WE can't.

At least, we can't through deterrence, which is what people usually have in mind when they talk about stopping the boats.

Most people seem to have made up their minds that because the boats stopped coming under the Howard Government and then restarted under the present Labor Government, the Howard Government's policies must have provided an effective deterrent and the current mob are just too soft.

That's never made a whole lot of sense to me for a few reasons.

Firstly, our approach to boat arrivals didn't change that much when the Labor Government took power in 2007. In both cases, people who arrived by boat were held on a distant island to have their claims to asylum processed and over 90% of them were found to be refugees (under Howard and the ALP). They generally waited quite a long time before being brought to Australia, and here they remained.

Yes, we had Temporary Protection Visas under Howard that theoretically meant refugees could be sent home once the danger they faced had passed, but in reality the circumstances they fled were so intractable that most of them remained here.

Secondly, boat arrivals remained low for a while after the change of government. Five boats showed up in 2007, and seven in 2008. The numbers only jumped from 2009 onwards (see Appendix A here).

Thirdly, while the change in boat arrivals does not correlate very well with the change of government, it does line up nicely with changes in asylum seeker arrivals in other countries, particularly countries in our region. It's a bit of a stretch to assume that these countries also changed their processing arrangements at the same time and in the same ways that we did.

And finally, since Labor got all muscular on this issue in August and brought back indefinite detention in neighbouring countries, more boats have arrived than in all of 2011 when they were supposedly being lured by our welcoming, open door policy.

Even the expert panel that recommended an encore of the Pacific Solution acknowledged that "assessing the specific relative weight of particular 'push' and 'pull' factors in influencing the flow of those seeking asylum in Australia on boat voyages, either now or in Australia's recent past, is more a matter of judgement than science" (at 2.3). In light of the above points, my judgement can't bring itself to accept that offshore processing is going to stop any boats.

So why do it then? We know from the Howard era that indefinite detention resulted in mental health problems, self-harm, and attempted suicide. We know from Amnesty International's visit to Nauru last week that conditions there are "cruel, inhuman and degrading".

We also know that this whole exercise is expensive. It has to be. It involves maintaining duplicate facilities in distant places, flying staff back and forth, maintaining a duplicate refugee status assessment procedure and until recently a duplicate refugee decision review procedure.

It's inefficient. Expensive. Cruel.

It only makes sense if it is deterring many other desperate people from getting on boats and risking death at sea. Then this suffering is protecting a much larger group of people from worse suffering while also saving on their potential accommodation, processing and settlement costs.

But if it's not deterring others, it is just wasting money causing pointless harm.

Adam Stone is the Queensland Green's lead Senate Candidate.