David Maddox: Greens punching above their weight
To understand the magnitude of his defiance you need to understand Holyrood geography.
The MSPs' tower has five floors, divided mostly evenly between the main parties. The Greens' two MSPs inhabit a small section at the end of one of the SNP floors known by some as "the SNP's pocket", which they share with the Nationalist Alex Neil.
This has always conjured up the image of Mr Neil blocking off the escape route on voting days as the SNP's two hard men – Bruce Crawford, the minister for parliamentary business, and chief whip Brian Adam – tramp down the corridor with a deal the Greens cannot refuse.
It also means other parties cannot sneak up to bargain with them without the shrill alarm call of Mr Neil echoing through the corridor. So more often than not, the Greens have propped up the SNP in tight votes. But now, not even Holyrood geography may rescue the SNP from embarrassing defeats.
Some said Mr Harvie risked everything over 11 million of lagging, but by showing an unwillingness to nod through an "anti-environmental" Budget including items such as the extension of the M74 without balancing measures, he has laid down a marker just as the SNP is prepare to push through its toughest legislation.
The Climate Change Bill will only get Green backing with real carbon emission reduction targets and a commitment to tackling air travel.
And more tellingly, the introduction of a local income tax will fail if the Greens are not given something on their proposed land value tax. Until last week both the SNP and Liberal Democrats had dismissively claimed the Greens could be bought off.
The Greens may only have two MSPs, but on Wednesday, for the first time since winning a Holyrood seat, they have shown they are tired of being pushed around.