the Science of Abrupt Climit Change. Main Site Mobile iPhone Lite Full Screen Downloads Settings Join Sign In Favorites ► ◄ Search Weather Maps & Radar Severe Weather Photos & Video Community News Climate Change The Science of Abrupt Climate Change: Should we be worried? By Jeffrey Masters, Ph.D. — Director of Meteorology, Weather Underground, Inc. Introduction We generally consider climate changes as taking place on the scale of hundreds or even thousands of years. However, since the early 1990s, a radical shift in the scientific understanding of Earths climate history has occurred. We now know that that major regional and global climate shifts have occurred in just a few decades or even a single year. The most recent of these shifts occurred just 8200 years ago. If an abrupt climate change of similar magnitude happened today, it would have severe consequences for humans and natural ecosystems. Although scientists consider an abrupt climate change unlikely in the next 100 years, their understanding of the phenomena is still a work-in-progress, and such a change could be triggered instantly by natural processes or by human-caused global warming with little warning. The National Academy of Sciences--the board of scientists established by Congress in 1863 to advise the federal government on scientific matters--compiled a comprehensive report in 2002 entitled, Abrupt Climate Change: Inevitable Surprises. The 244-page report, which contains over 500 references, was written by a team of 59 of the top researchers in climate, and represents the most authoritative source of information about abrupt climate change available. Most of the material that follows was taken from this report. The Greenland Ice Sheet: The Key to Understanding Earths Climate Record Ice cores hold an amazingly detailed record of Earths climate. Each year, snow falling on glacial areas accumulates, piling on top of thousands of years of past snow, compressing the snow into yearly layers of ice, like rings inside a tree trunk. Preserved in the ice are tiny bubbles of ancient air that tell us the composition of the atmosphere at that time. The amount of dust in the snow tells us how windy the climate was. The thickness of the layer tells how much precipitation fell that year. Most importantly, the amount of the heavy isotope of oxygen, 18O, lets us infer the average atmospheric temperature, since water vapor with heavy 18O molecules condenses out of clouds more readily at cold temperatures. Accessing this treasure-trove of climatic information is a huge undertaking--cores of ice must be drilled miles deep in some of the most inhospitable places on Earth. In 1989 the National Science Foundation funded the $25 million Greenland Ice Sheet Project II (GISP2) to drill an ice core through the entire two mile depth of the Greenland ice sheet. At the same time, a separate European project (GRIP), drilled through the ice just 20 miles away, providing a crucial independent check of the GISP2 data. By 1993, both the GRIP and GISP2 drills had hit bedrock, and two miles of ice cores, preserving 110,000 years of climate history in year-by-year layers, were taken to laboratories for analysis. What the scientists found was surprising and unnerving. They had known from previous ice core and ocean sediment core data that Earths climate had fluctuated significantly in the past. But what astonished them was the rapidity with which these changes occurred. Ocean and lake sediment data from places such as California, Venezuela, and Antarctica have confirmed that these sudden climate changes affected not just Greenland, but the entire world. During the past 110,000 years, there have been at least 20 such abrupt climate changes. Only one period of stable climate has existed during the past 110,000 years--the 11,000 years of modern climate (the Holocene era). Normal climate for Earth is the climate of sudden extreme jumps--like a light switch flicking on and off. Figure 1. Average Yearly Temperatures in Greenland over the past 100,000 Years as inferred from Oxygen isotope analysis of the GISP2 Greenland ice core. Source: Cuffey, K.M., and G.D. Clow, Temperature, accumulation, and ice sheet elevation in central Greenland throughout the last deglacial transition, Journal of Geophysical Research, 102, 383-396, 1997. As seen in Figure 1, the ice core record showed frequent sudden warmings and coolings of 15°F (8°C) or more. Many of these changes happened in less than 10 years. In one case 11,600 years ago, when Earth emerged from the final phase of the most recent ice age (an event called the Younger Dryas), the Greenland ice core data showed that a 15°F (8°C) warming occurred in less than a decade, accompanied by a doubling of snow accumulation in 3 years. Most of this doubling occurred in a single year. What causes abrupt climate change? Current theories on the cause of abrupt climatic change focus on sudden shut downs and start-ups of the Meridional Overturning Circulation (MOC) (also referred to as the thermohaline circulation), which is a global network of density-driven ocean currents. The Meridional Overturning Circulation transports a tremendous amount of heat northward, keeping the North Atlantic and much of Europe up to 9°F (5°C) warmer, particularly in the winter. A sudden shut down of this current would have a ripple effect throughout the ocean-atmosphere system, forcing worldwide changes in ocean currents, and in the path of the atmospheric