Do you know what your ecological footprint is? In other words, how many Earths would it take to supply all the needs of your lifestyle - food, material goods and energy - while absorbing your carbon dioxide and other waste?
You may not know, but the fact that we can ask the question at all is a tribute to the sustainability pioneer Dr Mathis Wackernagel, who spoke at the Dubai School of Government last Tuesday. He, with Professor William Rees, advanced the idea of the ecological footprint in his 1994 doctorate, and so introduced an easily comprehensible benchmark for explaining to the public and its leaders how sustainable their consumption is.
If global society were at the limits of sustainability, the footprint would be equal to one Earth. But on Dr Wackernagel's figures, we have already passed this boundary. At a footprint of 1.5, we need half an Earth again to continue living as we are. And with the colonisation of Mars unlikely to be funded under current budget conditions, Earth is all we have.
For a while, we can continue living beyond our means, just as spendthrifts can for a while keep shopping at Harvey Nichols with their credit cards. We can keep adding carbon dioxide from burning oil, gas and coal to the atmosphere, degrading agricultural soils and overfishing the oceans. But one day, the bill will arrive.
Dr Wackernagel went on to argue a country's footprint is not just a matter for environmentalists to worry about. A state living beyond its ecological means has four options.
It can eat into its natural capital, logging forests and extracting fossil fuels, but that cannot last forever.
It may develop a more sustainable society while maintaining the same or better living standards.
It can develop unique, resource-light economic advantages, such as Swiss high technology (Dr Wackernagel is Swiss) or Singaporean financial services, for which less ecologically challenged nations will pay. But of course, only a few nations can follow this path. Someone, somewhere has to be supplying them with food and energy.
The fourth option is the least palatable - to slide down the slope of environmental degradation, declining living standards, poverty and instability.
The calculation for the UAE is not a comfortable one. Dr Wackernagel's organisation, the Global Footprint Network, put the UAE's footprint at almost six Earths, the highest in the world, above even the consumerist US at 4.4.
Most of the countries using less than one Earth are desperately poor, although Egypt (0.9) perhaps deserves an honourable mention.
Dr Wackernagel frames the ecological footprint not as a moral issue but as a practical one, much like a trade deficit. He argues that countries with large footprints will simply become uncompetitive as global environmental strains intensify.
A food importer such as the UAE is hit particularly hard by the recent worldwide rises in food prices (although these are due primarily to one-off events and to fast-growing global demand).
Yet the story is not a simple one. With population growth levelling off around the world and substantial potential remaining for increased farming yields in Africa in particular, food may not be the main constraint.
A large part of the environmental footprint goes to absorb carbon dioxide from the atmosphere, which is already at a level that can trigger dangerous climate change. But as progress towards binding global limits on greenhouse gases is painfully slow, high emitters may be able to continue their polluting ways without real constraints other than world public opinion.
Of course, on this path the world's population is doomed to potentially catastrophic climate change, but that just brings us back to the problem of the collective international action with which environmentalists and policymakers have been wrestling for the past two decades.
From the UAE's viewpoint, the heavy weight of energy in its footprint points the way towards a more sustainable future.
The environmental footprint has been criticised for being a static measure. Earth is expanding - not literally, but in its ability to support humanity through more efficient agriculture and less carbon-intensive energy.
This suggests that in this country we need to intensify our efforts towards improved energy efficiency and low-carbon energy, a mix of solar and nuclear power, with carbon capture and storage.
By putting waste carbon dioxide underground, we effectively increase the area of our planet that can be devoted to more productive uses. And boosting technology, services and trade needs to be combined with improved international competitiveness on a broad measure including environmental externalities.
The ecological footprint should not be interpreted rigidly. But it is a valuable tool to convey, in terms everyone can understand, the challenges facing us - and to indicate paths to a more sustainable future.
Robin M Mills is an energy economist in Dubai and author of The Myth of the Oil Crisis and Capturing Carbon