Climate variation and its effects on our land and water : Part A, Earth science in climate research

CONTENTS

Preface - - - - - - - -- --- -- - iii Summary - - ---_________ _ ___ ____ ____ __ 1 Introduction ----- -- ________ _______ _ 2 Roles and methods of earth science in climate research - - _ - -- __ __ 4 Types of evidence available _____ - ____ 6 Lengths of time involved ---- ____ _ _ 8 Areas most affected by climate change --- _ 11 Agencies and institutions concerned with climate change --------- ----- _ _ _ 12

SUMMARY INTRODUCTION

Organization and the International Council of Scientific Unions.

Two reports by the Central Intelligence Agency that directed attention to the geopolitical consequences of climate change.

A wave of recent magazine and newspaper articles, television programs, and books. All these sources document beyond a doubt that climate greatly affects our water, food, energy, and land resources and that long-term variations and future change in climate would markedly affect our lives.

Although climate is considered by many to be an atmospheric phenomenon, those who study it realize the extent of interaction between the atmosphere and the other surf icial components of our globe the oceans, ice sheets, and land. Changes in any one component produce changes in all of the others. Past changes in climate are therefore also imprinted on the geologic record, and it is the evidence of those former climate changes in the oceans, ice sheets, and continents that is the object of study for a large number of earth scientists.

For nearly a century, earth scientists of the U.S. Geological Survey have been among those studying the record of past climate change as well as the geological consequences of our present climate. These studies, carried on within the same research organization for this length of time, have resulted in (1) advances in our understanding of past climates, (2) constantly improved bases for estimating the impact of future climate change on our land and water resources, and (3) maintenance of a nucleus of scientists that have developed high levels of expertise in these fields. Although most of the information generated by these studies is available to scientific journals, books, and maps, it is widely scattered as a result of the diversity of subject matter, and no center for coordination of such data currently exists because of the full-time commitment of Survey scientists to other programs and projects that also have high priorities.

As a start in coordinating information being generated by the Geological Survey, a workshop was convened near Denver on December 7-9, 1976, to exchange ideas about research that is oriented toward climate, climate variation1, and the effects of climate on the Nation's land and water resources. During workshop discussions, a consensus arose that: (1) the roles of earth scientists and the research methods available to them are not well known to many non-scientific groups and agencies, and that a brief and relatively non-technical summary would be helpful, (2) a very large amount of information related to present and past climates is being generated by current Survey projects, and that scientists, both in and outside the Survey, would benefit from a review of the scope and findings of these projects, and (3) a program of research by Survey scientists should be developed, emphasizing certain lines that are especially needed. This is the first of a three-part report that responds to these needs.

ROLES AND METHODS OF EARTH SCIENCE IN CLIMATE RESEARCH

The goals of climatic research are to improve our understanding of how the climate system works, what it may do in the future, and what may be the consequences. Earth science has three major roles to play toward the achievement of these goals:

(1) Defining the long-term records of climate variability.

(2) Determining geological, geochemical, and geophysical factors that influence climate change.

(3) Estimating the physical and biological consequences of possible future climates. The first responsibility stems from the principle that an understanding of the causes and the probability of future climatic variation requires knowledge of the timing, nature, and limits of past variations over long periods of time. This perspective comes from viewing past climates as recorded by the geologic record. The second role follows from the geologic evidence that changes in factors that strongly influence the climate system have occurred with time; these influences include the distribution and thermal properties of the oceans, ice sheets, and continents and the occurrence of events such as large volcanic eruptions. The third responsibility follows from the fact that it is the physical consequences of a new climate that would become most important to man in the event of future climatic change. Measuring the relations between climate and earth-surface processes can lead to estimates of the physical and biological consequences of future climatic variation. Quantitative interpretations of the relations between both present and past climates and their effects on the earth's surface become keys to assessing the human consequences of possible future climatic variations.

The relation between the earth sciences and meteorological, oceanographic, and other sciences involved in a climate program is complex because their scientific domains overlap extensively. Investigations of both present and past climates are inherently interdisciplinary; many branches of the theoretical, observational, and laboratory sciences are involved, and almost all of them draw on data, constraints, and techniques derived from others.

