Archives for October 2011

Distance travelled ~ 773'769'600 km

Noon is personal. It's the time of day when the sun is highest in the sky and your shadow is shortest. It's the reference point for a clock that is always with you, because you can be your own sundial. The spinning Earth provides us with a built-in natural chronometer. Brilliant!

That clock has served nature well for millennia - birds sing at dawn, foxes come out at dusk, humans go to sleep when it gets dark, and we all live day to day. One daily cycle follows another. But the growth of human civilizations and the need for greater co-operation than ever before meant that humans had to control time instead of being controlled by it. Clocks were standardized. The day was split up into hours, and humans had to agree to start work, meet or provide services at specific times. It was the only way of co-ordinating a civilization. But the Sun was still the reference point.

Faster travel, and inventions like the radio and telephones, meant that time zones had to be invented. Local noon where I am, in Southampton, happens four minutes later than local noon in London, so society agreed that all of the UK would be in a single time zone, for convenience. 12 o'clock in Southampton now happens at the same time as 12 o'clock in London. The Sun is no longer the reference point. The shortest shadows still happen around lunchtime, but you can't set your watch by that any more. And as clocks got more and more accurate, we discovered that the shape of Earth's orbit means that the length of a day varies by about a minute over the course of each year. Solar time seemed to be almost unhelpful in our standardized world.

So humans weren't living and working according to the Sun any more, but sunlight hadn't gone away.

The standardization of time meant that some people were sleeping when it was light and working when it was dark. And so Daylight Savings Time was invented, to try and compensate for the limitations imposed by standard time. The clocks go back in the UK Sunday 30 October 02:00am in a return to GMT, after a summer of allowing us an extra hour of daylight in the evenings (upcoming DST times). Of course, we don't actually get an extra hour of daylight - we just move our time reference to take that hour off the start of the day and tack it on the end. We couldn't have built the modern world without standardized time, and now we're trying to patch up some of its inconveniences.

Should we bother? Every clock change causes sleep deprivation, a demonstrated drop in productivity and a day where the whole country risks turning up at the wrong time. It's a nice ritual to mark the changing of the seasons, but is it worth it?

I think that the crux of the argument might be in how society is changing. Fifty years ago, a giant siren marked the time when work began and ended in factories. The development of our society relied on us all working together, at the same time. It was an enormous example of human co-operation. But now, we live less constrained lives. We work flexibly, and internationally. The standardization of the working day is disappearing - some businesses start work at 8am, some at 10am. I adapt my daily routine so that I can go running when it's light, whether that's in the morning or the evening.

As long as I get my work done, maybe it doesn't matter when I do it. So I can choose for myself what I do with my daylight hours, irrespective of the official time that they start and end.

Do we even need time zones any more? Maybe the logical end to this argument is that we could have just one Earth time, so that everyone has lunch at a different official time, but it's still when the sun is more or less overhead. I'm not necessarily advocating for that, but it's not as close to science fiction as you might think. Scientists in every country frequently record data using "Universal Time" or Zulu time, which is GMT. That way there's no confusion at all over when it was recorded, wherever you were on the planet.

So, is the era of British Summer Time/Daylight saving time over? What do you think?

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Distance travelled ~ 771'143'200 km

(Here Dr. Jeff Masters, Director of Meteorology, wunderground.com explores 2011's Atlantic Hurricane season. His previous post for 23 Degrees provided us with a detailed roundup of Maria, Nate and Katia's developments.)

The Atlantic hurricane season of 2011 is nearing its end, with Tropical Storm Rina, near Mexico's Yucatan Peninsula, likely to be one of last storms of the season. Atlantic hurricane activity peaks near September 10, and drops dramatically during the last half of October. It's been a very strange year for hurricanes in the Atlantic. There have been a near-record number of named storms--seventeen--making 2011 the 7th busiest year for tropical storms since record keeping began in 1851. However, only six of those storms--35%--have intensified to hurricane strength. In a typical year, 55 - 60% of all tropical storms make it to hurricane strength. A rare combination of near-record warm ocean temperatures but unusually dry, stable air over the Atlantic is no doubt partially responsible for this very unusual occurrence. Another unusual feature of this hurricane season is that relatively few storms hit the U.S. During the 15-year active hurricane period from 1995 - 2009, 33% of all named storms in the Atlantic hit the U.S., and 30% of all Atlantic hurricanes hit the U.S. at hurricane strength. Based on 1995 - 2009 levels of activity, the U.S. should been hit by six named storms, four of those being hurricanes, and two being intense hurricanes. So far, 2011 has seen less than half that level of landfall activity. Two tropical storms and one hurricane have hit the U.S. this year: Tropical Storm Don, which hit Texas with 50 mph winds, Tropical Storm Lee, which hit Louisiana with 60 mph winds, and Hurricane Irene, which hit North Carolina with 80 mph winds. This is the second consecutive year that the U.S. has benefited from favorable steering currents that have steered most of the storms out to sea. During 2010, only one tropical storm hit the U.S., despite a season with the 3rd highest number of named storms, nineteen. If 2011 finishes without a major Category 3 or stronger hurricane hitting the U.S.--which is likely--it will mark the first six-year period without a major hurricane strike on the U.S. since record keeping began in 1851. The last major hurricane to hit the U.S. was Category 3 Hurricane Wilma of October 2005.

