Are Superstorms “Weather” or “Climate”?

As fires engulf the West and record-breaking hurricanes pummel the Southeast, that favorite accusation of the climate denier is lighting up the internet: You’re confusing climate with weather!

Actually, more often than not, it’s the deniers who confuse these two, citing cold snaps as evidence that global “warming” isn’t happening. NASA provides an easy way to tell the difference—basically it comes down to time. “Weather refers to conditions of the atmosphere over a short period of time,” the agency states on its website. “And climate is how the atmosphere ‘behaves’ over relatively long periods of time.”

So, when climate scientists warn us that human activity is changing the climate in ways that will adversely affect all people living on this planet (because, side note: acting on climate change is about saving human lives; “the environment” doesn’t need us, we need it), they are not talking about a particular storm or heat wave, but about the way in which storms and heat waves in general are becoming more frequent and intense.

When I talked to firefighters in California this summer, for example, people who are fighting 18 massive fires at the moment (not to mention the fires raging in Oregon and Montana), I heard things like “I’ve never seen it this hot for this long.” Or, “We used to be able to count on getting ahead of these fires at night when temperatures dropped and humidity increased, that’s not happening this year.” Or, from CalFire chief Ken Pimlott: “I’m going to use the word ‘astounded.’ We are really astounded at just how many fires there have been. In the past few years, we’ve had maybe 150 to 200 fires a week during the most intense part of the fire season. This year, we’re seeing weeks with 400 or more.”

When I talk to U.S. foresters, they express concern over how long-term climate trends are leading to shifts in which trees grow where, and in which pests invade them. When I talk to members of the U.S. military, they say the increase in persistent droughts and extreme weather throughout the world is a threat multiplier (and they’ve been saying this for over a decade in their Quadrennial Defense Review, by the way—the military, not an outfit known for liberal fan fiction).

Last year, a groundbreaking study led by researcher Robert Kopp, at Rutgers University, quantified the extent to which human behavior has impacted sea level rise.

Kopp and his colleagues found that without human-induced warming, global sea level would have risen by less than half the observed 20th century increase and might even have fallen. “The 20th-century rise was extraordinary in the context of the last three millennia—and the rise over the last two decades has been even faster,” Kopp said when the paper was published.

Another popular outcry from climate deniers: It’s just part of normal global patterns! Sea level is rising because of the Ice Age! That’s not so; scientists have already accounted for these contributions in their calculations of the human impact on sea level rise.

“It’s critical to understand how much of the increased sea level is attributable to a human cause mediated by climate change,” says Ben Strauss, vice-president for sea level rise and climate impacts at Climate Central. “Because sea level at any one point is attributable to myriad factors, some of which are linked to human-caused climate change, and some not. Land is sinking from natural causes, for example, or there are places where people are removing water or oil and that’s a human cause too, but not one related to climate change. Then the 19th century was a bit of a cold spell so there may be some amount of sea level rise caused by returning from that cold spell as opposed to anything that was human-induced. So, you need a rigorous analysis to quantify the human contribution to sea level rise, versus just quantifying how much sea level rise there was total.”

Strauss, Kopp, and other scientists working in this space have done exactly that, precisely pinpointing the contribution of human-induced climate change to sea level rise. On average, globally, human causes have increased sea levels between five and six inches. The potential damage threatens coastal communities and infrastructure throughout the U.S., putting millions of people in harm’s way. Climate change not only intensifies storms or heat waves; it also exacerbates their impacts once they hit. On the storm front, for example, because more intense storms are hitting eroded coastlines at higher sea levels, the flood risk is increased.

“Chronic low-grade flooding is already being strongly influenced by human-induced climate change,” Strauss says. “Three out of four coastal floods in the last decade in the U.S. were tipped over the balance by human-caused sea level rising, meaning they would not have exceeded the National Weather Service definition of a flood if you removed that human-caused sea level rise.”

When we talk about human-induced climate change, we’re primarily talking about CO2 emissions, although there are a variety of other greenhouse gases that impact climate (methane, for example, is roughly 30 times more potent as a heat-trapping gas than CO2, which is why getting meat consumption under control is so critical). “In the period since 1980, atmospheric CO2 emissions attributable to man—and it doesn’t all stay in the atmosphere, some is deposited in oceans, forests, and so forth—but cumulative emissions from that period, 1980 to now, is equal to or greater than all previous emissions, going back to the pre-industrial age,” says Dan Cayan, a climate and atmospheric science researcher at the Scripps Institute of Oceanography at the University of California at San Diego.

“So in this relatively short period of time, we’ve almost doubled the amount of CO2 in the ecosystem.”

It’s hard to imagine how such an increase would have zero effect on the atmosphere. Cayan, who works with the state of California to determine the impacts of sea level rise and plan mitigation strategies, says both global and regional temperatures have responded to spikes in CO2 emissions. “According to most models, doubling emissions would increase temperatures in California by about 4 degrees Fahrenheit,” he says.

That might not seem like much, but even small shifts in natural systems tend to have a catastrophic domino effect. “In California, for every degree Fahrenheit of warming, we lose about 20 percent of the spring snowpack,” Cayan says.

Loss of that snowpack means reduced water storage for the state, which means when its usual droughts hit, they’re worse. So next time someone tells you a bad storm is just bad weather, you can tell them, “True, but it’s bad weather made worse by climate change.”