Climate is changing, we are the cause, and climate change is already exerting impacts that will become increasingly severe if we do not take action. Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) 2007 http://www.youtube.com/watch?v=oJAbATJCugs&feature=related

What is the difference between climate and weather? Climate: long term atmospheric conditions (what to buy) Weather: conditions at specific sites over hours or days. (what to wear)

Climate is always changing Milankovitch cycles The Earth varies in how far away it is from the sun Solar output: every so often the sun emits solar flares

El Nino Southern Oscillation (ENSO) Periodic but irregular cycle El Nino: western Pacific winds strengthen and push warm water East. Rain follows. Causes floods in southern U.S. and drought in Australia La nina: opposite of El Nino. Cold surface waters head westward.

Thermohaline Circulation The rapid melting of Greenland’s ice sheet may interrupt this cycle

The greenhouse effect allows life on our planet Greenhouse gases trap heat and reflect it back to Earth Without these gases Earth would be too cold to live Recently man has added more of these gases to the atmosphere

Greenhouse Gases (GHG) Water vapor is the most abundant greenhouse gas. Concentrations remain stable through time 2. CO2 contributes most to climate change as a result of its abundance Sources: burning fossil fuel and deforestation

Greenhouse Gases cont. 3. Methane: from fossil fuel extraction, livestock, landfill gas, rice growing 4. Nitrous oxide: feedlots, N-fertilizer 5. Ground level ozone O3: secondary pollutant forms in sunlight between VOC + Nox 6. CFCs

Since the industrial revolution concentrations of greenhouse gases have increased markedly CO2 levels are higher than they have been in the last 650,000 years.

Factors that warm or cool the planet Greenhouse gases warm the planet Albedo: how a surface reflects light. Aerosol droplets cool the planet by reflecting the sun’s rays

How do we know what our climate was like thousands of years ago? Proxy indicators are types of indirect evidence that substitute for direct measurement

Ice Cores Scientists collect a cylindrical section of ice from a glacier or an ice sheet Chemical analyses are performed on air trapped in the ice scientists can estimate the percentage of carbon dioxide and other trace gases in the atmosphere at a given time. We now have data for 740,000 years

Tree rings Plant Fossils

Pollen record Pollen grains can accumulate in sediment. Different types of pollen in sediment reflect the vegetation of that time From the vegetation we can determine the climate

How do we currently measure climate? Charles Keeling began monitoring global CO2 in 1958 Why Hawaii? Why does the data vary over the course of a year? The Keeling Curve

What does the future hold? climate models Use vast data sets Reliability of models is increasing