text: (CNN) Local communities almost always pull together on the ground after natural disasters like the torrential flooding that has submerged Houston. 
   
   But the aftermath of Hurricane Harvey is likely to strain America's fraying capacity to coalesce as a national community at a moment of heightened political conflict and division. 
   
   Amid the images of devastation and loss, Americans this weekend repeatedly watched stirring scenes of ordinary people organizing makeshift flotillas to rescue families trapped in the epic flooding. In the rising waters, partisan, racial and class lines all seemed to dissolve. 
   
   Yet, once the immediate danger has passed, the response to the storm will raise larger political questions on at least two major fronts: the cost of recovery and the role of climate change in intensifying the risk of such devastating storms. Each of those issues will challenge America's ability to surmount its differences enough to set a shared national direction. Like Hurricane Katrina and Superstorm Sandy before it, Harvey may demonstrate just how much the man-made gales of political polarization has diminished the nation's capacity to forge common cause against even the fiercest natural disasters. 
   
   A recent history of funding fights 
   
   The first issue that will test the nation's unity is funding the recovery from the storm. Federal figures put the cost of damages from Katrina in 2005 that devastated New Orleans and the Gulf Coast at $160 billion, and from Sandy in the New York and New Jersey area in 2012 at around $70 billion. Early estimates on the potential damages from Harvey vary, but experts are anticipating losses totaling tens of billions of dollars. 
   
   In recent years, Congress has faced unprecedented partisan divides over Washington's role in meeting those costs. In 2005, Vice President Mike Pence, then a Republican congressman from Indiana, led an effort by House conservatives to offset any post-Katrina aid with offsetting budget cuts in other programs, including highway projects and the new Medicare prescription drug benefit. "We simply can't allow a catastrophe of nature to become a catastrophe of debt for our children and grandchildren," Pence said at the time. 
   
   Even more partisan -- and regional -- conflict flared after Sandy slammed into New York and New Jersey just before the 2012 presidential election. That storm precipitated a succession of confrontations between conservative Republicans in both chambers against a coalition of Republicans from the region and Democrats. 
   
   In those debates, Mick Mulvaney, now director of the Office of Management and Budget and then a Republican congressman from South Carolina, echoed Pence during Katrina by proposing legislation to offset Sandy aid with across-the-board reductions in domestic programs. That amendment failed, but over two-thirds of House Republicans voted for it, including an array of prominent Texans still in Congress. That list of supporters included Representatives Kevin Brady (now chair of the House Ways and Means Committee); Jeb Hensarling (now chair of the House Financial Services Committee) and Pete Sessions. Also voting for Mulvaney's legislation was Paul Ryan, now the House Speaker. 
   
   Eventually the vast majority of Republicans in both chambers -- 179 in the House and 36 in the Senate -- voted against the final $50 billion federal aid package for Sandy, arguing that the bill was bloated with extraneous projects. The Republican opponents included both of Texas' senators -- John Cornyn and Ted Cruz -- and a lengthy list of Texas House Republicans, including Brady and Hensarling. 
   
   Demanding offsetting cuts complicates responding to natural disasters both at the tactical and philosophical level. The tactical problem is that it ensures a more partisan and protracted Congressional debate. The philosophical problem may be even more telling. Demanding cuts sets the interests of one geographic area against the national web of communities reliant on the programs facing reductions. In essence, demanding that some communities suffer funding losses in ongoing programs to offset assistance to places facing acute needs undermines the core idea that government exists in part to help share risks that individuals, and even individual communities, cannot reasonably bear alone. 
   
   "Saying, 'we will do this for hurricanes in the Gulf Coast or the East Coast or tornadoes in the Midwest or earthquakes in California,' is a way of saying government as a social institution is there to help society deal with things that at the levels of individuals you can't reasonably be expected to deal with," said Richard Kogan, a senior analyst at the Center on Budget and Policy Priorities a liberal research and advocacy group. 
   
   These earlier skirmishes raise the question of whether Congressional conservatives, including those from Texas, will again insist on offsetting any aid for Houston and the Gulf Coast with spending cuts elsewhere. Such a move would inevitably extend the Congressional debate over aid and provoke an instant partisan split. No floodwaters could sweep away any sense of shared national concern over the disaster faster than a Congressional debate that frames aid to Texas against programs that benefit communities elsewhere. 
   
   Climate change as a concern 
   
   The nation's ability to maintain a common purpose will be tested even more severely when the discussion eventually turns to whether climate change is increasing the risk of catastrophic storms like Harvey. 
   
   Scientists remain leery of attributing any individual storm to climate change. But the dominant scientific consensus is that climate change is increasing the odds that storms will be more powerful and destructive. 
   
   "There is no doubt that climate change increases the severity of disasters such as Hurricane Harvey," Jane Lubchenco, the administrator of the National Oceanic and Atmospheric Administration under former President Obama told me in an email exchange Monday. "Warmer ocean waters are more conducive to more intense hurricanes (heat = energy). Warmer air holds more moisture. Climate change is warming both the ocean and the air. In addition, higher sea levels mean greater storm surge. As we're seeing with Harvey, the combination is devastating: powerful winds, incessant downpours, significant flooding. " 
   
   In another email exchange on Monday, John W. Nielsen-Gammon, the Texas State climatologist and a professor of atmospheric sciences at Texas A&M, was quick to argue that it was premature to directly link Harvey specifically to changes in the climate. "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. 
   
   But Nielsen-Gammon added that the overall trajectory of extreme weather in Texas is unmistakable-and strongly linked to climate change. "Extreme rainfall, however, is getting heavier: The south-central United States has seen an increase in the frequency and intensity of one-day and two-day extreme rainfall events," he wrote. "My own analysis of Texas data shows an increase of about 30% in the likelihood of passing a given threshold [of total rain amount] in a given year, which corresponds to about a 5% increase in the intensity of the strongest rainfall over the past century." 
   
   That shift, he continued, "is a direct consequence of climate change and is expected to continue." Like Lubchenco and other climate scientists, Nielsen-Gammon said the increasing incidence of heavy storms is "driven by rising atmospheric temperatures and rising sea surface temperatures, which affect the capacity of the atmosphere to hold moisture and increases the total amount of water that can rain out when the air is saturated." 
   
   President Donald Trump has dismissed climate change as a "hoax"; the Environmental Protection Agency is in the process of uprooting the major regulatory initiatives Obama undertook to reduce carbon emissions from power plants, cars and trucks. Trump also withdrew the US from the Paris global climate accord. 
   
   In advancing this agenda, Trump has operated with a clear regional tilt, favoring the interests of the states that are most reliant on producing fossil fuels, or consuming them for electricity. That reflects Trump's electoral base: he won 13 of the 16 states that produce the most natural gas, 16 of the 20 that produce the most oil, and 11 of the 15 that mine meaningful amounts of coal. 
   
