by Luisa Cristini, PhD., University of Hawaii at Manoa
The study of past climate, or paleoclimatology, is one of the most important fields of climate science study. The study of the past, using all time scales, is the basis for climate projections. The past is highly relevant for modern climate change, because it helps us to understand the mechanisms regulating climate and, therefore, to correctly attribute the relative importance of the many factors contributing to climate change, including natural and anthropogenic forces.
The methods for studying the paleoclimate are many and their use depends on the time scale in which researchers are examining. Methods are based on investigating changes in the physical and chemical properties of natural archives, which record climatic patterns.
“Proxy data” is the data paleoclimatologists gather from natural recorders of climate variability. Natural archives can include historical records, tree rings, lake and marine sediments, ice cores, pollen, speleothems, loess and geomorphic features. Natural recorders have different resolutions and can cover different time scales, the shortest being historical data (thousands of years) and the longest marine sediments (millions of years). From these natural archives it is possible to derive past temperature, precipitation and humidity; chemical composition of air and water; as well as vegetation patterns, solar activity, volcanic eruptions, geomagnetic field variations and sea level. A scientist will use all these forms of data to reconstruct the climate of a specific period.
From the study of natural archives, scientists discovered that the ultimate source of natural climate change is Earth’s position with respect to the Sun. Periodic changes in the Earth’s orbit over hundreds of thousands of years gave origin to the ice ages as well as to the inter-glacial eras in between. Climate can change as a result of tectonic movements, as well as to changes in the atmospheric composition, including the concentration of greenhouse gases and dust in the air.
From proxy data networks detailed reconstructions of large-scale temperature patterns over the past millennium have been constructed. These estimates indicate relatively modest variations in Northern Hemisphere mean temperature prior to the marked warming of the twentieth century. This is the footprint of human activity, which started influencing global climate beginning in the Industrial Revolution.
Annually and seasonally resolved climate records are critical to describe year-to-year patterns of climate in past centuries. Spatial resolution of climate data helps to derive a detailed description of global climate patterns. It is key now, in order to understand past and present changes in climate, to assemble the most comprehensive possible data record and to make it accessible for analysis to climatologists all over the world.
References and Further Resources
- NOAA Paleoclimatology located at http://www.ncdc.noaa.gov/paleo/paleo.html
- Gornitz, S. (ed) Encyclopedia of Paleoclimatology and Ancient Environments. Springer.
- Solomon, S., D. et. al. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, (2007) Chapter 6: Paleoclimate. Retrieved at http://ipcc.ch/publications_and_data/ar4/wg1/en/ch6.html.