Ground-breaking new research findings posted on the internet in April have confirmed what many scientists and climate activists have already concluded — that the goals for reducing greenhouse gas emissions embraced by the European Union and Australia's Labor government are gravely inadequate.
The new findings, set out in a paper entitled Target Atmospheric CO2: Where Should Humanity Aim?, are the work of a nine-person international team led by Dr James Hansen, director of NASA's Goddard Institute for Space Studies. Hansen is widely regarded as the world's pre-eminent climate change scientist.
In a famous episode in 2005 and 2006, he faced down the Bush administration when it tried to censor his public statements on climate change issues.
"If humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted", Hansen and his team conclude, atmospheric "CO2 will need to be reduced from its current 385 ppm [parts per million] to at most 350 ppm".
This target, the researchers warn, may need to be reduced still further. If Arctic sea ice is to be restored to its area of 25 years ago — something that may be necessary if dangerous climate "tipping points" are not to be passed — the goal required may be as little as 300-325 ppm.
At present, atmospheric CO2 is increasing by 2-3 ppm each year. "Stabilizing atmospheric CO2 and climate", the scientists state, "requires that net CO2 emissions approach zero, because of the long lifetime of CO2." This insistence on near-zero emissions contrasts with the much more limited approach shown by the Australian government. PM Kevin Rudd and his ministers aim at a 60% cut in Australia's greenhouse gas emissions by 2050, compared to 2000 levels.
Averting catastrophic climate change "appears still feasible", Hansen and his co-authors observe. But unlike the Rudd government, the NASA scientists stress that ending "business as usual" is a matter of extreme urgency: "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 events."
In their paper, Hansen and his team place a key event in the evolution of the recent climate — the onset of glaciation in Antarctica some 34 million years ago — in the context of a long decline in atmospheric CO2 levels that began some 50 million years ago, and continued for tens of millions of years thereafter.
Using evidence of changes in the ratios of oxygen isotopes in deep-sea shells, they conclude that icecap formation in Antarctica began when atmospheric CO2 levels dipped to 425 ppm (plus or minus 75 ppm). When atmospheric CO2 was last at its present level, Antarctica was quite probably ice-free.
Important in themselves as a scientific advance, these findings have dramatic implications for the movement to avert climate disaster. In the first place, the findings take Earth's climate future at elevated CO2 levels out of the realm of hypothesis and place it on the basis of observed, real-world fact.
Through their use of paleoclimatic evidence — data from the remote past — Hansen and his team link specific concentrations of CO2 firmly to particular climatic conditions and events. As a result, one of the favourite arguments of climate sceptics — that the association between greenhouse gas emissions and drastic climate change exists nowhere except in the world of computer modelling — falls by the wayside.
Secondly, the work of Hansen and his team makes it possible to construct much more precise and authoritative climate models. A specific value can now be assigned to the combined impact of vital climate feedback processes which until now, have mostly been regarded as too ill-quantified to be included in computer modelling.
As listed in the paper, these processes include ice sheet disintegration, vegetation migration, and greenhouse gas release from soils, tundra or ocean sediments.
Armed with data for these feedbacks, Hansen and his colleagues have gone on to demonstrate something widely suspected by climate scientists — that the rises in global temperature corresponding to particular increases in atmospheric CO2 are much greater than earlier calculations indicated.
Previous attempts to define a value for "climate sensitivity" — the average warming that would result from a doubling of atmospheric CO2 — have suggested a figure of about 3ºC. Hansen and his team show that for today's Earth, the probable figure is around 6ºC.
The sea at Echuca
The world that results from unrestrained "business as usual", the paper indicates, will be profoundly different from the one on which civilisation evolved. Eventually, there will be no polar icecaps.
Scientists once assumed that the east Antarctic icecap would take thousands of years to melt, but recent work by Hansen and others has shown that icecaps are dynamic systems that can disintegrate far more rapidly, conceivably over a few centuries. In a world without ice, sea levels would be 75-80 metres higher than at present.
Not only would most large cities be submerged, but so too would vast swathes of Earth's fertile lowlands. The new mouth of the River Murray, for example, would be somewhere near Echuca in Victoria. Loss of agricultural land would be accompanied by the extinction of huge numbers of plant and animal species, creating a highly unstable biosphere.
Such a planet, we must conclude, would be ill-fitted to provide enough support more than a fraction of Earth's present human population. And with the sensitivity of the global climate to increased CO2 around twice earlier estimates, the time available for adaptation to the new conditions would be horrifyingly brief.
Science in revolt
To accept all this as inevitable would be a sort of treason to the planet. Accordingly, Hansen and his co-authors take steps which scientists almost never allow themselves. Not only do they voice blunt public warnings, but they speak frankly of policy changes needed if disaster is not to eventuate.
The crucial measure needed, as Hansen and his colleagues see it, is a rapid phasing-out of coal emissions: "Phase-out of coal emissions by 2030 keeps maximum CO2 close to 400 ppm, depending on oil and gas reserves and reserve growth."
Even such a rapid curtailing of coal emissions would allow atmospheric CO2 to remain above 350 ppm for more than two centuries. To avert catastrophe, the "drawdown" needs to be more rapid; therefore, the authors call for extracting carbon already in the atmosphere.
This could be done, they suggest, through reforestation and through sequestering carbon in the soil, especially in the form of biochar. In an appendix, they detail a forest/soil drawdown scenario that, they argue, would bring atmospheric CO2 back below 350 ppm late in this century.
In the final paragraphs of their paper, Hansen and his teams emerge openly as committed citizen-scientists, acting on the momentous political implications of what they have learned. The reasons for Hansen's fraught relations with the Bush administration become obvious: "Present policies, with continued construction of coal-fired power plants … suggest that decision-makers do not appreciate the gravity of the situation …
"The most difficult task, phase-out over the next 20-25 years of coal use …, 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."