This article is from the source 'bbc' and was first published or seen on . It last changed over 40 days ago and won't be checked again for changes.
You can find the current article at its original source at http://www.bbc.co.uk/news/world-us-canada-42251921
The article has changed 2 times. There is an RSS feed of changes available.
Previous version
1
Next version
Version 0 | Version 1 |
---|---|
Is climate change making hurricanes worse? | Is climate change making hurricanes worse? |
(about 1 month later) | |
The past year has been a busy one for hurricanes. | The past year has been a busy one for hurricanes. |
There were 17 named storms in 2017, 10 hurricanes and six major hurricanes (category 3 or higher) - an above average year in each respect. | There were 17 named storms in 2017, 10 hurricanes and six major hurricanes (category 3 or higher) - an above average year in each respect. |
The 10 hurricanes formed consecutively, without weaker tropical storms interrupting the sequence. | The 10 hurricanes formed consecutively, without weaker tropical storms interrupting the sequence. |
The only other time this has been recorded was in 1893. | The only other time this has been recorded was in 1893. |
Are these storms getting worse? And does climate change have anything to do with it? | Are these storms getting worse? And does climate change have anything to do with it? |
A year of records | A year of records |
This Atlantic hurricane season has been particularly bad. | This Atlantic hurricane season has been particularly bad. |
There was Harvey, which pummelled the United States in August. | There was Harvey, which pummelled the United States in August. |
It brought the largest amount of rain on record from any tropical system - 1,539mm. | It brought the largest amount of rain on record from any tropical system - 1,539mm. |
It caused the sort of flooding you'd expect to see once every 500 years, causing $200bn of damage to Houston, Texas. | It caused the sort of flooding you'd expect to see once every 500 years, causing $200bn of damage to Houston, Texas. |
Ironically, this was the third such "one every 500 years" flood Houston had suffered in three years. | Ironically, this was the third such "one every 500 years" flood Houston had suffered in three years. |
September brought Irma, which devastated Caribbean communities. It was the joint second strongest Atlantic hurricane ever, with sustained winds of 185mph. | September brought Irma, which devastated Caribbean communities. It was the joint second strongest Atlantic hurricane ever, with sustained winds of 185mph. |
Those winds were sustained for 37 hours - longer than any tropical system on record, anywhere in the world. | Those winds were sustained for 37 hours - longer than any tropical system on record, anywhere in the world. |
Next came Hurricane Maria - another category 5 hurricane, with sustained winds of 175mph - which destroyed Puerto Rico's power grid. | Next came Hurricane Maria - another category 5 hurricane, with sustained winds of 175mph - which destroyed Puerto Rico's power grid. |
Finally, Hurricane Ophelia span past Portugal and Spain - the farthest east any major Atlantic hurricane has ever gone. | Finally, Hurricane Ophelia span past Portugal and Spain - the farthest east any major Atlantic hurricane has ever gone. |
Despite this, 2017 wasn't the worst year in some key respects. | Despite this, 2017 wasn't the worst year in some key respects. |
It didn't produce the strongest storm - that was Hurricane Allen in 1980, with sustained winds of 190mph. | It didn't produce the strongest storm - that was Hurricane Allen in 1980, with sustained winds of 190mph. |
Nor did it have the greatest number of storms - that was 2005, which saw an incredible 28 named storms, including seven major hurricanes. One of them was the infamous Hurricane Katrina. | Nor did it have the greatest number of storms - that was 2005, which saw an incredible 28 named storms, including seven major hurricanes. One of them was the infamous Hurricane Katrina. |
But 2017 was probably the costliest. Estimates for the cost of the hurricane season vary and continue to be revised, ranging up to $385bn. | But 2017 was probably the costliest. Estimates for the cost of the hurricane season vary and continue to be revised, ranging up to $385bn. |
By comparison, 2005 racked up $144bn in damage according to the National Hurricane Center - about $180bn today, adjusted for inflation. | By comparison, 2005 racked up $144bn in damage according to the National Hurricane Center - about $180bn today, adjusted for inflation. |
It has certainly been a bad year. But over time, are hurricanes getting worse? | It has certainly been a bad year. But over time, are hurricanes getting worse? |
There have been 33 of the strongest category 5 hurricanes since 1924. Eleven of these have occurred in the past 14 years. | There have been 33 of the strongest category 5 hurricanes since 1924. Eleven of these have occurred in the past 14 years. |
We know that hurricanes are powered by warm seas and over the past 100 years global average sea temperatures have risen by about 1C. | We know that hurricanes are powered by warm seas and over the past 100 years global average sea temperatures have risen by about 1C. |
But when you look at the total strength of storms in each year since records began, some years are more fearsome than others. | But when you look at the total strength of storms in each year since records began, some years are more fearsome than others. |
