Global Climate Change: Vital Signs of the Planet NASA

Transcription

1 Global Climate Change: Vital Signs of the Planet NASA

2 Table of Contents Evidence... 2 Causes Effects 17 Scientific Consensus

3 Chapter 1 EVIDENCE Climate Change: How Do We Know This graph, based on the comparison of atmospheric samples contained in ice cores and more recent direct measurements, provides evidence that atmospheric CO 2 has increased since the Industrial Revolution. 1 The Earth's climate has changed throughout history. Just in the last 650,000 years there have been seven cycles of glacial advance and retreat, with the abrupt end of the last ice age about 7,000 years ago marking the beginning of the modern climate era and of human civilization. Most of these climate changes are attributed to very small variations in Earth s orbit that change the amount of solar energy our planet receives. 1 Vostok ice core data, J.R. Petit et al.; NOAA Mauna Loa CO2 record. Find out more about ice cores: 2

4 Scientific evidence for warming of the climate system is unequivocal. --Intergovernmental Panel on Climate Change The current warming trend is of particular significance because most of it is extremely likely (greater than 95 percent probability) to be the result of human activity since the mid-20 th century and proceeding at a rate that is unprecedented in millennia. 2 Earth-orbiting satellites have enabled scientists to see the big picture, collecting many different types of information about our planet and its climate on a global scale. This body of data, collected over many years, reveals the signals of a changing climate. The heat-trapping nature of carbon dioxide and other gases was demonstrated in the mid-19th century. 3 Their ability to affect the transfer of infrared energy through the atmosphere is the scientific basis of many instruments flown by NASA. There is no question that increased levels of greenhouse gases must cause the Earth to warm in response. Ice cores drawn from Greenland, Antarctica, and tropical mountain glaciers show that the Earth s climate responds to changes in greenhouse gas levels. Ancient evidence can also be found in tree rings, ocean sediments, coral reefs, and layers of sedimentary rocks. This ancient, or paleoclimate, evidence reveals that current warming is occurring roughly ten times faster than the average rate of ice-age-recovery warming. 4 2 IPCC Fifth Assessment Report, Summary for Policymakers 3 In the 1860s, physicist John Tyndall recognized the Earth s natural greenhouse effect and suggested that slight changes in the atmospheric composition could bring about climactic variations. In 1896, a seminal paper by Swedish scientist Svante Arrhenius first predicted that changes in the levels of carbon dioxide in the atmosphere could substantially alter the surface temperature through the greenhouse effect. 4 Church, J.A. and N.J. White (206), A 20 th Century Acceleration in Global Sea Level Rise, Geophysical Research Letters, 33. 3

5 The evidence for rapid climate change is compelling: Global Temperature Rise The planet's average surface temperature has risen about 2.0 degrees Fahrenheit (1.1 degrees Celsius) since the late 19th century, a change driven largely by increased carbon dioxide and other human-made emissions into the atmosphere. 5 Most of the warming occurred in the past 35 years, with 16 of the 17 warmest years on record occurring since Not only was 2016 the warmest year on record, but eight of the 12 months that make up the year from January through September, with the exception of June were the warmest on record for those respective months. 6 5 Church, J.A. and N.J. White (2006), A 20 th century acceleration in global sea level rise, Geophysical Research Letters, 33. The global sea level estimate described in this work can be downloaded from the CSIRO website

6 Warming Oceans The oceans have absorbed much of this increased heat, with the top 700 meters (about 2,300 feet) of ocean showing warming of degrees Fahrenheit since Shrinking Ice Sheets The Greenland and Antarctic ice sheets have decreased in mass. Data from NASA's Gravity Recovery and Climate Experiment show Greenland lost 150 to 250 cubic kilometers (36 to 60 cubic miles) of ice per year between 2002 and 7 Levitus, et al., Global Ocean Heat Content in light of recently revealed instrumentation problems Geophys. Res. Lett. 36 (2009). 5

