Saturday, February 16, 2008

Shrinking timeframe to prevent dangerous climate change?

Science Alert (Australia and New Zealand): A growing number of scientists are echoing the concern raised in the latest Intergovernmental Panel on Climate Change (IPCC)’s Fourth Assessment Synthesis Report that climate change is happening faster than at rates predicted by earlier IPCC reports.

A recent paper published in the US Proceedings of the National Academy of Science (PNAS) suggests that the Earth’s land and oceans are losing their capacity to absorb the excess carbon dioxide from anthropogenic emissions, accelerating the build-up of greenhouse gases in the atmosphere.

The lead author of the PNAS paper, CSIRO’s Dr Pep Canadell – Executive Director of the Global Carbon Project (GCP) – says the acceleration in climate change is due to global economic growth, a more ‘carbon-intensive’ economy, and a reduced capacity of the land and oceans to absorb carbon from the atmosphere.

‘Fifty years ago, for every tonne of CO2 emitted, 600 kg were removed by land and ocean sinks. However, in 2006, only 550 kg were removed per tonne and that amount is falling,’ Dr Canadell said.

In another PNAS paper published earlier this year,3 a team of experts led by Dr Mike Raupach – also from CSIRO – concluded that the growth rate of global CO2 emissions has risen from 1.1 per cent per year in the 1990s to over 3 per cent per year from 2000 onwards.

Dr Raupach said atmospheric carbon from fossil fuel emissions rose by 1.9 billion tonnes of carbon per year in the 11-year period 1995–2006, increasing from 6.5 billion tonnes per year in 1995 to 8.4 billion tonnes per year in 2006. (Additional carbon emissions from changes in land use remained constant over that period at 1.5 billion tonnes per year.) ‘No region in the world is decarbonising its energy supply,’ he commented.

…‘Observations from the last 10 years or so show that IPCC predictions are conservative not aggressive,’ Dr Raupach says. ‘The predictions made using models 10 years ago can now be compared with the reality. This comparison shows that while models are working well, if anything they are too conservative. But this should not be used as a reason for inaction. We don’t need to worry whether the safe stabilisation level is 550 or 500 ppm of CO2 equivalent in the atmosphere, but we do know it should not be 700 ppm.’

The widely reported shrinkage of the Arctic ice sheet during the 2007 northern summer – when the minimum area of sea ice was 22 per cent less than the previous minimum recorded in 2005 – was not predicted by any of the IPCC models.

…‘Even though there is uncertainty about how fast climate change will happen, we can be confident that it will happen, at least according to the IPCC predictions,’ Dr Raupach reiterated. ‘On the research side now, it’s a matter of working out probabilities for climate change outlooks, which are bad at best and catastrophic at worst. ‘But you don’t need to wait for the uncertainties to be quantified to know what to do next – the need for emissions reductions is urgent.’ . ..

Graphic by Gralo, Wikimedia Commons: The graphic shows "Greenhouse Gas Concentration Stabilization Level Scenario Categories." Self-drawn based on Figure SPM 8 in the IPCC Fourth Assessment Report, Working Group III, Summary for Policymakers. The text in the report reads: "Stabilization scenario categories as reported in Figure SPM.7 (coloured bands) and their relationship to equilibrium global mean temperature change above preindustrial, using (i) “best estimate” climate sensitivity of 3°C (black line in middle of shaded area), (ii) upper bound of likely range of climate sensitivity of 4.5°C (red line at top of shaded area) (iii) lower bound of likely range of climate sensitivity of 2°C (blue line at bottom of shaded area). Coloured shading shows the concentration bands for stabilization of greenhouse gases in the atmosphere corresponding to the stabilization scenario categories I to VI as indicated in Figure SPM.7. The data are drawn from AR4 WGI, Chapter 10.8. [i.e. from the IPCC Fourth Assessment Report, Working Group I]"

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