So, how did the Greens lose half a million votes in an election where the ALP was losing ground? Why did the number of people voting Green in the Senate fall in Adam Bandt's seat of Melbourne when his personal vote in the lower house rose by 8 per cent? Indeed, why was there a swing against the Greens' Senate vote in every one of the 150 lower house electorates?

ACT Greens candidate Simon Sheikh did what he said he would do in driving the Liberals' Zed Seselja below quota but in an election in which the Green vote fell across the country, he was unable to convert Seselja's failure into his own success. While they are still counting in the closest ACT Senate race in history, it looks like Gary Humphries' replacement will likely sneak in on the back of an unlikely preference deal with the Animal Justice Party.

Until September 7, the Greens' vote in the Senate had grown at every federal election since 1998. It is now back to the levels of 2004. Without the nationwide swing against the Greens it is likely that the ACT would have been the first jurisdiction in the country with no Coalition representation in the Commonwealth Parliament.

So what happened? How did the Greens lose a third of their vote in one election and what can they do about it?

This week Senator Milne suggested that while their deal with the ALP to support minority government had delivered a string of policy achievements, proximity to power is always bad for minor parties. While the ''Labor/Green alliance'' seems to have played a role in the Greens recent performance, local history suggests their problems are more complex. Senator Milne was a strong critic of the ACT Greens' decision to refuse ministries in the Stanhope government after they picked up four seats in the 2008 Legislative Assembly election. Indeed, when the Greens fared poorly at the 2012 ACT election, Senator Milne blamed their decision to refuse ministries.

It is possible to make the case that the Greens' recent failures were a result of being too close to power at the national level, and of course it is possible to make the case that at the local level the problem was they weren't close enough. But you can't argue both. Long-term strategy needs to be consistent, but the same is not true in selecting short-term excuses.

Another common excuse for the federal result seems to be that ''climate change wasn't an issue'' at this election, but whose fault is that? Kevin Rudd defeated John Howard in 2007 by making climate change and industrial relations an issue. The Coalition won the 2013 election by making asylum seekers and government spending an issue. In politics, the winners are the ones who make ''their issues'' the ''big issues''. The losers are the ones who blame others for the fact that ''their issues'' were ''non-issues''.

Another excuse, indeed the one the Greens played even before the election, was that there was a conservative tide sweeping the country, a tide that the Greens were swimming valiantly against. But this month's results show that no such tide existed. There was a small swing to the Coalition in the lower house and a swing away from the Coalition in the Senate.

Rather than a conservative tide, there were big swings to Nick Xenophon, Andrew Wilkie, Adam Bandt and Clive Palmer. Most pundits believe that if Tony Windsor had stood, he too would have retained his seat. High-profile candidates, both independents and those from minor parties across the political spectrum, saw large numbers of new voters swing their way. The strategic problem for the Greens is that in an election where the swing was against big parties, they were seen to take a leaf out of the Democrats' book, as one of ''the bastards''.

Senator Milne described her party's results as a ''remarkable achievement''. Indeed it was, but the most remarkable aspect was that the strong swing to Adam Bandt in his historic win in Melbourne was achieved in an environment in which his party lost about one third of electoral support.

Senator Milne has also blamed the big environment groups for not campaigning hard enough for the Greens. While there is no doubt the big environment groups were virtually invisible during the election, there is also no doubt that they have never seen themselves as boosters for the Greens as they instead prefer to try and align themselves with one or other of the major parties.

In a startling mismatch of strategy and excuses, in the same interview in which she blamed the environment groups for her drubbing at the ballot box, Senator Milne suggested that her strategy was to broaden the party's base beyond its green roots. Just how a ringing endorsement from the Green groups would have helped broaden the perception of her party was not made clear.

Some have ventured the excuse that the Greens lost votes because Bob Brown stood down from the leadership. There is no doubt the departure of Senator Brown left a big hole in the party's profile, but there is also no doubt that the transition to a new leader was poorly handled.

Rather than manage expectations by predicting the obvious and explaining that while the party's vote was likely to fall in the short term, Senator Milne set out her vision to grow their vote by shifting their focus to rural voters. That is, instead of setting out to consolidate the party's support among the growing number of inner-city professionals, she set out to woo the dwindling ranks of the Australian agricultural community. The strategy failed with the Greens' vote falling as fast in the bush as it did in the city.

In politics, as in sport, most teams would prefer an ugly win to an elegant defeat. But win, lose or draw, it is the teams which can be honest with themselves and their teammates after the match that have the best chance of improving their performance.

The Greens' parliamentarians met earlier this week to debate and discuss the election, to plot a course for the future and to spill the leadership and all other elected positions. The meeting was scheduled to begin at 10am and the media alert announcing that the new leadership team would be available for comment at 11am went out before the meeting even began.

It seems it took the Greens less than 60 minutes to talk about where their 500,000 voters went, debate their strengths and weaknesses and re-elect their current leader.

It is not obvious why the Greens lost about a third of their voters at this election, and it is not obvious what they should do about it. But it should be obvious that the one thing that won't work is more of the same.

In politics you are usually moving forwards or backwards. It is virtually impossible to stand still in the storm of internal and external events that shape the fortunes of individuals and parties. The Greens went back a long way this month, nearly all the way back to 2004.

As the ALP embraces the idea of members voting for its party leader, they are inevitably shifting to the left on a wide range of issues. If the ALP shifts ground on same-sex marriage and support for single mothers, the votes they pick up are unlikely to be from the Coalition. The next few months could be interesting.

Richard Denniss is executive director of the Australia Institute and a former adviser to Senator Bob Brown.