   Yet by prioritizing the immediate interests of these resource-producing states, Trump has slighted the national interest in controlling the risks associated with a changing climate. The irony is that, as Katrina and Harvey have both demonstrated, some of the states most invested in the fossil fuel economy are also at the greatest risk if climate changes spawns more severe storms. 
   
   "Unfortunately, climate change will most certainly make disasters like Hurricane Harvey more likely: Think of Harvey as a glimpse of the future," Lubchenco, now a distinguished university professor at Oregon State University, wrote me. "The smart move would be to be better prepared (i.e., to expect this to happen more often, not be surprised by it, and prepare accordingly), to reduce carbon emissions faster than we are now (much faster), and to invest in enhanced research and monitoring that will enable continued improvement of forecasting of events like this." ||||| Photo: David J. Phillip/AP 
   
   Now is exactly the time to talk about climate change, and all the other systemic injustices — from racial profiling to economic austerity — that turn disasters like Harvey into human catastrophes. 
   
   Turn on the coverage of the Hurricane Harvey and the Houston flooding and you’ll hear lots of talk about how unprecedented this kind of rainfall is. How no one saw it coming, so no one could adequately prepare. 
   
   What you will hear very little about is why these kind of unprecedented, record-breaking weather events are happening with such regularity that “record-breaking” has become a meteorological cliche. In other words, you won’t hear much, if any, talk about climate change. 
   
   This, we are told, is out of a desire not to “politicize” a still unfolding human tragedy, which is an understandable impulse. 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. It’s a decision to spare feelings and avoid controversy at the expense of telling the truth, however difficult. Because the truth is that these events have long been predicted by climate scientists. Warmer oceans throw up more powerful storms. Higher sea levels mean those storms surge into places they never reached before. Hotter weather leads to extremes of precipitation: long dry periods interrupted by massive snow or rain dumps, rather than the steadier predictable patterns most of us grew up with. 
   
   The records being broken year after year — whether for drought, storm surges, wildfires, or just heat — are happening because the planet is markedly warmer than it has been since record-keeping began. Covering events like Harvey while ignoring those facts, failing to provide a platform to climate scientists who can make them plain, all while never mentioning President Donald Trump’s decision to withdraw from the Paris climate accords, fails in the most basic duty of journalism: to provide important facts and relevant context. It leaves the public with the false impression that these are disasters without root causes, which also means that nothing could have been done to prevent them (and that nothing can be done now to prevent them from getting much worse in the future). 
   
   It’s also worth noting that the Harvey coverage has been highly political since well before the storm made landfall. There has been endless talk about whether Trump was taking the storm seriously enough, endless speculation about whether this hurricane will be his “Katrina moment” and a great deal of (fair) point-scoring about how many Republicans voted against Sandy relief but have their hands out for Texas now. That’s politics being made out of a disaster — it’s just the kind of partisan politics that is fully inside the comfort zone of conventional media, politics that conveniently skirts the reality that placing the interests of fossil fuel companies ahead of the need for decisive pollution control has been a deeply bipartisan affair. 
   
   In an ideal world, we’d all be able to put politics on hold until the immediate emergency has passed. Then, when everyone was safe, we’d have a long, thoughtful, informed public debate about the policy implications of the crisis we had all just witnessed. What should it mean for the kind of infrastructure we build? What should it mean for the kind of energy we rely upon? (A question with jarring implications for the dominant industry in the region being hit hardest: oil and gas). And what does the hyper-vulnerability to the storm of the sick, poor, and elderly tell us about the kind of safety nets we need to weave, given the rocky future we have already locked in? 
   
   People rest while waiting to board a bus headed for San Antonio at an evacuation center in Corpus Christi, Texas, on Friday, Aug. 25, 2017. Photo: Nick Wagner/Austin American Statesman/AP 
   
   With thousands displaced from their homes, we might even discuss the undeniable links between climate disruption and migration — from the Sahel to Mexico — and use the opportunity to debate the need for an immigration policy that starts from the premise that the U.S. shares a great deal of responsibility for the key forces driving millions from their homes. 
   
   But we don’t live in a world that allows for that kind of serious, measured debate. We live in a world in which the governing powers have shown themselves all too willing to exploit the diversion of a large-scale crisis, and the very fact that so many are focused on life-and-death emergencies, to ram through their most regressive policies, policies that push us further along a road that is rightly understood as a form of “climate apartheid.” We saw it after Hurricane Katrina, when Republicans wasted no time pushing for a fully privatized school system, weakening labor and tax law, increasing oil and gas drilling and refining, and flinging the door open to mercenary companies like Blackwater. Mike Pence was a key architect of that highly cynical project — and we should expect nothing less in Harvey’s wake, now that he and Trump are at the wheel. 
   
   We are already seeing Trump using the cover of Hurricane Harvey to push through the hugely controversial pardoning of Joe Arpaio, as well as the further militarization of U.S. police forces. These are particularly ominous moves in the context of news that immigration checkpoints are continuing to operate wherever highways are not flooded (a serious disincentive for migrants to evacuate), as well as in the context of municipal officials tough-talking about maximum penalties for any “looters” (it’s well worth remembering that after Katrina, several African-American residents of New Orleans were shot by police amid this kind of rhetoric.) 
   
   In short, the right will waste no time exploiting Harvey, and any other disaster like it, to peddle ruinous false solutions, such as militarized police, more oil and gas infrastructure, and privatized services. Which means there is a moral imperative for informed, caring people to name the real root causes behind this crisis — connecting the dots between climate pollution, systemic racism, underfunding of social services, and overfunding of police. We also need to seize the moment to lay out intersectional solutions, ones that dramatically lower emissions while battling all forms of inequality and injustice (something we have tried to lay out at The Leap and which groups, such as the Climate Justice Alliance, have been advancing for a long time.) 
   
   And it has to happen right now – precisely when the enormous human and economic costs of inaction are on full public display. If we fail, if we hesitate out of some misguided idea of what is and is not appropriate during a crisis, it leaves the door wide open for ruthless actors to exploit this disaster for predictable and nefarious ends. 
   
   It’s also a hard truth that the window for having these debates is vanishingly small. We won’t be having any kind of public policy debate after this emergency subsides; the media will be back to obsessively covering Trump’s tweets and other palace intrigues. So while it may feel unseemly to be talking about root causes while people are still trapped in their homes, this is realistically the only time there is any sustained media interest whatsoever in talking about climate change. It’s worth recalling that Trump’s decision to withdraw from the Paris climate accord — an event that will reverberate globally for decades to come — received roughly two days of decent coverage. Then it was back to Russia round-the-clock. 
   
