NASA climate scientist James Hansen has just co-authored a draft paper (“Target CO2: Where Should Humanity Aim?”), published on his website, on the targets we have to meet in order to prevent catastrophic, runaway climate change. Below is the summary.
Summary.
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 human history. The eventual response to doubling pre-industrial atmospheric CO2 likely would be a nearly ice-free planet.
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. 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.
Johann Hari offers some sound advice on what we need to be doing in response:
“The only way we will get to the situation where we are all required by law to burn fewer greenhouse gases is if enough people pressure the government, demanding it. Green consumer choices often drain away people’s political energies to do this. You have a limited amount of time to spend on any political cause. If you have an hour a week to dedicate to acting on global warming, and you spend it scouring the supermarket shelves for the product shipped the shortest distance, that time and energy is gone; you feel you’ve done what you can. Part of you might also assume: I’ve made these choices; other people will too; in time, we’ll all be persuaded. But we don’t have time. ...
“Every minute you would have spent shopping around for a greener choice, you should spend volunteering for Greenpeace, or Friends of the Earth, or Plane Stupid, or the Campaign Against Climate Change. Every hundred-pound premium you would spend to buy a greener product, donate it to them instead. Why? Because by becoming part of this collective action – rather than by clinging to dispersed personal choices – you will help to change the law, so everyone will have to be greener, not just nice people like you.”
