Scales of Climate Change: Pleistocene to Modern
 
Key Terms:

dendrochronology (the study of annual growth rings of trees) (dendron = tree, chronos = time, logos = word = the science of): The science that uses tree rings dated to their exact year of formation to analyze temporal and spatial patterns of processes in the physical and cultural sciences. 

Ice Age

interglacial period

Last Glacial Maximum: timing and characteristics (temperature state relative to today, sea level, extent of ice sheet or glacial coverage, concentration of carbon dioxide, vegetation distribution, precipitation, wind, ...)

Younger-Drayas (event): timing and characteristics

Heinrich Events

mid-Holocene maximum: timing and characteristics

Medieval Climatic Optimum: timing and characteristics

Little Ice Age: timing and characteristics

Maunder minimum

Pleistocene epoch

Alpine glaciers versus continental glaciers

Sea level changes as a result of glacial melt and isostatic rebound; Extent of glacial coverage and timing of the last glacial maximum

Oxygen-isotope ratio (of the ocean floor sediments and of the vertical ice cores in Antarctica and Greenland) and climatic change

Proxy data is data that paleoclimatologists gather from natural recorders of climate variability, e.g., tree rings, ice cores, fossil pollen, ocean sediments, coral and historical data. By analyzing records taken from these and other proxy sources, scientists can extend our understanding of climate far beyond the 140 year instrumental record.

Presently, glaciers cover only about 10 percent of the earth's land surface. The total volume of ice over the face of the earth amounts to a little more than 25 million cubic kilometers. Most of this ice is in the Greenland and Antarctic ice sheets, and its accumulation over time has allowed scientists to measure past climatic change. If global temperatures were to rise enough so that all of this ice melted, the level of the ocean would rise about 65 m (213 feet).

A higher ratio of oxygen 18 to oxygen 16 in the ocean floor sediment record suggests a (warmer/colder) climate, while a lower ratio suggests a (warmer/colder) climate.  

The colder the air when the snow fell, the richer the concentration of oxygen 16 in the core.

Bubbles of ancient air trapped in the ice can be analyzed to determine the past composition of the atmosphere.

Ice House and Hot House. The Earth is about 4.6 billion years old. Throughout much of its history, Earth has generally been a warm planet, much warmer than today. For at least 2.5 billion years of Earth history, sedimentary rocks and their fossil record show evidence of these warmer times and also of shorter colder periods. The cold periods of Ice House (low levels of carbon dioxide) last several tens of millions of years before the planet returns to its more prevalent Hot House ("greenhouse") state (high levels of carbon dioxide). There have been four reasonably well-documented Ice Houses. Ice Houses occurred about 2.5 billion, 700 million, and 300 million years ago, and the last Ice House began 35 million years ago. Within these Ice Houses, evidence of continental-scale glaciations is found in the sedimentary rock record. Ice ages are those periods of time when large areas of the continents were covered with thick glaciers.

 
Questions for Review:

Why do we study the earth's past climate?

How do we determine the earth's past climate?

Describe some of the methods scientists use to determine past climatic conditions?

What are the instrumented data? What are the proxy data?

What are Ice Ages? When did Ice Ages occur?

What is the temporal range (or time frame) that the proxy climate data can be used to describe the past climate? (billions of years, hundreds of millions of years, hundreds to tens of thousands of years, hundreds of years)

How does the current Climate Compare with that of the Past
How does the current temperature compare with the past 1000 years?
How has temperature and CO2 changed since the last ice age?
How does the current temperature compare with the past 400,000 years?
How does the current temperature compare with the past 600,000,000 years?
Have rapid increases in CO2 caused climate change in the past?

"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 the future." (NOAA Paleoclimatology Program)

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?
     
  • Can we find evidence in the paleoclimate record for mechanisms or climate forcings that could be causing recent climate change?
Additional Readings:
 
 

Last updated on 01/05/10 03:25 PM by Zong-Liang Yang