jet stream. Studies of North Atlantic Ocean sediments have revealed that the Meridional Overturning Circulation has shut down many times in the past, and that many of these shut downs coincide with the abrupt climate change events noted in the Greenland ice cores. How does one shut down the Meridional Overturning Circulation? First, one must examine the MOC itself. The MOC, or Great Ocean Conveyor Belt (Figure 2), is a system of interconnected ocean currents that girdle the planet. Figure 2. The Great Ocean Conveyor Belt Source: IPCC At the surface, warmer ocean currents (shown here in orange) are driven by the winds, and so move parallel to the wind direction, except where continental land masses block the way. Water can also move vertically in the ocean. High density water sinks, and low density water rises. Salty water is more dense than fresh water, and cold water is more dense than warm water, so that wherever we find cold, salty water, it tends to sink. Colder currents (shown here in blue) are deeper and have higher salinity. In the tropical Atlantic, the suns heat evaporates large amounts of water, creating relatively warm, salty ocean water. This warm, salty water flows westward toward North America, then up the East Coast of the U.S., then northeastward toward Europe, forming the mighty Gulf Stream current. As this warm, salty water reaches the ocean regions on either side of Greenland, cold winds blowing off of Canada and Greenland cool the water substantially (in Figure 2, these regions are marked with white circles labeled, Heat release to the atmosphere.) These cool, salty waters are now very dense compared to the surrounding waters, and sink to the bottom of the ocean. Thus, the oceanic areas by Greenland where this sinking occurs are called deep-water formation areas. This North Atlantic deep water flows southward toward Antarctica, eventually making it all the way to the Pacific Ocean, where it rises back to the surface to complete the Great Ocean Conveyor Belt. It takes about 1000 years for the water to make a complete circuit around the globe. Since the Great Ocean Conveyor Belt is driven in part by differences in ocean water density, if one can pump enough fresh water into the ocean in the key areas on either side of Greenland where the Gulf Stream waters cool and sink, this will lower the oceans salinity (and therefore its density) enough so that the waters can no longer sink. As a result, the Atlantic conveyor belt and Gulf Stream current would shut down in just a few years, dramatically altering the climate. How much fresh water is needed to shut down the MOC? It is unknown precisely how much fresh water is needed to shut down the MOC.. Scientists are fairly certain that the last two abrupt coolings seen the Greenland ice core, the Younger Dryas event and the 8200 years before present event (Figure 1), both occurred when huge North American glacial melt-water lakes flooded down the St. Lawrence River into the North Atlantic when the ice dams restraining the lakes broke. The sudden addition of low-density fresh water presumably partially or totally stopped the sinking of ocean waters in the North Atlantic, slowing or completely stopping the Meridional Overturning Circulation. Once the fresh water got into the North Atlantic, it stayed, puddling on top of the ocean and freezing in winter. The Meridional Overturning Circulation stayed shut off for about 1100 years during the Younger Dryas event, then suddenly restarted, for reasons scientists dont understand. Current computer models of the climate cannot reproduce the observed sudden shut-down or start-up of the Meridional Overturning Circulation at the beginning and end of the Younger Dryas period. Other sudden shut downs of the Meridional Overturning Circulation observed in ice core and ocean sediment records are not thought to be due to sudden melt-water floods into the North Atlantic. These events may have happened simply because Earths climate system is chaotic, or perhaps because some critical threshold was crossed when increases in precipitation, river run-off, and ice melt put enough fresh water into the ocean to shut down the Meridional Overturning Circulation. How likely is it that global warming will trigger abrupt climate change? Global warming will increase precipitation, river run-off, melting of the Greenland ice sheet, and melting of polar sea ice, all of which will increase the amount of fresh water flowing into the critical deep-water formation areas by Greenland. In the 2007 IPCC Fourth Assessment Report Summary for Policymakers (PDF File) it states that, based on current model simulations, it is very likely (90-99% confidence) that the meridional overturning circulation (MOC) of the Atlantic Ocean will slow down during the 21st century. It also confirms the scientific consensus that is very unlikely the MOC will undergo a large abrupt transition during this century. Todays science is such that any long-term assessments of the MOC cannot be made with confidence. A 2012 paper in Proceedings of the National Academy of Sciences used computer modeling to show that abrupt climate events in the past occurred as a result of a change in ocean currents due to the Bering Strait closing off because of low sea levels. The Bering Strait is the 50-mile-wide gap that separates Siberia from Alaska. As long as the Bering Strait remains open, said lead author Aixue Hu, a climate modeler at the National Center