Climate change makes the normal variability of Australian weather happen around rising temperatures and, in the southern latitudes, falling average rainfall. Bad bushfire summers are worse than bad seasons used to be. Bad years in the Murray Darling are worse than they used to be. The science has been telling us since and before my 2008 Climate Change Review that bad seasons will keep on getting worse until the world has zero net emissions. The science has been right.

Zali Steggall's private member's bill proposes a Commonwealth commitment to zero net emissions by 2050. The world has to be zero by 2050 or before to reach the Paris goal of temperature increases below 2 degrees and as close as possible to 1.5 degrees - if the whole world starts now and reduces emissions by about three and a half percent of current levels in every year between now and 2050. Start slowly or later and we will have to finish faster and earlier. We all agreed in Paris that rich countries like Australia will move faster and earlier. A zero by 2050 commitment and direct movement towards it would shift us from being a laggard to full participation in the global effort.

Why net emissions? First, a tonne of emissions of a long-life greenhouse gas like carbon dioxide increases concentrations in the atmosphere by about a tonne for thousands of years. Some short life gases, like methane, are more powerful, but affect concentrations for only a decade or so. So carbon dioxide has to go to zero by 2050, but methane can stabilise at a level below the present about 10 years in advance of 2050. Second, some carbon dioxide emissions from some activities can be balanced by negative emissions from others (like capturing carbon in soils or plants). Thirdly, some countries can have moderately positive emissions if others have negative emissions, with the positive countries buying credits from the negative.

Trade in carbon credits between Australia and Europe would have started July 1, 2014, if carbon pricing had been retained. At the time of my 2008 and 2011 Climate Change Reviews for governments, I expected Australia to be an importer of carbon credits, and to pay other countries to do some of our capture for us. I now expect that Australia would be an exporter of carbon credits, and carbon farming to be a major rural income source.

Is zero by 2050 good enough? Australia is the most vulnerable to climate change of all the developed countries. For the time being, 2050 is as good as we can get. But it is in Australia's national interest to encourage greater global ambition.

Does it matter what Australia does, if we account for only about 1.25 percent of global emissions? It matters morally that we do our full share, as Pope Francis makes clear in his authoritative letter. It matters because we always want to pull our weight on the great issues affecting our security. It matters because countries with emissions similar to or smaller than us (including the UK despite its much larger population) account for far more emissions than any single country. It matters because we are influential in diplomatic discussions. It matters because there is a difficult debate in all countries, and it is damaging to the outcomes of those discussions elsewhere for the developed country with the highest emissions per person (and twice as many emissions per person as China), and the developed country most vulnerable to climate change, to do less than its fair share. It matters because a good global outcome is more likely if there are common goals and broad participation in carbon trading- and it was our desire to avoid joining ambitious global goals that caused our stand at the Madrid climate change conference to be negative and a drag on global efforts to provide foundations for carbon trading.

Zero by 2050 would bring Commonwealth policy on this point in line with goals of all Australian states and territories - including those of Coalition governments in New South Wales, South Australia and Tasmania. So does it matter what the Australian Commonwealth government does? Yes, because only the Commonwealth is a participant in the formal international discussions. And yes, because the Commonwealth has access to a wider range of policy levers, and because the costs of reducing emissions would be lower, and the economic benefits greater, if there were similar incentives across states and territories.

Can we get to zero by 2050 without damaging employment and incomes, including in regions that mine coal and generate power from it? Yes. This is the exciting new story from my book Superpower: Australia's Low Carbon Opportunity. As the whole world moves to zero net emissions, Australia becomes the economically efficient home for processing much of the immense quantities of iron and aluminium ores and other mineral and agricultural products that we currently export in raw form. The new opportunities are overwhelmingly in provincial Australia, including in the old coal generation towns. Electricity becomes cheaper, and can also be more reliable through hot and dry and fire-prone summers. Rural Australia earns high incomes from selling carbon credits to countries that are less well endowed with renewable energy and opportunities for storing carbon in the landscape. Australia is the best placed of all countries to prosper in a zero-carbon world economy - just as we are the most vulnerable to global climate policy failure.