The climate summit in Madrid will achieve little, but 2019 could nonetheless turn out to be a turning point.
Worldwide emissions have risen again with yet further investment in new coal-fired power stations, but there is finally an acceptance that decisions are overdue and that emissions need to fall steadily for perhaps 20 years or more. Denial of the reality of climate change is no longer a credible political position, even in Donald Trump's USA.
The science of climate change is technically complex, and the experts are still unsure about the timing and severity of the damage that will be done if the policy failure continues. But there has been no serious scientific disagreement for 30 years or more that the growth in fossil fuel combustion cannot continue without catastrophic effects in the longer term.
The argument has been about how bad these impacts will be, and about when and where they will occur. 2019 has been the year when the public caught up with the climate science and overtook the politicians.
In the early 1990s, there had already developed a consensus among economists, led by Bill Nordhaus of Yale University - who won the 2018 Nobel Prize for his work - on the best policy path to keep down the cost of adjusting to a low-emission world.
Unlike the science, the economics of climate change turned out to be straightforward: make the consumption of carbon-intensive goods and services more expensive, start quickly - there appeared to be plenty of time - and rely on devices like a carbon tax. Tell everybody the tax will rise in the years ahead, providing the incentive to invest in low- or zero-carbon alternatives, and, crucially, avoid investing in high-carbon assets likely to become prematurely redundant.
Carbon pricing needs to be universal, since the planet has a shared atmosphere. Each unit of emissions, wherever the source, does the same damage. No country is a planet.
Nordhaus and his colleagues were unsuccessful in selling carbon pricing to policymakers and the 1997 Kyoto agreement instead assigned unenforceable emission limits to participating countries, leaving responsibility for implementation to each government.
Only 84 countries signed up (there are about 200 in the world) and some subsequently opted out. Fast-growing countries like China, now the world's largest emitter, were exempt and many of those who accepted targets did not stick to them.
Kyoto and the successor agreements have failed, another example of mistaking a target for a policy. In the absence of effective economic signals such as a universal carbon tax, the world has invested heavily in assets which must now be stranded, including high-carbon vehicles, heating and ventilation equipment and power stations.
The costs of adjustment will now be much higher than they needed to be because the wrong policy design was adopted at Kyoto.
Almost all the world's countries, 184 of the 200, were attendees at Madrid, and they meet again next November in Glasgow, a week after the US presidential election.
Widespread public alarm about climate change and the public support for the Extinction Rebellion protests around the world will make next November's meeting different - with or without Trump. If Trump is beaten and the next US president re-joins the international consensus, the Glasgow meeting could finally see the emergence of a coherent framework for policy which moves beyond aspirational, and unenforceable, national emission targets.
The European Union's climate policy has been criticised, but it has been more effective than elsewhere: per capita emissions in Europe have been falling and are lower than in other developed parts of the world. The USA is led by a climate change denier - remember the 'Trump Digs Coal' banners at the 2016 election rallies - even though Americans, according to Gallup, have recently been expressing record levels of concern about climate change.
China has become the largest emitter from fossil fuel combustion and per capita emissions are reaching European, though not American, levels. China is now responsible for more emissions than the USA and Europe combined. These three together produce about 55pc of the world total and will lead the world response whenever it comes.
Chinese president Xi Jinping addressed the World Economic Forum in Davos in January 2017, the month of Trump's bombastic inauguration address. Xi struck a very different note, espousing a stable international trading system and acknowledging the priority of climate action. It was a speech rather like US presidents used to make on inauguration day.
While China has been successful in promoting renewable technologies, it has also been relentless in expanding coal-fired generation capacity, which has begun to decline in the rest of the world.
Coal-fired power stations are responsible for most emissions from fossil fuel combustion and the power sector in turn is responsible for most emissions, double the worldwide total from the transport sector, for example.
Converting the world vehicle fleet to electric propulsion is pointless unless electricity generation is decarbonised in parallel. Installed coal capacity in China continues to rise rapidly but finally fell in the rest of the world in 2018 - even though many countries in Africa and Asia, with Chinese technical and financial aid, are building new coal-fired stations. President Xi has been slow to deliver on the promise of his Davos speech three years ago.
Coal-fired capacity is being retired rapidly in Europe despite a few maverick countries, including Poland, intent on building new plants. The continued development of coal-fired power stations is the biggest threat to a coherent climate policy.
These stations have useful lives of 40 or even 50 years. Existing stations in Asia have an average age of just 12 years, reflecting the extraordinary pace of construction over recent years.
The best contribution that Ireland and other small countries can make to fighting climate change is in their advocacy of better policies internationally.
Whatever can be done cost-effectively in Ireland should be done, but it can do no more than purchase a credible voice. One year's emissions in Ireland are exceeded by China's emissions in about 30 hours or US emissions in 60 hours.
Ireland will phase out its high-emission peat-fired power plants shortly and the Moneypoint coal-fired station is due to close in 2025, possibly sooner. Almost all European countries have ceased the construction of coal plants and the EU should seek specific commitments at Glasgow to a slowdown in coal-plant construction, not just in China but also in Australia, where a pro-coal government has just been installed, and in India, Africa and elsewhere.
If coal plant construction continues as planned, the International Energy Agency has calculated that the energy transition worldwide could be threatened by this factor alone.
Taoiseach Leo Varadkar made an important announcement at the recent conference of the European People's Party in Zagreb supporting a European Commission initiative to impose a carbon tax on jet fuel, hitherto exempt.
Ireland's Department of Transport had earlier expressed reservations, but the Taoiseach was right to grasp the nettle.
Europe can take the lead here in seeking a worldwide end to the extraordinary anomaly that international aviation is completely free of either excise on jet kerosene or VAT on tickets.
A first step to the universal carbon tax?