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Thread: Hurricanes and climate change

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    tWebber TheLurch's Avatar
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    Hurricanes and climate change

    Since it seemed like a relevant topic and is appearing in the news frequently, i thought i'd try to give a quick summary of where things stand in terms of what we know.

    All you have to accept to make sense of this is that the earth's temperature has gone up. If you think NASA, NOAA, the UK Met Office, and others are all in on some grand conspiracy with the glaciers to make the earth look like it's warmer, i can't help you. For the purposes of this discussion, however, you do not have to care about the cause of this warming.


    Hurricanes are primarily fueled by heat, partly atmospheric heat, but more prominently the temperature at the ocean's surface. They're a conduit for rapidly diffusing the energy carried by warm ocean waters. That's why they tend to pick up strength while over tropical waters, but fizzle out as they head north. Given that, there have been two proposed ways that they'd be influenced by our warming climate:

    More hurricanes. If more of the ocean is warmer, you should make more hurricanes, right? It seemed sensible, and was an idea taken seriously by the scientific establishment. But research eventually showed that the formation of hurricanes is dominated by dust that blows off the Sahara and West Africa and over the tropical Atlantic ocean. It influences things like cloud cover and the amount of sunlight the ocean receives. So, while warm temperatures in theory could produce more hurricanes, any effect that it has is completely swamped by the amount of dust in the atmosphere over this key region.

    There may still be a small effect due to the fact that warm ocean waters could push a few systems that would otherwise remain tropical storms over into the hurricane category. But this is a minor effect, and we'd probably need many decades more data to pick it out of the noise.

    Stronger hurricanes. If a hurricane has more warm water to feed on, and the water's warmer than normal, it'll gain more strength. And, so far at least, it looks like this effect is real. Globally, the overall strength of tropical cyclones, and the number of higher-strength storms has gone up. Obviously, this is bad news for anyone living in regions prone to be hit by hurricanes/typhoons.

    Note that this can also keep storms at hurricane strength further north, where they would otherwise be able to weaken. So this also influences people in areas like New York and New England, which receive hurricanes infrequently. Sandy, for example, was an unusually strong hurricane given its location and time of year.

    There's also an area of big uncertainty:
    Different hurricane tracks. It's possible that a warming climate could lead to certain weather patterns that steer hurricanes in specific directions (think of how a front pushed Irma north over Florida, and is pushing Juan north much further east). This could make some parts of the earth more likely to get hit. But there's so much random noise in weather patterns that it would take lots of years to build up the sort of data we'd need to examine this question.

    The last thing that can't really be ignored is climate change's role in sea level rise. In part due to the melting of land-based glaciers, and in part due to the fact that warmer water is less dense, the oceans have gone up by over a half-foot over the last century or so, and the rate of rise is accelerating. In many coastal areas, this is combining with a natural subsidence caused by compacting sediment, meaning that the ocean is over a foot higher relative to the land. This basically means that storm surges can reach further inland, and flood things like basements where the critical point - the height of the lip of a door frame, for example - would have protected them a century ago.

    This obviously isn't exhaustive, but i'm reasonably sure it's accurate.

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    tWebber shunyadragon's Avatar
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    One important issue not covered by the above is West Pacific and Indian Ocean hurricanes, which do not form under the same manner as Atlantic hurricanes, and East Pacific hurricanes.

    It is possible that global warming can have an overall negative impact on Atlantic and East Pacific hurricanes particularly during El Nino years due to increased wind sheer, and relative humidity. In recent years during El Nino conditions we had reduced hurricane activity particularly in the Atlantic and East Pacific due to wind sheer conditions, but an active West Pacific seasons.

    There is the possibility that increased growth of arid an semiarid conditions in Africa due to global warming may increase the dust coming off the African continent, and promote the formation of hurricanes, but in turn the increased wind sheer and relative humidity may blunt the hurricanes and dissipate their strength. There is a global increase in arid and semiarid regions of the world possibly due in part to global warming.

    At present we are in a neutral El Nino-La Nina weather pattern, which would be conducive to hurricane formation in the Atlantic and East Pacific.

    West Pacific and Indian Oceans may increase in frequency and intensity under global warming conditions.

    These comments are based on memory of my reading of sources. I will go back and check out the sources.
    Last edited by shunyadragon; 09-11-2017 at 11:59 PM.
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    tWebber Teallaura's Avatar
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    Quote Originally Posted by TheLurch View Post
    Since it seemed like a relevant topic and is appearing in the news frequently, i thought i'd try to give a quick summary of where things stand in terms of what we know.

