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The Scientific Guide to Global Warming Skepticism John Cook skeptical .com scie

The Scientific Guide to Global Warming Skepticism John Cook skeptical .com science Acknowledgements • Dr. John Abraham, Associate Professor of Engineering, University of St. Thomas, St. Paul, Minnesota • Paul Beckwith, Laboratory for paleoclimatology and climatology, Department of Geography, University of Ottawa, Canada • Prof. Andrew Dessler, Department of Atmospheric Science, Texas A&M University • Prof. Ove Hoegh-Guldberg, Director, Global Change Institute, University of Queensland • Prof. David Karoly, School of Earth Sciences, University of Melbourne • Prof. Scott Mandia, Physical Sciences, Suffolk County Community College • Dana Nuccitelli - Environmental Scientist, Tetra Tech, Inc. • James Prall, The Edward S. Rogers Sr. Department of Electrical and Computer Engineering, University of Toronto • Dr. John Price, www.grandkidzfuture.com • Corinne Le Quéré, Professor of Environmental Sciences, University of East Anglia, UK • Prof. Peter Reich, Sr. Chair in Forest Ecology and Tree Physiology, University of Minnesota • Prof. Riccardo Reitano, Department of Physics and Astronomy, University of Catania, Italy • Prof. Christian Shorey, Geology and Geologic Engineering, Colorado School of Mines • Suffolk County Community College MET101 students • Glenn Tamblyn, B Eng (Mech), Melbourne University, Australia • Dr. André Viau, Laboratory for paleoclimatology and climatology, Department of Geography, University of Ottawa, Canada • Dr. Haydn Washington, Environmental Scientist • Robert Way, Department of Geography, Memorial University of Newfoundland, Canada • Dr. Ray Weymann, Director Emeritus and Staff Member Emeritus, Carnegie Observatories, Pasadena, California; Member, National Academy of Sciences • James Wight • Bärbel Winkler, Germany First published in December 2010 For more information or to comment on this Guide, visit www.skepticalscience.com The Scientific Guide to Global Warming Skepticism is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License. Extracts may be reproduced provided Skeptical Science is attributed with a link to www.skepticalscience.com. The Scientific Guide to Global Warming Skepticism was written by John Cook (www.skepticalscience.com). Acknowledgements to the following who contributed and commented on this document: 1 Scientific skepticism is healthy. In fact, science by its very nature is skeptical. Genuine skepticism means considering the full body of evidence before coming to a conclusion. However, when you take a close look at arguments expressing climate ‘skepticism’, what you often observe is cherry picking of pieces of evidence while rejecting any data that don’t fit the desired picture. This isn’t skepticism. It is ignoring facts and the science. This guide looks at both the evidence that human activity is causing global warming and the ways that climate ‘skeptic’ arguments can mislead by presenting only small pieces of the puzzle rather than the full picture. What does it mean to be skeptical? Climate cherry picking Selective cherry picking could have you thinking this is a blue cherry tree. But what does the full body of evidence tell you? Scientists look for independent lines of evidence pointing to a single, consistent answer. The full body of evidence in climate science shows us a number of distinct, discernible human fingerprints on climate change. Measurements of the type of carbon found in the atmosphere show that fossil fuel burning is dramatically increasing levels of carbon dioxide (CO ) in the atmosphere. Satellite and surface 2 Human fingerprints on climate change measurements find that extra CO is trapping heat that would otherwise escape out to space. There are a number of warming patterns consistent with an increased greenhouse effect. The whole structure of our atmosphere is changing. The evidence for human caused global warming is not just based on theory or computer models but on . 