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Using Patterns of Recurring Climate Cycles to Predict Future Climate Changes D.J CHAPTER 21 Using Patterns of Recurring Climate Cycles to Predict Future Climate Changes D.J. Easterbrook Western Washington University, Bellingham, WA, United States OUTLINE 1. Introduction 395 4. Correlation of Temperature Cycles and the Pacific Decadal Oscillation 405 2. The Past is the Key to the Future: Lessons From Past Global Climate Changes 396 5. The Atlantic Multidecadal Oscillation 407 2.1 Past Climate Changes 396 6. Where Is Climate Headed During the Coming 2.2 Magnitude and Rate of Abrupt Climate Changes 396 Century? 407 2.3 Holocene Climate Changes (10,000 Years Ago 6.1 IPCC Predictions 407 to Present) 398 6.2 Predictions Based on Past Cyclic Climate 2.3.1 The Roman Warm Period 398 Patterns 407 2.3.2 Dark Ages Cool Period 398 2.3.3 Medieval Warm Period (900e1300 AD) 400 References 410 2.3.4 The Little Ice Age 401 2.3.5 Climate Changes During the Past Century 403 3. Significance of Past Global Climate Changes 404 1. INTRODUCTION Global warming that occurred from 1978 to about 1998 pushed climate change into the forefront of potential concern. Every day the news media is filled with dire predictions of impending disastersdcatastrophic melting of the Antarctic and Greenland ice sheets, drowning of major cities from sea level rise, drowning of major portions of countries, droughts, severe water shortages, no more snow, more extreme weather events (hurricanes, tor- nadoes), etc. With no unequivocal, cause-and-effect, tangible, physical evidence that increasing CO2 caused this most recent global warming, adherents of this ideology have had to rely on computer models that have proven to be unreliable. Abundant, physical, geologic evidence from the past provides a record of former periods of recurrent global warming and cooling that were far more intense than recent warming and cooling. These geologic records provide clear evidence of global warming and cooling that could not have been caused by increased CO2. Thus, we can use these records to project global climate into the future, ie, the past is the key to the future. Evidence-Based Climate Science, Second Edition http://dx.doi.org/10.1016/B978-0-12-804588-6.00021-5 395 Copyright © 2016 Elsevier Inc. All rights reserved. 396 21. USING PATTERNS OF RECURRING CLIMATE CYCLES TO PREDICT FUTURE CLIMATE CHANGES 2. THE PAST IS THE KEY TO THE FUTURE: LESSONS FROM PAST GLOBAL CLIMATE CHANGES 2.1 Past Climate Changes Those who advocate CO2 as the cause of global warming have stated that never before in the Earth’s history has climate changed as rapidly as in the past century, and that proves global warming is being caused by anthropogenic CO2. Statements such as these are easily refutable by the geologic record. Fig. 21.1 shows temperature changes recorded by oxygen isotope ratios from the GISP2 ice core from the Greenland Ice Sheet. The global warming expe- rienced during the past century pales into insignificance when compared to the magnitude of the profound climate reversals over the past 15,000 years. The GISP2 Greenland ice core isotope data have proven to be a great source of climatic data from the geologic past. Paleo-temperatures for more than 100,000 years have been determined from nuclear accelerator measurements of thousands of oxygen isotope ratios (16O/18O) (Grootes and Stuiver, 1997), and these data have become a world standard. Oxygen isotope ratios are a measure of paleo-temperatures at the time snow fell that was later converted to glacial ice. The age of such temperatures can be accurately measured from annual layers of accumulation of rock debris marking each summer’s melting of ice and concentration of rock debris on the glacier. Paleo-temperatures from the GISP2 ice core were also reconstructed using ice core temperatures (Fig. 21.2; Cuffy and Clow, 1997; Alley, 2000). These also show exceptionally high rates of warming and cooling near the end of the Pleistocene. The oxygen isotope and paleo-temperature data clearly show remarkable swings in climate over the past 100,000 years. In just the past 500 years, Greenland warming/cooling temperatures fluctuated back and forth about 40 times, with changes every 25e30 years (27 years on the average). None of these changes could have been caused by changes in atmospheric CO2 because they predate the large CO2 emissions that began about 1945. Nor can the e warming of 1915 45 be related to CO2, because it predates the soaring emissions after 1945. Thirty years of global e cooling (1945 77) occurred during the big post-1945 increase in CO2 emissions. 