Global warming in context We be looking at the following The natural greenhouse effect The fate of solar radiation The human effects on global warming Carbon dioxide in the atmosphere and its effects Some urban myths A Orme

The Natural Greenhouse Effect In 1862 Tyndall discovered that longwave infrared radiation emitted from the Earth’s surface is repeatedly absorbed and re-emitted by greenhouse gases naturally present in the Earth’s atmosphere. (CO2, CH4, N2 and O3) Eventually some of this re-emitted radiation goes back out into space. Back radiation from the atmosphere keeps the Earth’s surface warmer than it naturally would be. John Tyndall (1820-1893) Greenhouse effect- the warming of the surface by back radiation from the atmosphere

Exciting molecular vibrations The main way these molecules absorb infrared radiation is through the vibrations of their molecules. Key Points Chemical bonds that hold molecules together can stretch and flex causing the molecules to vibrate. Molecular vibrations have a characteristic frequency and absorbs its corresponding radiation (infrared). This causes the molecules to vibrate more quickly. A molecule must contain more than 2 atoms or 2 atoms of different elements. Greenhouse gases can vibrate in several ways allowing it to absorb a range of infrared radiation. The excited molecule loses energy re-emitting radiation or transfer energy as they bump into other molecules increasing ‘energy’ in the air equalling warming.

The fate of solar radiation Some radiation is absorbed in the atmosphere Ozone layer acts as a green house gas and absorbs long and short-wave radiation Water vapour contributes to 60% of global warming and absorbs near-infrared radiation

Radiative forcing as an agent to climate change Radiative forcing- anything that disturbs the radiation balance in the upper atmosphere has the ability to force the global climate change. Positive forcing- inputs that increase the temperature Changes in solar constant, albedo or longwave emission to space. One theory is the sun’s output varies through time and humans have little effect on global warming. Negative forcing- inputs that decrease temperature Volcanic eruptions increase sulphur aerosols that reflect incoming radiation causing cooling. They last 1-3yrs and are washed out as acid rain.

Natural Carbon Dioxide in the Atmosphere Terrestrial- Carbon is stored in living things. Plants and trees have the ability to fix carbon. They use carbon for cellular processes and making organic compounds. (Gross Primary Product GPP) Little is transferred back to the atmosphere during respiration.(Net Primary Product NPP)When they die their debris is transferred to the soil where they are broken down by decomposers. The residence time of fixed carbon is dependant on plant longevity and rate of decomposition. Human activity will lower NPP. Oceanic- Carbon is dissolved in water and transported around the globe. Carbon can only be dissolved in limited amounts leading to saturation and then out gassing of carbon back into the atmosphere. Phytoplankton use dissolved carbon for photosynthesis and will store carbon the same as plants. Phytoplankton live for up to 2 weeks. When they die they fall to the sea bed carrying the fixed carbon with them. If the plankton are consumed by zooplankton their carbon is too released back into the atmosphere.

Effects of Carbon Dioxide in the Atmosphere Benefits- CO2 fertilisation effect occurs as carbon dioxide in the atmosphere increases stimulating plant growth. Increased plant growth increases the amount of carbon that is fixed. Scientists have noticed an increase of 20-40% of plant growth from doubling the amount of CO2 in the atmosphere. Recent climate change effects- temperate/boreal forests are more productive with the increased rainfall caused by climate changed initiated by global warming. In the last 20yrs changes in rainfall have increased growing time and productivity in arid and semi arid area, therefore, increasing NPP. Increase nitrogen decomposition effects- enhances plant growth. Combustion of fuels increase nitric acid that rapidly converts into soluble nitrogen that are washed out by rain stimulating plant growth and increasing NPP. Land use management- in northern and mid-latitudes forests where logging occurs there is evidence of rapid re growth. Although this year-year increase increases the amount of organic material to the soil, decomposition in these areas have a slow time lag before decomposition release of carbon catches up There is no evidence of an increased uptake by oceans.

An Urban Myth Glaciers- Glaciers are sensitive to ablation caused by warming. Where Greenland is experiencing large amounts of albation, they are counterbalanced by areas like Antarctica that are experiencing increased precipitation. Large ice bodies- Large ice bodies suffer from a lag time between changes and effects. Response times range between 50-1000yrs depending on their surface area and thickness. Melting could be due to changes in climate during the last glacial/interglacial transition. West Antarctic ice sheet is continuously fed by ice streams.