Paper No. 8
Presentation Time: 4:00 PM


TANS, Pieter, National Oceanic and Atmospheric Administration, Earth Systems Research Laboratory, 325 Broadway, Boulder, CO 80304,

Future emissions scenarios in the international assessments of climate change are driven almost entirely by demographic and socio-economic factors, with potential resource limitations assumed to be overcome by technological innovation. This session calls those scenarios into question. We consider it more realistic to expect future emissions to remain near the low end of the range considered by the International Panel on Climate Change, with the lower emissions forced on us rather than by a deliberate policy choice. A low emissions scenario will not prevent human-caused climate change, but will prevent worse outcomes that we may be able to predict better after we have experienced the 21st century. The reasons are fundamental: 1. The longevity of the CO2 enhancement in the atmosphere and oceans is thousands of years. 2. CO2 removal strategies require much energy. 3. The impact of enhanced greenhouse gases on the Earth energy balance is known accurately. We calculate the partitioning of the CO2 enhancement between atmosphere and oceans, and thus climate forcing by CO2, until the year 2500. Poorly quantified long-term climate feedbacks, such as the melting of glaciers and ice caps, and degradation of permafrost in the Arctic, will come into play, but are not estimated. The integral of climate forcing by greenhouse gases alone until 2500 under a low emissions scenario is still so large that climate change may become an impediment to human development in addition to higher energy costs.