"Doc, just how long do I have left? A year?"
If the patient has a gradually failing heart, the physician's answer might be "One to two years if it’s just gradual deterioration. But you could also have a heart attack at any time. Don’t count on even six months."
Climate scientists similarly warn of an approaching catastrophe by climate creep—though a climate leap may kill off civilization even sooner as the human population crashes.
Were only business-as-usual emissions producing climate creep, the year of the 2°C fever would be 2049. Calculations which take account of the CO2 and methane released as the Arctic warms and the tundra thaws show we have even less time.
Serious emission reductions delay the 2°C fever by a mere nineteen years. Appallingly, that’s all that anyone talks about doing in response to our changing climate—despite the fact that it neither stops making things worse nor rids us of the accumulated past emissions.
There are other ways in which the current climate projections understate the problem we face. First, forecasts for climate creep operate on the assumption that climate change is gradual because CO2 accumulation is gradual. But that’s no longer a fair assumption, as we can see from the forest fires caused by the big 1997 El Niño.
Had its droughts lasted a second year, we could have lost two major rain forests (the Amazon and Southeast Asia) to fire and rot. That would have liberated enough CO2 to cause a fifty percent jump in the excess CO2 in a few years, setting off heat waves and drought worldwide. That’s a lot of climate refugees on the move.
Burn locally, crash globally.
In 2005 and again in 2007, Amazonia was even more flammable than it was in 1997 when global deforestation emissions temporarily tripled.
And once we lose this particular rain forest, it doesn’t grow back. Plant succession will stay stuck at grass for a long time, recovering very little of the CO2 that burning and rotting released into the air. We appear to be on the verge of a mass extinction of rain forest species.
Even when the CO2 accumulation remains gradual, the climate takes leaps for other reasons. They have been happening often enough since 1976 that we already have an alarming track record.
The leap mechanism can be as simple as a sudden circulation shift, the air's version of when a meandering river carves a shortcut during a spring flood—and leaves a U-shaped loop of the old river stranded as a new lake. The winds have similarly begun to rearrange themselves because global warming has not been uniform.
The land has been heating up twice as fast as the ocean surface, creating stronger winds that can punch through old barriers. When they discover an easier path, they deliver their moisture elsewhere.
We suppose that the resulting deluge and drought is just "weather" when it happens. It’s only when it repeats next year that we begin suspecting a climate leap. Global warming may be the root cause but a thermometer reading won’t necessarily help you understand such knock-on effects.
The excess CO2 has gradually doubled since 1976 and we’ve seen some climate leaps that are likely due to the overheating produced by CO2 creep. Most abrupt climate shifts are regional but for brevity I will survey only the leaps since 1976 that became global in extent or implications.
The percentage of land in the two most extreme stages of drought suddenly doubled in 1982. It wasn't just a pulse. It was a big step up, climate change rather than weather.
Global drought stayed that way for fifteen years, and then leapt to nearly triple in 1997, stepping back to double in 2005. Millions died.
In addition to those three steps, a persistent rearrangement of winds developed over the winter of 1976–1977 at the termination of a long, large La Niña. Ever since then, the warmer El Niños have been large or long and the cooler La Niñas have been small and brief. This is exactly the opposite of the pattern from 1950 to 1976.
Global land temperature, which had been without a noticeable trend from 1950 to 1976, started ramping up at the rate of about 2°C per century.
Besides the three near misses for rain forests, there were two occasions when an important safety margin was lost for a decade. Northern Europe, at the same distance from the equator as Alaska and Siberia, is warmer and wetter, thanks to a unique mechanism for attracting warm waters into high latitudes. After such waters lose their heat to the winds from Canada, they sink and flow southward in the ocean depths. That makes room for more warm waters to flow into the far north. But the flushing mechanism, a series of ten-mile-wide whirlpools, is vulnerable.
The largest flushing site for the ex-Gulf-Stream waters, in the Greenland Sea north of Iceland, shut down in 1978. It recovered over the next decade. Then the second largest, in the Labrador Sea between southern Greenland and Canada, shut down in 1997, suddenly recovering over the winter of 2007–2008. It also shut down back in the 1970s.
Were both to shut down, stopping much of the heat flow from the tropics into the northernmost Atlantic Ocean, we would expect massive climate change from the wind rearrangements that would follow the sea surface cooling. Europe might not get the quick freeze that such circulation shifts caused several dozen times in the last ice age, but the rainfall shifts would still threaten its agriculture and thus the viability of its big cities.
Thus it appears that world climate has already become highly unstable. In each decade since 1976, we have averaged several leaps and several near misses. That track record—not computer forecasts—is why we need a very fast intervention to head off future climate instabilities.
Climate leaps are like heart attacks, ranging unpredictably from minor to catastrophic—say, a human population crash from war, famine, pestilence, and genocide. It’s a very different time scale than for global warming, both sudden and sooner.
That means that this is no longer just about our grandchildren’s world. Or that of our children. It's about our future—even that of today's senior citizens.
We have been fiddling while the Earth burns. Though near-zero emissions are still essential for the long run, the most critical threat has become civilization collapsing in the meantime.
This is DRAFT for a book chapter, comments most appreciated.