for Atmospheric Research (NCAR), in a telephone interview posted at Climate Central, we will not see an abrupt climate event. With global sea levels rising due to melting icecaps, closure of the Bering Strait is not likely in the forseeable future. How would the climate change if the Meridional overturning circulation shut down? A shut down of the Meridional overturning circulation would suddenly decrease the amount of heat in the North Atlantic, leading to much colder temperatures in Europe and North America. A 2003 reportprepared for the Department of Defense outlines what would happen if an abrupt climatic change similar to the 8200 years before present event were to recur today: Annual average temperatures would drop up to 5° F in North America, and up to 6° F in northern Europe. This is not sufficient to trigger an ice age, which requires about a 10° F drop in temperature world-wide, but could bring about conditions like experienced in 1816--the famed year without a summer. In that year, volcanic ash from the mighty Tambora volcanic eruption in Indonesia blocked the suns rays, significantly cooling the globe. Snow fell in New England in June, and killing frosts in July and August caused widespread crop failures and famine in New England and northern Europe. Annual average temperatures would warm up to 4° F in many areas of the Southern Hemisphere. Multi-year droughts in regions unaccustomed to drought would affect critical agricultural and water resource regions world-wide, greatly straining food and water supplies. Winter storms and winds would strengthen over North America and Europe. Dr. Wally Broecker of Columbia University, the scientist who first pointed out the link between the Atlantics conveyor circulation and abrupt climate change, wrote a letter in March 2004 to Sciencemagazine, accusing the authors of the study of making exaggerated claims that only intensify the existing polarization over global warming. Broecker argued that a global-warming induced abrupt climate change is not likely to occur until 100 years or so into the future, by which time Earths temperature will have warmed sufficiently to offset much of the abrupt cooling a Meridional overturning circulation shut down would trigger. Broecker added: What is needed is not more words but rather a means to shut down carbon dioxide emissions. The authors of the study defend their scenario thusly: We have created a climate change scenario that although not the likely, is plausible, and would challenge United States national security in ways that should be considered immediately. On the freezing of the UK and Europe The possibility of the freezing of the UK and Europe will be determined by a tug-of-war of sorts, between the amount of greenhouse gases and the speed with which the MOC slows down. Greenhouse gases may have more of an impact than a slowing of the MOC, simply because they are more abundant today than ever in the earths record. (CO2 levels were at 380 ppm as of 2007, and were never above 300 ppm during the 400,000 years studied in Antarctic ice cores). Ocean experts see the MOC as having three levels: faster, slower, or off. A 2005 comparison of eleven climate models showed that the MOC will likely be slowed by 10-50%, however, because the levels of carbon dioxide are so elevated, any cooling produced by the MOC slowing would be modest because the greenhouse gases would more than compensate. As a result, a net warming is still shown by these models for the UK and surrounding countries. Improving our measurements to monitor the MOC will allow for better predictions and reduce uncertainty of the amount of warming or cooling these areas of northern Europe will encounter. What is being done about abrupt climate change? The immediate obvious needs are for accurate, long-term measurements of the temperature, salinity, and flow rates of the major ocean currents in the North Atlantic Ocean. An expedition set sail from Great Britain on Feb. 13 2004, to provide just that. The voyage was part of a joint US/UK research project called Rapid Climate Change, which began in 2001. In the U.S., Senator Susan Collins (R-Maine) sponsored bill S.1164 to authorize $60 million for the National Oceanic and Atmospheric Administration (NOAA) to study abrupt climate change. On March 9, 2004, the Senate Commerce Committee approved the bill. It defines abrupt climate change as a change in the climate that occurs so rapidly or unexpectedly that human or natural systems have difficulty adapting to the climate as changed. The bill would create a research program within NOAAs Office of Oceanic and Atmospheric Research to determine what causes sudden climate changes and using computer models to predict climate change events. This bill did not pass, and there is little chance for revival. The NTSC Joint Subcommittee On Ocean Science and Technology authored an Ocean Research Priorities Plan in January 2007, providing five key elements for reducing our vulnerability to abrupt climate change. These include: daily monitoring of ocean currents, temperature, and carbon, now-casting, model development, past-climate-change reconstructions, and additional climate-impact assessments. Conclusion The historical records shows us that abrupt climate change is not only possible--it is the normal state of affairs. The present warm, stable climate is a rare anomaly. It behooves us to learn as much as we can about the climate system so that we may be able