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The Magnitude and Rate of Past Global Climate Changes
John P. Bluemle,Joseph M. Sabel,Wibjörn Karlén
The earth's climate is constantly changing and currently warming. This paper is an evaluation of previous climate changes intended to test the validity of assigning causality to human activity. Records of glacial advances and retreats indicate changes in relative summer temperature. Lacustrine and subaerial sediments afford a record of glacier advances and retreats from the end of the Pleistocene. Palynology offers a record of species succession in response to climate changes. Dendrochronology indicates summer temperature. Isotope paleontology provides a measurement of temperature at the time of marine sediment deposition. Isotopic evaluation of continental ice is an indicator of temperature at the time of precipitation. Anthropologic sources provide significant climate data, such as information about villages overrun by glaciers, open-ocean iceberg density, or harbors filled with ice. Available sources record continual changes in climate. The temperature lowered 15 to 20°C from the Paleocene to the Neogene. Another 10°C change occurred in the Pleistocene. Correlative data from North America, Greenland, and Scandinavia indicate many climate changes were global in scope. It is difficult to develop precise paleothermometry, but qualitative evaluations indicate sudden and dramatic changes in climate. Some changes are perhaps as great as a change from conditions warmer than today, to a full glacial climate in as little as 100 years. The converse can be true. Current data indicate a trend of change that is severe but no greater in rate or magnitude, and probably less in both, than many changes that have occurred in the recent geologic past.
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Glacial and interglacial worlds
Key aspects of past variability This and the next two chapters are concerned with Earth-system history over the last ~420 000 years, with special emphasis on the last ~130 000 years, the period since the beginning of the last interglacial. In the present chapter, we are concerned with the changes that are associated with the last four glacial cycles, up to the end of the last glacial maximum (LGM). For much of this period, the mean state of the climate and hence Earth-system components linked to climate, differed greatly from that in the recent past. Our main goal is to elucidate the combination of forcings and feedbacks responsible for the major changes observed, with a view to understanding better the sequences and synergies arising from their interactions, especially during periods of rapid change. The high-latitude records show temperature variability to have been much greater during glacial periods than during interglacials, including the Holocene. By contrast, hydrological variability in lower latitudes has been extreme even during the Holocene. Variability of changing amplitudes, in both temperature and hydrology, is the norm throughout the period. This initial observation is of outstanding importance, for it tells us that even if we discount the likelihood of anthropogenic effects on climate, this does not dispose of future climate change. Scientists and policy makers across the whole spectrum, from the most sceptical about the impact of increasing atmospheric greenhouse-gas concentrations to the most firmly convinced, cannot afford to ignore all the evidence for natural climate variability.
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Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation
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EVIDENCE DELIMITING PAST GLOBAL CLIMATE CHANGES
Politicians and the media assume Earth's climate is warming as the result of human activity. Various types of evidence of previous climate changes were investigated as a means of testing the validity of assigning anthropogenic causes to this change. Data with broad geographic coverage indicative of temperature and climate were evaluated. It included records of glacial advance and retreat, sedimentologic evidence of sea level change and glacial activity, palynologic indications of species succession, dendrochronologic evidence of tree-growth response to environment, and continental-ice core parameters indicating accumulation rates as well as other climate surrogates. Also reviewed were historical sources such as explorers' journals, which document significant climate effects over time. Each type of evidence has particular value. Among these are preservation of regional versus local conditions, transport in or out of the system, age–date reliability, correlation between data types, and data (as well as human) bias. All the data indicate that the Holocene has been characterized by ten or more global “little ice ages” irregularly spaced. Each lasted a few centuries separated by sometimes sudden and dramatic global warming events. It is difficult to develop precise paleothermometry. Qualitative evaluations indicate frequent, sudden, and dramatic climate changes. Changes can be rapid, swinging from warmer than today to full glacial conditions within 100 years. The converse can be true. All available data indicate that current climate change is no greater in rate or magnitude, and probably less in both, than many changes that have occurred in the past.
