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It is now three years since the Paris Agreement persuaded 195 countries (all except Syria, and now the US) to try to keep average global temperature within 2degC above pre-industrial levels, and preferably within 1.5degC. There has been plenty of progress since then and the Paris Agreement remains our best hope to deal with humanity's biggest challenge since the black death wiped out one third of Europe's population. But (and I look forward to the day when there are no more buts) we have not yet got the world on target.
The non-binding promises made in Paris will only limit warming to 3degC, and hopes of lifting ambitions rest on article four of the agreement, which commits all countries to reporting their emissions to the international community. Excepting of course Syria and the US, for now anyway.
The Intergovernmental Panel on Climate Change, a periodic assembly of some 2000 scientists, normally reports on the climate every seven years, the last time in 2014. But given the Paris nod to a 1.5degC target and the scientists' own mounting concern at the speed of change, the IPCC released a special report on the reasons why our global target must be restricted to 1.5degC. Keeping within the lower limit will moderate all of the dangerous consequences of a warming world: sea level rise, ocean warming and acidification, ice loss and, depending on where you live, extremes of heat, drought and rainfall. These conclusions have already been given extensive coverage in the international media and, of course, here in the Otago Daily Times.
This latest IPCC report also gives us the best insight yet into some of the social consequences of a warming world. Since we humans are the problem, it is useful to know where we are most likely to feel the effects of our carbon addiction. If these hurt us enough, and in the right places, they should provide the incentive we need for us to change our ways. With so much of climate change being amplified by positive feedbacks (for example, rising Arctic temperatures releasing methane from melting permafrost), we badly need some powerful negative feedbacks that will act to put the brakes on further warming.
The IPCC simulations tell us that overshooting 1.5degC will have distinctively higher impacts on least developed nations and small-island developing nations; our close Pasifika neighbours. At first glance this will do little to discourage humanity's carbon addiction. These nations are among the lowest users of fossil fuels, and it is the rich nations - not the poor - who need to radically change their ways.
But in social systems, a powerful stimulus in one area inevitably provokes further change. The IPCC simulations also tell us that overshooting the 1.5degC target will expose several hundred million more people to climate risks, exacerbated by poverty. And that in turn will be a powerful driver of migration from the most affected regions to safer, richer countries.
Research by Dr Dennis Wesselbaum of the University of Otago's economics department has carefully teased out the effect of climate change on migration from poorer to richer countries. The most powerful stimulus to leave turns out to be the effect of climatic change on incomes, which, in poorer countries, are especially dependent on agriculture. Other significant drivers include weather-related disasters, damage to health from vector-borne diseases, and conflict over climate-affected resources.
Twelve years ago, Nicholas (now Lord) Stern estimated the quantum of climate migration at up to 200 million people. We can already see the effect on richer countries of migration pressures far smaller than these in Australia, Hungary, Brazil; the list goes on. Unwanted immigration has turned out to be a powerful weapon driving a return to nationalism and away from the international orders that have been the foundation of a long period of unprecedented (though not universal) peace and prosperity. Evidence Donald Trump's America, Brexit, Germany's Alternative fur Deutschland, and France's Front National.
So we can expect that one of the ways that climate change will reach into the lives of us rich people will be growing - and eventually overwhelming - migration. The rich will not escape the dislocations of climate change. They will appear in the form of millions upon millions of people driven from regions where a changed planet no longer supports viable life. And on present evidence one result of that could well be a return to a more dangerous world dominated by narrow self-interest. Is this a risk we want to run?
Perhaps one of the strongest reasons for us rich people to accept the IPCC challenge and keep warming within 1.5degC is that it would reduce by half the proportion of the world population exposed to climate-induced water stress.
Colin Campbell-Hunt is an emeritus professor at the CSAFE Centre for Sustainability, University of Otago. Each week in this column, one of a panel of writers addresses issues of sustainability.