   A little more than a year ago, Fort McMurray, the town at the heart of the Alberta boom in tar sands oil, nearly burned to the ground. For a time, the world was transfixed by the images of vehicles lined up on a single highway, with flames closing in on either side. At the time, we were told that it was insensitive and victim-blaming to talk about how climate change was exacerbating wildfires like this one. Most taboo was making any connection between our warming world and the industry that powers Fort McMurray and employed the majority of the evacuees, which is a particularly high-carbon form of oil. The time wasn’t right; it was a moment for sympathy, aid, and no hard questions. 
   
   But of course by the time it was deemed appropriate to raise those issues, the media spotlight had long since moved on. And today, as Alberta pushes for at least three new oil pipelines to accommodate its plans to greatly increase tar sands production, that horrific fire and the lessons it could have carried almost never come up. 
   
   There is a lesson in that for Houston. The window for providing meaningful context and drawing important conclusions is short. We can’t afford to blow it. 
   
   Talking honestly about what is fueling this era of serial disasters — even while they’re playing out in real time — isn’t disrespectful to the people on the front lines. In fact, it is the only way to truly honor their losses, and our last hope for preventing a future littered with countless more victims. ||||| A series of persistent, extreme summer weather events in recent years including the 2003 European Heat Wave, the 2010 Pakistan flood/Russian heatwave, 2011 Texas drought and the unprecedented, ongoing drought in California, has led to a continuing discussion in the scientific literature regarding the relationship between anthropogenic climate change and the spate of recent weather extremes1,2,3,4,5,6,7,8. 
   
   Some of the increase in extreme events can be explained by relatively straightforward thermodynamics, wherein modest shifts in mean temperature lead to increases in the frequency of heatwaves9,10,11,12 or wherein rising temperatures favor more intense precipitation events via moist thermodynamics13,14,15. However, a growing number of studies suggests that these mechanisms alone are not sufficiently explanatory, and more complex mechanisms may be involved as well in some (or many) of the recent strong or even unprecedented extremes16,17,18,19. Explanations include changes in soil-moisture17,18, changing tropical Pacific sea surface temperature20,21, and the potential impact of rapid Arctic warming19,22,23,24,25. 
   
   Coumou et al.19 showed that the Northern Hemisphere summer jet and associated storm activity have weakened since 1979 and hypothesized that this could lead to more persistent, and therefore more extreme, summer weather. Decreases in summer cyclone activity also lead to a decrease in cloud cover, giving rise to higher maximum temperatures24. This weakening in storm activity is seen in future climate model projections as well, linked to rapid warming in the Arctic, but the observed decline is faster than predicted19,26. 
   
   In earlier work, Hoskins and Karoly27 and Hoskins and Ambrizzi28 demonstrated that Rossby waves within a certain wavenumber range can become effectively trapped in a latitudinal waveguide depending on the structure of the mid-latitude westerlies. Petoukhov et al.29 showed that if these waves have similar length-scales to those imposed by orographic and thermal forcing, a pronounced amplification of waves can occur due to resonance1. The shape of the North-South profile of the zonal-mean westerlies influences the occurrence of this phenomenon of quasi-resonant amplification (QRA)1,2,3,4. This profile can change due to changes in the poleward temperature gradient and thus, to the Arctic amplification of greenhouse warming through the thermal wind equation. Tropical expansion can also affect the latitudinal position of the sharpest temperature gradients and latitudinal changes in the land-ocean temperature contrast might play a role as well. 
   
   While the underlying mechanisms have been explored in depth elsewhere1,2,3,4, the essence of the argument involves the relationship between changing zonal mean temperatures and the strength and position of maxima in the mid-latitude westerly jet. The main condition for resonance is the formation of a zonally-directed waveguide for a particular zonal wavenumber k, which depends only on the wavenumber and the shape of the zonal-mean zonal wind (U) profile. Such a waveguide is present when a mid-latitude region of positive squared meridional wavenumber l2 is bounded by latitudes both north and south where l2 vanishes, inhibiting the dispersion of wave energy and trapping excited planetary waves in the upper troposphere (300–500 mb). This can occur for zonal wavenumbers k = 6–81,2, with the waveguide found at the equatorward flank of the subtropical jet at latitudes around 30–45°N. 
   
   Such conditions are typically associated with a profile for U characterized by two maxima in the Northern Hemisphere, i.e. a double jet latitudinal structure. In contrast to a single jet, a double jet regime associated with a profile for U is characterized by a confined sub-tropical jet with sharp edges wherein wind speeds change rapidly with latitude3. Such sharp sub-tropical jets are highly effective waveguides30,31, a central requirement for QRA. Especially long-duration resonance events (as e.g. seen during the European and Russian heat waves in 2003 and 2010) have such double jet structures which in turn, through the thermal wind relationships, are characterized by a particular pattern of latitudinal variation in zonal-mean surface and lower tropospheric temperatures3. Recent work has reported a clustering of resonance events since 2000 during the satellite reanalysis era (1979-present) that coincides with rapid warming of Arctic surface temperatures, which is suggestive of a possible climate change connection4. 
   
   Here, we build on recent work by developing an observational temperature-based fingerprint for QRA conditions. 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. Our study focuses on hemispheric-scale trends as it has been shown1,2 that many recently observed QRA events were hemispheric in nature. A worthwhile extension of the study might focus separately on different (e.g. Atlantic vs. Pacific) sectors of the Northern Hemisphere. 
   
   Our approach is conceptually similar32,33 to statistical downscaling of climate model simulations: We utilize large-scale features of the climate model simulations considered reliable (in this case, meridional temperature gradients) and then exploit a robust empirical relationship that exists between that feature and the response of interest (planetary wave dynamics related to QRA). It is well-documented that climate models reasonably well capture changes in global patterns of surface temperature, which are primarily thermodynamically controlled. In contrast, there is much less confidence in circulation aspects of climate change, which are primarily controlled by dynamics34,35,36. We assume here that even models that don’t correctly simulate certain details of planetary wave dynamics responses37— an issue we will examine later– are still likely to get the QRA fingerprint right, allowing us to draw reliable real-world conclusions about how climate change may impact the phenomenon of QRA. 
   
   Meridional gradients in lower tropospheric temperatures, as discussed above, imply changes in mid and upper tropospheric zonal wind (U) through the thermal wind relationship. Advantages in using the former, rather than latter, as a measure of QRA-favorable conditions are that (a) long-term historical observations of surface temperature are available back through the late 19th century (this is not the case with upper level atmospheric variables) and (b) there is a fairly straightforward and robust impact of anthropogenic climate change on changes in the structure of lower tropospheric temperatures (e.g. via the mechanism of Arctic amplification and/or the enhanced land-ocean temperature contrast). 
   