    All you have to accept to make sense of this is that the earth's temperature has gone up. If you think NASA, NOAA, the UK Met Office, and others are all in on some grand conspiracy with the glaciers to make the earth look like it's warmer, i can't help you. For the purposes of this discussion, however, you do not have to care about the cause of this warming.


    Hurricanes are primarily fueled by heat, partly atmospheric heat, but more prominently the temperature at the ocean's surface. They're a conduit for rapidly diffusing the energy carried by warm ocean waters. That's why they tend to pick up strength while over tropical waters, but fizzle out as they head north. Given that, there have been two proposed ways that they'd be influenced by our warming climate:

    More hurricanes. If more of the ocean is warmer, you should make more hurricanes, right? It seemed sensible, and was an idea taken seriously by the scientific establishment. But research eventually showed that the formation of hurricanes is dominated by dust that blows off the Sahara and West Africa and over the tropical Atlantic ocean. It influences things like cloud cover and the amount of sunlight the ocean receives. So, while warm temperatures in theory could produce more hurricanes, any effect that it has is completely swamped by the amount of dust in the atmosphere over this key region.

    There may still be a small effect due to the fact that warm ocean waters could push a few systems that would otherwise remain tropical storms over into the hurricane category. But this is a minor effect, and we'd probably need many decades more data to pick it out of the noise.

    Stronger hurricanes. If a hurricane has more warm water to feed on, and the water's warmer than normal, it'll gain more strength. And, so far at least, it looks like this effect is real. Globally, the overall strength of tropical cyclones, and the number of higher-strength storms has gone up. Obviously, this is bad news for anyone living in regions prone to be hit by hurricanes/typhoons.

    Note that this can also keep storms at hurricane strength further north, where they would otherwise be able to weaken. So this also influences people in areas like New York and New England, which receive hurricanes infrequently. Sandy, for example, was an unusually strong hurricane given its location and time of year.

    There's also an area of big uncertainty:
    Different hurricane tracks. It's possible that a warming climate could lead to certain weather patterns that steer hurricanes in specific directions (think of how a front pushed Irma north over Florida, and is pushing Juan north much further east). This could make some parts of the earth more likely to get hit. But there's so much random noise in weather patterns that it would take lots of years to build up the sort of data we'd need to examine this question.

    The last thing that can't really be ignored is climate change's role in sea level rise. In part due to the melting of land-based glaciers, and in part due to the fact that warmer water is less dense, the oceans have gone up by over a half-foot over the last century or so, and the rate of rise is accelerating. In many coastal areas, this is combining with a natural subsidence caused by compacting sediment, meaning that the ocean is over a foot higher relative to the land. This basically means that storm surges can reach further inland, and flood things like basements where the critical point - the height of the lip of a door frame, for example - would have protected them a century ago.

    This obviously isn't exhaustive, but i'm reasonably sure it's accurate.

    Question: Stronger compared to what? Hurricanes over the past fifty years? One hundred? And how? Wind speed? Damage?

    I'm curious about the methodology here, not taking issue with anything.

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    tWebber TheLurch's Avatar
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    Quote Originally Posted by Teallaura View Post
    Question: Stronger compared to what? Hurricanes over the past fifty years? One hundred? And how? Wind speed? Damage?

    I'm curious about the methodology here, not taking issue with anything.
    Standard measures of hurricane strength are pressure in the eye and sustained wind speed.

    And it would be "stronger than at a point where the earth was cooler". In practical terms, we don't have much organized record keeping before the 1960s, though there are extensive historic reconstructions in many areas that go back for centuries, based on whether sand shows up in sediment records.

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    Troll Magnet Sparko's Avatar
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    What about the colder winters and stronger winter storms we have had recently?

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    tWebber TheLurch's Avatar
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    Quote Originally Posted by Sparko View Post
    What about the colder winters and stronger winter storms we have had recently?
    That's under active research. There's a leading idea, but i wouldn't say that the scientific community uniformly accepts it. That caution out of the way...

    The idea is that the jet stream winds form at the boundary of cold Arctic air and warmer mid-lattitude air. When the temperature difference is strong, the winds are strong, and serve to isolate the Arctic air. When the temperature difference is small, then the boundary is weak, and the jet stream starts to wander further north or south. Climate change is warming the Arctic faster than other regions, so the temperature difference is dropping, leading to a jet stream that wanders more frequently.

    This doesn't necessarily lead to colder weather - it really depends on which side of the wander you're on. If you're inside a southward bend, you'll get very cold air. You're just as likely, however, to be somewhere where the jet stream is drawing up warm air from the south. So what you'll tend to see is a winter that seems more extreme - either warmer or colder than expected - or even switches between the two.

