The World in 2050_ Four Forces Shaping Civilization's Northern Future - Laurence C. Smith [66]
The second important fact about climate change is that its geography is neither always global nor always warming. To be sure, it is mostly global and mostly warming. But because of the many complex natural mechanisms and feedbacks that inject themselves into the process, the final climatic manifestations of greenhouse forcing vary greatly in spatial pattern. Climate change is not only erratic in time, like the stock market, but also in geography. A globally averaged temperature increase of one degree Celsius does not mean temperatures rise everywhere around the globe by one degree Celsius. That’s just the average. Some places will heat up a great deal, others won’t or might even cool. Summing them all together gets you to the +1°C global average. But that seemingly small number masks some stunning differences around the world.
Consider the map below. It is a projection of our future temperature changes by the middle of this century. Some places are warming hugely but other places hardly at all.276 Why is this? Has some climate model gone haywire?
This map is not an oddball, but just one of a family of nine related maps released by the latest IPCC Assessment.277 They all show irregular geographic patterns and appear together on the following page in a three-by-three grid. From left to right they plot out a three-stage timeline for our century, with average, smoothed-out temperature changes apparent by 2011-2030, by 2046-2065, and by 2080-2099. Like the single map on page 126, each one is actually produced from not one but many climate models—much like a stock index—thus capturing where the models robustly agree rather than the quirks of any particular climate model over another.
Each of the three rows corresponds to a different concentration of greenhouse gas in the atmosphere. That, in turn, rests on all sorts of things, from political leadership to energy technology to gross domestic product. Rather than try to predict which outcome will actually transpire, the IPCC instead calculates outcomes for numerous possible social paths (called SRES scenarios 278), of which three are shown here. The first outcome (top row) may be described as a highly globalized world, with population stabilizing by midcentury and an aggressive transition to a modern information and service economy. This scenario (known to climate scientists as “B1”) is labeled “optimistic” on the figure.279 The second outcome also assumes a stabilizing population and fast adoption of new energy technologies, but with a balance of fossil and nonfossil fuels. That future (called “A1B” by climate scientists) is labeled “moderate.” The third outcome assumes a very divided world with high population growth, slower economic development, and slow adoption of new energy technology. This future (called “A2”) is labeled “pessimistic.”
The third important fact about global climate change is revealed by comparing these three rows of maps. They show that, regardless of technology path, we are already locked in to some degree of warming; but by century’s end, the actions or inactions taken now to curb greenhouse gas emissions really will matter enormously. By 2080-2099 the “pessimistic” world is indeed a cauldron compared to the “optimistic” one, with temperatures rising 3.5°-5.0°C (9°F) across the conterminous United States, Europe, and China, rather than 2.0°-2.5°C (4.5°F). While these numbers may seem small, in fact there is a huge difference between the two outcomes. A 2.5°C rise in average annual temperature is actually huge, equivalent to the difference between a record cool and record warm year in New York City. So even in the “optimistic” world, what is today considered an extreme warm year in New York will become the norm; and the new extremes