7 2006, while Antarctica lost about 152 cubic kilometers (36 cubic miles) of ice between 2002 and Glacial Retreat Glaciers are retreating almost everywhere around the world, including in the Alps, Himalayas, Andes, Rockies, Alaska and Africa. 9 Decreased Snow Cover 8 L. Polyak, et al., History of Sea Ice in the Arctic, in Past Climate Variability and Change in the Arctic and High Altitudes, U.S. Geological Survey, Climate Change Science Program Synthesis and Assessment Product 1.2, January 2009, Chapter 7. 9 National Snow and Ice Data Center: and World Glacier Monitoring Service: 6

8 Satellite observations reveal that the amount of spring snow cover in the Northern Hemisphere has decreased over the past five decades and that the snow is melting earlier. 10 Sea Level Rise Global sea level rose about 8 inches in the last century. The rate in the last two decades, however, is nearly double that of the last century C. Derkse and R. Brown, Spring Snow Cover Extent Reductions in the Period Exceeding Climate Model Projections 11 A 20 th Century Acceleration in Global Sea Level Rise, Geophysical Research Letters, 33. 7

9 Declining Arctic Sea Ice Both the extent and thickness of Arctic sea ice has declined rapidly over the last several decades. 12 Extreme Weather Events 12 L. Polyak, et al., History of Sea Ice in the Arctic, in Past Climate Variability and Change in the Arctic and High Altitudes, U.S. Geological Survey, Climate Change Science Program Synthesis and Assessment Product 1.2, January 2009, Chapter 7. 8

10 The number of record high temperature events in the United States has been increasing, while the number of record low temperature events has been decreasing, since The U.S. has also witnessed increasing numbers of intense rainfall events. 13 Ocean Acidification Since the beginning of the Industrial Revolution, the acidity of surface ocean waters has increased by about 30 percent. 14 This increase is the result of humans emitting more carbon dioxide into the atmosphere and hence more being absorbed into the oceans. The amount of carbon dioxide absorbed by the upper layer of the oceans is increasing by about 2 billion tons per year Attribution of Extreme Weather Events in the Context of Climate Change, National Academic Press, 2016 and Kunkel, K. et al., Probable Maximum Precipitation and Climate Change, Geophysical Research Letters, (12 April 2013) and Kunkel, K et al., Monitoring and Understanding Trends in Extreme Storms: State of the Knowledge, Bulletin of the American Meteorological Society, and 15 C.L. Sabine et al., The Oceanic Sink for Anthropogenic CO2, Science Vo. 305 (16 *July 2004), And Copenhagen Diagnosis. P

11 Chapter 2 CAUSES A Blanket Around the Earth A layer of greenhouse gases primarily water vapor, and including much smaller amounts of carbon dioxide, methane and nitrous oxide acts as a thermal blanket for the Earth, absorbing heat and warming the surface to a life-supporting average of 59 degrees Fahrenheit (15 degrees Celsius). Most climate scientists agree the main cause of the current global warming trend is human expansion of the "greenhouse effect" 16 that is, warming that results when the atmosphere traps heat radiating from Earth toward space. 16 IPCC Fifth Assessment Report, United States Global Change Research Program, Global Climate Change Impacts in the United 10

12 Certain gases in the atmosphere block heat from escaping. Long-lived gases that remain semi-permanently in the atmosphere and do not respond physically or chemically to changes in temperature are described as "forcing" climate change. Gases, such as water vapor, which respond physically or chemically to changes in temperature are seen as "feedbacks." Gases that contribute to the greenhouse effect include: 1. Water Vapor: The most abundant greenhouse gas, but importantly, it acts as a feedback to the climate. Water vapor increases as the Earth's atmosphere warms, but so does the possibility of clouds and precipitation, making these some of the most important feedback mechanisms to the greenhouse effect. States, Cambridge University Press, Naomi Oreskes, The Scientific Consensus on Climate Change, in Science 3 (December 2004), Vol