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Rate and Magnitude of Past Global Climate Changes
Abstract Existing data indicate that the Earth’s climate is probably warming. Politicians and the media typically assume this warming is the result of human activity. This article summarizes previous climate changes to test the validity of assigning causality to human activity. Records of glacial advances and retreats indicate relative summer temperature. Lacustrine and subaerial sediments afford a record of glacier advances and retreats from the Pleistocene to the present time. Palynology offers a record of species succession in response to climate changes. Dendrochronology is another indicator of summer temperature. Isotope paleontology offers a measurement of temperature at the time of marine sediment deposition, and isotopic evaluation of continental ice is an indicator of temperature at the time of precipitation. Anthropologic sources contain significant climate data such as information about villages overrun by glaciers, open-ocean iceberg density, or harbors filled with ice. Today, scientists are capable of direct measurement of climatic conditions. These sources record continual changes in climate. Broadly, the temperature changed 15 to 20°C from the Paleocene to the Neogene. Perhaps, there was as much as another 10°C change in the Pleistocene. Correlative data from North America, Greenland, and Scandinavia indicate many climate changes were truly global in scope. Although it is difficult to develop precise paleothermometry, qualitative evaluations indicate sudden and dramatic changes in climate. Some are perhaps as great as a change from conditions warmer than today to a full glacial climate in as little as 100 years. The converse can be true. Current data indicate a trend of change that is substantially severe but no greater in rate or magnitude, and probably less in both, than many changes that have occurred in the past.
Geological Perspectives of Global Climate Change: Introduction and Overview*
Global climate has varied since the most primitive atmosphere developed on earth billions of years ago. This variation in climate has occurred on all timescales and has been continuous. The sedimentary rock record reflects numerous sea-level changes, atmospheric compositional changes, and temperature changes, all of which attest to climatic variation. Such evidence, as well as direct historical observations, clearly shows that temperature swings occur in both directions. Past climates have varied from those that create continental glaciers to those that yield global greenhouse conditions. Many people do not comprehend that this means their living climate also varies--it gets warmer or cooler--but typically does not remain the same for extended periods of time. Human history shows us that in general, warmer conditions have been beneficial, and colder conditions have been less kind to society (Lamb, 1995). We currently are living in a not-yet-completed interglacial stage, and it is very likely that warmer conditions lie ahead for humanity, with or without any human interference. Interglacial stages appear to last for about 11,000 years, but with large individual variability. We have been in this interglacial for about 10,000 years.
Global Climate Changes During the Little Ice Age
The climate since 1500 A.D. has been highlighted in the field of global change. Recently, some studies, such as PAGES and WCRP, have opened up broad prospect for the detailed high-resolution climatic records, such as tree-rings, corals and ice-cores etc. More attention is focused on the global climate changes on the basis of paleoclimate information of annual-to-millennial time scales. Especially, the climate of the Little Ice Age(LIA), which may be regarded as a short-scale neoglacial episode or a series similar to the climate change from glacial period, is a very important time stream and have an important role in studying the variations of atmospheric circulation and environment and climate in regional or global extent, and in establishing scientifically contemporary climate matrix. Based on historical documents, dendroclimatic data and ice core records from Europe, Asia, North America, South America and Antarctica since the LIA, a synthetic analysis of the paleoclimatic information is made in this paper. The main results are given as follows: (1) The general tendency of global cold-warm change since the LIA exhibits a consistency in a certain degree, with a high spatial and temporal variation. There were strong cold periods in the 17th and 19th centuries and a strong warm period in the 1920's-1940's. (2) Because of apparent allocation difference between oceans and continents, there is a prominent distinction in the effect of atmospheric circulation patterns, radiation balance of underlying surface and abrupt events on regional and global climate. The strength of circulation systems between Atlantic, Arctic and Pacific, which have different power and duration, has different influence on the global climate change since the LIA from coast to continental interiors of Eurasia. Meanwhile, the uplift of the Tibetan Plateau further increases the regional difference and deeply influences global climate changes. (3) The large-scale effects of solar activity, violent volcanic eruptions and EL Nino events on ocean-atmospheric mechanism play a pivotal role in the global climate system. Especially, solar activity is the main factor affecting the global climate changes since the LIA. Those changes are further influenced by atmospheric circulation system enhanced by violent volcanic eruptions and EL Nino events.erentpowerand
Implications of abrupt climate change.
