begin to understand all the factors involved. (Certainly weather forecasts are far more accurate than they were 40 years ago.)
I think these models have several problems which I will discuss shortly, but first I will try to give you an idea of how difficult it is to model such complex and chaotic systems. I believe that the world's climate is at least as complex as the world economy. Despite all the money spent on climate modeling a lot more is spent on modelling the world economy, given all the cost/benefit involved. Despite this these models fail to predict risks, as the recent GFC has demonstrated.
There are such a huge number of variables to consider in climate modelling and they involve so many different areas of science (biology, physics, chemistry, geology, etc) it seems likely that there are huge gaps. Further, it is hard to estimate the exact size of feedback loops, time-lags etc. Due to the chaotic nature of the systems small variations in one factor can have large an unexpected effects elsewhere.
Another problems is that these models are based on data (such as the global temperatures we saw above) that may be inaccurate.
The main problem I have with these models is that they are not subject to the scientific method - ie make a prediction, test the prediction, then abandon the theory if the prediction is wrong (or else continue making and testing more predictions). With climate models if a prediction is proved incorrect then it's usually just a matter of tweaking a few variables until the model fits the facts again. In the best case if a prediction is incorrect then the "scientists" try to find some new factor(s) to explain the results, and then these factors are incorporated into the model until once again the model matches the data.
Never does anyone attempt to disprove the fundamental assumptions on which the model is based. Scientists should be trying to disprove their theory, not continually changing it to make it work.
Worse still, is that the model may be able to be tweaked in different ways to obtain the same result. The temptation would be to make adjustments that are more likely to gain more funding or have your latest academic paper pass peer review for publication in the Prestigious Climatologist Journal (not a real publication AFAIK).
Prediction Bias
This brings us to the discussion of whether climatologists tend to exagerate the effects of human-induced climate change. Unfortunately, recent leaked emails seem to indicate that many have a tendency to distort the facts. Whether this is purely for personal gain, or with the best of intentions is unclear, but the fact remains that a true scientist always seeks the truth despite personal beliefs or desires.
Their defence is that they are only trying to counter the disinformation being put out there by "skeptics". While it is true that there is a lot of unscientific nonsense being espoused by all sorts of idiots, I believe this occurs on both sides of the debate and the actual scientists should not get involved in such stupidity.
