New Hansen Paper Calls for Climate Change Action

The paper published by PLOS ONE calls for radical measures to curb carbon emissions to hold future temperature rises to 1oC. “We must make extraordinary efforts to achieve a course approximating the 1°C scenario or we may leave a deteriorating situation that is practically out of control of future generations,” it states.

The paper goes into some detail on the Earth’s energy imbalance quoting a net planetary energy imbalance for the six years 2005-2010 of +0.58 ±0.15 W/m2. With the majority, 0.41W/m2 coming from the upper 2000m of the world’s oceans and smaller contributions from heat gain by the deeper ocean (+0.10 W/m2), energy used in net melting of ice (+0.05 W/m2), and energy taken up by warming continents (+0.02 W/m2).

The paper calculates the reduction in atmospheric CO2 levels required to offset this calculated positive energy balance using currently assumed carbon sensitivities. A circa 10 per cent reduction to 360ppm is needed to offset a 0.5W/m2 imbalance and a reduction to 345ppm would be needed to counteract a 0.75W/m2 imbalance, the authors state.

A 6% per year decrease of fossil fuel emissions beginning in 2013, combined with a massive reforestation campaign designed to lock away 100 Gt of carbon would achieve a CO2 decline to 350 ppm near the end of this century, the authors state.

“Our analysis shows that a set of actions exists with a good chance of averting “dangerous” climate change, if the actions begin now. However, we also show that time is running out. Unless a human “tipping point” is reached soon, with implementation of effective policy actions, large irreversible climate changes will become unavoidable. Our parent’s generation did not know that their energy use would harm future generations and other life on the planet. If we do not change our course, we can only pretend that we did not know,”they conclude.

We assess climate impacts of global warming using ongoing observations and paleoclimate data. We use Earth’s measured energy imbalance, paleoclimate data, and simple representations of the global carbon cycle and temperature to define emission reductions needed to stabilize climate and avoid potentially disastrous impacts on today’s young people, future generations, and nature. A cumulative industrial-era limit of 500 GtC fossil fuel emissions and 100 GtC storage in the biosphere and soil would keep climate close to the Holocene range to which humanity and other species are adapted.

Cumulative emissions of,1000 GtC, sometimes associated with 2oC global warming, would spur ‘‘slow’’ feedbacks and eventual warming of 3–4oC with disastrous consequences. Rapid emissions reduction is required to restore Earth’s energy balance and avoid ocean heat uptake that would practically guarantee irreversible effects. Continuation of high fossil fuel emissions, given current knowledge of the consequences, would be an act of extraordinary witting intergenerational injustice. Responsible policymaking requires a rising price on carbon emissions that would preclude emissions from most remaining coal and unconventional fossil fuels and phase down emissions from conventional fossil fuels.

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