The Ghost Of Climate Yet To Come

Unlike Scrooge, we don’t get a spirit to show us what the future holds if we don’t change our ways.

In the past two years, though, we have gotten the tiniest glimpse of climate gone wild (see “Masters: “The stunning extremes we witnessed [in 2010] gives me concern that our climate is showing the early signs of instability” and A New Record: 14 U.S. Billion-Dollar Weather Disasters in 2011). And we did get dozens of scientific papers warning us of what is to come (see “An Illustrated Guide to the Science of Global Warming Impacts: How We Know Inaction Is the Gravest Threat Humanity Faces).

M.I.T. laid out the choice in its 2009 analysis:

Humanity’s Choice (via M.I.T.): Inaction (“No Policy”) eliminates most of the uncertainty about whether or not future warming will be catastrophic. Aggressive emissions reductions dramatically improves humanity’s chances.

Yes, it is increasingly unlikely that we will adopt the aggressive but low-net-cost policies needed to stabilize at 450 ppm atmospheric concentrations of carbon dioxide, and then quickly come back to 350 — thanks in large part to the deniers, along with their political pals and media enablers. But when reporters ask me if it’s “too late,” — or, as one did recently, “have we crossed a tipping point?” — I have to explain that the question doesn’t have a purely scientific answer.

It does seem clear that the most dangerous carbon-cycle feedback — the defrosting permafrost — hasn’t kicked in yet but is likely to with two decades (see “Carbon Time Bomb in the Arctic“).

If humanity gets truly serious about emissions reduction — and by serious I mean “World War II serious” in both scale and urgency — we could go to near-zero global emissions in, say, 2 decades and then quickly go carbon negative. It wouldn’t be easy, far from it (see “The full global warming solution: How the world can stabilize at 350 to 450 ppm“). But even in the 2020s it would be vastly cheaper and preferable to the alternative (see Scientists find “net present value of climate change impacts” of $1240 TRILLION on current emissions path, making mitigation to under 450 ppm a must).

Delay is very risky and expensive. In releasing its 2009 Energy Outloook, the International Energy Agency explained, “we need to act urgently and now. Every year of delay adds an extra USD 500 billion to the investment needed between 2010 and 2030 in the energy sector”. In releasing its 2011 Energy Outloook, the IEA said “On planned policies, rising fossil energy use will lead to irreversible and potentially catastrophic climate change” and “we are on an even more dangerous track to an increase of 6°C [11°F].” They concluded:

Delaying action is a false economy: for every $1 of investment in cleaner technology that is avoided in the power sector before 2020, an additional $4.30 would need to be spent after 2020 to compensate for the increased emissions.”

This is all by way of introduction to a holiday rerun repost. Three years ago I wrote about a NOAA led paper, which found:

…the climate change that is taking place because of increases in carbon dioxide concentration is largely irreversible for 1,000 years after emissions stop…. Among illustrative irreversible impacts that should be expected if atmospheric carbon dioxide concentrations increase from current levels near 385 parts per million by volume (ppmv) to a peak of 450-600 ppmv over the coming century are irreversible dry-season rainfall reductions in several regions comparable to those of the “dust bowl” era and inexorable sea level rise.

And we know that large parts of the currently habited and arable land are at risk of turning into Dust Bowls, gravely threatening global food security.

We most certainly do not want to significantly exceed 450 ppm for any length of time, as Dust-Bowlification isn’t the only impact that is irreversible:

•New study of Greenland under “more realistic forcings” concludes “collapse of the ice-sheet was found to occur between 400 and 560 ppm” of CO2
•Science: CO2 levels haven’t been this high for 15 million years, when it was 5° to 10°F warmer and seas were 75 to 120 feet higher “” “We have shown that this dramatic rise in sea level is associated with an increase in CO2 levels of about 100 ppm.”
•Nature Geoscience study: Oceans are acidifying 10 times faster today than 55 million years ago when a mass extinction of marine species occurred
•2009 Nature Geoscience study concludes ocean dead zones “devoid of fish and seafood” are poised to expand and “remain for thousands of years”
That said, RealClimate made a good point with the title of its 2009 post, “Irreversible Does Not Mean Unstoppable“:

snip
The whole world has become Dickensian (see “A Tale of Two Disasters“), which just happens to remind me of another Dickens story relevant to the theme that irreversible does not mean unstoppable:

“Before I draw nearer to that stone to which you point,” said Scrooge, “answer me one question. Are these the shadows of the things that Will be, or are they shadows of things that May be, only?”

Still the Ghost pointed downward to the grave by which it stood.

“Men’s courses will foreshadow certain ends, to which, if persevered in, they must lead,” said Scrooge. “But if the courses be departed from, the ends will change. Say it is thus with what you show me.”

The Spirit was immovable as ever.

Scrooge crept towards it, trembling as he went; and following the finger, read upon the stone of the neglected grave his own name, EBENEZER SCROOGE.

“Am I that man who lay upon the bed?” he cried, upon his knees.

The finger pointed from the grave to him, and back again.

“No, Spirit! Oh no, no!”

The finger still was there.

“Spirit!” he cried, tight clutching at its robe, “hear me. I am not the man I was. I will not be the man I must have been but for this intercourse. Why show me this, if I am past all hope?”

For the first time the hand appeared to shake.

“Good Spirit,” he pursued, as down upon the ground he fell before it: “Your nature intercedes for me, and pities me. Assure me that I yet may change these shadows you have shown me, by an altered life.”

The kind hand trembled.

Or, as RealClimate put it less poetically:

But you have to remember that the climate changes so far, both observed and committed to, are minor compared with the business-as-usual forecast for the end of the century. It’s further emissions we need to worry about. Climate change is like a ratchet, which we wind up by releasing CO2. Once we turn the crank, there’s no easy turning back to the natural climate. But we can still decide to stop turning the crank, and the sooner the better.

More at the link