Transcript climate2
Climate change – “science catfight” or not? The Record Of Climate Change Proxy Data Causes of climate change Natural Anthropogenic Milankovitch cycles Eccentricity 100,000 yrs Obliquity (tilt) 41,000 yrs Precession (wobble) 26,000 yrs Other factors Solar energy output variability Correlations with sunspot cycles Variations < 0.1% of irradiance Figure 21.21 (left) Positive feedback mechanisms Other factors Continental position Continents in polar regions promote ice sheet growth Other factors Ocean current circulation patterns Thermohaline circulation Temperature or salinity induced density differences Cold water sinks to bottom at high latitudes Restricted flow to poles may promote ice sheet growth Other factors Changes in CO2 CO2 levels track ice core temps Other factors Changes in CO2 CO2 levels track ice core temps. May be positive feedback, slight warming releases CO2 from oceans, causes further warming… Source: GRID/Arendal Climate Variations and Tectonics These are linked in various ways Plate motions mean moving large continental masses around Move away from equator: more water to absorb solar radiation near equator, overall warming Move towards equator: less water, can cool General change in ocean circulation patterns Uplift of large mountains can change atmospheric circulation Opening of oceans mean large lava outputs Likely add gases to aid warming through greenhouse effect Recent Times Last 2 million years, have had several ice ages Most recent peaked ~20,000 years ago Other factors Volcanic activity Suspended material reflects solar radiation Mt. Pinatubo, 1991 (Photo: USGS) Volcanoes and Climate Large eruptions can put a lot of ash into atmosphere can reduce amount of sunlight reaching ground surface and cooling Pinatubo eruption 1991 20 million tons of SO2 put in the atmosphere Reflected 2-4% of incoming solar radiation Led to average cooling of earth by 0.5-1°C that persisted for ~1-2 years “Cloud” from Mt. Pinatubo eruption Temperature change 1815 eruption of Tambora volcano in Indonesia lowered global temperature 3°C 1816 know as “the year without summer” Source: NASA But, volcanoes also emit CO2 Cretaceous warm period may have been caused by large volcanic eruptions Cretaceous chalks record expansion of marine life in warm climate Human impact Human Effects on the Carbon Cycle Human activities release ~7.1 Gt* of carbon into the atmosphere each year New plant growth and …yielding a net Air-sea exchange atmospheric increase removes ~3.8 Gt/yr of ~ 3.3 Gt/yr. Projected Changes in Global Temperature Under Three Different Scenarios Continued reliance on fossil fuels increased reliance on nonfossil fuels Rapid conversion to cleaner and more resource-efficient technologies Range of uncertainty Likely temperature change by the end of the 21st century, relative to 1960-1990 A. Fossil-fuel intensive world B. More conservationoriented world Consequences for sea level Melting land ice Thermal expansion of water >100 m rise since last glacial maximum Global warming is projected to reduce the north polar ice cap, disrupting Arctic ecosystems, but possibly improving navigation. Land surface slope near shoreline influences effect of sea level change Raisz • Over next century, Arctic could warm by 3 - 5 ˚C (similar to last interglaciation) • Last interglacial caused by changes in Earth’s tilt and orbit • Next century changes due to increased CO2 in atmosphere Figure 18.6 Why are these linked? 2005 study suggesting that hurricane intensity (more cat 4 and 5) has increased over last 15 years, corresponding to ~0.3° increase in temperature Reducing greenhouse gases Conservation Alternative energy Sequestration Biomass Deep ocean Geological Deep ocean injection Liquid CO2 denser than water in cold high pressure environment Per capita emissions UNEP/GRID Another example of human effect on atmospheric composition: Ozone depletion Ozone gas in smog : bad Ozone in stratosphere: good Protects from UV radiation which damages cells Depleted by reacting with human made compounds (particularly CFCs) Ozone hole found near Antarctica in 1985 Led to passage of legislation (Montreal Protocol) to get rid of CFCs Projected Changes in Ozone Concentration With and Without the Montreal Protocol