Estimates vary for the amount of oil escaping from BP's Deepwater Horizon rig. BP's own estimate is 5,000 barrels a day but no independent estimate is less than 20,000 barrels a day. According to an article by Alan Foljambe independent estimates are converging on 70,000 barrels per day. Wow! That sounds like a lot - but how much? Not many people have a good sense of scale for quantities like that.
Would it help to think about it as a continuous volume instead of a discrete number of barrels? It turns out that 70,000 barrels is 11,130 m3. It would fill 4.5 Olympic swimming pools a day or a cube over 22 metres tall (see picture). It is 129 litres per second.
This volume of oil is escaping from the Deepwater Horizon well every day
But volume is not a good measure. Oil spills devastate areas, not volumes. What works better (for me at least) is to imagine a layer of oil 1 mm thick. That's plenty thick enough to kill anything it coated. Imagine walking through a puddle 1 mm thick - it would be slippery and you'd make schlopp sclopp noises as you walked. So - how much oil is spewing from the rig if we think of it as a 1 mm thick layer?
- It's 129 m2 per second.
- It's a 13 metre wide puddle of oil every second
- It would cover an area the size of Hyde Park and Kensington Gardens (London) in 5 hours
- It would cover an area the size of Central Park (NYC) in 7 hours
- It would cover the whole of Manhattan in 5 days
- It would cover Rhode Island in 40 weeks
- It would cover Wales in 5 years - that's one μWales (a 'micro-Wales') every 2 days
(For those not familiar with the units, a μWales is one millionth of the area of Wales. It's about 2 hectares or 5 acres)
Oil from the Deepwater Horizon would cover Hyde Park & Kensington Gardens (left) in 5 hours and Central Park (right) in 7 hours
70,000 barrels per day is equivalent to a puddle 1mm deep and 12.8 metres across every second
It makes a difference if you can relate quantities a) to you your own body; b) to things you know. I know Hyde Park well and Central Park a bit. They are very special places, but not intrinsically more special than the areas of coastline under threat, nor even the marine ecosystems being destroyed. One reason the 'Hyde Park' and the 'Wales' are good units of area - better than the hectare or square kilometre - is that they remind you that it is not a mathematical quantity being covered in oil, but a precious eco-system.
UPDATE: 27 May 2010
I made a movie showing what a rate of 70,000 barrels a day looks like in real-time. See: BP's Deepwater Horizon - oil animation