Ian McLean Spokesperson for the Green Party

Any risk assessment must include consequence as well as event probability. Thus, the risk of an oil spill from offshore drilling should be balanced against the scale of its impact, which we know from direct experience to be enormous.

Energy and Resources Minister Simon Bridges has assured us the risk of a spill from offshore oil drilling is low, and acceptable, at 0.025 per cent, which equals one chance in 4000.

Dubious probabilities taken out of context and not properly explained should not be used to allay fears about an offshore oil drilling accident. That statistic is actually the probability of a US-operated oil rig sinking or spilling in the Gulf of Mexico, so its relevance to New Zealand conditions is at best questionable.

However, if we assume it is an annual value, then it should be multiplied through by the average life-span of an oil well. Do this and the numbers quickly become quite threatening.

If the average life of a well is 10 years, then the risk is one in 400. If the well's lifespan is 40 years, the risk is one in 100.

The Rena grounding demonstrated the massive environmental and human consequences of what was a relatively small oil spill. So 350 tonnes of oil, or 2500 barrels, on the beaches is barely enough to enter the international oil spill statistics. Spills below 1000 barrels are not recorded.

Thousands of people spent many weeks cleaning up and an estimated 20,000 dead birds. The effects on animals, such as dolphins, fish and invertebrates, can only be guessed. There is no acceptable risk for such consequences.