A study out from the United Nations Environment Program (UNEP) has tried to calculate the cost for African states to adapt to a rise in the world's average temperature by the turn of the next century. "Warming limited to below 2°C still implies major adaptation costs for Africa. A 4°C of warming by 2100 will hit the continent very hard." What does "hit the continent very hard" mean, specifically?

The water picture is particularly chaotic. According to the report, the average sea rise along the continent's coast would be one meter, which is 10 percent higher than the expected increase globally. Delta regions in Egypt, Cote d'Ivoire, Mozambique, Nigeria, and Tunisia are among the countries expected to take the brunt of the ocean rise. In those places, whole cities, including capitols and major ports, would face Hurricane Sandy-esque conditions, with human and economic impacts to match.

Whole cities, including capitols and major ports, would face Hurricane Sandy-esque conditions, with human and economic impacts to match.

At the same time the sea encroaches, rainfall will crash and aquifers become unreliable. If temperatures rise four degrees by 2100, rain will fall by 30 percent in the continent's south and 20 percent in North Africa, the U.N. office estimates. Wells for drinking water and crop use become dramatically insufficient at that rate. "Parts of north, west and southern Africa may see decreases in groundwater recharge rates of 50–70 percent as well as reductions in annual river discharge."

Urban effects lean toward disease and migratory stress. The report notes that cities tend to be hotter than rural areas when faced with similar weather, a condition called the "urban heat island effect." (If you've ever gone to New Jersey from Manhattan or to Virginia from Washington, D.C., in August, you've experienced this.) That would become more pronounced as average temperatures increased, particularly in summer.

As urban temperatures rose, water problems in rural areas would provoke migration to these same warming cities, where newcomers would be likely to begin in substandard housing. "Climatic risk factors in rural areas may exacerbate an already significant urbanisation trend in Africa," said the report, "potentially placing more people in vulnerable conditions as settlements become more crowded and resources are stretched." Urban concerns on the continent are similar to those elsewhere: ventilation, insect-borne diseases like malaria and dengue fever, and greater discomfort from overcrowding, producing a general "heat stress."

The cost to "adapt" to all this—building infrastructure to mitigate it, developing insurance to pay for it, and business and agricultural practices to respond to it—is estimated to cost $35 billion per year if the world's temperature rises two degrees on average. That climbs as high as $70 billion per year, or three-quarters of a trillion per decade, if the world's average temperature rises four degrees.

If it goes beyond that, they don't calculate it—probably because it's beyond money's ability to solve.