"The climate change impact on the strength of Harvey is unknown; climate change is expected to increase the intensity of the strongest storms, but it's not clear whether Harvey was in that category," he wrote me. We examine, both in long-term historical observations and state-of-the-art (“CMIP5”) climate model simulations, the changes over time in the projection of this fingerprint. We’re learning to say things like, “There’s only a 5 percent chance the storm would have been this severe in the absence of climate change.” 
 
 But still, saying a storm “probably wouldn’t have happened this way in the absence of climate change” is not the same as saying climate change caused the storm. Sea surface temperatures in the region have risen about 0.5C (close to 1F) over the past few decades 
 
 Harvey was almost certainly more intense than it would have been in the absence of human-caused warming, which means stronger winds, more wind damage and a larger storm surge. Not only are the surface waters of the Gulf of Mexico unusually warm right now, but there is a deep layer of warm water that Harvey was able to feed upon when it intensified at near record pace as it neared the coast. In addition to that, sea surface temperatures in the region have risen about 0.5C (close to 1F) over the past few decades from roughly 30C (86F) to 30.5C (87F), which contributed to the very warm sea surface temperatures (30.5-31C, or 87-88F). More tenuous, but possibly relevant still, is the fact that very persistent, nearly “stationary” summer weather patterns of this sort, where weather anomalies (both high-pressure dry hot regions and low-pressure stormy/rainy regions) stay locked in place for many days at a time, appears to be favoured by human-caused climate change.
– As the deluge continues in Houston, one big question being debated is what role, if any, climate change played in the storm. As with most debates on climate change—particularly when talking about a single weather event—the views are all over the map. And some are suggesting that we need to frame the question differently to get the most accurate response. The details: Wrong question: Did climate change cause Harvey? That's not the right question, writes Dino Grandoni at the Washington Post. "The better way to frame thinking about the connection is through the question: Does climate change make storms like Harvey more likely?" This is a theme repeated in multiple posts on the subject, and Grandoni thinks the answer is yes, for reasons spelled out below. 'Worsened': One of the most cited pieces is from Penn State professor Michael Mann in the Guardian. "We can't say that Hurricane Harvey was caused by climate change," he writes. "But it was certainly worsened by it." The three big factors: Higher ocean levels made the storm surge worse, warmer water made the storm more intense, and Harvey stayed "locked in place" thanks to atmospheric changes brought on by humans. (The latter was the subject of a paper by Mann.) Maybe 'slightly': University of Washington atmospheric scientist Cliff Mass is skeptical the link is that strong. "You really can't pin global warming on something this extreme," he tells Fox News. "It has to be natural variability. It may juice it up slightly but not create this phenomenal anomaly." Link is 'unknown': Texas State climatologist John Nielsen-Gammon thinks it's too early to assess any link. "The climate change impact on the strength of Harvey is unknown," he writes to CNN. "Climate change is expected to increase the intensity of the strongest storms, but it's not clear whether Harvey was in that category." Still, he notes that heavier rain in general is a "direct consequence" of climate change, and Harvey certainly fits that pattern. Too 'fussy': David Leonhardt at the New York Times thinks "it's time to shed some of the fussy over-precision about the relationship between climate change and weather." The evidence is overwhelming that human-caused climate change results in storms such as Harvey, he writes, and our timidness in admitting it is holding up solutions. All about the rain: The jury is out on whether climate change increases the frequency of hurricanes, writes David Roberts in a wide-ranging Q&A at Vox. But he, too, says it's clear that heavier rain is an undisputed consequence. "In fact, due to sea level rise and more moisture in the air, I expect flooding to be the most frequent public face of climate change over the next decade or so." Media coverage: You won't hear much about climate change in the current news coverage because reporters don't want to "politicize" the situation, writes Naomi Klein at the Intercept. "But here's the thing: Every time we act as if an unprecedented weather event is hitting us out of the blue, as some sort of Act of God that no one foresaw, reporters are making a highly political decision," she notes. In contrast, panelists on Fox's The Five spotted a CNN banner mentioning climate change and accused the network of pushing a liberal agenda. "It's called the weather," said co-host Jesse Watters.