 

The strongest hurricane of 2011 was Hurricane Ophelia, which peaked as a Category 4 hurricane with 140 mph winds and a central pressure of 940 mb on October 2 just northeast of Bermuda. Ophelia hit Southeast Newfoundland as a tropical storm with 70 mph winds on October 3, but caused little damage. The longest-lived storm was Hurricane Philippe, which lasted 15 days from September 24 to October 8. The most damaging was Hurricane Irene, which caused at least $7 billion in damage from North Carolina to New England. Irene was also the deadliest storm of 2011, with 55 deaths in the Caribbean and U.S. being blamed on the storm.

 

Figure 3. Hurricane Irene's storm surge and winds carved two new channels through Pea Island on North Carolina's Outer Banks. This cut, near the town of Rodanthe, is the smaller of the two cuts, and severed Highway 12 connecting the Outer Banks to the mainland.

What do you think of this year's season?

 

 

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Distance travelled ~ 765'997'600 km

Across Asia, several areas are severely flooded after unusually heavy monsoon rains since July. Over 200 houses were swept away by flash floods in Burma, where up to 50 people are thought to have died. Thailand and Cambodia are also badly affected, with the worst flooding in 50 years.

 

The above images captured by Alexis Taylor 23 October. "They were taken in the center of Bangkok town...10 min from Khaosan road on foot. The hotel I was staying in on Khao San was bricking the doors up - 1 meter high. You have to enter over sand bags"

 

Ari Honka took this photo of the first signs of flooding in China Town, Bangkok on 23 October.

 

 

 

The above images were captured by Derek Armstrong 23 October. "The exact location is outside my house on the Rangsit Nakon Nayok highway which is normally a very busy road linking Bangkok with NE Thailand. It is located in Pathumthani province, just to the north of Bangkok and about 10km from the old Don Mueang Airport.

The situation has deteriorated somewhat as the level of the klong(canal) is now climbing up to near the brim of the temporary sandbag/clay dykes. The road is also flooding over both sides and spilling into the canal as a result of water run-off from the North (see attached pictures taken yesterday at 9.00 am, Monday 24th October). We are now virtually marooned as we cannot get out of our estate to travel to Bangkok. Vipavadee Rangsit Road, to the west, where Don Mueang airport is located is heavily flooded now. To the east, we cannot access the Outer Ring Road, as there is heavy flooding up to Rangsit Klong 6 where that road is located."

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Distance travelled ~ 765'461'600 km

Over the Americas:

• A large area of low pressure will track eastwards through the Bering Sea and Alaska towards Nunavut in Canada from Sunday through to Thursday, bringing very wet and windy conditions, particularly to the more populated southern/western seaboard of Alaska and Canada.

• Hurricane Rina, Category two, is moving slowly at 3mph northwest over the western Caribbean - Belize, the east coast of the Yucatan Peninsula and adjacent Islands should monitor the progress of Rina. A hurricane watch is in effect for the east coast of the Yucatan Peninsula from north of Punta Gruesa to Cancun.

According to the National Hurricane Centre additional strengthening seems likely until increasing south-southwesterly shear halts the intensification process which is expected to occur in about 48 hours.

• A second area moving into the eastern Caribbean into the new working week, tracking eastwards past Venezuela before likely losing its impetus by Thursday.

• A deep area of low pressure is forecast to bring very heavy rain and strong winds to Uruguay and southern Brazil during the middle of the week.

Across Europe:

• Systems of low pressure near the UK will bring unseasonably wet and windy weather to Morocco, Iberia, Biscay and the UK at the start of the week.