The methods used by the earth sciences to fulfill their roles are many and varied. One way of dividing them is on the basis of the area from which the record is collected from the ocean floors, the ice sheets, or the continents. Records from the ocean floors have yielded exciting and rather complete evidence of climatically induced changes in the fauna and in the temperature, salinity, and isotopic composition of sea water during the ice ages. Work on existing ice caps has also produced important information about the history of global climate in the polar regions. The continents account for only 30 percent of the Earth's surface, and they influence climates the least, but they respond to climate change most rapidly. As they also provide the main source of food and shelter for most of the Earth's population, relatively direct benefits stem from investigations of the ways in which climate interacts with natural processes in the continental environment. One major goal of a climate program, therefore, must be to understand more about how that environment could be affected by inadvertent or naturally caused climatic variation. Most of the climate research now in progress in the Geological Survey, described in Part B of this Circular, is concerned with this aspect of the climate problem.

Long cores from the deep sea floor have been available in large numbers only during the past decade or two. The methods used by earth scientists in studying them, therefore, have mostly been developed or improved during that period. Sea-floor sedimentation tends to be slow but continuous, and the records from these cores are valuable for their completeness. Climate data from the cores are chiefly derived from fossil, mineralogical, chemical, and isotopic variations that indicate past changes in the composition and temperature of the ocean water and the volume of water locked in the polar ice sheets. Other records include volcanic ash layers, which record major eruptions that possibly altered the atmospheric transparency, and debris dropped by melting icebergs, which record the existence of sea-level glaciers. The ages of events in sea-floor cores are commonly based on a combination of biostratigraphic, radiometric, paleomagnetic, and sedimentation rate methods. Dated cycles of ocean-wide isotopic variations provide a secondary correlation and dating method; these cycles were caused by the changing proportions of the isotopes oxygen-18 and oxygen-16 in the oceans and the polar ice sheets (which concentrate oxygen-16 more than does sea water) as the ice sheets expanded and contracted. Continuous records of the past several million years are recorded in many cores. Reports by the CLIMAP research group 2 exemplify paleoclimatic data obtained from the sea floor, and those papers plus the references in them to the work of others encompass a part of the known techniques and sources of data.

Earth scientists studying ice sheets in the Antarctic and Greenland, and glaciers in mountainous regions, derive data on climate from the hydrogen and oxygen isotopes of successive layers of snow and ice, or the chemical, biological, or clastic variations in the stratigraphy provided by the annual accumulation layers. Isotopic variations in the oxygen-18 and deuterium (hydrogen-2) of the ice reflect changes in atmospheric temperatures where the snow crystallized. Variations in the other ingredients reflect atmospheric transport phenomena and conditions in ice-free areas of those latitudes. The climates that were responsible for large expansions and contractions of ice sheets and glaciers in the past are also estimated on the basis of variations in the present glacier sizes that occur in response to observed variations in climate. Records based on the stratigraphy of glacier ice extend back several tens of thousands of years; ages are assigned by counting annual layers in the younger deposits and calculating theoretical rates of compaction and flow in the older deposits.

Climate leaves its imprint on the continents in an extraordinarily large number of ways, and the earth science record of continental climate consists of the numerous kinds of imprints that leave a permanent record. Almost all of them are indirect measurements of the climate itself, and much of the science concerned with the reconstruction of past climates thus involves translating these records of climatic response back into separable climate elements temperature, precipitation, wind, storm frequency, humidity, cloudiness, and storm trajectories. However, a very large number of these imprints are direct records of the very phenomena that would be of importance to man in the event of future climatic variation floods, erosion, avalanches, landslides, mudflows, hurricanes, dust storms, droughts, and many others. Earth science records of these types, therefore, can commonly be used directly for estimating climate-related climatic conditions allows actual values of past temperatures and precipitation to be estimated. Lakes in closed basins that enlarged during periods of wetter climates indicate, by their sizes and areas, a definite ratio of inflow (related to precipitation) to evaporation (related to temperature). Similar and comparably accurate estimates of these climatic elements can be made on the basis of the former increased extent of glaciers. The mineralogy and ratios of stable isotopes in some sediments and cave deposits provide approximations of the mean annual temperatures of the surrounding areas. The geometry of a stream channel that is underfit or no longer occupied indicates the size of the largest stream that occupied it, and this allows estimates of peak runoff volumes in the past that may suggest the seasonal distribution of maximum rainfall. Evidence indicating variations in the past elevations of perennial snow and permafrost at high latitudes and altitudes quantitatively documents past variations in the mean annual temperatures of the regions. The distribution and annual variation in the vertical positions of near-surface thermal profiles record the mean annual temperatures of an area during the past century or more.

