Projecting what the climate will be like more than three decades from now is inherently uncertain. The New York City Panel on Climate Change, a group of scientists from the area’s top research institutions first convened by Mayor Michael Bloomberg, understood that. The panel expresses their predictions not through a single prediction for heat, sea level rise, etc., number but through a range of predictions.
That's because there is no single widely accepted model for determining how the climate will change. In fact, there are dozens of them. That panel used 24 models for sea level rise and 35 models for temperature, all of them widely accepted in the climate community. To achieve predictions for the New York metropolitan region, the researchers took the area’s climate data, poured it into those models, and then ran them through two different scenarios. One scenario assumes society will gradually curb greenhouse gas emissions. The other scenario assumes emissions will grow at the current rate. The panel then arrayed the different results from smallest to greatest impact. The stories in NYC 2050 are largely based on predictions developed last year that are still in draft form. (A previous report came out in 2010 and an interim report was released last year.)
According to middle half of these calculations, for example, in the year 2050:
TEMPERATURE: The average temperature is expected to rise between 4.1 and 5.7 degrees Fahrenheit;
HEAT: The city will experience between 39 and 52 days, on average, at or about 90 degrees annually;
RAIN: Average annual precipitation will increase by 4 to 11 percent;
SEA LEVEL: Sea levels will rise between 11 and 21 inches from the level it was in the 2000s.
A quarter of the calculations resulted in predictions that were less severe than these; another quarter project that the climate will be even more severe in the 2050s.
In other words, it is hard to say exactly how much worse the climate will be by that point. But the overwhelming majority of these projections indicate it will be worse.
“We emphasize a projection range rather than an individual number and the reason is that the city understands there is uncertainty in climate science,” said Radley Horton, a member of the panel and a climate scientist at Columbia University’s Earth Institute. “But spring is coming earlier and fall is coming later. And if you put all of these things together, you see you are better off starting from the assumption that the climate is changing.”
For the purposes of our on-air content, WNYC and NBC 4 New York simplified these results by focusing on the middle of the predictions. We say temperatures will likely rise 5 degrees; there will be about 45 days at or above 90 degrees, and that sea levels will rise about a foot and a half. The benchmark of 2050 is something of a necessary fiction. There is so much variability in weather from one year to the next – or even one decade to the next – that climatologists tend to measure temperatures in 30-year chunks rather than year by year. Hence, the heat we say is expected in 2050 is really an average of what’s expected between 2030 and 2060. The predictions for sea level rise are for the entire decade of the 2050s.
There is a reason for these simplifications that goes beyond journalistic expediency, however. As you see in this series, government agencies, businesses and private homeowners are already taking steps to prepare for 2050. They need shorthand to help them determine how high to make their levees or raise their homes. There is extra expense if they over-prepare, but potential for catastrophe if they do not prepare enough. They are also looking at these predictions and trying to find the right point in the middle.