13 2. Carbon Dioxide (CO 2 ): A minor but very important component of the atmosphere, carbon dioxide is released through natural processes such as respiration and volcano eruptions and through human activities such as deforestation, land use changes, and burning fossil fuels. Humans have increased atmospheric CO 2 concentration by more than a third since the Industrial Revolution began. This is the most important long-lived "forcing" of climate change. 3. Methane: A hydrocarbon gas produced both through natural sources and human activities, including the decomposition of wastes in landfills, agriculture, and especially rice cultivation, as well as ruminant digestion and manure management associated with domestic livestock. On a molecule-for-molecule basis, methane is a far more active greenhouse gas than carbon dioxide, but also one which is much less abundant in the atmosphere. 4. Nitrous Oxide: A powerful greenhouse gas produced by soil cultivation practices, especially the use of commercial and organic fertilizers, fossil fuel combustion, nitric acid production, and biomass burning. 5. Chlorofluorocarbons (CFCs): Synthetic compounds entirely of industrial origin used in a number of applications, but now largely regulated in production and release to the atmosphere by international agreement for their ability to contribute to destruction of the ozone layer. They are also greenhouse gases. On Earth, human activities are changing the natural greenhouse. Over the last century the burning of fossil fuels like coal and oil has increased the concentration of atmospheric carbon dioxide (CO 2 ). This happens because the coal or oil burning process combines carbon with oxygen in the air to make CO 2. To a lesser extent, the clearing of land 12

14 for agriculture, industry, and other human activities has increased concentrations of greenhouse gases. The consequences of changing the natural atmospheric greenhouse are difficult to predict, but certain effects seem likely: On average, Earth will become warmer. Some regions may welcome warmer temperatures, but others may not. Warmer conditions will probably lead to more evaporation and precipitation overall, but individual regions will vary, some becoming wetter and others dryer. A stronger greenhouse effect will warm the oceans and partially melt glaciers and other ice, increasing sea level. Ocean water also will expand if it warms, contributing further to sea level rise. Meanwhile, some crops and other plants may respond favorably to increased atmospheric CO 2, growing more vigorously and using water more efficiently. At the same time, higher temperatures and shifting climate patterns may change the areas where crops grow best and affect the makeup of natural plant communities. 13

15 Not enough greenhouse effect: The planet Mars has a very thin atmosphere, nearly all carbon dioxide. Because of the low atmospheric pressure, and with little to no methane or water vapor to reinforce the weak greenhouse effect, Mars has a largely frozen surface that shows no evidence of life. Too much greenhouse effect: The atmosphere of Venus, like Mars, is nearly all carbon dioxide. But Venus has about 154,000 times as much carbon dioxide in its atmosphere as Earth (and about 19,000 times as much as Mars does), producing a runaway greenhouse effect and a surface temperature hot enough to melt lead. 14

16 The Role of Human Activity In its Fifth Assessment Report, the Intergovernmental Panel on Climate Change, a group of 1,300 independent scientific experts from countries all over the world under the auspices of the United Nations, concluded there's a more than 95 percent probability that human activities over the past 50 years have warmed our planet. The industrial activities that our modern civilization depends upon have raised atmospheric carbon dioxide levels from 280 parts per million to 400 parts per million in the last 150 years. The panel also concluded there's a better than 95 percent probability that human-produced greenhouse gases such as carbon dioxide, methane and nitrous oxide have caused much of the observed increase in Earth's temperatures over the past 50 years. 17 Solar Irradiance It's reasonable to assume that changes in the sun's energy output would cause the climate to change, since the sun is the fundamental source of energy that drives our climate system. Indeed, studies show that solar variability has played a role in past climate changes. For example, a decrease in solar activity is thought to have triggered the Little Ice Age between approximately 1650 and 1850, when Greenland was largely cut off by ice from 1410 to the 1720s and glaciers advanced in the Alps. 17 The Panel s full summary for Policymakers Report is online: 15

17 But several lines of evidence show that current global warming cannot be explained by changes in energy from the sun: Since 1750, the average amount of energy coming from the sun either remained constant or increased slightly. If the warming were caused by a more active sun, then scientists would expect to see warmer temperatures in all layers of the atmosphere. Instead, they have observed a cooling in the upper atmosphere, and a warming at the surface and in the lower parts of the atmosphere. That's because greenhouse gases are trapping heat in the lower atmosphere. Climate models that include solar irradiance changes can t reproduce the observed temperature trend over the past century or more without including a rise in greenhouse gases Mike Lockwood, Solar Change and Climate: An Update in the Light of the Current Exceptional Solar Minimum, Proceedings of the Royal Society A (2 December 2009). And Judith Lean, Cycles and Trends in Solar Irradiance and Climate, Wiley Interdisciplinary Reviews: Claimte Change, Vol. 1 (January-Feburary 2010, ). 16

