Discussing future economic growth and not mentioning climate change is like staging Hamlet and forgetting to mention that his father recently died. Greg Jericho previews the G20.

The G20 this week in Brisbane will discuss a number of topics. But one topic that won't come up, due to Tony Abbott's insistence that it not, is climate change.

This is nothing new; in fact, it is just another example of purposeful intransigence from climate change sceptics that has been going on now for over a quarter of a century.

The 25th anniversary of the end of the Berlin Wall had me searching through my archives of news magazine from 1989. The adverts and articles within the pages of my old Time and Newsweek copies reminded me of how much the world has changed.

But when it comes to climate change, the magazines revealed just how much remains the same.

The Newsweek edition contained an article written by its science reporter, Sharon Begley, titled "Is it all just hot air?". It concerned new computer modelling that estimated the impact of the CO2 emissions on global temperatures. It also contained lines that have echoed down through the past 25 years.

For example, because there was some uncertainty regarding the modelling, the then White House chief of Staff John Sununu was quoted saying that the uncertainty was reason to do nothing, because "you do not establish policies on the basis of incomplete models".

He then argued, as have many climate change deniers since, that they really wanted to do something - and they would - but just not yet. He suggested, "We have the time and obligation to find out what's going on. We're going to do the right thing. We want to know what that right thing is."

But better modelling and 25 years of data, of course, hasn't done anything to change this view. Indeed, even in 2009, Sununu was still worried about moving too fast. In a speech to The Heartland Institute, he warned of the "rush to judgement".

Similarly, the head of Tony Abbott's Business Advisory Council, Maurice Newman, in January suggested a bet that global temperatures would be lower in 20 years' time.

At this point it is worth noting the NASA GISS land-sea temperature index is on track to record this year as either the hottest or second hottest ever. Moreover, the average temperature of the past five years has been hotter than any other five-year period, and the same goes for the past 10, 15, 20, 25 (and so on) years:

But yeah, we need to wait to decide whether or not we do "the right thing".

Of course, relying on incomplete modelling is no barrier for other policies.

At this week's G20 conference, much will be made of the call to lift world economic growth by an extra 2 per cent over the next four years. The plan involves some 1,000 separate proposals developed by, among others, the IMF and the OECD.

Now I'm a big fan of economics, but when I read, as was reported in The Weekend Australian, that the OECD was claiming the reform proposals would achieve "1.8 per cent" of growth, compared to the IMF's earlier modelling that they would achieve 1.6 per cent, well, my eyes started rolling.

Forecasting the projected growth for one country for one year is hard enough, let alone world growth for four years based on 1,000 different initiatives.

And when you have Australia including in its projections the extra growth gained from "reforms to Australia's higher education" then you know you're in horse-manure country.

In the past two years, the IMF's estimates for world GDP growth in 2014 alone have changed by 1 percentage point from the 4.36 per cent it predicted in October 2012, to its latest prediction of 3.31 per cent

I guess some modelling means you don't have to wait to implement policy.

Similarly, this week there are reports that a free trade agreement with China could be worth "$18bn over the next decade". That sounds great until you recall in 2010 the Productivity Commission reviewed the benefits of such agreements and concluded "their potential impact is limited and other options often may be more cost-effective".

It also found "little evidence from business" that indicated free-trade agreements "provided substantial commercial benefits".

But the $18bn figure gets reported as though it is a given.

None of this means the G20 should not push for higher growth. And there may even be some benefits from a China free trade agreement.

Doing things to improve growth can have a positive impact even if the outcome is not all that precise. Similarly, acting on climate change has some rather nice side benefits even if climate change ends up being less than the models predict.

Back in 1989, Sharon Begley noted these, suggesting:

Changes that would mitigate the greenhouse would actually bring other benefits. Energy conservation reduces dependence on imported oil; fuel efficient cars and planting trees clean the air.

Climate change mitigation also has an economic growth aspect as has been noted by the same IMF which Joe Hockey and Tony Abbott place so much store in for their extra 2 per cent of world growth. In July, the head of the IMF, Christine Lagarde, noted:

A degraded environment leads to a degraded economy. Environmental damage has macroeconomic implications, and implications for the design and impact of fiscal policy.

The UN's IPCC Synthesis Report of its 5th assessment released last week also observed the economic growth impact of climate change. Its "summary for policy makers" noted that climate change is "projected to slow down economic growth, make poverty reduction more difficult, further erode food security, and prolong existing and create new poverty traps, the latter particularly in urban areas and emerging hotspots of hunger".

So discussing future economic growth and not mentioning climate change is like staging Hamlet and forgetting to mention that his father recently died.

Of course, some, such as Sophie Mirabella, suggest the G20 is right to exclude climate change discussion. She concluded in an op-ed in The Australian that "it is only when countries become wealthy that they can afford, both financially and politically, to invest in environmental priorities and policies".

Such a line is just another of the sceptic's standard excuses - similar to the recent coal-company propaganda spouted by the government that coal production is all about curing poverty. It also just reiterates Sununu's line from 1989 that they really want to do "the right thing" - just not now. Forget incomplete modelling, now apparently we have to wait for the poorer nations to first get wealthy.

But given the G20 contains some of the richest nations in the world, it's a pretty shallow argument.

Moreover, as Begley noted presciently 25 years ago in her Newsweek article, "if a rich, technologically advanced nation won't put its house in order, then developing countries - potentially worse greenhouse villains - have a perfect excuse to do nothing".

It would be wrong to say the past quarter of a century has been a complete waste for action on climate change, but there certainly has been no end of people trying to come up with reasons for why nothing should be done.

Tony Abbott and Joe Hockey at this week's G20 are just the latest in a 25-year-long line of climate change do-nothings.

Greg Jericho writes weekly for The Drum. His blog can be found here and he tweets at @grogsgamut. View his full profile here.