The Ghost Of Climate Yet To Come

If your car is headed for a collision with a concrete wall, and you know you won’t be able to stop the car before you hit the wall, you don’t just continue as usual. You hit the break as hard as possible to minimize the damage.

http://thinkprogress.org/climate/2012/12/25/1376141/the-ghost-of-climate-yet-to-come-2/#comment-628361

By Joe Romm on Dec 25, 2012
Irreversible does not mean unstoppable

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 Experts Warn ‘Near Ice-Free Arctic In Summer’ In A Decade If Volume Trends Continue).

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“).
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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 last year, “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.”
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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“:
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http://www.realclimate.org/index.php/archives/2009/02/irreversible-does-not-mean-unstoppable/

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Perhaps the despair we heard in our interviewers’ questions arose from the observation in the paper that the temperature will continue to rise, even if CO2 emissions are stopped today. 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.