Maximum wind velocities and directions during storms are indicated by the shape and internal structures of stable or buried sand dunes, by wind-eroded landform's, and by the location and size of erosional shorelines and sand or gravel bars formed in extinct lakes. The sizes of fragments transported by winds or waves allow estimates of maximum wind velocities. High-altitude wind directions are indicated by the downwind distribution of volcanic ash from major eruptions.

Brief periods of unusual climate droughts, drenching rains, floods, hot spells, cold snaps, dust storms, and hurricanes also are recorded in the record available to the earth scientist. Long droughts, for example, are indicated by soils or interlayered thin beds of salts in lake beds, by strata that contain unusual amounts of windblown sand, by the development of bad land topography, and by concentrations of certain fossils the remains of terrestrial animals that died for lack of water, of aquatic animals that succumbed to increased salinities, or of dry land plants that moved into areas formerly occupied by lakes or swamps. Times of drenching rain and major floods are suggested by deposits indicative of widespread landslides and mudflows and by layers of abnormally coarse sediments in stream deposits or nearshore lake and marine records. Brief periods of atypical warming or cooling are suggested by temporary changes in fossil assemblages. Periods of exceptional wind or reduced vegetation cover are documented by wind-eroded landforms and by isolated layers of windblown silt or sand in both continental and marine deposits.

The characteristic storm paths and the synoptic meteorological patterns that prevailed during successive periods also can be inferred. The directions of the strongest winds, deduced from the criteria noted above, indicate the synoptic regimes that produced the strongest barometric gradients. The isotopic composition of samples of "fossil" water in glaciers, permafrost, ground water, and certain saline minerals provide information on the storm tracks and condensation-level temperatures that produced rain and snow during past intervals of time. Plant communities are sensitive to the seasonal distribution of precipitation as well as the amount, and changes in the composition of a fossil fauna and flora can indicate changes in the synoptic nature of the seasonal climates.

Dated chronologies of climatic change are established by a variety of radiometric and other laboratory age-dating techniques, by field methods that produce both absolute and relative ages, and by correlation of undated strata with strata in other areas where they are dated. Ages are usually expressed in terms of years (before the present, B.P.) or geologic periods (see back cover).

Climate records may be viewed in terms of the time span and time resolution they provide. Time resolution and accuracy of climatic reconstruction are progressively better for younger events. This point can be illustrated by describing the climatic histories and the nature of their record for six progressively longer blocks of time; successive blocks contained comparably greater climatic changes, but the quality and resolution of their records become progressively less: (1) the past 100 years, (2) the past 1,000 years, (3) the past 15,000 years, (4) the past 150,000 years, (5) the past 1,000,000 years, and (6) the past 50,000,000 years.

Climatic variation during the past 100 years is reconstructed from instrumental, written, photographic, and geologic records from much of the globe. The waning stage of a centuries-long cold period produced temperatures during the first part of this period that were still 0.2 to 0.4 degrees (C) below present normal values. A gradual warming trend that lasted until the 1940's reversed this pattern, with comparably above-normal temperatures being recorded over much of the globe. Since that time, temperatures have lowered to values nearer the averages of this millenium. Weather events in this period can generally be reconstructed to the nearest hour or day. forests, and the grasslands and deserts. Deltas, estuaries, and coasts are also highly sensitive to climate change because they represent delicate physical and biological balances between runoff volume and velocity, and they are markedly affected by the frequency and character of coastal storms.

Past climate variations in the transition zones between the arctic tundra and subarctic forest can be reconstructed on the basis of well-preserved plant and animal remains, permafrost thickness, cryogenic soil structure distribution, vertical temperature profiles in permafrost and in boreholes, lake and swamp stratigraphies, glaciers and glacial deposits, and tree ring variations and chronologies. The arctic and subarctic regions are especially affected by climate change because the inherent nature of the atmospheric circulation system tends to magnify the change in those areas relative to that felt in temperate latitudes.

Past changes in the elevations of the upper and lower treeline zones of the western mountain forests, as determined from the fossil remains of the plants and animals associated with them, are themselves sensitive criteria of climate although the relative importance of changes in precipitation, temperature, and wind is not always clear. Evidence of past migrations in elevation of vegetational zones on steep slopes are most informative because the accompanying temperature changes can be estimated on the basis of normal atmospheric lapse rates. -Minor climate fluctuations, especially in precipitation, result in major changes in the boundaries between the grasslands and deserts. These are recorded in the geologic record by fossil remains, the type of soil development, and by the intensity of erosion.

