Global Warming and Climate Change
Weather vs. Climate Weather refers to short term conditions (e.g. 24 hrs.) in meteorological conditions such as temperature, pressure and rainfall Climate is average weather conditions recorded over long periods of time (e.g. decades) Similar climates produce similar kinds of ecosystems Knowing the climate we can make predictions as to the kinds of live that would occur/survive there
Atmospheric Processes Temperature Measure of thermal energy (kinetic energy) Relative warmth/coldness of materials Pressure Force per unit area Caused by the weight of the overlying atmospheric gasses High Pressure systems Low Pressure systems Water vapour content Varies from 1% to 4% of air by volume Dependant on air temperature, pressure, availability of water vapour from surface Atmosphere moves due to Earth s rotation and differential heating of the surface and atmosphere These produce global circulation patterns and prevailing winds
Generalized Circulation of the Atmosphere (Hadley Cells)
How We Study Climate Instrumental Record Use of instruments to make climatic measurements began 1860 s Temperatures measured at various places on land and in oceans Concentration of CO 2 measured continuously since 1957 Measured of solar energy for the past several of decades Problems: Few places have a complete record since 1850 (i.e. small dataset) Places that do not representative of global climate Until advent of satellites temp over oceans only measured by passing ships Many areas on Earth have never had good long-term ground based temp. monitoring
How We Study Climate Historical Record People s written recollections (books, journals etc.) Farmer s logs (dates of harvests etc.) Paintings Mostly qualitative data
How We Study Climate Paleo-Proxy Record Refers to data that are not strictly climatic in nature Can be correlated with climate data (such as temperature of the land or sea) Examples Ice Cores Tree Rings Sediments Corals
How We Study Climate Ice Cores Polar ice caps and mountain glaciers have an accumulation record of snow Ice cores often contain small air bubbles (we can measure the gas content of these) Two important gasses used include CO 2 and CH 4 Ice cores also contain a variety of other substances such as volcanic ash and dust etc. Tree Rings Growth of trees influenced by climate Alternating rings indicate periods of rapid/slow growth based on the thickness of the ring Serves as a proxy for variability in climate
How We Study Climate Sediments Biological material (esp. pollen from plants) can accumulate in sediments Can be stored for long periods of time Pollen useful because Quantity of pollen indicator of relative abundance of plant species Pollen can be dated Based on plant assemblage climate can be reconstructed Coral Consists of CaCO 3 Contains isotopes of oxygen as well as a variety of other trace metals Used to determine the temp of the water in which the coral grew
Climate Change Climate is always changing and this has been happening since the initial formation of the Earth High temperature involves ice-free periods (inter-glacials) Low temp. correspond to glacials
Causes of Climate Change Milankovitch Cycles Has to do with the way the Earth revolves around its own axis and how it revolves around the sun 1. The spinning Earth is like wobbling top The wobble means the Earth is unable to keep its angle constant in relation to the sun (Precession of the Equinoxes) One complete cycle in 26 000 years 2. Earth s axis (angle regarding the ecliptic) changes over a period of 41 000 years 3. Elliptic orbit of the Earth changes from very elliptical to more circular (occurs over 100 000 years)
Greenhouse Effect Energy and the Atmosphere Sunlight consists of electromagnetic radiation The hotter the surface the shorter the dominant radiation Earth receives short-wave radiation from sun and emits long-wave radiation back into space
Greenhouse Effect Energy and the Atmosphere Atmosphere reflects approx. 30% of EM radiation from sun and absorbs 25% Remaining 45% reaches the surface and heats up the surface (leads to long-wave radiation being emitted) Gasses in atmosphere absorbs some of these longer wavelengths, heats up and reradiates back to Earth s surface and to space
Greenhouse Effect Each gas has its own absorption spectrum (which wavelengths it absorbs and which it transmits) Certain gasses are strong absorbers in the infrared (long-wave) Major greenhouse gasses Water vapour CO 2 Methane Oxides of nitrogen CFCs Keeps Earth s temp. 30 C warmer than it would be otherwise Limits temperature swings from day to night and maintains a relatively comfortable surface temperature
Potential Effects of Global Warming Glaciers and Sea Ice Lead to a decline in the volume of water stored as ice Potential to increase sea levels and reduce water availability for ecosystems Glaciers in North America & Europe are retreating rather than advancing Not all change in glaciers due to warming (e.g. Kilimanjaro) Areas covered by sea ice reducing (arctic could be seasonally ice free by 2030) Thickness of ice also an issue Melting of Greenland ice sheet has doubled since 1998 (could lead to further destabilizing of the ice sheet)
Potential Effects of Global Warming Changes in river flow Increased warming leads to increased melting of glaciers and decreased rates of snow accumulation Reduces water availability in regions dependant on meltwater Rise in sea level Sea level rises for two reasons Thermal expansion of water Addition of new water as glaciers and ice caps melt Rise predicted: 20cm to 2m Potential increase in flooding of coastal regions (serious threat when coupled with increasing population in these areas) Potential increase in coastal erosion Threat to island nations Could lead to saltwater intrusion of groundwater
Adjusting to Potential Global Warming People can adjust in two ways: 1. Adapt: Learn to live with future global climate change over the next 20 years 2. Mitigate: Work to reduce the emissions of greenhouse gasses and take actions to reduce the undesirable effects of global warming Reduction in CO 2 emissions Energy conservation Transport Carbon sequestration International agreements Montreal Protocol (phasing out of CFCs) Kyoto Protocol (limit the emission of greenhouse gasses) Carbon trading