It’s not over yet, but scientists have no doubt: 2015 is the hottest year in recorded history

The World Meteorological Organization, a branch of the United Nations, has announced that 2015 is firmly on pace to be the hottest year on record, capping what would be the warmest five-year period (2011-2015) on record.

The findings, which are based on global average surface temperatures, “are consistent with established long-term warming trends, the dominant cause of which is the emission of anthropogenic greenhouse gases,” WMO secretary-general Michel Jarraud said in a statement issued today (Nov. 25). The strong El Niño weather system this year has also had a warming impact that’s expected to last into 2016, he added.

Global surface temperatures are monitored constantly by governmental and non-governmental meteorological agencies, on land and sea, and the key numbers are historical monthly and annual averages. Scientists and policymakers refer to the “pre-industrial average,” usually understood to mean the world’s average surface temperatures between 1850 and 1899, to contextualize current averages. The day the world’s average surface temperature is calculated at 2° Celsius above the pre-industrial average is supposedly the day the Earth is doomed.

It’s a somewhat arbitrary threshold that scientists decided on a couple decades ago: The world can warm up by about 2°C, we think, before climate change turns apocalyptic. But if that’s the case, then the world is halfway to doomsday. “It is probable that the 1°C Celsius threshold will be crossed” this year, says Jarraud.

Vox’s Brad Plumer argued last year that it was delusional to think humanity could slow down global warming enough to prevent a 2°C average temperature rise:

By now, countries have delayed action for so long that the necessary emissions cuts will have to be extremely sharp. In April 2014, the UN’s Intergovernmental Panel on Climate Change (IPCC) concluded that if we want to stay below the 2°C limit, global greenhouse-gas emissions would have to decline between 1.3 percent and 3.1 percent each year, on average, between 2010 and 2050.

Global greenhouse gas emissions have not declined at that rate, though.

Policymakers can still act to cut greenhouse gas emissions, and will be meeting in Paris next month to decide just how to do so. But there’s nothing to be done about El Niño, a natural weather pattern that is expected to make 2016 even warmer than 2015. As Jarraud says:

Whilst a strong El Niño event is currently in progress, the impact of El Niño (and La Niña) on global annual mean temperatures is typically strongest in the second calendar year of the event, and hence the year whose annual mean temperature is likely to be most strongly influenced by the current El Niño is 2016 rather than 2015.

UNICEF, another UN agency, released a report on Nov. 24 claiming that children will bear the brunt of future temperature rises and their associated effects. Oxfam has published a new analysis of how expensive climate change will be for the world’s poorest countries; it will cost developing nations $790 billion a year, minimum, to adapt to the consequences of rising sea levels, extreme storms, and irregular temperatures.

If the countries holding court at the upcoming climate talks in Paris make drastic pledges, however, and somehow manage to prevent global temperatures from warming 2°C above the pre-industrial average, then poor nations might be spared some adaptation costs and only expend around $500 billion per year.

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