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I started writing these columns on climate change more than four years ago and now it is time for me to stop.
In late 2014 there were so many reasons to shout out loud that climate change was going to threaten the future of all generations to come if we didn't take it seriously - and it seemed that few people did. At the University of Otago, Assoc Prof Bob Lloyd had been explaining the risks we are running in powerful seminars, but his students' response then was to urge him to "Cheer up, Bob".
I doubt young people would take climate change so lightly now. This month, thousands of schoolchildren across Australia skipped class for a day to protest their government's lack of action. When I gave my own seminars, there was always someone in the room who told me I had the science wrong and nothing unusual was happening to the climate. Not any more.
Above all, the threat of climate change is now being taken seriously by governments at every level: local, national and international. Dunedin is having to face up to the certainty areas of South Dunedin will eventually lose the battle with rising seas and storm surges. Our year-old coalition Government is bringing in a broad suite of climate-mitigation policies: setting a target of zero net emissions by 2050; installing a Zero Carbon Act that will require governments of all political hues to report on progress towards that target; an emissions trading scheme that will give strong price disincentives to using carbon; positive incentives to the new low-carbon technologies of the future - electric vehicles, improved insulation of buildings, renewable sources of energy; and ambitious expansion of forests. The Productivity Commission is recommending agriculture be given the incentives (both stick and carrot) to make its contribution to getting carbon (and in this case methane) out of our lives.
What a change from the policies in place just four years ago. Back then, we were justifying our widespread inaction on climate change by claiming we would be a "fast follower". This fig leaf was supposed to convince us, and the international community, our then-target of reducing 2030 emissions by 11% below 1990 levels was a responsible offering to the international community. They were not fooled. New Zealand was identified, along with Australia and Canada, as among the countries doing the least to keep temperatures rising more than 2degC above pre-industrial levels.
Surely the biggest change over these four years has been the emergence of international acknowledgement of the climate change challenge and a growing determination to address it. Four years ago, we were still living with the complete failure of the Copenhagen climate conference. Then in December 2015, 195 countries came together to sign the Paris Agreement, making public their "intended nationally-determined contributions" to the international effort.
It is true that, taken together, these INDC take us only halfway to the emission reductions we must achieve to meet the 2degC target. If the Paris targets are all that is achieved, the planet will warm by more than 3degC and we can expect the unleashing of a series of unstoppable changes to our planet's temperatures, sea levels, agricultural productivity, and ocean health. But we must also remember that prior to Paris, a continuation of business-as-usual then would have led to 5 or 6degC of warming. And just last week, a follow-up meeting in Katowice has agreed on the ways in which all countries will have their emissions recorded and presented for international approbation or discipline.
We all know we are not yet on a path to a sustainable, low-carbon future; but I must conclude we are a lot closer now than when these columns began just four years ago.
Given the inertia built into a global system that has been dependent on carbon-intensive technologies for over a century, the amount of change we have seen over the past four years is truly remarkable. As in any complex system, change on the scale needed now can be expected to come about in a relatively brief period following unremitting pressure on the old ways of doing things.
For a long time yet, we will cling to the old ways because they are the only ways we know. But the guardians of the old carbon-dependent order (and that includes every one of us) are now clearly on notice their days are numbered.
So there is no reason I can see to give up and write letters to our grandchildren explaining why we failed them so completely. This is a battle that can be won, but we have only just begun the fight.
In the advanced G20 countries, collectively responsible for 75% of global emissions, emissions are still rising and have increased by one-third since 1990. Several of the drivers of radical change in the climate system are already in play: Arctic and Antarctic summer sea-ice melting, release of carbon dioxide and methane from permafrost, and reduction in northern hemisphere spring snow. The vast Greenland ice sheet is shedding water into the ocean at a rate 50% higher than pre-industrial times, nearly all the increase occurring over the past 20 years. Over the last four years, the concentration of CO2 in the atmosphere has passed 400 parts per million. The last time that happened, sea levels were 15m higher than they are now, and we will not halt the rise in CO2 levels until 2050 - if all goes well.
We are still prospecting for new sources of oil and gas - even in a rapidly melting Arctic - when most of the proven reserves of fossil fuels need to be left in the ground as "unburnable carbon". Fifty percent of species now alive on Earth are threatened with extinction if we continue as we are.
If you are like me, you will find some reason to despair in every day's worth of news about our changing climate. But I also see increasing evidence of a sea change in opinion and a rising determination not to be carried away by the forces unleashed by our century-long addiction to carbon.
I am profoundly grateful to the Otago Daily Times for making room for these columns over the past four years, and I know many people have followed them. Reviewing the 36 that have preceded this one, the idea that struck me most was the hope the politics of the 21st century will add to the struggle for fair shares of the income pie the more important struggle to protect the only pie we have, a struggle between exploitation and sustainability.
Colin Campbell-Hunt is a member of the Otago Climate Change Network, a group of University of Otago staff who promote awareness of climate change and the need to defend a liveable world for future generations.
Each week in this column, one of a panel of writers addresses issues of sustainability.