Records of past climates contained in ice cores, ocean sediments, and other archives show that large, abrupt, widespread climate changes have occurred repeatedly in the past. These changes were especially prominent during the cooling into and warming out of the last ice age, but persisted into the modern warm interval. Changes have especially affected water availability in warm regions and temperature in cold regions, but have affected almost all climatic variables across much or all of the Earth. Impacts of climate changes are smaller if the changes are slower or more-expected. The rapidity of abrupt climate changes, together with the difficulty of predicting such changes, means that impacts on the health of humans, economies and ecosystems will be larger if abrupt climate changes occur. Most projections of future climate include only gradual changes, whereas paleoclimatic data plus models indicate that abrupt changes remain possible; thus, policy is being made based on a view of the future that may be optimistic.
PALEOCLIMATE RECONSTRUCTION | The Last Millennium
Evidence for climate variability and change during the period of roughly the past millennium is reviewed. Insights are available from both empirical reconstructions based on natural archives (‘proxy’ records) of climate and from the results of simulations using theoretical models of the climate system. Both empirical and model-based approaches provide a fairly consistent picture of past changes. Significant regional climate changes are established as having taken place in past centuries, including periods of substantial cooling and warming in certain regions (e.g., Europe) and notable periods of drought and wetness in other regions (e.g., equatorial Africa and the desert Southwest of the United States). Some of these changes may be associated with the response of the climate to natural changes in radiative forcing of the climate, variations in solar output over time, and the effects of atmospheric aerosols due to past explosive volcanic eruptions. At hemispheric or global scales, the late twentieth-century warming appears to be without precedent in at least the past 1000 years. Model simulation studies suggest that this warming is due, in large part, to human or ‘anthropogenic’ climate impacts, particularly the increased concentration of greenhouse gasses in the atmosphere due to fossil fuel burning.
Climate future in a warming world: lessons from the ice ages
Global warming is real and has been with us for at least two decades. Questions arise regarding the response of the ocean to greenhouse forcing, including expectations for changes in ocean circulation, in uptake of excess carbon dioxide, and in upwelling activity. The large climate variations of the ice ages, within the last million years, offer the opportunity to study responses of the ocean to climate change. A histogram of sealevel positions for the last 700,000 years (based on a new d/sup 18/O stratigraphy here compiled) shows that the present is near the margin of the range of fluctuations, with only 6 percent of positions indicating a warmer climate. Thus, the future will be largely outside of experience with regard to fluctuations of the recent geologic past. The same is true for greenhouse forcing. Our inability to explain sudden climate change in the past, including the rapid rise of carbon dioxide during deglaciation, and differences in ocean productivity between glacial and interglacial conditions, demonstrates a lack of understanding that makes predictions suspect. This is the lesson from ice age studies.
OBSERVED CLIMATE CHANGE AND TRANSPORTATION
In this paper the current instrumental evidence regarding climate variations and change during the Twentieth Century is reviewed. The questions addressed include: (1) what is the observational evidence for a changing climate, both globally and in the United States, and (2) what are the relevant results from the recently completed U.S. National Assessment examining the potential consequences of climate change in the U.S. Based on global near-surface temperature measurements for the Twentieth Century it is clear that a warming of approximately 0.6 deg C has occurred for the globe and a similar warming has occurred in the U.S. More importantly, however, are the observed asymmetric changes in daily maximum and minimum temperature, with the minimum temperatures increasing at a rate approximately twice that of the maximum temperature. Other temperature sensitive measures, such as glacial and snow cover extent reinforce the observed temperature trends. Examination of the hydrologic cycle indicates that changes also appear to be occurring, although less confidence can be placed on these analyses than those for temperature. Recent studies suggest that precipitation has increased in higher latitudes, particularly in the Northern Hemisphere. The final question regarding climate extremes is much more difficult to assess due to a lack of high temporal resolution climate databases. Of the few studies that have been performed, however, there is evidence that precipitation extremes, particularly heavy rainfall events, are increasing in the U.S., also suggesting an enhanced hydrologic cycle as the planet warms.
“The Magnitude and Rate of Past Global Climate Changes” is a paper by John P. Bluemle Joseph M. Sabel Wibjörn Karlén published in the journal Environmental Geosciences in 2000. It was published by AAPG/Datapages. It has an Open Access status of “closed”. You can read and download a PDF Full Text of this paper here.