The federal election has resulted in the Albanese Labor government achieving a majority in its own right in the House of Representatives where governments are formed.

At one level this will create stability as deals will not have to be made with the crossbench to pass legislation in the Lower House, as would be the inevitable consequence of minority government. I say one level because instability will emerge in the Senate where Labor will only be able to pass legislation if it is supported by either the Coalition or the Greens.

The Greens voting with Labor will have exactly half of the Senate numbers. Enough to block but not to pass legislation. The crucial extra deciding vote may come from the new Canberra independent senator, David Pocock, who has been elected on a teal platform that is very similar to the Greens platform.

Pocock’s crucial vote may yet see the teals, who are rendered impotent in the Lower House, raise their heads and demand outcomes to pass legislation in the Senate. But then they would be acting like a political party – which they claim they are not. An alternative to dealing with the teals may be Jacqui Lambie. But the central point of difference with previous governments is that nothing passes the Senate without either the Greens or the Coalition supporting it. There is no third way.

The electoral outcome has therefore effectively rendered the crossbench, other than the Greens, largely ineffectual. They cannot block the government in the lower house and there is not enough of them to secure an outcome in the Senate by voting with Labor against the combined vote of the Greens and the Coalition, or by voting with the Coalition against the combined vote of Labor and the Greens.

If the crossbench is ineffectual, there is one alliance that can stymie the government’s agenda. It is an unholy alliance that can emerge in the right circumstances between the Greens and the Coalition in the Senate. Let me illustrate how this can occur with some examples.

On climate Labor’s election commitment is 43 per cent reduction in emissions on 2005 levels by 2030 and net zero by 2050.

The Greens want 75 per cent reduction by 2030 and net zero by 2035. The Coalition policy at the election was 26-28 per cent by 2030 and net zero by 2050. It’s pretty obvious that the government will be caught between the Greens’ desire to increase targets and the Coalition’s lesser targets.

Based on their past actions the Greens are likely to oppose the good in favour of what they think is the perfect. Problem is, it’s not perfect. It is the irresponsible economy wrecking option – but that won’t stop the Greens. They will threaten to block 43 per cent unless they get their way. The Coalition may also threaten to block the government’s target – unless Peter Dutton suddenly decides to respect the government’s mandate.

The point is that the government has no middle road. It must convince either the Greens or the Coalition to support its 43 per cent target. If it fails to convince either, it may have to take a non-legislative route as foreshadowed by Energy Minister Chris Bowen.

Or take the government’s commitment to establishing an ICAC. The Greens have offered to support it provided it is able to hold unconstrained public hearings, act on anonymous tip-offs, and investigate historical matters.

Labor may decide not to have a completely unfettered ICAC able to publicly bring down both the guilty and the innocent based on anonymous tip-offs. Labor may again find itself between a Greens’ Star Chamber approach and a Coalition ultra-cautious preference.

Or take the fossil fuel dilemma.

The Greens want to stop new gas and coal fields being developed and close gas and coal-powered electricity generators which, as we have seen in the current energy crisis, are still needed to provide energy security.

Gas in particular is the only viable affordable interim back-up to renewables. The Greens’ agenda goes well beyond shutting down exploration, exports and power stations. It extends to getting rid of all gas appliances in Australian homes. The Greens’ stance will clash with the Coalition’s unfettered support for coal and gas. Labor’s balanced approach may be the casualty.

On national security the Greens have a policy of appeasement of China. This includes accepting a Chinese presence in the Pacific, giving up on Taiwan and avoiding raising human rights issues. The Greens also want a softer line on border protection. The Coalition has opposing views on all these counts. Labor is likely to mostly side with the Coalition, but the Greens may exact revenge by obstructing other government priorities.

I am not saying that with some smart negotiation and clever politics that Labor cannot weave its way through these (and many other) diabolical challenges. But for the first time in decades the Senate presents the new government with a stark choice. Either deal with the Greens or deal with the Coalition.

The new government has huge challenges on the economic and budgetary front that will be further challenged by the Greens and the Coalition pulling in opposite directions in the Senate on a range of policies from climate to ICAC to gas to national security.

It’s a new political setting where outcomes may depend on the vagaries in the Senate of the extreme left and the extreme right.

Theo Theophanous is a commentator and a former Victorian Labor Minister. The article was originally published in The Herald Sun.