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NATS 101 Lecture 25 Climate Change (cont’d) The Natural Greenhouse Effect: clear sky O3 8% Carbon Dioxide 26% CH4 N20 6% Water Vapor Water Vapor 60% Carbon Dioxide Ozone Methane, Nitrous Oxide Clouds also have a greenhouse effect Kiehl and Trenberth 1997 CO2 makes the biggest contribution to the climate forcing Global Warming Potential (GWP) Different gases has different warming potentials which are defined relative to the warming effect of CO2 Gas Carbon dioxide (CO2) Methane (CH4) Nitrous oxide (N2O) Hydrofluorocarbons Ahrens, Fig 2.10 Perfluorocarbons Sulfur hexafluoride GWP 1 21 310 560-12,100 6,000-9,200 23,900 Changing CO2 concentrations • CO2 concentrations have varied naturally by ~3050% over the past few hundred thousand years (ice ages) • Fossil fuel burning since the industrial revolution has created a recent sharp increase in CO2 concentrations • CO2 concentrations are now higher than at any time in past few hundred thousand years Last 4 Ice Age cycles: • And concentrations are increasing faster with time 400,000 years Man made You are here See http://epa.gov/climatechange/science/recentac.html CO2 Temp. Increasing CO2 concentrations • How high will they go? How warm will it get??? • If CO2 concentrations stay within factor of 2 of pre-industrial, then warming of 3+1oC is expected • If concentrations go still higher => larger uncertainty because the climate is moving into unprecedented territory See http://epa.gov/climatechange/science/futureac.html You are going to be somewhere in here Last 4 Ice Age cycles: 400,000 years Man made You are here Ice age CO2 range Predictions of increased CO2 & Temperature Emissions High Medium Low Constant 2000 CO2 Multi-model global averages of surface warming (relative to 1980-99) for the scenarios A2, A1B and B1, as continuations of the 20th century simulations. Shading is plus/minus one standard deviation range of individual model annual averages. Trenberth/IPCC Missing Carbon Sink Woods Hole web page • CO2 is accumulating in the atmosphere more slowly than expected (believe it or not) • Based on our understanding of CO2 emissions and ocean and atmosphere uptake, there is a missing sink/uptake of about 25% NASA OCO mission Ocean Carbon Uptake QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. Ocean Uptake of CO2 QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. SciAm article The Oceans & Global Change • Much of this material is courtesy of – Julia Cole, here in Geosciences at UA and – Kevin Trenberth at the National Center for Atmospheric Research [NCAR] QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. Ocean Transport of Heat QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. 3D “Conveyor Belt” Concept QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. Potential Changes Related to the Ocean QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. Change in Thermohaline Circulation QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. Change in Ocean Chemistry QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. Ocean Acidification (SciAm article) • Currently ~1/3 of CO2 released by burning fossil fuels ends up in the ocean. • Absorbed CO2 forms carbonic acid in seawater, lowering the slightly alkaline pH level, changing the balance of carbonate & bicarbonate ions. • Shift toward acidity & ensuing changes in ocean chemistry, make it more difficult for creatures to build hard parts out of calcium carbonate. • Decline in pH thus threatens a variety of organisms, including corals, which provide one of the richest habitats on earth. • Within a century, Southern Ocean surface will be corrosive to shells of tiny snails key in the marine food chain within this highly productive zone. Sea level is rising: from ocean expansion and melting glaciers Since 1993 Global sea level has risen 43 mm (1.7 inches) • 60% from expansion as ocean temperatures rise, • 40% from melting glaciers from Steve Nerem via Trenberth Observed Ocean Warming • Most oceans are warming • Figures from Hansen et al 2006 Evidence for reality of climate change Glaciers melting Muir Glacier, Alaska 1909 Toboggan Glacier Alaska 2000 1900 2003 Alpine glacier, Austria Research indicates that less than 8°F of Arctic warming caused Greenland to lose enough water to raise sea level by up to 12 feet during the Last Interglacial Period Today 125,000 years ago QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. Image from Bette Otto-Bliesner, National Center for Atmospheric Research BUT, sea level rise during the Last Interglacial Period appears to have been more… it was likely up to 21 feet. A reduced Greenland Ice Sheet could only have contributed up to 12 feet… Where did the rest of the water come from? Today Most likely Antarctica… East Antarctic QuickTime™ a Ice