   Using ERA interim reanalysis data and the QRA detection scheme presented in Kornhuber3 (see Methods for details) we produced a composite of boreal summer (JJA) zonal mean near-surface (1000 mb) temperature profiles during QRA-favorable time intervals (Fig. 1a). Differencing the QRA-favorable and climatological mean profiles, we define an anomalous zonal mean temperature profile associated with QRA conditions (Fig. 1b). We restrict the profile to the mid-latitude (25–75N) region of interest and center the profile on zero, yielding a “fingerprint” (Fig. 1c) in the zonal mean temperature field associated with QRA-favorable conditions. The fingerprint exhibits negative values in the subtropics, increases to near-neutral values at 40N, a decline toward more negative values through 50N, and pronounced positive values again at higher sub-polar latitudes. While Arctic-amplified warming projects onto this latitudinal anomaly pattern, the fingerprint has considerably more latitudinal structure (including the contribution from an enhanced land/ocean contrast along the Arctic Ocean shore) than is characterized simply by polar amplification alone. 
   
   Figure 1: Boreal Summer (JJA) Zonal Mean Temperature Profiles. Shown are (a) JJA 1000 mb temperatures from ERA reanalysis data (1979–2015) for both climatological mean and QRA-favorable conditions (at 2.5° latitudinal resolution), (b) The difference between the two i.e. the anomalous zonal mean temperature profile associated with QRA-favorable conditions, (c) The QRA fingerprint defined as the former quantity, confined to the extatropical region 25–75N, centered on zero, and interpolated onto 5° latitudinal grid commensurate with model simultions, and (d) the associated meridional temperature gradient. Full size image 
   
   The anomalous meridional temperature gradient associated with the fingerprint (Fig. 1d) is characterized by a large positive peak in the mid-latitude zone of 50–65N, which, via thermal wind, implies a more-pronounced minimum in the zonal mean zonal wind and thus promotes the formation of a double jet. More poleward (i.e. beyond 65N) the reduction in the temperature gradient (and thus a stronger negative gradient) implies stronger westerlies in sub-polar regions. These are precisely the conditions that Pethoukov et al.1 identify as QRA-favorable. 
   
   Having defined a fingerprint for QRA-favorable conditions, we next examined mid-latitude (25–75N) zonal mean temperatures from the historical simulations of the Coupled Model Intercomparison Project Phase 5 (CMIP5) experiments16 (see Supp Info for details) which comprise N = 164 distinct simulations (Table 1) in the anthropogenic+natural “all-forcing” case and N = 40 simulations for the “anthropogenic-only” forcing experiments (see Supp. Info.). 
   
   Table 1: Post-1970 Trend in QRA fingerprint series. Full size table 
   
   The multimodel ensemble zonal mean surface temperatures for the relevant (JJA) season (Fig. 2) show the expected polar amplification of warming, with higher-latitude regions tending to warm more than lower-latitude regions (Fig. 2a). This pattern is expected from the warm-season ice-albedo feedback associated with anthropogenic greenhouse warming, and it is considerably more pronounced in the anthropogenic-only forcing experiments (Fig. 2b) where the complicating effects of volcanic forcing are absent. The full distribution of trends among the multimodel ensemble is shown for the mean extratropical (25–75N average) temperature series (Fig. 2c,d). The series show considerable variability, emphasizing the potentially confounding role of internal variability in identifying clear trends in the zonal mean profiles in individual historical realizations (including the actual observed realization). 
   
   Figure 2: Zonal mean temperatures for 5 degree bands from 25–75N in the CMIP5 historical simulations. Shown are the multimodel means for the (a) all-forcing and (b) anthropogenic-only simulations. Rainbow scale is used to denote increasing latitude from 25N (violet) to 75N (red). The extratropical 25–75N mean series is shown for comparison (black). Shown also for both the (c) all-forcing and (d) anthropogenic-only simulations is the extratropical mean series for each member of the multimodel ensemble (colored curves) along with the multimodel mean (black) series. Full size image 
   
   The next step in the analysis involves projecting the QRA fingerprint (i.e. Fig. 1c) onto the CMIP5 zonal mean temperature profiles (Fig. 3) using linear regression (see Methods). Examining both the full CMIP5 all-forcing simulations, (Fig. 3a) and anthropogenic-only simulations (Fig. 3b), we observe a large amount of variability among the individual realizations of the multimodel ensemble, again emphasizing the significant role of internal variability. A positive long-term trend is nonetheless evident in most realizations, and is clearly evident in the ensemble means (Fig. 3a,b). This trend is formally independent of global warming, since it reflects a change over time in a relative latitudinal pattern of temperature variation rather than any change in mean hemispheric or global warmth. Comparing the ensemble mean fingerprint series to the ensemble mean extratropical (25–75N) mean temperature for the all-forcing simulations (Fig. 3c) nonetheless reveals a similar long-term increase consistent with polar amplification from anthropogenic warming. 
   
   Figure 3: QRA Fingerprint Series. Shown for both the (a) all-forcing and (b) anthropogenic-only simulations is the QRA series for each member of the multimodel ensemble (colored curves) along with the multimodel mean (black) series. The corresponding multimodel mean QRA series are shown along with the exatropical mean temperatures series for the (c) all forcing and (d) anthropogenic-only simulations, along with the linear trend over 1970–2005 (red line). Full size image 
   
   The post-1970 trend of 0.006 units/year in the multimodel mean fingerprint series (Fig. 3c) is highly significant (p < 0.0001). Of greater interest, however, is the behavior of individual ensemble members given that the historical changes observed reflect a single realization of internal natural variability. Examining the distribution of trends from the full multimodel ensemble, the median trend lies close to the mean trend, and 68% of the multimodel realizations exhibit a positive trend, which is highly unlikely to have arisen from chance (p < 0.0001 based on the null hypothesis of red noise; see Table 1 and Methods). Nonetheless, nearly one third of the realizations thereby do not display a positive trend, suggesting that, if the CMIP5 historical simulations are an accurate representation of the distribution of possible historical scenarios, an anthropogenic increase in QRA-favorable conditions is only likely (and not very likely) in the IPCC lexicon, to be observed in any specific realization of historical temperature variability, including the unique realization that we have actually observed. 
   
   For the anthropogenic-only case (Fig. 3d), the post-1970 trend is greater (0.01 units/year), and an increase is found in 88% of the multimodel ensemble members (also significant at the p < 0.0001 level; Table 1), nearly breaching the IPCC “very likely” threshold (Table 1). The more dominant trend in this case appears to be a consequence of the absence of volcanic forcing, particularly the absence of the prominent 1982 El Chichon and 1991 Pinatubo eruptions. It is reasonable to conclude that these volcanic events have likely acted to obscure an anthropogenic signal in the QRA fingerprint. 
   