18 Chapter 3 EFFECTS The Consequences of Climate Change The potential future effects of global climate change include more frequent wildfires, longer periods of drought in some regions, and an increase in the number, duration, and intensity of tropical storms. Global climate change has already had observable effects on the environment. Glaciers have shrunk, ice on rivers and lakes is breaking up earlier, plant and animal ranges have shifted and trees are flowering sooner. Those effects that scientists in the past had predicted would result from global climate change are now occurring: loss of sea ice, accelerated sea level rise, and longer more intense heat waves. 17

19 Taken as a whole, the range of published evidence indicates that the net damage costs of climate change are likely to be significant and to increase over time. --Intergovernmental Panel on Climate Change Scientists are highly confident that global temperatures will continue to rise for decades to come, largely due to greenhouse gases produced by human activities. The Intergovernmental Panel on Climate Change (IPCC), which includes more than 1,300 scientists from the United States and other countries, forecasts a temperature rise of 2.5 to 10 degrees Fahrenheit over the next century. According to the IPCC, the extent of climate change effects on individual regions will vary over time and will vary according to the ability of different social and environmental systems to mitigate or adapt to the changes. The IPCC predicts that increases in global mean temperature of less than 1.8 to 5.4 degrees Fahrenheit (1 to 3 degrees Celsius) above 1990 levels will produce beneficial impacts in some regions and harmful ones in others.. Taken as a whole, the IPCC states, the range of published evidence indicates that the net damage costs of climate change are likely to be. 18

20 A Degree of Difference So, the Earth's average temperature has increased about 2 degrees Fahrenheit during the 20th century. What's the big deal? Two degrees may sound like a small amount, but it's an unusual event in our planet's recent history. Earth's climate record, preserved in tree rings, ice cores, and coral reefs, shows that the global average temperature is stable over long periods of time. Furthermore, small changes in temperature correspond to enormous changes in the environment. For example, at the end of the last ice age, when the Northeast United States was covered by more than 3,000 feet of ice, average temperatures were only 5 to 9 degrees cooler than today. Future Effects Some of the long-term effects of global climate change in the United States are as follows, according to the Third National Climate Assessment Report: 19

21 Change will continue through this century and beyond Global climate is projected to continue to change over this century and beyond. The magnitude of climate change beyond the next few decades depends primarily on the amount of heat-trapping gases emitted globally, and how sensitive the Earth s climate is to those emissions. Temperatures will continue to rise Because human-induced warming is superimposed on a naturally varying climate, the temperature rise has not been, and will not be, uniform or smooth across the country or over time. 20

22 Frost-free season (and growing season) will lengthen The length of the frost-free season (and the corresponding growing season) has been increasing nationally since the 1980s, with the largest increases occurring in the western United States, affecting ecosystems and agriculture. Across the United States, the growing season is projected to continue to lengthen. In a future in which heat-trapping gas emissions continue to grow, increases of a month or more in the lengths of the frost-free and growing seasons are projected across most of the U.S. by the end of the century, with slightly smaller increases in the northern Great Plains. The largest increases in the frost-free season (more than eight weeks) are projected for the western U.S., particularly in high elevation and coastal areas. The increases will be considerably smaller if heat-trapping gas emissions are reduced. 21

23 Changes in precipitation patterns Average U.S. precipitation has increased since 1900, but some areas have had increases greater than the national average, and some areas have had decreases. More winter and spring precipitation is projected for the northern United States, and less for the Southwest, over this century. Projections of future climate over the U.S. suggest that the recent trend towards increased heavy precipitation events will continue. This trend is projected to occur even in regions where total precipitation is expected to decrease, such as the Southwest. More droughts and heat waves 22

24 Droughts in the Southwest and heat waves (periods of abnormally hot weather lasting days to weeks) everywhere are projected to become more intense, and cold waves less intense everywhere. Summer temperatures are projected to continue rising, and a reduction of soil moisture, which exacerbates heat waves, is projected for much of the western and central U.S. in summer. By the end of this century, what have been once-in- 20-year extreme heat days (one-day events) are projected to occur every two or three years over most of the nation. Hurricanes will become stronger and more intense The intensity, frequency, and duration of North Atlantic hurricanes, as well as the frequency of the strongest (Category 4 and 5) hurricanes, have all increased since the early 1980s. The relative contributions of human and natural causes to these increases are still uncertain. Hurricaneassociated storm intensity and rainfall rates are projected to increase as the climate continues to warm. 23

