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The “pessimistic” numbers are even more alarming. They approach the magnitude of average temperature contrast between the world of today and the world of twenty thousand years ago during the last ice age, when global temperatures averaged about 5°C (9°F) cooler. Many areas of North America and Europe were under ice, sea levels were more than 100 meters (330 feet) lower, and Japan was actually connected to the Asia mainland.280

All of these maps are conservative in that they awaken no hidden “climate genies” that give climate scientists nightmares.281 Instead, they chart out the plain vanilla, predictable intensification of the greenhouse effect, covering a realistic range of options lying well within control of human choices.

The fourth important fact to take from these nine maps is that the irregular geography of climate change presented in the first single map is not at all random. Important spatial patterns remain broadly preserved in all model simulations, for all carbon emissions scenarios, and across all time frames. Temperature increases are higher over land than over the oceans. A bull’s-eye over the northern Atlantic Ocean stubbornly refuses to warm up. And without fail, regardless of which emissions path is followed, or what time slice is examined, or what climate models are run, all of the model projections—and measured observations too—consistently tell us something big. Again and again, they tell us that global climate change is hugely amplified in the northern high latitudes.282

Even our “optimistic” scenario projects that the northern high latitudes will warm 1.5-2.5°C by midcentury and 3.5-6°C by century’s end, more than double the global average. Our “pessimistic” scenario suggests rises of +8°C (14.4°F) or more. Global climate change will not raise temperatures uniformly around the world. Instead, the fastest and most furious increases are under way in the North.

There is another robust trend expected for the northern high latitudes. For much of the world it is very difficult to project future precipitation patterns with confidence. Cloud physics and rainfall are more complicated and tougher to model than greenhouse physics, especially at the coarse spatial resolution of today’s climate models. To the frustration of policy makers, model projections of future rainfall often lack statistical confidence, and even disagree as to whether it will increase or decrease. But not in the North. If there is one thing that the climate models all agree on,283 it’s that precipitation (snow and rain) will increase there, especially in winter. It must increase, in obedience to physics284 and rising evaporation from open lakes and seas as they become unfrozen for longer times during the year.

The plainest manifestation of this will be snowier winters and higher river flows. Across southern Europe, western North America, the Middle East, and southern Africa, river flows are projected to fall 10%-30% by 2050. However, they will increase by a similar amount across northern Canada, Alaska, Scandinavia, and Russia.285 This has already happened in Russia. Through statistical analysis of old Soviet hydrologic records, one of my own projects helped to confirm rising river flows there, including sharp increases in south-central Russia beginning around 1985.286

Recall the bleak future of stressed human water supply all around the planet’s dry latitudes from Chapter 4? That future is not shared by the North. It is water-rich now and, except for Canada’s south-central prairies and the Russian steppes, will become even more water-rich in the future.

Uncapping an Ocean

To most people, there is nothing visceral about computer model projections of average climate statistics decades from now. But in September 2007 we got a taste of what the real world inside those maps might look like. For the first time in human memory, nearly 40% of the floating lid of sea ice that papers over the Arctic Ocean disappeared in a matter of months. The famed “Northwest Passage”—an ice-encased