Lessons from the Past, Roadmap for the Future
The present-day climate of the Earth is influenced by a combination of natural climate variability, increased concentrations of greenhouse gases in the atmosphere since the Industrial Revolution, and changes in land cover (such as conversion from forest to agriculture and back again).
To understand the potential range and effect of future climate and how its changes may affect marine and terrestrial systems and society, scientists rely on instrumental records that are at most a few hundred years long and longer geologic records that extend back over thousands and millions of years. The reconstructed records of paleoclimate provide important insights into potential rates and magnitudes of change, warm and cold extremes that lasted for 1000s of years, and large changes in sea level.
Combining paleoclimate data with climate modeling experiments provides a powerful method for discovering and understanding the processes and feedbacks that underlie gradual and abrupt climate change and is an essential component of testing and improving climate models that are used to project possible future climates. Paleoclimate data show how past ecosystems responded to a range of climate and environmental changes and provide an overview of their resilience. The resulting understanding of how natural systems respond to climate forcing can help guide policy makers and managers as they make plans to adapt to climate change.
What is paleoclimatology?
Paleoclimatology is the study of Earth's climate during the entire history of the Earth. Paleoclimate research uses geologic and biologic evidence (climate proxies) preserved in sediments, rocks, tree rings, corals, ice sheets and other climate archives to reconstruct past climate in terrestrial and aquatic environments around the world. Paleoclimate reconstructions provide evidence for the baseline level of climate and environmental variability before humans began using instruments to measure different aspects of climate and weather.
How far back in Earth's history can paleoclimate be reconstructed?
Paleoclimate research spans the history of the Earth. Studies that focus on the last few centuries to millennia produce high-resolution temporal reconstructions of temperature and precipitation that establish a basis for quantifying and understanding natural climate variability. Studies that focus on the past tens-of-thousands to millions of years reveal climate change and variability associated with Earth-Sun geometry and variations in greenhouse gases that controlled the waxing and waning of ice ages, abrupt changes associated with changes in ocean circulation, and geologic processes such as mountain uplift. "Deep-time" paleoclimate studies (prior to ~2.6 million years ago) provide a means to understand extreme climate states and long-term patterns of atmospheric carbon dioxide and climate.
How is past climate reconstructed?
Past climates are reconstructed from a variety of geologic and biologic archives that preserve climate proxies, or evidence of past climate and environment. Examples of archives include terrestrial or aquatic sediments, ice cores from glaciers and ice sheets, tree rings, corals, and packrat middens. These archives contain climate proxies, which are physical, chemical, or biological features that provide information on past climate and environment (such as sea level, air and ocean temperature, atmospheric composition, and precipitation).
How do we know the time period represented by a paleoclimate record?
A variety of analytical techniques are used to determine the ages of the archives and proxies. Typically, dating is used to establish the time of onset, termination, and rate of change of climate events. Many of the dating techniques employed are based on analyzing the nature of radioactive isotopes (e.g., radiocarbon, uranium-thorium) present in sample material. These dating techniques are used in conjunction with other methods such as biostratigraphy (which uses the fossil assemblages contained within a sample to estimate its age) and counting tree rings or annual sediment layers deposited ice and lakes. Other techniques such as surface exposure dating methods are used to estimate the amount of time a sample material such as a boulder deposited by an ice sheet or shoreline has been exposed on the Earth's surface to cosmic rays. Whenever possible, scientists utilize more than one dating method in order to maximize the accuracy and precision of their findings.
How can paleoclimate studies help us better understand potential consequences of future climate change?
Every component of the Earth system affects or is affected by climate. Ecosystems, water availability, carbon cycling, sea level rise, ocean circulation, and ocean acidification all interact with the climate system and respond to changes in climate. Paleoclimate studies provide an essential perspective for assessing the potential impacts of future climate on natural systems and the people who rely on them.
How is paleoclimate research useful for policy and resource managers?
Understanding the response of natural systems to climate forcing can help guide policy makers and managers as they prepare adaptation and mitigation plans for climate change. For example, knowing how past changes in the frequency and amplitude of climate phenomena such as El Niño affected ecosystems provides a framework for exploring policy and management alternatives to mitigate or adapt to future changes. Paleoclimate research that documented the natural range of variability in dissolved oxygen levels was integrated with other evidence to develop dissolved oxygen targets for Chesapeake Bay, and it increasingly is being integrated into management efforts in other critical habitats around the world.