25 Sea level will rise 1-4 feet by 2100 Global sea level has risen by about 8 inches since reliable record keeping began in It is projected to rise another 1 to 4 feet by This is the result of added water from melting land ice and the expansion of seawater as it warms. In the next several decades, storm surges and high tides could combine with sea level rise and land subsidence to further increase flooding in many regions. Sea level rise will continue past 2100 because the oceans take a very long time to respond to warmer conditions at the Earth s surface. Ocean waters will therefore continue to warm and sea level will continue to rise for many centuries at rates equal to or higher than those of the current century. 24

26 Arctic likely to become ice-free The Arctic Ocean is expected to become essentially ice free in summer before mid-century. U.S. Regional Effects Below are some of the impacts that are currently visible throughout the U.S. and will continue to affect these regions, according to the Third National Climate Assessment Report 19, released by the U.S. Global Change Research Program: Northeast Heat waves, heavy downpours, and sea level rise pose growing challenges to many aspects of life in the Northeast. Infrastructure, agriculture, fisheries and ecosystems will be increasingly compromised. Many states and cities are beginning to incorporate climate change into their planning. 19 USGCRP 2014, Third Climate Assessment. 25

27 Northwest Changes in the timing of streamflow reduce water supplies for competing demands. Sea level rise, erosion, inundation, risks to infrastructure, and increasing ocean acidity pose major threats. Increasing wildfire, insect outbreaks, and tree diseases are causing widespread tree die-off. Southeast Sea level rise poses widespread and continuing threats to the region s economy and environment. Extreme heat will affect health, energy, agriculture and more. Decreased water availability will have economic and environmental impacts. Midwest Extreme heat, heavy downpours and flooding will affect infrastructure, health, agriculture, forestry, transportation, air and water quality, and more. Climate change will also exacerbate a range of risks to the Great Lakes. Southwest Increased heat, drought and insect outbreaks, all linked to climate change, have increased wildfires. Declining water supplies, reduced agricultural yields, health impacts in cities due to heat, and flooding and erosion in coastal areas are additional concerns. 26

28 Chapter 4 SCIENTIFIC CONSENSUS Scientific Consensus: Earth's Climate is Warming Above: Temperature data from four international science institutions. All show rapid warming in the past few decades and that the last decade has been the warmest on record. Data sources: NASA's Goddard Institute for Space Studies; NOAA National Climatic Data Center; Met Office Hadley Centre/Climatic Research Unit; and the Japanese Meteorological Agency. 27

29 Multiple studies published in peer-reviewed scientific journals 20 show that 97 percent or more of actively publishing climate scientists agree*: Climate-warming trends over the past century are extremely likely due to human activities. In addition, most of the leading scientific organizations worldwide have issued public statements endorsing this position. The following is a partial list of these organizations, along with links to their published statements and a selection of related resources. The number of papers rejecting AGW [Anthropogenic, or human-caused, Global Warming] is a miniscule proportion of the published research, and that percentage has been decreasing over time. Among papers expressing a position on AGW, an overwhelming percentage 97.2% based on self-ratings, 97.1% based on abstract ratings endorses the scientific consensus on AGW. Among abstracts that expressed a position on anthropogenic climate change, 97.1% endorsed the scientific consensus. Among scientists who expressed a position on Anthropogenic climate change in their abstract, 98.4% endorsed the consensus. American Scientific Societies Statement on climate change from 18 scientific associations: Observations throughout the world make it clear that climate change is occurring, and rigorous scientific research demonstrates that the greenhouse gases emitted by human activities are the primary driver J. Cook, at al., Consensus on consensus: A Synthesis of Consensus estimates on Human-Caused Global Warming, Environmental Research Letters, Vol. 1 No. 4 (13 April, 2016) 21 Statement on Climate Change from 18 Scientific Associations, _letter1.pdf 28

