Introduction to Global Warming and Climate Change

Global warming refers to an increase in surface temperatures that may come about due to the activities of humans. This can be due to anthropogenic emissions of greenhouse gases (enhancing the natural atmospheric greenhouse effect), anthropological changes in land use (for example, deforestation or city-building), or other human activities. We usually include any climate response to the anthropogenic forcing in this discussion. For example, if the average global surface temperature goes up, this will shift weather patterns causing some areas to warm, some areas to cool, some areas to become wetter, and some areas to become drier. No one expects that all areas will be affected in the same way by anthropogenic perturbations. Perhaps it would have been better to use a term such as "anthropogenically-induced climate changes" rather than global warming, which seems to imply that everywhere will get warmer by the same amount.

This issue is hotly debated and will continue to be for the foreseeable future. Some of you may find yourself in a position either in government or industry where you will have to make a decision that takes into account how human activities may affect the environment in which we live (both short-term and long-term changes). Even if all you do is vote for a particular issue or candidate based on the their stance about global warming, I think it is important that you can all make informed decisions. Too often, we are only told part of the story, especially by those who would like to sway opinions over to their point of view. If you don't know better, their arguments can be quite convincing. You need to understand this issue well enough to be able to make up your own mind about how to act.

As we go along, I will try to point out some common misconceptions about global warming. One that I would like to mention at the outset is that global warming and the ozone hole are not the same thing. They are two separate issues, although both result from anthropogenic activities.

What is Climate Change?

Climate change reflects significant shifts in the mean state of the atmosphere-ocean-land system that results in shifts in the atmosphere and ocean circulation patterns, which in turn impacts regional weather. It is not just changes in the average temperature for a region that determines climate change. Other examples of climatic components were listed in a previous lecture page difference between weather and climate. The distribution and frequency of extreme events is more important in determining what type of life can exist in a given ecosystem than the average conditions. You should also realize that a relatively small change in the average conditions can correspond to relatively larger changes in the frequency of extreme events. An illustrative diagram will be drawn in class.

People often talk about climate change only in terms of the changes in the average surface temperature of the Earth. You may have heard predictions such as "the global average temperature is expected to increase by 4°C over the next 100 years." The change in global average temperature is only part of the story. A change in the global average surface temperature does not mean all regions of the Earth will experience the same change in temperature. In some areas, the average temperature may change drastically, while in other areas, no changes may occur. Also keep in mind that temperature is only one component of climate as discussed above. There are many different climate zones around the Earth. It is the regional changes in a particular climate zone that are most important to the inhabitants of that area, not the change in global average temperature. The ultimate question is will the inhabitants of a particular ecosystem be able to adapt to the changes?

Perhaps the biggest misunderstanding by the general public concerning weather vs. climate is to cite extreme weather events as evidence that something is up with the climate. For example: the debate about global warming seems to get more attention during a prolonged summer heat wave; or after a disasterous severe weather event such as a tornado outbreak or a strong hurricane, you get people saying that the climate is becoming more hostile (possibly due to the evil actions of people). We need to realize that a particular extreme weather event by itself tells us nothing about climate change. Extreme weather events have been noted all through human history and will continue to occur into the future. Changes in climate take place over many years, thus for climate change, there would have to be a measurable change in the frequency of extreme events over a prolonged period.