Page - 167 - in Water, Energy, and Environment - A Primer

atmosphere allow sunlight to pass throughwhile restricting the outward passage of infrared re-radiation from the Earth’s land andwater surfaces. This impacts on the energy balance between the Earth and the Sun, and determines the Earth’s average temperature. In turn, the energy exchange among the Earth’s atmosphere and its oceans and landmasses determines climate, whichWikipedia defines as ‘the statistics of weather over long periods of time.’The difference betweenweather and climate is that weather describes the conditions of the atmosphere over a short time period. Climate change refers to the shift in global weather patterns associated with an increase in global average temperatures. While it is well documented that the climate system can exhibit randomchanges in global temperatures for short periods of time (up to decades), long-term temperature trends derive fromso-called ‘external forcings’ such as changes in theEarth’s orbit around the Sun, changes in the amount of radiation emitted by the Sun, and volcanic eruptions. Changes in the Earth’s atmosphere due to increasing concentrations of greenhouse gases such as carbon dioxide andmethane also fall into this latter category. The link between CO2 and the Earth’s temperature was first suggested by Joseph Fourier in 1824. It was experimentally observed in 1860 by John Tyndall, and was first investigated quantitatively in 1896 by the Swedish scientist and Nobel Laureate Svante Arrhenius, who is often referred to as ‘the father of climate change science’. His interest in this subject arose from the scientific debate aboutwhat could have triggered Earth’s many ice ages and whether large swings in levels of atmospheric CO2were responsible. The science of this concept was developed further by Guy Stewart Callendar in the period 1930–1960. JimHansen, thenNASA’s chief climate scientist, drewpublic attention to global warmingwith his 1988 testimony to theUS Congress about the dangers of human-caused climate change. Policy considerations 167