CLIMATE CHANGE What is the role of humans? The climate record of the last 2000 years is fairly well-established. The last few decades have been the warmest in this time period. Scientists are observing tremendous warming with instruments today. Natural causes alone cannot explain this warming but increased greenhouse gases can. DETERMINING PAST CLIMATE Scientists use “proxy data” such as: • tree-rings • marine sediment • mineral deposits • lake deposits • ice cores • corals • historical documentary series Riebeek (2006b) Mann, et al. (2008) A 2,000 year cooling trend was reversed during the 20th century, with four of the five warmest decades of the 2000-year-long reconstruction occurring between 1950 and 2000. studentsagainstclimatechange.blogspot.com CO2 CONCENTRATION (Hayhoe, 2010) Higher Values Last Occurred over 15 Million Years Ago! (Cook, 2010) (Hayhoe, 2010) NATURAL CAUSES Ruddiman (2008) Tectonic-Scale Climate Change (Millions of Years) NATURAL CAUSES Ruddiman (2008) Milankovitch Cycles (41,000 – 100,000 Years) NATURAL CAUSES Mantua (2000) Pacific Decadal Oscillation (Decades) Cook (2008) PDO cannot explain the long term warming trend observed in the modern climate record (Hayhoe, 2010) HOW WE KNOW IT IS WARMING FROM CO2 • Satellites measure decreasing outgoing LW radiation from CO2 • Ground instruments measure increased downwelling LW radiation from CO2 • Nights are warming faster than days • Stratosphere is cooling • Arctic regions are warming the fastest All of these are consistent with GHG warming and there is no natural cause that explains these. IPCC (2007) Black line = actual temperatures, red line = modeled temperatures Climate models with GHGs and natural forcing mechanisms IPCC (2007) Black line = actual temperatures, blue line = modeled temperatures Climate models with only natural forcing mechanisms SCIENTIFIC CONSENSUS Nobel Prize winning IPCC (2007) report states: Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic (human) greenhouse gas concentrations. No Scientific Body of National or International Standing Holds a Dissenting Opinion A 2008 poll of 3,146 Earth scientists showed 96.2% of climatologists who are active in climate research believe in modern global warming, and 97.4% believe that human activity is a significant factor in this warming. (Doran & Zimmerman, 2009) EARTH IS LOSING ICE (National Snow & Ice Data Center) (Hayhoe, 2010) (Kwock & Rothrock, 2009) Ice Thickness is Decreasing (World Glacier(Rothrock Monitoring, et Service,al., 1999) 2009) Glaciers are Losing Mass and 90% of Global Glaciers are Retreating (Hayhoe, 2010) (IPCC, 2007) Droughts are Increasing (red = drier climate) (IPCC, 2007) (Nerem et al., 2010) Sea Level is Rising New York City with 3 meter rise (Possible by year 2100) Stronger Hurricanes in a Warmer World Stronger Hurricanes in a Warmer World (Hayhoe, 2010) (Hayhoe, 2010) (Hayhoe, 2010) Information provided by Professor Scott A. Mandia (S.C.C.C.) from the Global Warming: Man or Myth? Web site: http://www2.sunysuffolk.edu/mandias/global_warming/ & Katharine Hayhoe, Research Professor at Texas Tech University. Many more slides available at: http://temagami.tosm.ttu.edu/khayhoe/climate_slides/index.htm.