One of the thorniest issues dividing nations at the Lima climate talks involves the looming costs of adapting to global warming. For poorer countries, climate assistance from rich nations that caused most of the problem is a prerequisite for a deal.
Now, a new report by the United Nations Environment Programme says the costs of adaptation will likely run at least two or three times more than previously estimated, and as much as four or five times more.
The current estimate of between $70 billion and $100 billion a year is "likely to be a significant underestimate, particularly in the years 2030 and beyond," said The Adaptation Gap Report: A Preliminary Assessment.
By 2050, the report said, "costs of adaptation are plausibly four to five times higher than current estimates," which were developed by the World Bank.
That means if the world's nations are to commit to both mitigation (cutting emissions to stop climate change) and adaptation, the bill could easily run into trillions of dollars over the years.
It's harder to estimate the uncertain costs of future adaption than to project mitigation spending, the authors said. The previous adaptation estimates did not completely cover all the many sectors that are vulnerable to the risks of a rapidly changing climate. The new estimates tried to do better by going country by country to see what is already expected.
Also, the old estimates used rosier assumptions. They didn't factor in that unless emissions are reined in sharply, the world will be destined to hit 4 degrees Celsius of warming in the coming century, rather than the 2-degree target that negotiators are seeking to achieve.
The slower the cuts in carbon emissions, the faster the costs of dealing with global warming impacts will rise, the report said.
"Ambitious and immediate mitigation action is the best insurance against an insurmountable adaptation gap," it said.
At present, the world's governments and their global financial institutions are spending at least $25 billion a year—and probably more that goes uncounted—on early adaptation efforts, it said.
There's a major effort underway at the Lima talks to beef up the Green Climate Fund, which has just received initial commitments of about $10 billion. It is meant to be investing $100 billion a year by 2020 on mitigation and adaptation together.
If UNEP's assessment of future costs proves correct, a lot more than that will be needed.