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.
Arctic Biogeochemical Response to Permafrost Thaw (ABRUPT)
Understanding long-term drivers of vegetation change and stability in the Southern Rocky Mountains with paleoecological data and ecological models
Quaternary Hydroclimate Records of Spring Ecosystems
Past Perspectives of Water in the West
Impacts of coastal and watershed changes on upper estuaries: causes and implications of wetland ecosystem transitions along the US Atlantic and Gulf Coasts
Drivers and Impacts of North Pacific Climate Variability
Wetlands in the Quaternary
Pacific Ocean Patterns, Processes, and Productivity (POP3): Impacts of ancient warming on marine ecosystems and western North America
Sea Level and Storm Hazards: Past and Present
Reconstructing Ocean Circulation & Hydroclimate in the Subtropical Atlantic
Natural Drought and Flood Histories from Lacustrine Archives
Geological Investigations of the Neogene
- Overview
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).
Sources/Usage: Public Domain.Researchers from the USGS, US Naval Research Laboratory, the College of William & Mary, and the Virginia Institute of Marine Science prepare to section and sample a 20 meter long sediment core collected in Chesapeake Bay by the R/V Marion Dufresne. This core and others provide documentation for how water quality and temperature varied naturally, as well as the impacts of human activities in the watershed. Learn More 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).
Paleoclimate Archives and Proxies 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.
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Arctic Biogeochemical Response to Permafrost Thaw (ABRUPT)
Warming and thawing of permafrost soils in the Arctic is expected to become widespread over the coming decades. Permafrost thaw changes ecosystem structure and function, affects resource availability for wildlife and society, and decreases ground stability which affects human infrastructure. Since permafrost soils contain about half of the global soil carbon (C) pool, the magnitude of C losses...Understanding long-term drivers of vegetation change and stability in the Southern Rocky Mountains with paleoecological data and ecological models
Drought and fire are powerful disturbance agents that can trigger rapid and lasting changes in the forests of western North America. Over the last decade, increases in fire size and severity coincided with warming, drought, and earlier snowmelt, factors that projected climatic changes are likely to exacerbate. However, recent observations are brief relative to the lifespans of trees and include...Quaternary Hydroclimate Records of Spring Ecosystems
Desert springs and wetlands are among the most biologically productive, diverse, and fragile ecosystems on Earth. They are home to thousands of rare, endemic, and endangered plants and animals and reflect the availability and health of emergent groundwater. Despite the ecological importance of these wetlands, our knowledge of how they might respond to predicted future climate change is limited...Past Perspectives of Water in the West
In the intermountain west, seasonal precipitation extremes, combined with population growth, are creating new challenges for the management of water resources, ecosystems, and geologic hazards. This research contributes a comprehensive long-term context for a deeper understanding of past hydrologic variability, including the magnitude and frequency of drought and flood extremes and ecosystem...Impacts of coastal and watershed changes on upper estuaries: causes and implications of wetland ecosystem transitions along the US Atlantic and Gulf Coasts
Estuaries and their surrounding wetlands are coastal transition zones where freshwater rivers meet tidal seawater. As sea levels rise, tidal forces move saltier water farther upstream, extending into freshwater wetland areas. Human changes to the surrounding landscape may amplify the effects of this tidal extension, impacting the resiliency and function of the upper estuarine wetlands. One visible...Drivers and Impacts of North Pacific Climate Variability
Climate model forecasts indicate an increase in extreme hydrologic events, including floods and droughts, for California and the western U.S. in the future. To better understand what the consequences of this future change in climate may be, USGS scientists are studying the frequency, magnitude, and impacts of past hydroclimate variability and extremes in the region. This project produces well...Wetlands in the Quaternary
Wetlands accumulate organic-rich sediment or peat stratigraphically, making them great archives of past environmental change. Wetlands also act as hydrologic buffers on the landscape and are important to global biogeochemical cycling. This project uses wetland archives from a range of environments to better understand how vegetation, hydrology, and hydroclimate has changed on decadal to multi...Pacific Ocean Patterns, Processes, and Productivity (POP3): Impacts of ancient warming on marine ecosystems and western North America
Projections for AD 2100 suggest warming of +1-4°C in the North Pacific Ocean, which will result in widespread transformations throughout the marine environment and western North America. Many of these changes are beyond the predictive capabilities of current climate models. To better address this future uncertainty, our team is developing a geological framework using past warm intervals as...Sea Level and Storm Hazards: Past and Present
Sea level and Storm Hazards: Past and Present is a multidisciplinary study of past changes in sea level. Prehistoric shorelines can be used as a baseline for current and future sea level changes under warmer-than-present climate. Emphasis is placed on looking at sea levels during warm periods of the last 500,000 years as well as how base level changes increase the risk of coastal inundation during...Reconstructing Ocean Circulation & Hydroclimate in the Subtropical Atlantic
Changes in rainfall patterns as a result of anthropogenic climate change are already having large ecological and socioeconomic impacts across the globe. Increases in flood damage, wildfire damage, and agricultural losses can all be attributed to anomalous rainfall events and prolonged droughts across the United States in recent years. Additionally, Atlantic Ocean circulation, which has a large...Natural Drought and Flood Histories from Lacustrine Archives
Previous work performed as part of the USGS Holocene Synthesis project illuminated complex centennial-scale patterns of drought and wetter-than-average conditions across the North American continent interior during the past two millennia, where paleorecord data coverage is sparse. In order to explain the patterns of naturally-occurring drought, floods, and storms for the past, identified by the...Geological Investigations of the Neogene
More than a third of the United States population lives in counties directly on the shoreline, making them vulnerable to hazards associated with changing sea level and storm surges associated with hurricanes and severe storms. The geologic record contains many examples of past intervals of warm climate and high sea level. "Geological Investigation of the Neogene" is examining proxy records of... - Data
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