   It is noteworthy that the anthropogenic-only ensemble mean QRA fingerprint series exhibits a more monotonic increase through the 1950s and 1960s than the corresponding extratropical mean temperature series (Fig. 3d), the latter of which shows a more pronounced downturn during the 1950–1970 interval of enhanced negative anthropogenic aerosol forcing. This difference in the temporal evolution of the two series ostensibly arises from the fact that anthropogenic aerosol forcing exhibits a regionally heterogeneous spatial pattern of temperature influence, and projects very weakly onto the meridional structure of QRA fingerprint. Thus, it is the more temporally monotonic anthropogenic greenhouse gas forcing that projects primarily onto the QRA fingerprint, and the fingerprint series continues to increase due to greenhouse warming even during a period of pronounced anthropogenic aerosol forcing. 
   
   We next project the QRA fingerprint series onto the zonal mean 300 mb zonal velocity (U) field for each of the CMIP5 simulations. These projections (Fig. 4) show the expected double jet structure, with a substantial negative zonal wind anomaly in the 50–65N mid-latitude zone and a pronounced positive zonal wind anomaly at higher subpolar latitudes. These features are evident in nearly every simulation for both all-forcing and anthropogenic-only experiments. The precise location and magnitude of the mid-latitude negative peak varies among simulations, and a handful of simulations don’t exhibit the feature at all, consistent with previous work34 finding that some models do exhibit biases in upper level winds and especially the bimodality of the jet stream. Such caveats notwithstanding, our results suggest the QRA fingerprint detected in the CMIP5 simulations is indeed associated with a thermal wind-driven anomalous double peak zonal jet structure, consistent with the planetary wave dynamics associated with QRA. 
   
   Figure 4: Projection of QRA Fingerprint Series onto 300 mb Zonal Wind (U) in individual CMIP5 historical Simulations (colored curves) and averaged over ensemble (black). Shown are results for (a) all-forcing and (b) anthropogenic-only forcing experiments. Full size image 
   
   Finally, we apply the QRA fingerprint approach to observational surface temperature data available through 2015 (Fig. 5). As with the CMIP5 historical simulations, we see the expected pattern of polar amplification of warming, regardless of which of three different surface temperature products (GISTEMP, HadCRUT4, and Cowtan & Way) is used (Fig. 5a,b,c). When we project the QRA fingerprint onto the zonal temperature profiles (Fig. 5d,e,f), we observe a significant trend in the QRA fingerprint during the post-1970 interval during which the CMIP5 simulations display a prominent trend. The trend is significant at the p = 0.05 level for all three instrumental temperature datasets (Table 1). While the trends in the observational fingerprint series are modestly greater (0.016–0.022 units/year) than those for the CMIP5 multimodel mean series, both are in agreement taking into account respective one sigma ranges (Table 1). The QRA fingerprint series for one of the surface temperature datasets (GISTEMP) exhibits positive values during the early decades of the 20th century that rival recent values. Examining Fig. 5a–c, it is apparent that high-latitude warmth substantially exceeds low-latitude warmth during these decades for GISTEMP, though this is not seen in the other datasets. We suspect that the GISTEMP approach of spatially-interpolating across the Arctic based on what data are available, becomes increasingly susceptible to large sampling uncertainties as data in this region become exceptionally sparse in earlier decades. That could lead to spurious amplification of high-latitude meridional temperature gradients that project substantially onto the QRA fingerprint. 
   
   Figure 5: Observational Series. Shown are the zonal mean temperatures for 5 degree bands from 25–75N (colors—same conventions as in Fig. 2a) and the extratropical 2–75N mean series (black) for (a) GISTEMP, (b) HadCRUT4, and (c) Cowtan & Way instrumental temperature series. Shown are the corresponding QRA fingerprint series (d–f) along with linear trend from 1970–2015 (black dashed). Full size image 
   
   If we restrict the time interval under examination to the period of overlap between the observations and CMIP5 historical simulations that terminates earlier in 2005, we find that the trend in the fingerprint series is statistically significant at the p = 0.05 level for only one (GISTEMP) of the three surface temperature datasets (Table 1). Combined with inferences drawn above from the analysis of CMIP5 historical simulations, these observations suggest that the anthropogenic signal in the QRA fingerprint has emerged from the background noise of natural variability only within the past decade or so. 
   
   In summary, our analysis of both historical model simulations and observational surface temperature data, strongly suggests that anthropogenic warming is impacting the zonal mean temperature profile in a manner conducive to wave resonance and a consequent increase in persistent weather extremes in the boreal summer. Combined with other additional proposed mechanisms for climate change impacts on extreme weather, this adds to the weight of evidence for a human influence on the occurrence of devastating events such as the 2003 European heat wave, the 2010 Pakistan flood and Russian heat wave, the 2011 Texas heat wave and recent floods in Europe. ||||| What can we say about the role of climate change in the unprecedented disaster that is unfolding in Houston with Hurricane Harvey? There are certain climate change-related factors that we can, with great confidence, say worsened the flooding. 
   
   What we know so far about tropical storm Harvey Read more 
   
   Sea level rise attributable to climate change – some of which is due to coastal subsidence caused by human disturbance such as oil drilling – is more than half a foot (15cm) over the past few decades (see here for a decent discussion). That means the storm surge was half a foot higher than it would have been just decades ago, meaning far more flooding and destruction. 
   
   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). 
   
   
   
   There is a simple thermodynamic relationship known as the Clausius-Clapeyron equation that tells us there is a roughly 3% increase in average atmospheric moisture content for each 0.5C of warming. Sea surface temperatures in the area where Harvey intensified were 0.5-1C warmer than current-day average temperatures, which translates to 1-1.5C warmer than “average” temperatures a few decades ago. That means 3-5% more moisture in the atmosphere. 
   
   That large amount of moisture creates the potential for much greater rainfalls and greater flooding. The combination of coastal flooding and heavy rainfall is responsible for the devastating flooding that Houston is experiencing. 
   
   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. Human-caused warming is penetrating down into the ocean. It’s creating deeper layers of warm water in the Gulf and elsewhere. 
   
   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. (As an example of how this works, we have shown that climate change has led to a dramatic increase in storm surge risk in New York City, making devastating events like Hurricane Sandy more likely.) 
   
   Finally, the more tenuous but potentially relevant climate factors: part of what has made Harvey such a devastating storm is the way it has stalled near the coast. It continues to pummel Houston and surrounding regions with a seemingly endless deluge, which will likely top out at nearly 4ft (1.22m) of rainfall over a days-long period before it is done. 
   
