The global warming issue has been labeled the "Science of Uncertainty": (1)Although we are able to measure a significant rise in global average temperatures in recent years, we are unable to determine how much of the warming is due to the increases in greenhouse gases and how much is part of some natural cycle; (2)We are unable to predict exactly how climate will change in the future with higher levels of greenhouse gases and exactly what the impacts of climate changes will be on humans and other life on the planet. This makes it difficult for all people to come together and agree on what, if anything, should be done. Scientists are working on reducing the uncertainties, but due to the complex nature of the climate system, we should not expect certain answers to all questions. We have to make decisions which weigh uncertain risks against the costs of taking action. See Global Warming Facts and Uncertainties
If nothing else, the human race is in the process of performing a huge experiment on global climate by increasing greenhouse gas concentrations. The concentration of carbon dioxide in the atmosphere is probably greater now than at any time over the last several hundred thousand years. The outcome of this experiment is uncertain. Are we ready and willing to take the risks? So far the answer is yes, because in spite of all the talk about global warming, the rate of greenhouse gas emissions continue to increase. This is especially relevant for the people of the United States who by far emit more greenhouse gases per person than any other nation on Earth. By the way, if you are one of those people who believe that even though adding greenhouse gases is probably not a good thing, we should wait to deal with the problem until we are more sure that greenhouse gases are causing us problems, you need to keep in mind that there will likely be no "quick fix". Once released into the atmosphere, greenhouse gases remain for quite some time, and there is a significant delay before the complete climate change, at the higher greenhouse gas concentrations, is fully realized. In accordance with those who believe that we should not take the potential risks associated with climate change here is an interesting comparison between climate change and tobacco use.
Still others do not perceive much risk at all. While most anthropogenic global warming "skeptics" do not deny that the world is getting warmer, they do doubt that human activity is the cause. Some say the changes now being witnessed are not extraordinary - similar, rapid changes can be seen at other times in Earth's history when humans either did not exist or were incapable of effecting climate change. There are many reputable physicists and climatologists who have concluded that natural variations in the Sun's energy output are the prime influence on both historical and recent temperature trends (e.g., It's the Sun Stupid). These researchers claim that many of the historical climate changes that have occurred on Earth, including recent climate changes that have been documented by human civilizations, are caused by variations in the energy output of the Sun. An appealing aspect of the solar theory of climate change is that it may partially explain many of the long ago fluctuations in climate. If changes in solar output mattered in the past, then there is a good chance that it is still an important factor in modern climate changes. Certainly changes in greenhouse gas concentrations cannot explain historical changes in climate ... only possibly changes that have occurred in recent decades after human activities significantly increased the amounts of these gases in the atmosphere. It is difficult to sift through and evaluate all of the arguments for and against variaitions in the sun as being the most important driver of long term climate changes. I will try to briefly summarize here. Some researchers have reported strong correlations between various measures of solar activity (e.g., number of sunspots, length of the ~11 year solar cycle, etc.) and climate changes in temperature and precipitation patterns. Reconstructions of past changes in solar activity and past changes in temperature and precipitation are uncertain, so there are disagreements about the degree of correlation. Another issue (to some) is that the changes in solar activity are seemingly too small to explain the changes in temperature. This because climate models predict that the temperature changes related to changes solar activity are very small and insignificant compared to changes caused by increases in greenhouse gases. Although correlation does not prove causation, there must be correlation for there to be causation. Also noting that there is much about the climate system that we do not understand (and are not able to simulate with climate models), there is a very reasonable chance that changes in solar activity are very important in understanding climate changes. Until we can prove otherwise, the solar theory of climate change should not be dismissed.
As mentioned on the previous page, other research groups point to known geophysical oscillations, such as the Pacific Decadal Oscillation (PDO), to explain recent and past temperature changes. Thus there are a good number of researchers who believe that recent temperature changes are not much influenced by human emissions of greenhouse gases. Recent climate changes are just part of natural variations in climate, and humans and most other forms of life have survived past changes just fine. Nevertheless, there are many climate scientists who believe that, even on top of the natural variability of the climate, something out of the ordinary is happening and humans are to blame. The next 30 years or so may help us better determine what is most responsible for for modern climate changes. There are quite a few researchers that are predicting a decades-long period of global cooling based on their assertions that we are beginning a period of lower solar activity and/or a cold phase of the PDO. This contrasts strongly with global climate models that predict continued warming due to greenhouse gas forcing.
Yet another group of people do not deny that temperatures are warming and also believe that it may be caused by human activity (although we cannot be sure at this point mainly because climate models are not good enough to answer this question), but they are unconcerned about the possible consequences. In essense they do not believe the doom and gloom future senarios projected by the IPCC 2007 report. This group wonders why we should go through economic and personal hardships required to signficantly reduce our emissions of greenhouse gases, since in comparison, those hardships will be much worse than the consequences of any climate changes that we may or may not cause. For example see the recent Newsweek article written by Havard atmospheric scientiest Richard Lindzen Learning to Live with Global Warming: Why So Gloomy?
There are many diverse opinions on how to deal with the global warming issue. Each of us needs to make up our own mind. Are you willing to make sacrifices now to reduce the potential (and uncertain) consequences of global warming? Personal sacrifices would be consciously limiting your activities which release greenhouse gases (like driving or energy usage). Societal sacrifices would be government regulations that force individuals and companies to reduce emissions of greenhouse gases.