[Published by On Line Opinion, 24 August.]

As the national election campaign approaches its climax, with global warming all but ignored by the major parties, the Australian Academy of Sciences has issued a report summarising the current state of climate change science.  Its conclusions are clear and concerning.  Global warming continues to occur, and the evidence is now strong that human emissions of greenhouse gases are the main cause.  The evidence supporting supporting climate sceptics is melting like the Arctic snow.

The report, The Science of Climate Change: Questions and Answers, confines itself to the state of the evidence, and does not address policy responses.  It is only one of many studies and reports, by scientists and scientific bodies from around the world, that frequently update the science of climate change.

Public concern about global warming has wavered over the past few years in response to a sustained campaign by climate sceptics to discredit the broad consensus of most climate scientists.  Claims have been made that there is no evidence linking recent global warming to human activities, and some have even claimed that warming has ceased.  Scientists have been accused of conflicts of interest, corruption, malfeasance and dishonesty.

The most dramatic and damaging accusations against scientists came from the so-called “climategate” emails that were illegally hacked from the University of East Anglia in 2009.  Three separate enquiries in Britain have failed to find any substance in the allegations.  The scientific integrity of the scientists and of their scientific results have been affirmed.  Allegedly damaging comments made in private correspondence concerned secondary issues and in any case did not translate into the scientists’ published work.  The episode provides no basis for doubting the broad conclusions of the larger community of climate scientists.

Another argument put by sceptics is that global warming ceased in 1998, which was the hottest year ever in a compilation by the British Meteorological Office.  However a NASA compilation shows 2005 as the warmest year.

Both organisations are now showing that so far 2010 is on track to be the warmest year ever, as the cooling la Niña condition of 2007-9 has eased.  La Niña conditions tend to cool the globe, whereas the complementary el Niño conditions tend to warm the globe.  The strongest-ever el Niño occurred in 1998, and temperatures were relatively high.  The fluctuations around the long-term warming trend were misinterpreted by many sceptics to indicate that the long-term trend had ceased.  However similar pauses occurred in the 1980s and the 1990s, and they were followed by sharp jumps in temperature.  A similar sharp jump is occurring this year, indicating that the underlying warming trend is as persistent as ever.

The other main argument put by sceptics is that there is no evidence that human activities have caused the warming of recent decades.  On the contrary, there is by now quite a lot of evidence, some of it quite direct.

First of all, the general warming trend is unfolding very much according to predictions from two or three decades ago, from well before the trend could be distinguished among competing short-term fluctuations.  In other words, the central prediction of climate science has been vindicated, and is continuing to be vindicated.  Given the potentially disastrous consequences of global warming, this alone gives us a strong reason to take the climate warnings seriously.

More directly, it was predicted that night temperatures would increase more than day temperatures, and that is observed.  If the warming were due to changes in the sun’s heat, as claimed by many sceptics, the reverse would be true.  It was predicted that greenhouse gases would warm the lower atmosphere and cool the upper atmosphere, and that has now been observed.  Extra heat from the sun would heat the whole atmosphere, contrary to the recent observations.  It has also been claimed the warming could be due to volcanic emissions of greenhouse gases, but they have amounted to only about one percent of human emissions.

Climate scientists have also predicted for some time that as warming progressed there would be more extreme weather-related events.  Unprecedented drought in Russia, unprecedented floods in Pakistan and extreme floods in China are only the most recent examples of a general trend of increasingly extreme events.  The trend has been painfully evident in Australia, with a decade of drought and fire culminating in the Black Saturday fires of 2009.  The number of record high temperatures around the world has also risen steadily, and is dramatically higher already in 2010.

The Earth is showing many other clear signs of global warming, including rapid shrinkage of mountain glaciers and Arctic sea ice, melting Arctic tundra, shifting regional climates, disrupted seasonal responses of plants and animals, and rising temperatures and acidity in the oceans.

Climate sceptics will probably continue their noisy disparagement of climate science.  However the evidence supporting their scepticism, never strong, is melting away like the Arctic snow.  The evidence is growing steadily stronger that we are the cause of recent global warming.

The trend of global warming is clear, and dangerous.  It is time we moved forward from our recent, perilous indecision, and commenced immediate action to reduce our greenhouse gas emissions.