Climate targets not nearly good enough to avoid catastrophic climate change
April 7th, 2008 by Jim JustNASA scientist James Hansen is warning that we must urgently rethink targets for cutting carbon dioxide in the atmosphere because we have grossly underestimated the scale of the problem.
The biggest part of the solution is pretty simple and straightforward: turn off the coal plants.
Hansen says atmospheric CO2 needs to be slashed from the current 385 ppm to at most 350 ppm if “humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted.”
The paper Hansen co-authored with eight other climate scientists is titled Target Atmospheric CO2: Where Should Humanity Aim? Instead of using theoretical models to estimate the sensitivity of the climate, his team turned to evidence from the Earth’s history, which they say gives a much more accurate picture.
The Intergovernmental Panel on Climate Change (IPCC) warned that global warming of more than 2-3°C – implying CO2 levels of about 550 ppm – may be dangerous. The European Union adopted 2°C above pre-industrial global temperature as a goal. Hansen and others had previously argued for a limit of 1°C global warming (relative to 2000, 1.7°C relative to pre-industrial time), aiming to avoid practically irreversible ice sheet and species loss. This 1°C limit implies maximum CO2 ~ 450 ppm. Gavin at RealClimate has reviewed the paper and concludes:
“However, even with the (substantial) uncertainties in the calculations and underlying assumptions, the conclusion that the Earth System sensitivity is greater than the Charney sensitivity is probably robust. And that is a concern for any policy based on a stabilization scenario significantly above where we are now.”
Hansen says a 350 ppm CO2 target may be achievable by phasing out coal use except where CO2 is captured and adopting agricultural and forestry practices that sequester carbon.
He warns that if the present overshoot of this target CO2 is not brief, there is a possibility of seeding irreversible catastrophic effects.
Joseph Romm at Climate Progress is optimistic we can solve the global warming problem using existing technologies. Meeting the challenge requires:
- Major political change — to deploy the technologies fast enough.
- Major price change — to add a cost to emitting greenhouse gases that approximates the terrible damage done by them. We need to make coal too expensive to burn.
- Major behavior change — People need to get that unrestricted greenhouse gas emissions are by far the gravest threat to the health and well-being of future generations that we face. Climate change may have to get much more visibly worse before that happens.