Wednesday, April 22, 2009

Copy of summary from Hansen et al, 2008, in PNAS

The full text, with the calculations to support the conclusion that coal phase out and replacement with renewables is the priority, is at

Humanity today, collectively, must face the uncomfortable fact that industrial civilization itself has become the principal driver of global climate. If we stay our present course, using fossil fuels to feed a growing appetite for energy-intensive life styles, we will soon leave the climate of the Holocene, the world of prior human history. The eventual response to doubling pre-industrial atmospheric CO2 likely would be a nearly ice-free planet, preceded by a period of chaotic change with continually changing shorelines. Humanity’s task of moderating human-caused global climate change is urgent. Ocean and ice sheet inertias provide a buffer delaying full response by centuries, but there is a danger that human-made forcings could drive the climate system beyond tipping points such that change proceeds out of our control. The time available to reduce the human-made forcing is uncertain, because models of the global system and critical components such as ice sheets are inadequate.

However, climate response time is surely less than the atmospheric lifetime of the human-caused perturbation of CO2. Thus remaining fossil fuel reserves should not be exploited without a plan for retrieval and disposal of resulting atmospheric CO2. Paleoclimate evidence and ongoing global changes imply that today’s CO2, about 385 ppm, is already too high to maintain the climate to which humanity, wildlife, and the rest of the biosphere are adapted. Realization that we must reduce the current CO2 amount has a bright side: effects that had begun to seem inevitable, including impacts of ocean acidification, loss of fresh water supplies, and shifting of climatic zones, may be averted by the necessity of finding an energy course beyond fossil fuels sooner than would otherwise have occurred.

We suggest an initial objective of reducing atmospheric CO2 to 350 ppm, with the target to be adjusted as scientific understanding and empirical evidence of climate effects accumulate.

Although a case already could be made that the eventual target probably needs to be lower, the 350 ppm target is sufficient to qualitatively change the discussion and drive fundamental changes in energy policy. Limited opportunities for reduction of non-CO2 human-caused forcings are important to pursue but do not alter the initial 350 ppm CO2 target. This target must be pursued on a timescale of decades, as paleoclimate and ongoing changes, and the ocean response time, suggest that it would be foolhardy to allow CO2 to stay in the dangerous zone for centuries. A practical global strategy almost surely requires a rising global price on CO2 emissions and phase-out of coal use except for cases where the CO2 is captured and sequestered. The carbon price should eliminate use of unconventional fossil fuels, unless, as is unlikely, the CO2 can be captured. A reward system for improved agricultural and forestry practices that sequester carbon could remove the current CO2 overshoot. With simultaneous policies to reduce non-CO2 greenhouse gases, it appears still feasible to avert catastrophic climate change.

Present policies, with continued construction of coal-fired power plants without CO2 capture, suggest that decision-makers do not appreciate the gravity of the situation. We must begin to move now toward the era beyond fossil fuels. Continued growth of greenhouse gas emissions, for just another decade, practically eliminates the possibility of near-term return of atmospheric composition beneath the tipping level for catastrophic effects.

The most difficult task, phase-out over the next 20-25 years of coal use that does not capture CO2, is Herculean, yet feasible when compared with the efforts that went into World War II. The stakes, for all life on the planet, surpass those of any previous crisis. The greatest danger is continued ignorance and denial, which could make tragic consequences unavoidable.


Steve said...

"The largest uncertainty in the target arises from possible changes of non-CO2 forcings." In other words, the predictions are valid as long as we don't consider that other climate drivers, like solar radiation, albedo from cloud cover, levels of other trace gases which occur in much greater concentrations, volcanic activity, etc, etc, may have a greater influence than CO2 levels. Why the fear mongering? Don't you understand that there is no way the world is going to stop burning fossil fuels because renewables do not have the the ability to replace them to a significant degree.
Covering every available mountain in Maine and Vermont with wind turbines will only provide 6% of the electricity of the ISO NE grid daily demand. That is what RGGI has forced us to allow. The destruction of fragile mountain habitat, the ripping of the fabric that holds communities together as those who love the mountains are strong armed by the dollar blinded majority who merely want the "tangible benefits" like TIF payments. You are not saving the planet, but your are destroying New England's treasured wilderness resource - its mountains. Have your class do the math on wind power. I'd love to see the results. Let them study wind turbine syndrome, as it affects wildlife as well as humans. This rush to industrializing the mountains is a HUGE mistake.

Mick said...

I'm not mongering fear.

I'm trying to get people to read, learn, and understand the science.

The most worrisome non-CO2 forcing Hansen refers to is the methane feedback, particularly arctic methane release, which is one of the possible if not probable causes of "large scale discontinuity."

So one attempt to misread a science paper whose conclusion are unpalatable to you, and you resort to rhetoric before even fully understanding the main point? Is that really the best you can do?

Climate change doesn't require that wind turbines be placed everywhere, on all the mountains of Maine, or anywhere in particular. It requires that we identify our energy options, evaluate them, and choose a portfolio going forward.

You should be able to evaluate the climate material without being terrified that it wins the argument for wind (and thus you lose the argument). It doesn't at all. Everyone with intelligence knows that.

Climate change has to be evaluated on its own merits. Then you choose a response.

So now you have identified what you think is a flaw in the reasoning, explore it.

Go read up on arctic methane release, particularly the consequences of that release for climate change acceleration. See if you still think the "non-CO2 forcing" reasoning is flawed after you've done so.