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.
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.
Comment