To understand and predict changes in the climate system, we need a more complete understanding of seasonal to century scale climate variability than can be obtained from the instrumental climate record. The instrumental temperature record indicates that the Earth has warmed by 0.5°C (0.9°F) from 1860 to the present. However, this record is not long enough to determine if this warming should be expected under a naturally varying climate, or if it is unusual and perhaps due to human activities. Paleoclimatic proxy data can be used to extend climate records and provide a longer time frame (hundreds to tens of thousands of years) for evaluating the warming of the last 140 years. The cause of global warming over the last century remains a heated debate with significant economic and societal implications. Many scientists attribute the current global warming to the enhancement of the greenhouse effect by human activities. Other scientists have suggested that other factors not affected by humans, such as changes in the number and size of volcanic eruptions or an increase in the sun's output (such phenomena are referred to as climate forcings), are responsible. A paleoclimate perspective provides information about long term changes in different climate forcings that may be the underlying cause of the observed climate change. An analogy of how paleoclimatic data improves our understanding of climate can be explained in terms of the stock market. Stock market analysts use longer term trends (one, two, three, or six months) in the stock market indexes (DOW, NASDAQ, etc.) rather than depending on changes from one day to the next or over a week to predict what the market will do next (i.e., Bull or Bear Market). In much the same way, the paleoclimate perspective allows us to evaluate climate change many decades and centuries into the past, in order to develop a more reliable estimate of how climate may change in the future.
The paleoclimate perspective can help us answer many questions, including...
- Is the last century of climate change unprecedented relative to the last 500, 2000, and 20,000 years?
- Do recent global temperatures represent new highs, or just part of a longer cycle of natural variability?
- Is the recent rate of climate change unique or commonplace in the past?
- What does it mean if the last century is unprecedented in terms of warming?
- Can we find evidence in the paleoclimate record for mechanisms or climate forcings that could be causing recent climate change?