30 American Association for the Advancement of Science: The scientific evidence is clear: global climate change caused by human activities is occurring now, and it is a growing threat to society. 22 American Chemical Society: Comprehensive scientific assessments of our current and potential future climates clearly indicate that climate change is real, largely attributable to emissions from human activities, and potentially a very serious problem. 23 American Geophysical Union Human induced climate change requires urgent action. Humanity is the major influence on the global climate change observed over the past 50 years. Rapid societal responses can significantly lessen negative outcomes AAAS Board Statement on Climate Change, ACS Public Policy Statement: Climate Change ( ) 24 Human-Induced Climate Change Requires Urgent Action by AGU, Adopted 2003, revised and reaffirmed 2007, 2012,

31 American Medical Association Our AMA supports the findings of the Intergovernmental Panel on Climate Change s fourth assessment report and concurs with the scientific consensus that the Earth is undergoing adverse global climate change and that anthropogenic contributions are significant. 25 American Meteorological Society It is clear from extensive scientific evidence that the dominant cause of the rapid change in climate of the past half century is humaninduced increases in the amount of atmospheric greenhouse gases, including carbon dioxide (CO2), chlorofluorocarbons, methane, and nitrous oxide. 26 American Physical Society The evidence is incontrovertible: Global warming is occurring. If no mitigating actions are taken, significant disruptions in the Earth s physical and ecological systems, social systems, security and human health are likely to occur. We must reduce emissions of greenhouse gases beginning now Global Climate Change and Human Health by AMA, Climate Change: An Information Statement of the American Meteorological Society, APS National Policy 07.1 Climate Change,

32 The Geological Society of America The Geological Society of America concurs with assessments by the National Academies of Science, the National Research Council, and the Intergovernmental Panel on Climate Change that global climate has warmed and that human activities (mainly greenhouse gas emissions) account for most of the warming since the middle 1900s. 28 Science Academies International Academies: Joint Statement Climate change is real. There will always be uncertainty in understanding a system as complex as the world s climate. However there is now strong evidence that significant global warming is occurring. The evidence comes from direct measurements of rising surface air temperatures and subsurface ocean temperatures and from phenomena such as increases in average global sea levels, retreating glaciers, and changes to many physical and biological systems. It is likely that most of the warming in recent decades can be attributed to human activities GSA position on Climate Change, Joint Science Academic s Statement: Global Response to Climate Change,

33 U.S. National Academy of Sciences The scientific understanding of climate change is now sufficiently clear to justify taking steps to reduce the amount of greenhouse gases in the atmosphere. U.S. Government Agencies U.S. Global Change Research Program The global warming of the past 50 years is due primarily to human-induced increases in heat-trapping gases. Human 'fingerprints' also have been identified in many other aspects of the climate system, including changes in ocean heat content, precipitation, atmospheric moisture, and Arctic sea ice Global Climate Change Impacts in the United States by U.S> Government Departments and Agencies,

34 Intergovernmental Bodies Intergovernmental Panel on Climate Change Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, and sea level has risen. 31 Human influence on the climate system is clear, and recent anthropogenic emissions of greenhouse gases are the highest in history. Recent climate changes have had widespread impacts on human and natural systems. 32 Other Resources List of worldwide scientific organizations. The following page lists the nearly 200 worldwide scientific organizations that hold the position that climate change has been caused by human action: 31 IPCC Fifth Assessment Report, Summary for Policymakers, Ibid. 33

35 U.S. agencies The following page contains information on what federal agencies are doing to adapt to climate change. Consensus Technically, a consensus is a general agreement of opinion, but the scientific method steers us away from this to an objective framework. In science, facts or observations are explained by a hypothesis (a statement of a possible explanation for some natural phenomenon), which can then be tested and retested until it is refuted (or disproved). As scientists gather more observations, they will build off one explanation and add details to complete the picture. Eventually, a group of hypotheses might be integrated and generalized into a scientific theory, a scientifically acceptable general principle or body of principles offered to explain phenomena. 34

36 Scientific evidence for warming of the climate system is unequivocal. The current warming trend is of particular significance because most of it is extremely likely (greater than 95 percent probability) to be the result of human activity since the mid-20 th century and proceeding at a rate that is unprecedented in millennia. 35