2 many independent, direct observations made in the real world Less heat escaping to space 4 Cooling upper atmosphere 1 More heat returning to Earth 8 Shrinking upper atmosphere 2 Rising tropopause 3 More fossil fuel carbon in coral 9 Human Fingerprints on Climate Change More fossil fuel carbon in the air 5 Less oxygen in the air 5 Pattern of ocean warming 10 Winter warming faster than summer 7 Nights warming faster than days 6 Humans are raising CO levels 2 When you look through the many arguments from global warming ‘skeptics’, a pattern emerges. They tend to focus on small pieces of the puzzle while neglecting the bigger picture. A good example of this is the argument that human carbon dioxide (CO ) emissions are tiny compared to natural emissions. The argument goes like this. Each year, we send over 20 billion tonnes of CO into the atmosphere. Natural emissions come from plants breathing out CO and outgassing from the ocean. Natural emissions add up to 776 billion tonnes per year. Without a full understanding of the carbon cycle, our emissions seem tiny when compared to nature’s contribution. The missing part of the picture is that nature doesn't just emit CO - it also CO . Plants breathe in 2 2 2 2 2 11 12 absorbs Human Fingerprint #1 Fossil fuel signature in the air & coral CO and huge amounts of CO dissolve into the ocean. Nature absorbs 788 billion tonnes every year. Natural absorptions roughly balance natural emissions. What we do is upset the balance. While some of our CO is being absorbed by the ocean and land plants, around half of our CO emissions remain in the air. Because of fossil fuel burning, atmospheric CO is at its highest level in at least 2 million years. And it’s still going up! The “human CO is tiny” argument misleads by only giving you half the picture. 2 2 2 2 2 2 14 Measurements of 13C (ratio of Carbon-13 to Carbon-12) from corals in the Great Barrier Reef. δ 9 332 444 23 332 338 444 450 23 2 1800 1840 1880 1920 1960 2000 Year -3.6 -3.0 -2.4 -1.8 -1.2 δ13C‰ Ratio of Carbon-13 to Carbon-12 in coral There are different types of carbon in the air known as carbon isotopes. The most common type is Carbon-12. A heavier type of carbon is Carbon-13. Plants prefer the lighter Carbon-12. Fossil fuels like coal or oil come from ancient plants. So when we burn fossil fuels, we’re sending more of the lighter Carbon-12 into the air. So we expect to see the ratio of Carbon-13 to Carbon-12 fall. This is just what we observe, in measurements of the atmosphere , in corals and sea sponges. So we have strong evidence that the increase in carbon dioxide in the air is directly linked to human emissions. 5 9 15 The weight of CO emitted by humans is comparable to 8,000 Gulf of Mexico oil spills. 2 each day 13 Ocean Vegetation & Land Fossil Fuel Burning An incomplete picture of the carbon cycle Carbon cycle for the 1990s. Numbers are in billion tonnes of CO2. 12 Ocean Vegetation & Land Fossil Fuel Burning The complete picture of the carbon cycle Carbon cycle for the 1990s. Numbers are in billion tonnes of CO2. 2 Carbon dioxide traps infrared radiation (commonly known as thermal radiation). This has been proven by laboratory experiments and satellites which find less heat escaping out to space over the last few decades (see ). This is direct evidence that more CO is causing warming. The past also tells an interesting story. Ice cores show that in the Earth’s past, CO went up temperature initially increased. This “CO lag” means temperature affects the amount of CO in the air. So warming causes more CO and more CO causes extra warming. Put these two together and you get positive feedback. Positive or negative feedback don’t necessarily mean good or bad. Positive feedbacks strengthen any climate change already underway while negative feedbacks suppress (weaken) any climate change. In the past when climate warmed due to changes in the Earth’s orbit, this caused the ocean to release more CO into the atmosphere resulting in the following effects: 16 4 5 Human Fingerprint #2 2 2 2 2 2 2 2 after The evidence that more CO causes warming 2 • The extra CO in the atmosphere amplified the original warming. That’s the positive feedback. • The extra CO mixed through the atmosphere, spreading greenhouse warming across the globe. The ice core record is entirely consistent with the warming effect of CO . In fact, the dramatic warming as the planet comes out of an ice age cannot be explained without the feedback from CO . The CO lag doesn’t disprove the warming effect of CO . On the contrary, it provides evidence of a positive climate feedback. 2 2 2 2 2 2 17,18 Human Fingerprint #2 Less heat is escaping out to space Satellites measure infrared radiation as it escapes out to space, clearly observing the greenhouse effect. A comparison between satellite data from 1970 to 1996 found that even less energy is escaping to space at the wavelengths that greenhouse gases absorb energy. Researchers described this result as . This has since been confirmed by subsequent measurements from several different satellites. “direct experimental evidence for a significant increase in the Earth’s greenhouse effect” 4 19,20 Change in outgoing radiation spectrum from 1970 to 1996 due uploads/Geographie/ guide-to-skepticism.pdf