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A Final Word

The goal of a "Paleo Perspective on Global Warming" was to clear up some of the confusion surrounding the issues of global warming, greenhouse warming, the ozone hole, and related change in the Earth's climate system. In particular, we wanted to highlight what paleoclimatic data are, where they come from, and what the data contributes to the global warming debate.

When one reviews all the data, both from thermometers and paleotemperature proxies, it becomes clear that the Earth has warmed significantly over the last 140 years; Global Warming is a reality. Multiple paleoclimatic studies indicate that the recent year, decade, and century are all the warmest, on a global basis, of the last 600, and most likely 1200 years. It appears that the global warming of the last century is unprecedented in the last 1,200 years.

There are, however, questions remaining concerning Global Warming. For instance, what is causing all this warming and what are the implications for the future? The answers to these questions are not simple.

There is considerable debate centered on the cause of 20th century climate change. Few people contest the idea that some of the recent climate changes are likely due to natural processes, such as volcanic eruptions, changes in solar luminosity, and variations generated by natural interactions between parts of the climate system (for example, oceans and the atmosphere). There were significant climate changes before humans were around and there will be non-human causes of climate change in the future.

Just the same, with each year, more and more climate scientists are coming to the conclusion that human activity is also causing the climate of the Earth to change. First on the list of likely human influences is greenhouse warming due to human-caused increases in atmospheric trace-gases. Other human activities are thought to drive climate as well. As this web document points out, there is no doubt that humans are causing the level of atmospheric trace-gases to increase dramatically - the measurements match the predictions. There is also no doubt that these gases will contribute to global warming (since they warmed the Earth before humans). However, there is uncertainty about some issues. For example, these questions remain to be answered with complete confidence:

  • How much warming has occurred due to anthropogenic increases in atmospheric trace-gas levels?
  • How much warming will occur in the future?
  • How fast will this warming take place?
  • What other kinds of climatic change will be associated with future warming?

Paleoclimatology offers to help answer each of these questions. Several of the paleoclimate studies reported on in this web document (Briffa et al., Mann et al., Overpeck et al.) have begun efforts to attribute past climate change to both natural and human causes, and to use this information to estimate how much of the current warming is due to humans (i.e., greenhouse warming). The best estimate is that about 50% of the observed global warming is now due to greenhouse gas increases. Although this number will continue to be refined, it indicates that the climate modeling community is on target with their estimates that the earth may warm an additional 2 to 7 degrees F in the next century.

What future global warming means to society is beyond the scope of these www pages. However, the paper by Overpeck et al. also includes an analysis of what the unprecedented 20th century warming has meant so far to the Arctic environment. Because the warming already seems to be causing unprecedented changes in glaciers, permafrost, lakes, ecosystems and the oceans, it is likely that future changes will be even more dramatic as the warming continues.


For links to other www sites dedicated to Global Warming, please click here. For an overview of authors and designers who worked to create "A Paleo Perspective on Global Warming", please click here.

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