    I don't know where you are, but here in the US Northeast, that's the sort of thing we've seen over the last decade or so - freakishly warm winters one year, followed by a winter that makes the idea of global warming feel like a joke. The problem is that this is pretty variable normally, so we need more years to build up the data to have confidence that it's a real pattern.

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    Troll Magnet Sparko's Avatar
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    Quote Originally Posted by TheLurch View Post
    That's under active research. There's a leading idea, but i wouldn't say that the scientific community uniformly accepts it. That caution out of the way...

    The idea is that the jet stream winds form at the boundary of cold Arctic air and warmer mid-lattitude air. When the temperature difference is strong, the winds are strong, and serve to isolate the Arctic air. When the temperature difference is small, then the boundary is weak, and the jet stream starts to wander further north or south. Climate change is warming the Arctic faster than other regions, so the temperature difference is dropping, leading to a jet stream that wanders more frequently.

    This doesn't necessarily lead to colder weather - it really depends on which side of the wander you're on. If you're inside a southward bend, you'll get very cold air. You're just as likely, however, to be somewhere where the jet stream is drawing up warm air from the south. So what you'll tend to see is a winter that seems more extreme - either warmer or colder than expected - or even switches between the two.

    I don't know where you are, but here in the US Northeast, that's the sort of thing we've seen over the last decade or so - freakishly warm winters one year, followed by a winter that makes the idea of global warming feel like a joke. The problem is that this is pretty variable normally, so we need more years to build up the data to have confidence that it's a real pattern.
    All I know is that when AGW deniers point out the cold winters and blizzards, they are told "that is weather, not climate" yet when the same thing happens with hurricanes it is "climate" -- seems like a double standard. And we have actually had a pretty long lull in hurricane activity until this year.

    It seems to me that it is a bit of a double standard to me. When the weather is unseasonable cold, why that is because of global warming! (Or a "pause") And when it is unseasonably warm why that is global warming!

    Personally, I do think we are having some global warming, but I don't believe it is man-made to any great extent. I think it is a natural cycle.

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    Troll Magnet Sparko's Avatar
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    Source: Hurricanescience.org

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    tWebber TheLurch's Avatar
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    Regarding the hurricanes that happen to hit the US - what matters from the climate perspective is hurricanes total. The climate doesn't respect human-drawn nation borders.

    Quote Originally Posted by Sparko View Post
    Personally, I do think we are having some global warming, but I don't believe it is man-made to any great extent. I think it is a natural cycle.
    What evidence do you base that on? And what's doing the cycling?

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    Quote Originally Posted by TheLurch View Post
    And what's doing the cycling?
    Nature? Where I sit in New England it was once covered in 50 foot glaciers, the Arctic was once tropical.

    Earth's Climate During the Last Ice Age

    Unlike the relatively stable climate Earth has experienced over the last 10,000 years, Earth's climate system underwent a series of abrupt oscillations and reorganizations during the last ice age between 18,000 and 80,000 years ago (Dansgaard 1984, Bond et al. 1997, 1999). These climate fluctuations were first discovered when scientists reconstructed past temperature variability over Greenland by analyzing tiny changes in the relative abundance of the oxygen-16 isotope versus the oxygen-18 isotope (noted as δ18O and reported in parts per thousand) in ice cores recovered from Greenland glaciers. Each successively deeper ice layer represents a snapshot of Earth's climate history from the past, and together, the oxygen isotope record told a story of abrupt, millennial-scale climate shifts in air temperatures over Greenland between extremely cold stadial conditions and relatively mild interstadial periods during the last ice age (Figure 1) (Alley 2000, Alley et al. 2003). There are twenty-five of these distinct warming-cooling oscillations (Dansgaard 1984) which are now commonly referred to as Dansgaard-Oeschger cycles, or D-O cycles. One of the most surprising findings was that the shifts from cold stadials to the warm interstadial intervals occurred in a matter of decades, with air temperatures over Greenland rapidly warming 8 to 15°C (Huber et al. 2006). Furthermore, the cooling occurred much more gradually, giving these events a saw-tooth shape in climate records from most of the Northern Hemisphere

    Although the D-O climate cycles have now been found in many other climate proxy records around the globe (Voelker 2002), the reason why Earth's climate was so much more variable during the last ice age is still unknown. Some theories suggest that changes in ocean circulation due to natural variations of North Atlantic surface water salinity were the trigger for the D-O events (the salt oscillator hypothesis) (Birchfield & Broecker 1990, Broecker et al. 1990a, Zaucker & Broecker 1992), while others argue changes in atmospheric circulation were the driver (the wind field oscillation hypothesis)

    https://www.nature.com/scitable/know...t-ice-24288097
    Last edited by seer; 09-12-2017 at 05:21 PM.
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