[I recently spoke to a teachers’ group about the state of the evidence on global warming. Having updated myself, and seen various reports of complacency, confusion or plain arrogant stupidity, I have written a summary here.]

As delegates argue in a Cancun resort on your behalf about who will reduce their greenhouse gas emissions first, what’s your own feeling about global warming? With record rain and floods all over the southeast and a big freeze in Europe, it may seem that global warming has taken a holiday.

Perhaps, like 36% of Australians, you think “We are just witnessing a normal fluctuation in the earth’s climate”, or like another 19% you don’t know.  The proportion of Australians who think “Climate change is happening and is caused by human activity” has dropped below 50%, to 45%, for the first time since Essential Media Communications began polling on the topic in 2008.

Perhaps, like Bronwyn Bishop, at The Punch on line, you would put it more strongly, as in “where ‘The Science’ told us it would never rain again, millions of litres of rain water is being dumped”.  She’s referring to “climate science”, which she thinks should be called climate theory.

Unfortunately for Ms. Bishop no such prediction was ever made in the name of climate science.  What was said is that weather extremes would increase in intensity as the world warmed, and that includes freezes and flooding rains as well as droughts.  Remember the big snow dump on Washington D.C. last northern winter?  That was also supposed to signal the end of global warming, but it didn’t.

Also unfortunately for Ms. Bishop and all those who believe global warming stopped in 1998, 2010 is on track to be equal warmest ever, and is right on the warming trend of the past 25 years, European freezes and local La Niña conditions notwithstanding.  That statement is based on actual measurements of temperature all over the world.  It is not based on theory, nor on assumptions, nor on the “arbitrary elements” that Ms. Bishop claims climate science is based on.  Nor is it based on the current weather at any particular locality.  It is not called global warming for no reason.

There are many who claim that although there is clearly some warming there is no proof we are causing it.  Well, the evidence just keeps getting stronger.  The guns, the bullets and the smoke have now been detected.  The heat that is supposed to be trapped by carbon dioxide in the atmosphere has been detected re-radiating to the Earth’s surface, at just the wavelengths predicted for carbon dioxide.  That’s the smoke.  And the carbon dioxide in the atmosphere, and in corals, contains the signature mix of isotopes that identifies it as coming from fossil fuels.  That’s the bullets.  The guns are our smokestacks and tailpipes.

Perhaps, nevertheless, you’re not sure if you should believe any of these measurements, because weren’t those British scientists caught red-handed fudging their data and trying to block publication of contrary conclusions?  That would be “climategate”, wherein thousands of emails were hacked (illegally) from the University of East Anglia, and a very few, selectively quoted out of context, were claimed to show fudging and other cheating.

Three eminent committees examined the claims of cheating and found there was none.  None.  No published work deliberately hid issues or fudged data.  Newsweek called the controversy a “highly orchestrated, manufactured scandal”.

Extremely demanding and unprecedented FOI requests were made of the scientists by people who the scientists had reasonable grounds to believe could use nefarious means to try to discredit them.  This was in the context of a well-reported systematic campaign of disinformation funded by ExxonMobil and other companies.  The scientists were also concerned about certain authors and editors who had published papers without following proper peer review processes.

“Climategate” would be one of the greatest beat-ups, with the least foundation, ever.  The supposed scandal was loosed upon the world just before the crucial climate summit in Copenhagen last year.  Unfortunately the propaganda campaign was all too effective, as it contributed to the failure of the summit, and public concern about global warming dropped noticeably.

There are many clear symptoms of global warming.  A good summary was given by NOAA’s Ten indicators of a warming world in their report State of the Climate in 2009.  The symptoms include declining glaciers, snow cover and sea ice and increasing temperatures within and over the ocean, over land and in the troposphere, rising sea levels and higher humidity.

There are also many lines of evidence pointing to the greenhouse gases that we have emitted, mainly carbon dioxide and methane, as the culprits.  These include the smoke and guns already mentioned, but also a cooling stratosphere, nights warming faster than days and other more esoteric changes in the atmosphere.  Excellent recent summaries of the science have been provided by the Australian Academy of Science (The Science of Climate Change) and by The Copenhagen Diagnosis.

Perhaps you’re suspicious of the sometimes dire warnings of scientists?  Would global warming just mean a few more heat waves, a bit less rain and better crops in Siberia?  Or would it threaten civilisation?  A recent collection of papers published by the British Royal Society suggests things will be worse rather than better.  They now  say that 2°C would be worse than previously thought, and is the threshold for “dangerous” warming, though we are now unlikely to stay below that level.  With warming of 4°C, which could arrive by as early as 2060, there would be widespread crop failures, hundreds of millions in food stress, flooded cities and infrastructure, plagues and extinctions and a very dangerous prospect of runaway feedbacks.

If, finally, you still think these assessments are exaggerated, then you could reflect that the very different world of the ice ages was only 5°C colder than at present, and  the current level of greenhouse gases in the atmosphere is approaching what it was several million years ago when there was much less polar ice and sea level was 10-20 m higher than at present.  The scientists’ warnings are all-too plausible in the larger context of geological history.