Paleoceanographic history of the Guaymas Basin, Gulf of California, during the past 15,000 years based on diatoms, silicoflagellates, and biogenic sediments
Impact of millennial-scale Holocene climate variability on eastern North American terrestrial ecosystems: Pollen-based climatic reconstruction
Topographic, bioclimatic, and vegetation characteristics of three ecoregion classification systems in North America: Comparisons along continent-wide transects
Late Quaternary eolian and alluvial response to paleoclimate, Canyonlands, southeastern Utah
Record of the North American southwest monsoon from Gulf of Mexico sediment cores
Reconstructing a 180 yr record of natural and anthropogenic induced low-oxygen conditions from Louisiana continental shelf sediments
Species-energy relationship in the deep sea: A test using the Quaternary fossil record
Middle Pliocene sea surface temperature variability
Multiproxy evidence of Holocene climate variability from estuarine sediments, eastern North America
Ecology and shell chemistry of Loxoconcha matagordensis
Mid-Pliocene deep-sea bottom-water temperatures based on ostracode Mg/Ca ratios
High resolution climate of the past 3,500 years of coastal northernmost California
Lessons from the Past, Roadmap for the Future
The present-day climate of the Earth is influenced by a combination of natural climate variability, increased concentrations of greenhouse gases in the atmosphere since the Industrial Revolution, and changes in land cover (such as conversion from forest to agriculture and back again).
To understand the potential range and effect of future climate and how its changes may affect marine and terrestrial systems and society, scientists rely on instrumental records that are at most a few hundred years long and longer geologic records that extend back over thousands and millions of years. The reconstructed records of paleoclimate provide important insights into potential rates and magnitudes of change, warm and cold extremes that lasted for 1000s of years, and large changes in sea level.
Combining paleoclimate data with climate modeling experiments provides a powerful method for discovering and understanding the processes and feedbacks that underlie gradual and abrupt climate change and is an essential component of testing and improving climate models that are used to project possible future climates. Paleoclimate data show how past ecosystems responded to a range of climate and environmental changes and provide an overview of their resilience. The resulting understanding of how natural systems respond to climate forcing can help guide policy makers and managers as they make plans to adapt to climate change.
What is paleoclimatology?
Paleoclimatology is the study of Earth's climate during the entire history of the Earth. Paleoclimate research uses geologic and biologic evidence (climate proxies) preserved in sediments, rocks, tree rings, corals, ice sheets and other climate archives to reconstruct past climate in terrestrial and aquatic environments around the world. Paleoclimate reconstructions provide evidence for the baseline level of climate and environmental variability before humans began using instruments to measure different aspects of climate and weather.
How far back in Earth's history can paleoclimate be reconstructed?
Paleoclimate research spans the history of the Earth. Studies that focus on the last few centuries to millennia produce high-resolution temporal reconstructions of temperature and precipitation that establish a basis for quantifying and understanding natural climate variability. Studies that focus on the past tens-of-thousands to millions of years reveal climate change and variability associated with Earth-Sun geometry and variations in greenhouse gases that controlled the waxing and waning of ice ages, abrupt changes associated with changes in ocean circulation, and geologic processes such as mountain uplift. "Deep-time" paleoclimate studies (prior to ~2.6 million years ago) provide a means to understand extreme climate states and long-term patterns of atmospheric carbon dioxide and climate.
How is past climate reconstructed?
Past climates are reconstructed from a variety of geologic and biologic archives that preserve climate proxies, or evidence of past climate and environment. Examples of archives include terrestrial or aquatic sediments, ice cores from glaciers and ice sheets, tree rings, corals, and packrat middens. These archives contain climate proxies, which are physical, chemical, or biological features that provide information on past climate and environment (such as sea level, air and ocean temperature, atmospheric composition, and precipitation).
How do we know the time period represented by a paleoclimate record?
A variety of analytical techniques are used to determine the ages of the archives and proxies. Typically, dating is used to establish the time of onset, termination, and rate of change of climate events. Many of the dating techniques employed are based on analyzing the nature of radioactive isotopes (e.g., radiocarbon, uranium-thorium) present in sample material. These dating techniques are used in conjunction with other methods such as biostratigraphy (which uses the fossil assemblages contained within a sample to estimate its age) and counting tree rings or annual sediment layers deposited ice and lakes. Other techniques such as surface exposure dating methods are used to estimate the amount of time a sample material such as a boulder deposited by an ice sheet or shoreline has been exposed on the Earth's surface to cosmic rays. Whenever possible, scientists utilize more than one dating method in order to maximize the accuracy and precision of their findings.
How can paleoclimate studies help us better understand potential consequences of future climate change?
Every component of the Earth system affects or is affected by climate. Ecosystems, water availability, carbon cycling, sea level rise, ocean circulation, and ocean acidification all interact with the climate system and respond to changes in climate. Paleoclimate studies provide an essential perspective for assessing the potential impacts of future climate on natural systems and the people who rely on them.
How is paleoclimate research useful for policy and resource managers?
Understanding the response of natural systems to climate forcing can help guide policy makers and managers as they prepare adaptation and mitigation plans for climate change. For example, knowing how past changes in the frequency and amplitude of climate phenomena such as El Niño affected ecosystems provides a framework for exploring policy and management alternatives to mitigate or adapt to future changes. Paleoclimate research that documented the natural range of variability in dissolved oxygen levels was integrated with other evidence to develop dissolved oxygen targets for Chesapeake Bay, and it increasingly is being integrated into management efforts in other critical habitats around the world.