You may have read or heard that the shrinkage of the Arctic sea ice recently smashed the previous 2007 record low.  You may not have heard of a new study that says we might, just, still have a chance of keeping global warming below 2°C.  You may or may not have heard that some prominent climate scientists, including James Hansen, think 2°C is too high, and we need to keep warming below 1.5°C or even 1°C.

All this means we might still have a chance of avoiding “dangerous” global warming, but the chance is already small, and diminishing very rapidly.  It also means we are not doing nearly enough to reduce greenhouse gas emissions, even though there is a great deal more we can do at quite modest cost to our economies.

Clearly many people are fatigued with warnings about global warming.  However the scientific evidence only gets stronger, the so-called sceptic arguments only get weaker, and the estimates of the danger only get worse.  The hour is very late, but still everything we do will help to reduce the chance of dire consequences.  That is why we need to refocus on this issue.

This year’s Arctic sea ice minimum is fully 18% lower than the previous 2007 record.  It reflects the well-documented dramatic warming of the Arctic, itself a long-predicted effect of global warming.

The weight of opinion among climate scientists that global warming is happening and humans are the main cause is something like 97% for, 1% against, 2% undecided.  The climate science on which those assessments are based is filtered for quality and credibility by the peer-review process, in which every paper is vetted by other scientists before it is allowed to be published.  The main assessments of the state of climate science involve further rounds of review of findings.

The claims of so-called sceptics, on the other hand, are not subject to any filtering for quality and credibility.  Many of them emanate from a few sources that are dedicated to creating as much confusion as they can.  The credibility of sceptic claims is now so low that really the only argument left is of a conspiracy of scientists, perhaps also involving greenies, jews, socialists and others allegedly trying to set up a world dictatorship.

You may have thought the “climate-gate” email scandal severely damaged the global warming case in 2010.  In fact that was one of the biggest beat-ups ever.  A comment that a scientist would “hide the decline” referred to a minor set of data with no bearing on the overall assessment that global temperatures are rising, not declining.  No fewer than eight enquiries found there was no significant misrepresentation of the science, nor misconduct by the scientists involved.  A much-publicised recent study by a sceptical scientist at Berkeley confirmed that the temperature estimates of other groups are largely correct.

The new study of how fast we might reduce greenhouse gas emissions finds that, without dramatic means to actively extract gases from the atmosphere, global warming can be limited to 2°C only if emissions peak by 2016 and then trend down by 3.5% per year, a rate considered to be quite ambitious.  These requirements are well beyond any policies that governments have been willing to contemplated so far.  The study allows that if gases can be recaptured there is a little more room to breathe, but all such recapture schemes are currently speculative.  Indeed it is ironic that the much touted “carbon capture and storage” idea has a much flimsier basis in evidence than does climate science.

Revised estimates of damage from rising temperature

To limit warming to 1.6°C would require the most ambitious limits on emissions combined with a big effort to recapture gases already emitted.  The limit of 1°C, and relative safety, may now be beyond our reach.

Climate scientist James Hansen’s projections have been broadly correct for about three decades.  His most recent argument does not depend on computer models of climate.  Rather, using paleoclimate data from thousands to millions of years ago, he says we must limit the atmospheric concentration of carbon dioxide to 350 parts per million.  We are already over 390 ppm.  If we can bring it back down quickly, by 6% per year starting now or 15% per year starting in 2020, we may escape the worst.  If we don’t, the results may be dire, or apocalyptic.

The great danger is not just extremes of weather and disruption of food supplies, already starting to happen.  The greatest danger is a tipping point beyond which warming becomes irreversible until temperatures are 4-6°C higher.  That could transform the Earth so much the current distributions of population and food would be dramatically changed.

Choose your metaphor.  If a plane had a 20%, or 5%, or even 1% chance of crashing, would you get on it?  Scientists are saying the iceberg is dead ahead and the chance of avoiding it is diminishing rapidly, but the Titanic’s officers are arguing about the best kind of fuel and paying little attention.

Governments still have their heads in the sand.  The sad and simple truth is that governments avoid any action that will offend powerful fossil fuel lobbies and some sections of the media.  Kevin Rudd’s fate at the hands of mining companies weighs heavily on our democracy.  That will change only if we, the people, loudly demand serious action, now.