• Further heavy rain from a second low pressure system is expected to affect Iberia midweek.

• High pressure is expected to dominate the weather across eastern Europe, bringing increasingly cool conditions to the Black Sea and Caucasus.

Across Asia:

• Cool and windy conditions should affect northeastern China at the start of the week. Moving westwards into Vietnam and Laos over the next few days, bringing further heavy rain to these regions.

Across Australasia:

• Significantly warmer and wetter than average over New South Wales and Victoria at the start of the week, with heavy rain and strong winds later affecting the South Island of New Zealand during Monday.

• Very heavy rain is likely to push into Western Australia around Perth from the Indian Ocean around midweek.

Across Africa:

• Becoming warm or very warm for the time of year over southeastern Africa, particularly Mozambique and Madagascar, whilst in contrast Namibia and the Cape region of South Africa should see cooler than average weather.

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Distance travelled ~ 755'224'000 km

(Mark Thompson's previous blogs for 23 Degrees include a post on the Perseids meteor shower and Jupiter's Great Red Spot. Here he explores octobers's second Meteor Shower, The Orionids.)

Halley's Comet returns to the neighbourhood of the Sun every 76 years, yet each year, around the 21/22 October it's possible to catch glimpses of this famous comet in the Orionid Meteor Shower.

There are hundreds of comets that orbit the Sun and each one is a lump of rock mixed ices. When they get closer to the Sun, the growing heat turns the ice straight into a gas in a process called sublimation. We can see this process as comets approach in the growing coma around the rocky core. As it gets closer to the Sun, the solar wind (streams of charged particles from the Sun) push against the coma producing the comet's trademark tail. It's a common misconception that the tail of a comet flows out behind it but in reality, it simply points away from the Sun regardless of its direction of travel. As the comet's journey along its orbit continues it leaves behind a trail of debris. If the Earth happens to move through or close to a comet's orbit in its 365 day journey around the Sun, then it will sweep up some of this material and we will see nature's own firework show, a meteor shower.

At around 22:00 (BST) on Friday evening (21st) the Earth is expected to pass by the densest part of the debris left by Halley and we should see the peak of the shower. However, meteor showers are difficult to predict and always tend to be best observed just after midnight so it's worth keeping an eye out in the early morning hours of the 22nd too. Unfortunately this year, the Moon is a day passed last quarter so its light may affect the number of meteors visible. Even so, there could be up to 30 meteors visible per hour. The best tip to catch a glimpse of this spectacle is to wrap up warm, get outside around 22:00 tonight just before moonrise and watch the sky. Be patient and keep an eye on the sky for the rest of the night just in case it happens later than expected. Happy hunting.

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Distance travelled ~ 745'308'000 km

At least four people are thought to have died in Mexico, when Hurricane Jova made landfall on Tuesday. A hurricane warning was issued for a 100-mile stretch of coast and Manzanillo, one of Mexico's biggest cargo ports, was shut down during the storm.

Guatemala was also affected by tropical rains, with flash floods and landslides reported to have killed at least 18 people. The storms have triggered widespread flooding, threatening several communities. Transport has been severely affected, with at least a dozen landslides and significant damage to roads and bridges.

The week ahead

Across Europe:
• Very heavy rain in central and southern Scotland on Monday, with up to 60mm of rain likely in places. The rain will turn to snow over ground above about 400m in the southern Grampians. Strong winds are also expected, with the potential for 60mph gusts on the Irish Sea coasts causing some damage.

• For the rest of the week, the UK can expect cold and windy weather with sunny spells and blustery showers. Some rain may fall as snow over high ground in the north.

Over the Americas:
• Heavy rain continuing across parts of western Mexico and Central America.

• Heavy rain and strong to gale force winds are also expected over north east Canada and the USA, brought by a complex area of low pressure. There is also the risk of snow on the western flank of the low pressure around the Hudson Bay area and also over the Great Lakes.

• A tropical disturbance in the western Caribbean may develop into a tropical storm over the next few days.

• Persistent rain and thunderstorms around Paraguay, North Argentina, Uruguay and the Santa Catarina.

Across Asia:
• Very wet and unsettled over Japan next few days as well as parts of eastern China associated with active fronts and developing lows.

• High probability of heavy rain in north of Bay of Bengal and adjacent land areas. Low to moderate probability of a tropical cyclone forming.

Across Australasia:
• Warm across Adelaide and southern parts of Australia for the time of year, while northwestern parts of Queensland can expect very unsettled conditions.

