Climate Change - I

Climate and Weather Phenomena

Climate and Urbanization Microclimate: the climate of a relatively small area Human impact on climate cities are warmer than rural areas (urban heat island effect) Pollution: smog, haze Example: the branches nearest the street lamp receive more light and warmth, get confused about the season, do not shed their leaves

The Earth as of 18,000 years ago Alpine glaciers cover Canada and most of Northern US Glaciers periodically advance then retreat Presently they cover ~10% - Greenland and Antarctica

Is Florida in danger? If all the ice were to melt, the level of the ocean would rise by 65 m ~ 210 ft. The highest point in FL is 345 ft.

Determining past climate The methods used to study the past climate typically involve physical, chemical, biological processes sensitive to: temperature changes, the presence of water, solar activity, etc. The records must have survived over a long period of time. We must be able to date the records relatively accurately. Geological evidence – examples: Advancing and retreating glaciers (surface temperature) Ice cores from Antarctica and Greenland (the amount of snow accumulation, isotopic ratios, the crystal structure of the ice, trapped air bubbles, solar activity, volcanic eruptions, fine dust and plant pollen, microorganisms) Plant fossils in sedimentary rocks (plants are sensitive to long-term temperature changes) Core samples of the ocean floor sediments (contain shells and microorganisms that live within some temperature range) Dendrochronology (the rate of growth of tree rings-for trees which are sensitive to temperature or drought stress)

Glaciers

Ice Cores from the Antarctic and Greenland

Sedimentary Rocks

Fossils in Sedimentary Rocks

Ocean Floor Cores

Climate through the Ages: overview Throughout the geological history of the Earth, the temperature has been warmer than today (8 to 15 deg C) There have been several periods of glaciations (ice ages) In the interglacial (warm ) periods the glaciers retreat and the polar regions are ice free, the sea level is elevated. Some of the changes occur over thousands of years, some as quickly as a few years.

Earth Temperature through the Ages During the last 2 billion years the Earth's climate has alternated between A frigid "Ice House", like today's world A steaming "Hot House", like the world of the dinosaurs

Paleoclimatology Long-term evolution of oxygen isotope ratios as measured in fossils. Relative changes in oxygen isotope ratios can be interpreted as rough changes in climate. Quantitative conversion between this data and direct temperature changes is a complicated process subject to many systematic uncertainties, however it is estimated that each 1 part per thousand change in δ18O represents roughly a 1.5-2 °C change in tropical sea surface temperatures

Paleoclimatology Temperature change for the past 150,000 years at the VOSTOK site in Antarctica, based on the deuterium proxy found in ice cores.

Temperature changes in the last 18k years 18k y.a. - max thickness of most recent glaciers, 120 m lower sea level 14k y.a. – ice retreats, gradual warming 12.7k -11k y.a. – cold spell Since then: more or less constant T, with a maximum around 5k y.a.

Ocean temperatures today versus 18,000 years ago Colder North Atlantic during the Ice Age – the Gulf Stream shifted direction. 18,000 YEARS AGO TODAY

The Ocean Conveyor Belt Thermohaline circulation: driven by differences in T and/or salinity Evaporation increases salinity -> density; cooling in the North Atlantic Note: intersecting/overlapping currents are at different depths Gulfstream causes abnormally mild, wet winters in Europe The belt has switched on and off in the past -> sudden climate change

Climate During the last 1000 years Little Ice Age Eighteen hundred and froze-to-death Medieval Climatic Optimum

Temperature trend during the past 100-plus years