and Sheet TIFF (Uncompressed) decompressor are needed to see this picture. West Antarctic Ice Sheet http://svs.gsfc.nasa.gov 125,000 years ago - the West Antarctic Ice Sheet may have been gone Late Quaternary diatoms and anomalously high 10Be found in sediments under the ice sheet East Antarctic Ice Sheet 1 meter 2 meters www.gfdl.noaa.gov 4 meters 8 meters Surface melt on Greenland Increasing melt zones. Melt descending into a moulin: a vertical shaft carrying water to the base of the ice sheet. NSIDC (above) Braithwaite: Univ. Manchester Greenland ice mass budget A great deal of effort is going into estimating how the Greenland ice sheet is changing Researchers Mass Change Method Time Span (GT/year) Krabill et al. 2000 -47 Aircraft Surveys 1994-1999 Velicogna et al. 2006 -200 to -260 GRACE 2002-2006 Luthcke et al. 2007* -145 to -175 GRACE 2003-2006 Zwally et al. 2007* -80 to -100 ICESat 2003-2005 GRACE is a gravity recovery mission ICESat is a lidar topographymission NASA website on Greenland ice sheet 100 GT/yr ~ 0.3 mm/yr sea level rise Snow cover and Arctic sea ice are decreasing Arctic sea ice area decreased by 2.7% per decade (Summer: -7.4%/decade) 2007: 22% (106 km2) lower than 2005 Spring snow cover shows 5% stepwise drop during 1980s Trenberth/IPCC Arctic sea ice disappears in summer by 2050 Already 2007 lowest on record by 22% Abrupt Transitions in Summer Sea Ice 2007 x • Gradual forcing results in abrupt Sept ice decrease • Extent decreases from 80 to 20% coverage in 10 years. • Relevant factors: • Ice thinning • Arctic heat transport • Albedo feedback Trenberth from Holland et al., GRL, 2006 Land surface temperatures are rising faster than SSTs SST Land Annual anomalies of global average SST and land surface air temperature Land increased 0.4oC vs ocean suggesting 3% decrease in RH over land Trenberth/IPCC Human body: sweats Homes: Evaporative coolers (swamp coolers) Planet Earth: Evaporation (if moisture available) e.g., When sun comes out after showers, the first thing that happens is that the puddles dry up: before temperature increases. Trenberth Water vapor increase at higher temperatures Water holding capacity of atmosphere increases about 7% per oC (4% per F) increase in temperature. Observations show that water vapor in LOWER troposphere is indeed increasing. Surface temperature increase: 0.6 C since 1970 over global OCEANS and 4% more water vapor. Total water vapor Since late 1970’s, ocean surface has been warming at ~0.14 C/decade => ~1% WV increase/decade. Observed WV trend since 1988 is ~1.2% per decade From Trenberth/IPCC Land precipitation is changing significantly over broad areas Increases Decreases Smoothed annual anomalies for precipitation (%) over land from 1900 to 2005; other regions are dominated by variability. Trenberth/IPCC Proportion of heavy rainfalls: increasing in most land areas Regions of disproportionate changes in heavy (95th) and very heavy (99th) precipitation Trenberth/IPCC Declining Snow Pack in many mountain and continental areas contributes to drought • more precipitation falls as rain rather than snow, especially in the fall and spring. • snow melt occurs faster and sooner in the spring • snow pack is therefore less • soil moisture is less as summer arrives • the risk of drought increases substantially in summer •Along with wild fire Trenberth Drought is increasing most places The most important Mainly decrease in rain over spatial (top) land in tropics and pattern subtropics, of the but enhanced by monthly increased Palmer Drought atmospheric demand with Severity Index warming (PDSI) for 1900 to 2002. The time series (below) accounts for most of the trend in PDSI. Trenberth/IPCC Rising greenhouse gases are causing climate change, and arid areas are becoming drier while wet areas are becoming wetter. Water management:dealing with how to save in times of excess for times of drought – will be a major challenge in the future. Trenberth Heat waves and wild fires Impacts on human health and mortality, economic impacts, ecosystem and wildlife impacts Trenberth Extremes of temperature are changing! Observed trends (days) per decade for 1951 to 2003: 5th or 95th percentiles From Alexander et al. (2006) Trenberth/IPCC Global Atmo Energy Imbalance Increasing GHG concentrations decrease Energy out So Energy IN > Energy OUT and the Earth warms IR Out is reduced Ahrens, Fig. 2.14 Solar in Atmosphere Heat waves are increasing: an example Extreme Heat Wave Summer 2003 Europe 30,000 deaths Trend plus variability? Trenberth/IPCC Trenberth CO2 emissions in different regions in 2000 in terms of emissions per capita (height of each block); population (width of each block); and total emissions (product of population and emissions per capita = area of block). Source: M. Grubb, http://www.eia.doe.gov/iea/ Trenberth Trenberth