Meteorologists use something called accumulated cyclone energy (ACE) to calculate the total wind power of all the storms in any given year. | Meteorologists use something called accumulated cyclone energy (ACE) to calculate the total wind power of all the storms in any given year. |
As you can see from the following chart, there's no clear upward trend. | As you can see from the following chart, there's no clear upward trend. |
Why not? | Why not? |
Even though seas are getting warmer, other factors can prevent hurricanes forming in particular years. | Even though seas are getting warmer, other factors can prevent hurricanes forming in particular years. |
Saharan dust can interfere with hurricane formation as can the close proximity of African storms to the equator. | Saharan dust can interfere with hurricane formation as can the close proximity of African storms to the equator. |
But one of the great weather ironies is that hurricanes hate strong winds. | But one of the great weather ironies is that hurricanes hate strong winds. |
Strong winds in the Atlantic interfere with the circulation of air through a developing storm. This stops the storm growing into a hurricane. | Strong winds in the Atlantic interfere with the circulation of air through a developing storm. This stops the storm growing into a hurricane. |
During a phenomenon called El Niño, the Pacific Ocean near the equator gets warmer than usual. This affects global wind patterns, leading to stronger winds in the Atlantic. | During a phenomenon called El Niño, the Pacific Ocean near the equator gets warmer than usual. This affects global wind patterns, leading to stronger winds in the Atlantic. |
That means El Niño years tend to be quiet years for hurricanes. | That means El Niño years tend to be quiet years for hurricanes. |
But when the Pacific is cooler (known as La Niña), the reverse is true - making it easier for hurricanes to form. And 2017 is a La Niña year. | But when the Pacific is cooler (known as La Niña), the reverse is true - making it easier for hurricanes to form. And 2017 is a La Niña year. |
In fact, the total storm strength in La Niña years has been rising decade by decade. | In fact, the total storm strength in La Niña years has been rising decade by decade. |
Land drainage | Land drainage |
High winds are just part of the story. Climate change affects hurricane seasons in other ways, too. | High winds are just part of the story. Climate change affects hurricane seasons in other ways, too. |
Rainfall during hurricanes can be devastating. Hurricane Harvey would have brought severe flooding to Houston regardless of climate change. | Rainfall during hurricanes can be devastating. Hurricane Harvey would have brought severe flooding to Houston regardless of climate change. |
But it is reasonable to assume that Harvey brought more rain than it would have done 100 years ago. | But it is reasonable to assume that Harvey brought more rain than it would have done 100 years ago. |
Global air temperatures have also increased by about 1C in the past 100 years, and warmer air holds more water. | Global air temperatures have also increased by about 1C in the past 100 years, and warmer air holds more water. |
That's likely to be behind the increasing frequency of extreme rainfall events seen in the US in recent decades. | That's likely to be behind the increasing frequency of extreme rainfall events seen in the US in recent decades. |
But the location of housing compounded the damage. | But the location of housing compounded the damage. |
Houston's population has more than doubled since 1960 to more than two million people. Housing developments are expanding into more marginal, poorly drained land. | Houston's population has more than doubled since 1960 to more than two million people. Housing developments are expanding into more marginal, poorly drained land. |
This puts more people in harm's way. | This puts more people in harm's way. |
Climate change is also causing seas to rise. | Climate change is also causing seas to rise. |
Melting glaciers and land-based ice sheets contribute to higher sea levels. | Melting glaciers and land-based ice sheets contribute to higher sea levels. |
Also warmer water occupies a larger volume. So as seas warm up, sea levels rise. | Also warmer water occupies a larger volume. So as seas warm up, sea levels rise. |
In the US, the largest sea-level rise is around the coast of the Gulf of Mexico - about 9.6mm each year at Eugene Island, Louisiana. | In the US, the largest sea-level rise is around the coast of the Gulf of Mexico - about 9.6mm each year at Eugene Island, Louisiana. |
All of this is increasing vulnerability to flooding when hurricanes and their associated storm surge reach land. | All of this is increasing vulnerability to flooding when hurricanes and their associated storm surge reach land. |
Scientists are still analysing what this data will mean, but a warmer world may bring us a greater number of more powerful category 4 and 5 hurricanes and could bring more extreme rainfall. | |
There's an increased risk of flood damage - whether related to climate change, rising sea levels or more people moving into flood-prone areas. | There's an increased risk of flood damage - whether related to climate change, rising sea levels or more people moving into flood-prone areas. |
Correction 29 January 2018: This story has been updated to clarify that it is modelling rather than historical data that predicts stronger and wetter hurricanes. | |
What do you want BBC Reality Check to investigate? Get in touch | What do you want BBC Reality Check to investigate? Get in touch |
Read more from Reality Check | Read more from Reality Check |
Follow us on Twitter | Follow us on Twitter |
Previous version
1
Next version