• Also becoming very unsettled over New Zealand once again.

Across Africa:
• Heavy showers and thunderstorms affecting parts of the far north - mainly north Libya and perhaps also the far north west of Egypt - for the next few days. Showers becoming lighter by midweek but temperatures well below normal.

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Distance travelled ~ 727'298'400 km

After a period of record-breaking settled weather last week, most of the UK saw a return to normal autumn conditions by Tuesday. A band of cloud spread across most of England and Wales, and showers continued in Scotland and Northern Ireland.

Wednesday and Thursday saw strong northwesterly winds for many, reaching gale force on higher ground in the north. On Thursday a yellow warning was in place for gusts of up to 65mph for parts of the North West and Northern Ireland, with winds in excess of 40mph recorded widely. The strongest gust at low levels was 66mph at Machrihanish in Scotland.

Temperatures fell compared to last week but were still above average in many areas for October, with a high of 22.1 °C in Bridlington on Wednesday. Although on Friday it was a chilly start for many, with temperatures falling into single figures and a low of -1.5 °C at Cairngorm in Scotland.

Elsewhere in the world, Winnipeg in America has also been experiencing warm autumn weather, with temperatures 18 °C above what is seasonally normal. It reached 31 C on Thursday, the hottest October day in Winnipeg since records began.

Several days of heavy rain in central Algeria have caused the deaths of eight people and widespread damage to roads and bridges. There has also been heavy rain in Haikou, China, where 17,000 people were evacuated after days of torrential rain raised the level of the Nandu river higher than the warning line.

One man has been killed and 12 injured in a massive pile-up after a dust-storm rolled across an interstate in Arizona. The collision on Interstate 10 near Picacho - midway between Phoenix and Tucson - involved 16 vehicles.

In Australia, almost 11,000 homes are without power after severe thunderstorms battered Queensland. However, damage from flooding has been minimal, with only 22 calls made to the State Emergency Service for leaking roofs.

Severe weather watch: The week ahead

Across Europe:

• Unsettled conditions are expected to continue to affect some northern parts of Europe through the start of the week.

• Warm and quiet conditions are expected to return to many areas from midweek as high pressure builds once again across Europe.

• The former Hurricane Philippe is set to head well north across the Atlantic, bringing gales and heavy rain to Iceland and East Greenland. In so doing, Philippe will give the UK a wide berth and will have no direct weather impact here.

Over the Americas:

• In the eastern Pacific Hurricane Jova and Tropical Storm Irwin are both moving towards Mexico. Jova is a Saffir-Simpson Category 3 Hurricane moving East (winds ~120 mph) and is expected to make landfall somewhere near Manzanillo on Tuesday.

Irwin is forecast to approach the west coast of Mexico on Thursday or Friday. Maximum sustained winds 35knots; 40mph moving east at 7mph.

Across Asia:

• There are unsettled conditions to the east of the Philippines at the moment and this may develop into a typhoon this week.

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Distance travelled ~ 725'583'200 km

The first weekend of October saw UK beaches packed with day-trippers, while Londoners headed to the parks in an effort to stay cool during what turned out to be the hottest October weekend on record. Gravesend in Kent reached 29.9C, hotter than most days this summer.

Just a few days later the shorts were back in the drawer, the coats were on and happy hikers were tramping through fresh snow on the Scottish mountains. Elsewhere, late summer warmth was replaced by snow in the Alps and in California's Sierra Nevada, just 3 months after the last of the previous winter's snow had melted, 2 feet of fresh stuff arrived.

Such wild swings in the weather are not unusual at this time of year as the seasons change. The exceptional UK heatwave was caused by persistent southerly winds bringing very warm air from North Africa and the Mediterranean, while the early Scottish, Alpine and Californian snowfalls were brought in by a rapid switch to northerly Arctic airstreams.

Having passed the equinox, the longer nights and shortening days in the northern hemisphere lead to a net loss of warmth during each 24-hour cycle. The Arctic ocean, surrounded by rapidly cooling land, begins to freeze over. Further south, the cooling is slower. The warm waters of the Atlantic and Mediterranean act as huge stores of summer heat. As executive producer Jonathan Renouf said recently in this blog (In a constant search for Equilibrium), weather is all about gradients. In this case it's the north/south temperature gradient that's tightening, which means a switch of wind direction can bring a big change in temperature.

So, wondering what to wear tomorrow? The answer, my friend, is blowing in the wind.