   The stalling is due to very weak prevailing winds, which are failing to steer the storm off to sea, allowing it to spin around and wobble back and forth. This pattern, in turn, is associated with a greatly expanded subtropical high pressure system over much of the US at the moment, with the jet stream pushed well to the north. This pattern of subtropical expansion is predicted in model simulations of human-caused climate change. 
   
   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. We recently published a paper in the academic journal Scientific Reports on this phenomenon. 
   
   In conclusion, while we cannot say climate change “caused” Hurricane Harvey (that is an ill-posed question), we can say is that it exacerbated several characteristics of the storm in a way that greatly increased the risk of damage and loss of life. Climate change worsened the impact of Hurricane Harvey. ||||| The recent Category 4 hurricanes making landfall in the US have revived the perennial discussion about the relationship between extreme storms and climate change. Despite what you might think from the dueling headlines, it’s actually a fairly complicated issue — complicated not just because of the physics, but because of the politics. 
   
   Here are nine things you can say about Harvey, Irma, and climate change. 
   
   1) These hurricanes are not centrally about climate change 
   
   Talking about climate change during a disaster always runs the risk of insensitivity. The story that most matters about Harvey and Irma right now are the effects they are having on lives and land in Texas and Florida, and the efforts underway to prevent more suffering. 
   
   More broadly, climate is never going to be central to stories like these. There have always been hurricanes and floods in Texas and Floriday. The things making those states’ coastal developments vulnerable to severe weather — heedless development, sandy subsoil, insufficient drainage — would be problems even in the absence of climate change. 
   
   Climate is not central, but by the same token it is grossly irresponsible to leave climate out of the story, for the simple reason that climate change is, as the US military puts it, a threat multiplier. The storms, the challenges of emergency response, the consequences of poor adaptation — they all predate climate change. But climate change will steadily make them worse. 
   
   2) “Did climate change cause this hurricane?” is a malformed question 
   
   Climate change does not cause things, because climate change is not a causal agent. “Climate change” is a descriptive term — it describes the fact that the climate is changing. What’s causing the changes is an increase in heat energy trapped in the atmosphere, due to greenhouse gases. 
   
   But saying that heat energy caused a hurricane is also somewhat problematic. Let’s explain by way of an analogy. 
   
   Say I turned up Earth’s gravity by 1 percent. More people around the world would trip and fall. Does it make sense to say, of a particular person tripping and falling, that the increase in gravity (“gravity change”) caused it to happen? No. Does it make sense to say that gravity cause it to happen? No. 
   
   For any particular instance of tripping and falling, there will be proximate causes — a slippery patch on the sidewalk, a moment’s inattention, whatever. Gravity is a background condition of anyone tripping, but no one would say gravity caused them to trip. If it’s true, it’s trivially true. 
   
   What we might say is that the increase in gravity raised the probability of tripping and falling, or raised the average severity of tripping and falling. Those are measurable facts that can be entirely true without increased gravity causing any particular fall. 
   
   Increased gravity is a causal condition in every fall, but it is not the primary causal agent in any one fall. Similarly, increased heat energy is a causal condition in every storm (not just the bad ones) — every storm forms and travels in the same global climate — but it is not the primary causal agent in any storm. 
   
   There is, to be sure, increasing sophistication in the science of attribution — that is, in distinguishing the climate signal from the “normal weather” noise. 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. What caused the storm is warm air, atmospheric moisture, and weird high/low pressure systems, just like all storms. Climate change just gave it its winning personality. 
   
   3) Yes, climate change made these hurricanes worse 
   
   Thanks to the recent profusion of great climate journalists and communicators, this story has been well told already. Probably the best source is this Facebook post from climate scientist Michael Mann, but also see Chris Mooney, Robinson Meyer, John Schwartz, Emily Atkin, and Susan Mathews. 
   
   It’s a complex story, especially in its particulars, but in broad strokes, climate change made Harvey and Irma worse in two ways (Harvey possibly in three). 
   
   First, it raised sea levels more than half a foot in recent decades. Higher seas mean worse storm surges. 
   
   Second, it raised the temperature of the water in the region, which means more evaporation and more water in the air. Mann: 
   
   Sea surface temperatures in the area where Harvey intensified were 0.5-1C warmer than current-day average temperatures, which translates to 1-1.5C warmer than the 'average' temperatures a few decades ago. That means 3-5% more moisture in the atmosphere. 
   
   More moisture in the atmosphere means more rain. 
   
   Finally (and most speculatively), in the case of Harvey, one of the most damaging aspects is how it hung around in one place, thanks to weak prevailing winds. Mann recently published a paper suggesting that such near-stationary summer weather patterns are made more common by climate change. 
   
   All these factors contributed to the size and severity of the storms. Exactly how much they contributed will have to await peer-reviewed attribution science, but logic, experience, and measurements all make clear that the damage was worse than it would have been absent recent changes in the climate. Harvey “is a bit more intense, bigger and longer lasting than it otherwise would be,” climate researcher Kevin Trenberth told Mooney. 
   
   4) We don’t know if climate change is making hurricanes more likely 
   
   The scientific battles over hurricanes and climate change go way, way back, and run hot. They are also, for a nonpartisan outsider, quite technical and boring. 
   
   So I’ll skip to the end: The evidence is mixed, and the jury is still out. We’re still not sure if climate change increases hurricane frequency. 
   
   5) We know climate change is making severe downpours more likely 
   
   Severe downpours in the Houston area have become 167 percent more frequent in the past decade, which is commensurate with one of the best-understood and most confident predictions of climate science: Climate change is going to bring lots more heavy rains (and thus flooding). See Andrea Thompson’s great rundown at Climate Central on this. 
   
   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. 
   
   6) Climate change is nowhere near the biggest determinant of Harvey’s damages, but it’s in there 
   
   Another hotly contested area of climate research has to do with climate change’s role in rising natural disaster damages. 
   
   Financial damages from natural disasters are definitely rising worldwide, but that’s not just being driven by climate change. Most of it has to do with increasing populations building unsafe buildings on land vulnerable to disasters. 
   
   These big demographic and economic trends are putting more people and property in harm’s way, so naturally there’s more harm, financial and otherwise. (Andy Revkin is good on this connection; see here and here.) To truly pick out the climate signal from that noise, you’d have to run a model with all the same trends and no climate change. For understandable reasons, that is extremely difficult. 
   
   Some researchers believe there is no climate signal discernible at all yet. (Spare a thought for Roger Pielke Jr.’s long, lonely crusade on this question.) Others disagree, and the battle wages on, but that battle has always struck me as less important than its participants take it to be. 
   
