Saturday, March 11, 2017

How we know that climate change is happening—and that humans are causing it



[Popular Science] “People come to Asheville to retire,” says Deke Arndt, “and data comes to Asheville to retire, too.”He should know. Arndt and his colleagues sit atop a vast trove of current and historical climate data—data so valuable, it’s protected by multiple failsafes and even backed up on tape at an undisclosed, secure location, where it’s carried by hand in a nondescript suitcase several times a week. The data in question isn’t bank account information, or Social Security Numbers, or nuclear codes. It’s even more important than that: their data encompasses everything we know about our changing climate.
Arndt is chief of the monitoring section of the National Oceanic and Atmospheric Administration’s National Centers for Environmental Information, and he stewards data collected at weather stations, from satellites, by buoys, and covering every weather and climate condition you can imagine. How hot is the ocean? How big was that tsunami? What’s the weather like in space? The NCEI can (and does) answer every single one of those questions. All told, they host a mind-boggling 28.6 petabytes—data equivalent to 18 Eiffel Towers’ worth of stacked-up smart phones. Arndt and his colleagues spend their days poring over data, comparing the incoming numbers to the baseline they call “normal.” Using daily, weekly, monthly, and annual rhythms, they coordinate data collection and sharing, keeping an eye on the quality of the numbers and how they stack up compared to yesterday, last week, and longer.
For Arndt, climate is all about scale—and the information that passes through his office tells a story that’s become all too familiar. “The upper atmosphere is cooling while the lower atmosphere is warming,” he says. “You don’t get that without changing the composition of the atmosphere. We’re seeing changes you would theoretically see in a warming world. More big rain—that’s an expectation. More big heat—that’s an expectation. The frozen stuff is generally melting or going away, based on the time of year and the location on the planet.”
He pauses for a moment, then continues. “I think the basics are more than settled.” But what are the basics? How can we know if the climate is really changing? And does it really present the kinds of threats that have now become a familiar, but jarring, refrain? Simply put, climate change is a change in the climate. If this is “no duh” territory, hang in for a second—it’s a bit more complicated than that. To really get climate change, it helps to understand a couple of other factors that often get lost in the shuffle.
The events that happen on a day-to-day basis in the atmosphere—from rain to snow to wind and heat—are known as weather. The average of weather over time is climate. So while weather isn’t climate, climate is weather, just looked at over a longer period of time.
Then there’s climate variability: the ways in which climate changes over periods of time like seasons. If a weather phenomenon like temperature or humidity goes above or below the long-term average for a certain time period of seasons or years, it’s known as climate variability. For example, some years experience a higher-than-average sea surface temperature. When the average numbers go over a certain threshold, it’s an El Niño event. When they go below a certain threshold, it’s a La Niña. But both phenomena are an example of climate variability, because they’re cyclical. They come and go naturally. However, as Earth’s atmosphere and oceans continue to warm, El Niños could get more severe—or even stop being cyclical altogether—because of climate change. When the average climate changes in a consistent upward or downward direction over the longer term, that’s what we call climate change. That change shifts the average weather of a place (or the entire planet) into a new normal. Read More