to predict when the next abrupt shift in climate will come. Until we know better when this might happen, it would be wise to stop pouring so much carbon dioxide into the air. A nasty surprise might be lurking just around the corner. In the words of Dr. Wally Broecker, the climate system is an angry beast, and we are poking it. Related Blogs Dr. Jeff Masters Recent Climate Change Blogs Save the Keeling Curve! - March 11, 2014 Record Cold in a Warming World - March 4, 2014 U.S. Cold Blast WInds Down, Fails to Set Any All-Time Cold Records - January 8, 2014 Brrrr! -135.8°F Measured at Earths New Coldest Spot - December 10, 2013 Super Typhoon Haiyans Intensification and Unusually Warm Sub-Surface Waters - November 13, 2013 Dr. Ricky Roods Recent Climate Change Blogs Enjoying the Cold - March 4, 2014 The whole silly warming pause, warming hiatus thing - February 21, 2014 Are the changes in the Arctic messing with our weather? The Future of Blocking - February 5, 2014 Are the changes in the Arctic messing with our weather? Analysis - January 26, 2014 Are the changes in the Arctic messing with our weather? Background - January 14, 2014 Further Reading: IPCC 4th Assessment, Chapter 5: Observations: Oceanic Climate Change and Sea Level2007. How a Patch of Ocean Helps Keep Europe from Freezing, by Michael Lemonick, Climate Central, 2012. Who ya gonna call?, a RealClimate.org post by Gavin Schmidt and Michael Mann, August, 2007. NASAs A Chilling Possibility press release, March 2004. Abrupt Climate Change: Should we be worried? Analysis by Woods Hole Oceanographical Institute, January 2003. The Great Climate Flip-flop, a 1998 Atlantic Monthly article. Abrupt Climate Change, a report prepared by Global Business Network (GBN) for the Department of Defense, October 2003. The Two-Mile Time Machine : Ice Cores, Abrupt Climate Change, and Our Future, by Dr. Richard Alley, 2001. An excellent book on the Greenland ice cores findings. The Day After Tomorrow: Could it really happen?, a Weather Underground feature article. Resources Hot Topics Introduction to Climate Change CO2 and the Greenhouse Effect The IPCC Report on Climate Change The Scientific Consensus on Climate Change Hurricanes and Climate Change Extreme Weather Impact of Climate Change on Wildfires Sea Level Rise Arctic Sea Ice Glaciers The Science of Abrupt Climate Change Stratospheric Cooling Ozone Hole Volcanoes PETM: Global Warming, Naturally Heat Mortality Acid Oceans Snow and Ice Arctic Sea Ice Antarctica The Northwest Passage Opens Polar Bears Greenland Permafrost In a Warming World Glaciers Going Green Grocery Shopping Guide Driving Guide Battery Basics Dr. Jeff Masters Top 10 Climate Change Blogs 1. 2011: Earths 11th warmest year; where is the climate headed? 2. The Manufactured Doubt industry and the hacked email controversy 3. Our extreme weather: Arctic changes to blame? 4. Tropical Storm Lees flood in Binghamton: was global warming the final straw? 5. 2010 - 2011: Earths most extreme weather since 1816? 6. The future of intense winter storms 7. Is the Atlantic hurricane season getting longer? 8. The Biggest Control Knob: CO2 in Earths Climate History 9. The climate is changing: the Arctic Dipole emerges 10. My worst global warming fear: buckeyes in Ann Arbor The Best Of Dr. Ricky Roods Climate Blogs Climate Science and the 2012 Election Definition of Climate: Average versus Accumulation Science, Belief and the Volcano Heat Waves: A Climate Case Study Climate Case Study: The 2010 Russian Heat Wave Essay on Climate Change Opinion Dont Shoot the Messenger More CO2 = Healthier Planet? Climategate The Manufactured Doubt Industry Is Carbon Dioxide a Pollutant? The Skeptics vs. the Ozone Hole Richard Lindzens Climate of Fear Opinions and Anecdotal Evidence Book And Movie Reviews The Hockey Stick and the Climate Wars Into the Storm: A book review Storms of My Grandchildren by Dr. James Hansen The Rough Guide to Climate Change: A book review Extreme Weather: a book review Oscar time for Al Gores movie Field Notes from a Catastrophe book review Al Gores An Inconvenient Truth movie review wunderground/news/abrupt-drastic-climate-change-greenhouse-ga Local Weather My Favorites History Data Weather Stations Maps & Radar Radar Satellite WunderMap™ Severe Weather Tropical & Hurricane Storm Reports U.S. Severe Alerts Photos & Video Photo Galleries World View Webcams Blogs Dr. Jeff Masters Meteorology Blogs Member Blogs Travel & Activities Travel Planner Road Trip Planner Ski & Snow Climate Climate Change Evidence Record Extremes Get Free Weather Stickers® Upload Your Photos Weather™ API for Developers NEW! Become a Site Member Find us on Facebook Follow us on Twitter Custom Weather Services In addition to this website, we provide a number of free and professional weather services. Weather™ API for Developers - JSON Newspapers Weather Stickers® About Our Data Advertise On This Site Weather Underground has extensive targeting capabilities to fulfill all of your clients advertising needs. Advertise With Us Media Kit (PDF) Ad Choices Self Service Copyright © 2014 Weather Underground, Inc. About Us - Contact - Support - Employment - Press Releases - Terms of Service - Privacy Statement -WU Gear We can either have democracy in this country or we can have great wealth concentrated in the hands of the few. But we cant have both. Supreme Court Justice Louis Brandeis
Posted on: Tue, 25 Mar 2014 18:19:42 +0000
Trending Topics
Recently Viewed Topics
© 2015