   Humanity is growing more financially vulnerable to natural disasters for lots of reasons, so there are, correspondingly, lots of ways to reduce vulnerability. Most of them are far more direct than climate mitigation — changing the location and nature of settlements, mainly, along with reforms in building codes, insurance, and government emergency planning. If your main goal is to reduce vulnerability as much and as quickly as possible, reducing greenhouse gases would be a silly way to do it. 
   
   But again, at the same time, it’s grossly irresponsible to leave climate out of the picture. We know it’s going to get worse. We know it’s going to make every other challenge more challenging, every damage more damaging, every expense more expensive. 
   
   Whether the climate signal is discernible now, it surely will be by the end of the century. By then, our opportunity to prevent some of it will be long past. 
   
   7) Adapting to climate change is very, very different than mitigating it 
   
   Obama presidential adviser John Holdren is credited with what has become a familiar way of formulating the challenge of climate change: We will end up with some mix of prevention, adaptation, and suffering; it is for us to determine the ratio. 
   
   This is a powerful way to approach the subject. It emphasizes the consequences of inaction. We prevent what we can, we adjust to what we can’t prevent, and we suffer what we can’t adjust to. The status quo is not an option. 
   
   But in another way, it is misleading, making it seem as though mitigation (that is, preventing greenhouse gas emissions) and adaptation (adjusting to a changed climate) are two sides of the same coin, fungible even. A dollar spent on one is as good as a dollar spent on the other. 
   
   Indeed, many conservatives — at least among those who accept the reality of climate change — argue that humans have adapted to all sorts of climates and it’s better to just adapt again than to upend the global energy system. And it’s not just conservatives. Economists generally have great faith in the power of human beings to adapt. 
   
   But adaptation is not fungible with mitigation. They are different beasts entirely, not only practically but on a profound moral level. I wrote a big post about this once, but to make a long story short: Mitigation has local costs and egalitarian global benefits; adaptation has local costs and inequitable local benefits. 
   
   Because every ton of greenhouse gases mixes into the atmosphere and affects the entire global climate, preventing the emission of a ton of GHGs offers a global benefit. Climate mitigation generates benefits that are unavoidably egalitarian (distributed across the globe, to everyone who lives in the atmosphere) and progressive (the poor are most vulnerable, so they benefit first and most from harm prevention). 
   
   There’s plenty of self-interest in climate mitigation, but there’s also an ineradicable element of altruism. 
   
   Adaptation is different. The benefits of adaptation — higher sea walls, better drainage systems, more effective emergency response — are unavoidably both local (only those who happen to live behind the sea wall benefit) and regressive (wealthy people and places will adapt first, best, and most). 
   
   So adaptation is not some easier alternative route to the same goal. It is every bit as politically difficult as mitigation (mitigation has multiple co-benefits, e.g., cleaner air, while adaptation rarely does), much, much more expensive, and less morally admirable. (Joe Romm had a magnificent post on this back in 2012.) 
   
   8) Without mitigation, adaptation is a cruel joke, and these hurricanes show why 
   
   Houston’s situation is unique in many ways, well captured in this tweetstorm: 
   
   A Houston floodsplainer: 
   
   (caveat, I'm not a pro, just someone interested in how my city works. If a real pro finds an error, please LMK) — Matt Corbett (@CorbettMatt) August 28, 2017 
   
   There are several reasons why flooding is so bad in Houston (among them ever-growing amounts of impermeable surfacing and a not-very-absorptive soil substrate). And there are several reasons why evacuating people beforehand was a complicated and fraught decision. 
   
   The debate of whether Houston should have issued a mandatory evacuation is more complicated than many probably realize 1/x — Aman Batheja (@amanbatheja) August 27, 2017 
   
   Similarly, every island and city in Irma’s path will have its own idiosyncratic challenges in rebuilding and becoming more resilient. Lessons about how to prepare and respond will inevitably have a local flavor. 
   
   Still, while there are undoubtedly ways Houston could do better (see Natasha Geiling for much more on that), take a step back and ponder: What is good or adequate adaptation to 40 to 50 inches of rain falling on your head in 72 hours? 
   
   What is a good way to adapt to periodic 5 to 10 feet storm surges? 
   
   5:16 p: Eye of Hurricane Irma is over Naples. Wind gusts 60-70 mph continue across the Keys, with storm surge of 5-10 feet still possible pic.twitter.com/QS8Vhg0uFO — NWS Key West (@NWSKeyWest) September 10, 2017 
   
   There’s just no way to prepare for that and no painless way to respond to it. There’s no adapting. There’s destruction and suffering, followed by slow rebuilding. 
   
   In the absence of some pretty radical mitigation, such massive rainfall events will just get more frequent and worse on the Gulf Coast, every year, year on year, more or less forever. The worst hurricanes will just get worse. What would adaptation in those circumstances even look like? What kind of long-lasting infrastructure do you build when the climate is changing that fast? How many cycles of destruction and rebuilding can a city cope with? How many simultaneous cities in crisis can a country handle? 
   
   The fact is, we already know that sea level rise and frequent flooding are going to make lots of coastal cities uninhabitable over coming decades (though exactly how many, and when, remains maddeningly uncertain). Think, for a moment, about Miami slowly becoming unlivable. “Adaptation” will mean figuring out who has to leave, who has to pay for resettlement, and who bears the cost of the abandoned city’s infrastructure as it rots, crumbles, and pollutes. 
   
   That’s a lot of fateful decisions to be made about people’s lives, homes, land, families, and legacies. It is politically explosive stuff. Raise your hand if you think it will be done in an egalitarian or equitable way. 
   
   (Recall, in the wake of Katrina, House Speaker Dennis Hastert saying that New Orleans might as well just be bulldozed. Recall that 20 members of the Texas congressional delegation, who are now desperately requesting help, voted against federal aid to New York City in the wake of Hurricane Sandy. If adaptation decisions are made so callously within the US, imagine how they’ll be made internationally.) 
   
   Rebuilding after Harvey and Irma will be a test case — adaptation in action. Let’s watch to see if it’s done in a wise and equitable way. My hopes are not high. 
   
   Without mitigation, if we just let climate change get worse and worse, adaptation is only going to look uglier and uglier, more and more of a euphemism for abandoning poor people to their suffering. 
   
   9) Climate change is part of every story now, including Harvey and Irma 
   
   Everything human beings do, we do in a climate (except hang out on the space station, I suppose). 
   
   Our climate has been in a rough temperature equilibrium for about 10,000 years, while we developed agriculture and advanced civilization and Netflix. 
   
