The World in 2050_ Four Forces Shaping Civilization's Northern Future - Laurence C. Smith [116]
At their core, climate modelers seek to understand how the atmosphere functions, and how it responds to changing drivers. By studying when and where the models break down, we improve scientific understanding of how the real world works, and our models become more accurate. After more than fifty years of trial and error, they have now evolved far beyond their primitive ancestors of the 1960s. We’ve learned a great deal about how Earth’s climate system actually operates. In today’s generation of models, complicated things like El Niño and the Hadley Circulation emerge organically without programmers having to “add” them at all. That is very encouraging, because it tells us the models’ assumptions and physics486 are realistic and working correctly.
The big push now is to hone down climate model spatial resolutions (i.e., the “pixel size” of their simulations) from hundreds of kilometers, useful for broad-scale projections like the ones presented in this book, to kilometers, which is what local planners need. But even at the coarser spatial scale of today’s generation of models, many important conclusions about our future are now well vetted and uncontroversial. All of the megatrends discussed so far—rising global average temperature, the amplified warming in the Arctic, rising winter precipitation around the northern high latitudes—fall within this uncontroversial category.
More troublesome are the short-sellers and inside traders of natural climatic variability. Volcanoes, wildfires, and sunspot cycles are just a few of many phenomena imprinting their own natural variations over the underlying greenhouse gas signal. But now these volatile (and fairly common) phenomena, too, are being added to climate models and tested.
Where climate models suffer most is in capturing rare events lying totally outside of our modern experience. Most weather stations are less than a century old; the satellite data era began only in the 1960s and ’70s. These records are far too short to illuminate the full range of our Earth’s twitchy behavior. Shifting oceans and ice sheets are key drivers of climate yet contain toggles and circuits with longer patience than our short instrumental records. They add boosts, buffers, and dips to the overall greenhouse effect, so we must understand them as well.
Unfortunately, a naturally twitchy climate makes the steady, predictable push from anthropogenic greenhouse gases more dangerous, not less. From the geological past we know the Earth’s climate has not always been so quiet as it is now. Therefore, through greenhouse loading we are applying a persistent pressure to a system prone to sudden jumps in ways we don’t fully understand. Imagine a wildcat quietly sleeping on your porch—it looks peaceful but is by nature an ill-tempered, unpredictable beast that might spring into a flurry of teeth and claws in an instant. Greenhouse gases are your knuckles pressing inexorably into its soft slumbering belly; the global ecosystem is your exposed hand and arm.
Rare or threshold behaviors—like a permanent reorganization of rainfall patterns, accelerated sea-level rise, or a giant burp of greenhouse gas from the ground—all pose legitimate threats to the world. We know they are plausible but, unlike greenhouse gas forcing, don’t know yet how probable. But their behaviors, too, must be added to climate models somehow. Just because something seems unlikely doesn’t mean it won’t happen, or that its impacts are not potentially enormous if it does. These are the climate genies, and we are just beginning to discern the outline of their various sleeping forms. To find them at all, we must turn to the prehistoric past.
The Flickering