2.2 Magnitude and Rate of Abrupt Climate Changes But what about the magnitude and rates of climates change? How do past temperature oscillations compare with recent global warming (1977e98) or with warming periods over the past millennia? The answer to the question of magnitude and rates of climate change can be found in the d18O and ice core temperature data (Steffensen et al., 2008). Temperature changes in the GISP2 core over the past 25,000 years are shown in Figs. 21.1 and 21.2. The temper- ature curve in Fig. 21.2 is a portion of the Cuffy and Clow (1997) original curve. The horizontal axis is time and the vertical axis is temperature, based on ice core borehole temperature data. Details are discussed in their paper. Places where the curve becomes nearly vertical signify times of very rapid temperature change. Keep in mind that these are temperatures in Greenland, not global temperatures. However, correlation of the ice core temperatures with FIGURE 21.1 Oxygen isotope ratios from the GISP2 ice core, Greenland. Note the extremely sharp rises in temperature (red) at about 14,500 years and 11,500 years, which had much greater magnitude and rate of rise than the past century. Plotted from data by Grootes, P.M., Stuiver, M., 1997. Oxygen 18/16 variability in Greenland snow and ice with 103 to 105eyear time resolution. Journal of Geophysical Research 102, 26455e26470. IX. CLIMATE PREDICTIONS 2. THE PAST IS THE KEY TO THE FUTURE: LESSONS FROM PAST GLOBAL CLIMATE CHANGES 397 FIGURE 21.2 Greenland temperatures over the past 25,000 years recorded in the GISP2 ice core. Strong, abrupt warming is shown by nearly vertical rise of temperatures, strong cooling by nearly vertical drop of temperatures. Modified from Cuffey, K.M., Clow, G.D., 1997. Temperature, accumulation, and ice sheet elevation in central Greenland through the last deglacial transition. Journal of Geophysical Research 102, 26383e26396. worldwide glacial fluctuations and correlation of modern Greenland temperatures with global temperatures con- firms that the ice core record does indeed follow global temperature trends and is an excellent proxy for global tem- perature changes. For example, the portions of the curve from about 25,000 to 15,000 represent the last Ice Age (the Pleistocene), when huge ice sheets, thousands of feet thick, covered North America, northern Europe, and northern Russia, and alpine glaciers readvanced far downvalley. Some of the more remarkable sudden climatic warming periods are listed later in this section and in Fig. 21.3. The numbers in Fig. 21.3 correspond to the temperature curves in Fig. 21.2. How do the magnitude and rates of change of modern global warming/cooling compare to warming/cooling events over the past 15,000 years? We can compare the warming and cooling in the past century to approximate 100-year periods in the past 25,000 years. The scale of the curve does not allow enough accuracy to pick out exactly 100-year episodes directly from the curve, but that can be done from the annual dust layers in ice core data. Thus, not all of the periods noted here are exactly 100 years. Some are slightly more, some are slightly less, but they are close enough to allow comparison of magnitude and rates with the past century. 1. Temperature changes recorded in the GISP2 ice core from the Greenland Ice Sheet (Figs. 21.1 and 21.2) show that the global warming experienced during the past century pales into insignificance when compared to the magnitude of profound ice sheets that covered Canada and the northern United States, all of Scandinavia, and much of northern Europe and Russia. 30 25 20 15 10 5 0 1 2 3 4 5 6 7 8 9 1011 12 13 1415 16 17 FIGURE 21.3 Magnitudes of the largest warming/cooling events over the past 25,000 years. Temperatures on the vertical axis are rise or fall of temperatures in about a century. Each column represents the rise or fall of temperature shown in Fig. 21.2. Event number 1 is about 24,000 years ago and event number 15 is about 11,000 years old. The sudden warming about 14,000 years ago caused massive melting of these ice sheets at extraordinary rates. IX. CLIMATE PREDICTIONS 398 21. USING PATTERNS OF RECURRING CLIMATE CYCLES TO PREDICT FUTURE CLIMATE CHANGES 2. Shortly thereafter, temperatures dropped abruptly about 10 C (20 F) and temperatures then remained cold for several thousand years. 3. About 13,000 years ago, global temperatures plunged sharply (w12 C; w21 F) and a 1300-year cold period, the Younger Dryas, began. 4. 11,500 years ago, global temperatures rose sharply (w12 C; w21 F), marking the end of the Younger Dryas cold period and the end of the Pleistocene Ice Age. The end of the Younger Dryas cold period warmed by 5 C(9F) over 30e40 years and as much as 8 C (14 F) over 40 years. Fig. 21.2 shows comparisons of the largest magnitudes of warming/cooling events per century over the past 15,000 years.
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