This week, we have learnt that the Greens are now a bigger party than Ukip. Their membership rocketed up 2,000 overnight to reach 43,829. We already know that Labour, in response to the surge in support and membership of the small left-wing party over the past few months, has set up an anti-Green unit under shadow justice secretary Sadiq Khan in an attempt to counter the threat to its votes from Natalie Bennett's troops.

What we've also learnt this week is that the Prime Minister sees the Greens as such an important potential threat to his rivals that he has refused to take part in the leaders' televised debates unless Bennett is also included.

And news has broken today of Tory MPs' plans to split Labour's vote by encouraging left-wing voters in their constituencies to support the Greens, who are aiming to run in 75 per cent of seats this election.

However, one thing that has fallen under the radar, under all this political greenery, is Ed Miliband's launch of something called "action/2015" yesterday at a London school. There, he commited the next Labour government to seeking to "raise global ambitions for combating extreme poverty, inequality and climate change".

Here's what he promised on the latter subject:

In 2015, after the General Election here, the countries of the world will come together to agree two plans. The first plan aims to eradicate poverty over the next fifteen years. And the second will tackle climate change. These two plans affect all of us: everyone in this room, everyone across the world, and especially, everyone in your generation because they will help determine the world you will live in. They matter. And what the British government does at these conferences – what it does in your name - matters too. I know tackling climate change, global poverty and inequality are not as fashionable as they once were. But I also know they are more important than ever. For me, they are not luxury items in our programme for change. They are not part of a branding exercise. They go to the heart of my beliefs and the reason why I entered politics. This is about ensuring the next generation can do better than the last in this country and around the world . . . The progress of the last 15 years in the tackling poverty, improving health, on food security and access to sanitation could all be eroded if global temperatures are allowed to soar. I believe tackling climate change is the most important thing I can do in politics for my children’s generation. It demands leadership and resolve. So in Paris next year, a Labour government would be pushing for global targets for reducing carbon emissions that rise every five years with regular reviews towards the long-term goal of what the science now tells us is necessary – zero net global emissions in the latter half of this century.

All admirable promises, and from a man who was the first ever Secretary of State for Energy and Climate Change. However, his green policy proposals will not help him counter the threat to his party's support from the Greens. This is due to three reasons:

It's not as "fashionable"

Miliband's own acknowledgement that climate change is not a "fashionable" subject is truer than maybe even he realises. The Labour leader was referring to David Cameron's 2005 rebrand of the Tories – hugging huskies and generally making his green credentials central to his image as Tory leader – and how it was all really a hollow "branding exercise".

However, green policy is no longer top of the agenda due to a number of reasons. Chiefly, economic realities have pushed it down the list of spending priorities. And it seems even the Greens have accepted this. They are no longer supported simply because they are the party of eco-friendly policies. Like the other parties, the Greens have been concentrating far more on economic policies in this parliament. However, their economic policies are formulated to tackle inequality and challenge austerity – free education, scrapping the welfare cap, reducing the pay gap, and turning the minimum wage into a living wage, for example. People are voting Green because the party provides a radical alternative to the economic policies, and consensus on the need for further austerity, of the Conservatives and Labour.



Playing on enemy turf

A little like the Tory leadership having to speak more than they'd like about EU membership and immigration, in an ill-advised attempt to shoot Ukip's fox, Labour talking about the environment is playing on the Greens' turf. Voters whose main priorities concern the environment are unlikely to vote for Miliband's handful of green proposals, emphasised almost as an afterthought a few months before the general election, when there is another party that historically has dedicated itself to environmentally-friendly policies.



Picking the wrong battle

There is a way for Labour to combat the Greens' popularity, but the environment isn't it. As I have reported before, the best rhetoric Labour can use is to emphasise the costly, predominantly middle-class nature of the "green lifestyle". Key figures in the Green Party admit that this is an area where it needs to improve, trying to broaden the appeal of living sustainably beyond the narrow section of society that can afford to do so. One of Miliband's aides revealed to my colleague, Tim, that this is Labour's best bet against the Greens, commenting: “We’ve found the best line of attack is to attack the Greens as an upper-middle class lifestyle choice.” There hasn't been much evidence of the party publicly using this attack line, but it would serve it well, and would be more effective than hoping a few green pledges will do the trick.