The Enhanced Greenhouse Effect without Analogues in Climate History

Going beyond chapter 2, we introduce here the uniqueness of the present state of the Earth system from the point of view of its physical boundaries. From greenhouse gas concentrations derived from air bubbles in ice cores drilled into the ice sheets of Antarctica, but also Greenland, down to the bedrock we know that the second most important greenhouse gas, CO2, was varying between about 190 ppmv during glaciation maxima and slightly less than 300 ppmv during the interglacials, often called warm periods. Hence, the present CO2 concentration, already above 380 ppmv, never occurred since at least 750,000 years. We are therefore in a non-analogue state for homo sapiens. Can we estimate the future climate then although climate history gives no analogues? In principle yes, but only with Earth system models validated with climate history, thus comparing them with so-called proxy-data. Only very recently did such testing become possible, but mainly for Earth models of intermediate complexity (EMICs), because the computer time requests of higher spatial resolution models are still too high. As EMICs and first fully coupled higher resolution models with 3-D ice sheet representation have shown that bifurcations are close for business as usual scenarios of human behaviour in the 21st century, sustainability is threatened by further climate change or in other words a stringent global climate policy is needed to approach sustainability in the 21st century. As figure 6.1, taken from Vizcaino (2006), demonstrates, sea level rise up to several meters would follow the continuation of the present development path, where energy supply is based on fossil fuels. Many millions, living in marshlands at unprotected coastlines, would then become refugees. Strange as it may seem, a stop of the North Atlantic Drift (vulgo Gulf Stream) would, it occurs for scenario A2 and for some realisations already for scenario A1B, reduce sea level rise, because more ice on Greenland would continue to exist. It is clear from figure 6.1 that our climate policy in the next decades decides about sea level rise in centuries and millennia to come and thus about the further existence of coastal cities without very costly major local protection measures.

2000 2500 3000 3500 " 4000 time (year)

Figure 6.1 Melting of the Greenland ice sheet, given in meters of sea level equivalent for several realisations of scenarios A2 and A1B during the coming millennia. Please note that emissions are decaying after the year 2100 or 2200 (for A2) exponentially but global warming and sea level rise continue over centuries and millennia (Vizcaino, 2006)

2000 2500 3000 3500 " 4000 time (year)

Figure 6.1 Melting of the Greenland ice sheet, given in meters of sea level equivalent for several realisations of scenarios A2 and A1B during the coming millennia. Please note that emissions are decaying after the year 2100 or 2200 (for A2) exponentially but global warming and sea level rise continue over centuries and millennia (Vizcaino, 2006)

Guide to Alternative Fuels

Guide to Alternative Fuels

Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.

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