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Distance travelled ~ 714'327'200 km

While we have been enjoying the wonderful sunshine down on Earth (especially the recent record october warmth in the UK) - space has also been throwing up some pretty stunning weather. Yesterday, October 4th, a massive solar flare exploded from the surface on the far side of the Sun. It blasted a spectacular coronal mass ejection or CME into space. A CME is a massive burst of solar wind and plasma containing electrons and protons that blast out from the Sun's surface. They are associated with solar flares and tend to develop in areas of high solar activity such as Sun spots.

The October 4th CME was recorded by the Solar and Heliospheric Observatory

Scientists from the Goddard Space Weather Lab have plotted the course of the CME and discovered it is heading directly for the planet closest to the Sun, Mercury. The cloud of highly energised plasma and particles won't affect the planet but could disrupt the MESSENGER probe in orbit around Mercury.

It is possible that the CME may then hit Venus on Oct. 6th, but it is not predicted to hit Earth.

What happens when CME's hit Earth?
When CMEs do come our way the shockwave from the highly energized particles can cause a geomagnetic storm that can disrupt our magnetic shield. This can trigger dynamic auroras or Northern Lights [aurora borealis] in the northern hemisphere or Southern Lights [aurora australis] in the southern hemisphere. CMEs hitting earth can also cause disruption to radio transmissions, damage satellites and cause power cuts by knocking out electrical power cables.

They don't present a health risk for us on the surface because of our protective magnetic shield and atmosphere. But they can present problems for astronauts and even people in high altitude planes due to increased risk of exposure to radiation. But it is thought that any long-term health risk are unlikely.

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(Jonathan Renouf is an Executive TV Producer making documentaries for the BBC Science department. His most recent projects are 'Wonders of the Universe' with Brian Cox, history of global warming "Earth: The Climate Wars", the BAFTA nominated "Earth: Power of the Planet" and the highly popular and critically acclaimed 'How Earth Made Us', which transmitted in January and February 2010. Here he shares his insights on making 23 Degrees (working title) due to transmit early 2012.)

Distance travelled ~ 713'844'800 km

A couple of days ago my baby son woke me up early, and even though I got him back to sleep, I was too awake to settle down. Eventually, at about 6.00, I gave up, got out of bed and decided to go out on my bicycle. I live in Cookham, close to a picturesque stretch of the River Thames, so I cycled down the lane towards the river. As soon as I left our suburban close behind, my heart leapt. A mist lay over the fields - just a few metres thick, but dense, and tinged magenta by the dawn light. Down by the river the mist hung over the water, and a grebe drifted into view on the mirror flat surface. In the distance I heard an early train clanking along the branch line towards London. A few last stars flickered above me as the sky lightened. And all around there were cobwebs thick with dew. I settled down to take some photos of the cobwebs, happily absorbed in the task of trying to capture their fragile, jewel-like beauty.



Isolated in my riverside reverie it would be easy to forget that we are hurtling through space, on a planet that is tilted over on its axis, spinning as we go, travelling on an orbit that takes us closer and then further from the Sun. And yet one of the wonderful things about working on 23 degrees is that it has given me a magical new perspective on mornings like this. Intensely local phenomena such as the dawn mist I experienced are also part of a much bigger picture. Dawn mists are a consequence of the longer - and therefore cooler - nights, which in turn relate to our 23 degree tilt and the seasons it creates. 



But the most revealing insight I've gained from the series is the notion that all our weather is driven by gradients - and by the way the Earth seeks to even them out. Gradients are created whenever two (or more) parcels of air (or water or ground) are next to each other, but with different properties - for example, a hot parcel of air next to a cool parcel of air. This means there is a temperature gradient between them, and the Earth system always seeks to even out these differences. The trouble is, there are constant energy inputs creating (or adding to) these differences. Put another way, the climate system is in a constant search for equilibrium, but our journey around the Sun keeps throwing the system out of kilter.



Gradients exist at every scale of the climate system, and crouched down with my camera in the cool, clammy air, I was experiencing one very directly. As the nights lengthen into Autumn, the ground radiates more and more heat back to space. The land cools down, setting up a temperature gradient between the land and the air above. The ground cools the air - attempting to equalise the gradient - until the air reaches its condensation point, forming mist. But then, as the Sun rose, the ground warmed, the air warmed with it, and within a few minutes the mist vanished - the gradient gone.

When I got home almost an hour after leaving I was relieved to find the house still quiet. Just enough time to download this photograph...