Changes in climate affect the coasts by altering the frequency and intensity of storms and the wave directions associated with them, and these changes affect the rate and location of erosion and deposition. Estuaries and deltas are markedly sensitive to even short-term changes in the volume of runoff and in water level; sediment and vegetation changes sensitively record such fluctuations. The much longer term variations in climate, which caused changes in sea level and the locations of shorelines as a result of major glaciations and deglaciations, produced downcutting or filling of channels, burial of marshes and forests, emergence of reefs, migration of beaches and bars, and the erosion of terraces.

AGENCIES AND INSTITUTIONS CONCERNED WITH CLIMATE

An understanding of climatic change and its effects is necessary to fulfill the responsibilities of many national and international groups and agencies. Careful coordination of efforts is required because of the number and diversity of international organizations and U.S. Government agencies that produce or require information on climate (see boxes). To assure coordination between agencies in the United States, recommendations were made in 1974 by the Domestic Council and in 1975 by the National Academy of Sciences. These were combined by an interdepartmental committee under the auspices of the Federal Coordinating Council for Science, Engineering, and Technology into a document published in 1977 entitled "A United States Climate Program Plan." That plan spells out the major objectives of a coordinated interagency Federal Program and identifies involved agencies. It also identifies priority research and service in five categories:

Impact assessments of climatic variability on crop yields, livestock production, energy demand , land and water resources, transportation, national security, and other activities.

Diagnosis and projection of observed climatic variations, particular seasonal and interannual anomalies and fluctuations.

Research to gain basic understanding of natural climate variability and of man's potential impact on climate, such as the long-term increase in the amount of carbon dioxide in the atmosphere, dioxide.

Observations by satellite and other means to help determine the earth's radiation budget, air composition, sea-air interactions, and other processes that cause climate to vary.

Management of the vast array of measurements needed for climate research and services oceanic, atmospheric, hydrologic, solar, and other types of data. The National Research Council of the National Academy of Sciences has, in turn, established a Climate Research Board that is expected to provide overview and advice to the Government on research carried out as part of the Climate Program Plan.

The elements of the Climate Program Plan underlined here are the ones that are most directly related to the effects of climate on our land and water resources or that require major components of the earth science data. The two Government agencies most concerned with the earth science record of climate are the Geological Survey (USGS) and the National Science Foundation (NSF), so that the research activities of these two agencies require careful coordination. The activities of the NSF consist mostly of support for work carried out in universities and university-sponsored research institutions.

The Geological Survey performs a wide variety of climate-related earth science investigations. Most of the research is done by USGS scientists, but some is done by universities, state surveys, and other institutions on a grant or contract basis. These investigations are coordinated with and used by many U.S. Government agencies as well as several international programs. Data on water quantity and quality collected by the Survey, for example, are used by and coordinated with various agencies in the Departments of Interior; Health, Education, and Welfare; Defense; Commerce; Energy; and Agriculture. Many State and local governmental agencies use these data and also perform earth-science investigations related to climate.

Much of the research sponsored by NSF dealing with-science aspects of climate is being conducted by research institutes and centers linked to educational institutions: Center for Climatic Research (University of Wisconsin), Coastal Studies Institute (Louisiana State University), Desert Research Institute (University of Nevada), Great Lakes Research Center (University of Michigan), Institute of Arctic and Alpine Research (University of Colorado), Institute of Arctic Biology (University of Alaska), Institute of Marine Sciences (University of Miami), Institute of Polar Studies (Ohio State University), Institute of Quaternary Studies (University of Maine), Laboratory of Tree-Ring Research (University of Arizona), Lamont-Doherty Geological Observatory (Columbia University), Limnological Research Center (University of Minnesota), Museum of Applied Science Center for Archeology (University of Pennsylvania), and Quaternary Research Center (University of Washington).

Earth science researchers in these climate-related studies that have been institutes, the USGS, and scores of applied to every geologic time period colleges, universities, and private as well as the present. The notable research organizations have combined to breadth of the Geological Survey's produce an impressive array of current efforts is the subject of Part B in this Circular.

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