   Now our climate is about to rocket out of that equilibrium, in what is, geologically speaking, the blink of an eye. We’re not sure exactly what’s going to happen, but we have a decent idea, and we know it’s going to be weird. With more heat energy in the system, everything’s going to get crazier — more heat waves, more giant rainstorms, more droughts, more floods. 
   
   That means climate change is part of every story now. The climate we live in shapes agriculture, it shapes cities and economies and trade, it shapes culture and learning, it shapes human conflict. It is a background condition of all these stories, and its changes are reflected in them. 
   
   So we’ve got to get past this “did climate change cause it?” argument. A story like Harvey is primarily a set of local narratives, about the lives immediately affected. But it is also part of a larger narrative, one developing over decades and centuries, with potentially existential stakes. 
   
   We’ve got to find a way to weave those narratives together while respecting and doing justice to both. ||||| By the time the rain stops, Harvey will have dumped about 1 million gallons of water for every man, woman and child in southeastern Texas — a soggy, record-breaking glimpse of the wet and wild future that global warming could bring, scientists say. 
   
   While scientists are quick to say that climate change didn't cause Harvey and that they haven't determined yet whether the storm was made worse by global warming, they do note that warmer air and water mean wetter and possibly more intense hurricanes in the future. 
   
   "This is the kind of thing we are going to get more of," said Princeton University climate scientist Michael Oppenheimer. "This storm should serve as warning." 
   
   There's a scientifically accepted method for determining if some wild weather event has the fingerprints of man-made climate change, and it involves intricate calculations. Those could take weeks or months to complete, and then even longer to pass peer review. 
   
   In general, though, climate scientists agree that future storms will dump much more rain than the same size storms did in the past. 
   
   That's because warmer air holds more water. With every degree Fahrenheit, the atmosphere can hold and then dump an additional 4 percent of water (7 percent for every degree Celsius), several scientists say. 
   
   Global warming also means warmer seas, and warm water is what fuels hurricanes. 
   
   When Harvey moved toward Texas, water in the Gulf of Mexico was nearly 2 degrees (1 degree Celsius) warmer than normal, said Weather Underground meteorology director Jeff Masters. Hurricanes need at least 79 degrees F (26 C) as fuel, and water at least that warm ran more than 300 feet (100 meters) deep in the Gulf, according to University of Miami hurricane researcher Brian McNoldy. 
   
   Several studies show that the top 1 percent of the strongest downpours are already happening much more frequently. Also, calculations done Monday by MIT meteorology professor Kerry Emanuel show that the drenching received by Rockport, Texas, used to be maybe a once-in-1,800-years event for that city, but with warmer air holding more water and changes in storm steering currents since 2010, it is now a once-every-300-years event. 
   
   There's a lot of debate among climate scientists over what role, if any, global warming may have played in causing Harvey to stall over Texas, which was a huge factor in the catastrophic flooding. If the hurricane had moved on like a normal storm, it wouldn't have dumped as much rain in any one spot. 
   
   Harvey stalled because it is sandwiched between two high-pressure fronts that push it in opposite directions, and those fronts are stuck. 
   
   Oppenheimer and some others theorize that there's a connection between melting sea ice in the Arctic and changes in the jet stream and the weather patterns that make these "blocking fronts" more common. Others, like Masters, contend it's too early to say. 
   
   University of Washington atmospheric scientist Cliff Mass said that climate change is simply not powerful enough to create off-the-chart events like Harvey's rainfall. 
   
   "You really can't pin global warming on something this extreme. It has to be natural variability," Mass said. "It may juice it up slightly but not create this phenomenal anomaly." 
   
   "We're breaking one record after another with this thing," Mass said. 
   
   Sometime Tuesday or early Wednesday, parts of the Houston region will have broken the nearly 40-year-old U.S. record for the heaviest rainfall from a tropical system — 48 inches, set by Tropical Storm Amelia in 1978 in Texas, several meteorologists say. 
   
   Already 15 trillion gallons of rain have fallen on a large area, and an additional 5 trillion or 6 trillion gallons are forecast by the end of Wednesday, meteorologist Ryan Maue of WeatherBell Analytics calculates. That's enough water to fill all the NFL and Division 1 college football stadiums more than 100 times over. ||||| Before Hurricane Harvey even made landfall in Texas, Fox News was already whining about its coverage on CNN. In this case, the poutrage was over a CNN host daring to ask about the effect of climate change on the storm's intense rainfall. 
   
   The whining began with cohost Lisa Boothe: “You could see this coming. CNN didn’t wait long to bring up climate chance in its Hurricane Harvey coverage.” 
   
   A clip was played of CNN’s John Berman asking Bill Read, former director of National Hurricane Center, whether the intensity of the rain expected was connected to climate change. Read did not want to make that conclusion: “This is not an uncommon occurrence to see storms grow and intensify rapidly in the western Gulf of Mexico,” he said. 
   
   Boothe groused again, this time to the lone liberal cohost, Juan Williams: “Juan, why is CNN using a crisis like this to drive a political narrative?” 
   
   Williams ignored how Fox was politicizing the storm under cover of playing the victim. He even helped the messaging by saying it’s premature to blame climate change. 
   
   Fox reinforced its own politicization with a ridiculous lower-third banner: “CNN USES DANGEROUS STORM THREATENING AMERICANS TO ADVANCE LEFTIST AGENDA.” 
   
   Next up was cohost Jesse Watters. He snarked, “I’m surprised CNN is not blaming the storm on racism … or Russia. If the storm was named 'Robert,' they’d probably have to make a little name change there.” 
   
   Boothe had no complaint, though, with that politicization. In fact, she suggested the “or Russia” before Watters repeated it. 
   
   Watters then played the role of a climate expert (despite lacking a single credential): “Hurricanes have been happening since the beginning of time. There was no Industrial Revolution hundreds of years before when they were having hurricanes," He opined, ignoring the fact that it's the increase in intensity of hurricanes, not their existence, that experts blame on climate change. 
   
   "So they haven’t had one for the last, almost decade, like this and Obama was president. So I don’t know if it’s fair to blame global warming on these things." FNC expert Watters continued. "These things just happen. It’s called the weather." 
   
   Boothe called it “particularly cheap” to talk about climate change given the fact a lot of lives are at risk in Texas. She lectured CNN that it should be informing viewers instead. As if Fox was informing anyone in this segment. 
   
   Cohost Kimberly Guilfoyle piled on: “They’re never gonna miss an opportunity to be politically opportunistic,” she said without a trace of irony. Then she put on her own credential-free, climate-expert hat: “We haven’t had a major hurricane hit the United States in twelve years so their theory isn’t really holding up.” 
   
   Watch the hypocritical attacks on CNN below, from the August 25, 2017 The Five.
target: – 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.