FIGURE 2.1 Global air and ocean temperatures and sea level have risen over the course of the 20th century, while average annual snow cover in the Northern Hemisphere has declined. SOURCE: IPCC (2007; Figure 1-1).

anthropogenic greenhouse gas emissions show an increase in temperatures that closely tracks observations.

SCENARIOS OF FUTURE CLIMATE CHANGE

On the basis of models that assume different technology, economic, and policy trajectories, the IPCC has developed several scenarios of future emis-



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