Working on 23 Degrees has given me terrific new insights into how our world works, why it is the way it is, and what makes it change. Hopefully when the series is transmitted early next year, you'll get to enjoy those insights too.

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Distance travelled ~ 710'146'400 km

Across Europe:
• A marked change in the weather is expected across the UK and much of northern Europe this week as the high pressure gives way and allows Atlantic depressions to bring much more unsettled weather in from the northwest. Ophelia is now a post-tropical storm and is expected to be swept up in to a normal autumn Atlantic depression. This area of depression is forecast to bring gales to parts of the North and West of the UK on Wednesday and Thursday. So it is not Ophelia that is bringing the wind and rain.

• Many parts of England and Wales can expect a drop in temperature of between 10 and 15 degrees by Friday compared to last week with severe gales for a time affecting the northwest of Scotland for a time on Wednesday and Thursday.

Over the Americas:
• High pressure looks set to bring much drier weather to the northeast USA during the week. The area has been experiencing unsettled conditions recently but the weather is expected to improve through the week, with dry conditions dominating by the end of the week.

• Pacific fronts are set to bring some early season rain and snow to the west of the USA during the week. An active cold front is expected to arrive Tuesday night into early Wednesday with rain and high mountain snow becoming widespread throughout the region. Rain may make it as far south as Southern California by midweek. Gusty winds will accompany the storm and temperatures will drop off dramatically as the week goes on.

• Some heavy tropical downpours are expected across northern coastal areas of Brazil, through the Guyanas to Venezuela in the first parts of the week.

Across Asia:

Minimal tropical storm Nalgae

• Nalgae is bringing torrential rains and winds of up to 56mph to south China as it makes landfall over Hainan island. Nalgae will continue to move westwards into Vietnam and Laos over the next few days, bringing heavy rain to these regions.

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Distance travelled ~ 709'020'800 km

Sharks and stalactites may be close to each other in the dictionary, but you would think that reality keeps them a safe distance apart. For a start, sharks aren't known for inhabiting caves, and every stalactite I've ever seen has been in a cave. Secondly, stalactites can't grow underwater and sharks can't breathe if they're taken out of water. That sounds like a clinching argument if ever I heard one, but the thing I love about science is that our world is more complicated and interesting than that. Not only did I see lots of sharks swim past lots of stalactites this week, but this weird combination tells us something fundamental about our planet. And it's not that a flock of flying sharks has started spelunking because they suddenly fancied bats for dinner.

Belize is just next to Guatemala and south of Mexico, tucked into the back of the Caribbean sea. Its coastline is littered with islands and coral reefs, but what brought Jacques Cousteau here in 1970 is circular deep blue hole in the reef. We arrived in Belize last Monday laden with SCUBA gear, all ready to explore that hole.

Going into the hole was pretty eerie. There is sand and coral right up to the edge, and then the vertical wall just drops away into the darkness. We left all the brightness and light and colourful fish behind, and sank slowly. After going down a little way, all I could see was the rock wall stretching into the gloom. I found looking away from the wall a bit disconcerting because it felt as though anything could swim out of the black, even though I knew perfectly well how unlikely that was. We kept going down further and further, and I stared at the wall, straining to see what on earth brings people here. A reef shark swam past just two metres underneath me. And then the gloom readjusted itself just in front of me and I was looking at a stalactite that was nearly a metre wide at the top where I was, and was probably 5 metres long, pointing downwards into the depths. It was monstrous. There was an overhang, like an upside-down shelf a few metres deep, and looking along it I could see other stalactites hanging down, all of a similar size. We swam along the overhang, and the sharks cruised past us a few metres further out from the wall.

Dives that deep have to be short, and we had work to do, so it was only that night that the scale and the incongruity of what I'd seen sank in.

The size of the stalactites helps you understand the size of the story they're telling. Both are gigantic, almost too big to fit into a human brain. The reason that the stalactites are down there at all is that during ice ages, sea level gets much much lower. 15,000 years ago, the last time those stalactites were growing, they were on a cliff in dry air because sea level was 120 metres lower than it is today. That's the sort of fact that you can read and understand logically, and it's something that I had known for years, but it's hard to digest properly. Read it again: 120 metres lower. That is an awful lot of ocean that wasn't there. Floating in the darkness with 40 metres of water above me, next to a rock wall that kept going downwards as far as I could see, I came closer than I ever have to really understanding the enormity of the changes that ice ages bring to Earth. Oh yeah, and there were sharks too.

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