Mother Jones
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According to NASA, all of the following statements are true:
2014 was the warmest year on record, dating all the way back to 1880.
2014 is far more likely than any other year since 1880 to have been the warmest.
There’s a 62 percent chance that 2014 was NOT actually the warmest year since 1880.
Wait. What??
OK, let’s rewind a bit. It’s a scientific fact that humans are warming the planet by releasing greenhouse gases. This has already resulted in “considerable costs,” explains Kevin Trenberth of the National Center for Atmospheric Research—ice is melting, sea levels are rising, and heat waves and fires are getting worse. Global warming is a very clear trend stretching back a century, and temperatures in any given year aren’t really that important.
Still, it was big news last month when NASA and the National Oceanographic and Atmospheric Administration jointly announced that, in separate analyses, they had both concluded that 2014 was the warmest year on record. “When averaged over the globe, 2014 was the warmest year on record,” explained NASA earth sciences director Michael Freilich during a January 16 conference call announcing the new findings. As you can see in the chart below, both agencies calculated that 2014 was just slightly warmer than other extremely hot years—specifically, 2010 and 2005.
NOAA/NASA
Of course, calculating the warmth of the entire Earth over a full year is difficult. To do this, climate scientists analyze air and water temperature data collected from thousands of weather stations, buoys, and ships around the world. As explained in this helpful Wired article, this involves complex algorithms that correct for various inconsistencies and potential sources of error.
By far the most important source of uncertainty—at least when trying to calculate the warmest year—is the uneven distribution of temperature measurements around the world. According to NOAA climate scientist Deke Arndt, the agency has adequate temperature data for roughly 88 percent of the planet’s surface. The biggest gaps are in the Southern Ocean that surrounds Antarctica, as well as in parts of Africa and the Arctic. (NASA uses a different methodology that includes data covering a greater portion of the globe.)
In other words, the figures reported by NASA and NOAA represent their best estimates of what the temperature readings they do have mean for the Earth’s climate as a whole. When it comes to detecting the broader warming trend, those estimates are extremely reliable. But ranking individual years is more complicated. “According to our tools, 2014 had the warmest temperature…that’s indisputable,” explains Arndt. The uncertainty, he says, comes from assessing how well those tools measure what’s actually happening, as well as from “what may have happened in the areas we didn’t measure.”
When they released their findings, NASA and NOAA attempted to quantify this uncertainty. As NOAA scientist Tom Karl explained to reporters at the time, this table (PDF) shows the probability that 2014 (as opposed to other extremely warm years like 2010 and 2005) was really the warmest year:
NOAA/NASA
So both agencies found that 2014 was far more likely than any other year to be the warmest. NOAA put the probability at 48 percent—that’s more than two-and-a-half times higher than the next likeliest year. NASA put the probability that 2014 was the warmest year at 38 percent—lower than NOAA but still much higher than any other year.
Unsurprisingly, critics pounced on the 38 percent figure. “NASA climate scientists: We said 2014 was the warmest year on record…but we’re only 38% sure we were right,” blared London’s Mail on Sunday, a frequent source of climate change skepticism. The Mail story blasted NASA for having issued a press release that didn’t include the uncertainty.
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Source:
Was 2014 Really the Warmest Year? Here’s Why It Doesn’t Matter.
