If you despair of Australia’s lacklustre climate policies, you might take heart from the Greens’ stated goal of limiting global warming to 1.5℃. But are the party’s own policies up to the job?

Shortly after announcing this target late last year, the Greens launched an ambitious renewables policy, promising to achieve 90% renewable electricity by 2030 and save money in the process.

But as wonderful as it sounds, even this plan is insufficient to meet a 1.5℃ target.

The arithmetic is simple. According to the Intergovernmental Panel on Climate Change (IPCC), to preserve a two-thirds chance of avoiding 1.5℃ warming, future carbon dioxide emissions must not exceed 200 billion tonnes. As annual global emissions are now around 40 billion tonnes, we will blow the budget within five years.

Now let’s suppose that the entire world achieves the Greens’ emissions reduction targets of 60-80% by 2030 (relative to 2000 levels), and 100% by 2040. Assuming a steady trajectory to 70% in 2030 and another steady move to full decarbonisation a decade later, that puts global CO₂ emissions by 2040 at more than 400 billion tonnes – far beyond the budget described above.

Idealism vs realism

Does it matter if the numbers don’t add up? After all, the rest of the world has exactly the same problem. If we want to avoid losing hope of averting dangerous climate change, surely wishful thinking and calls to action are better than no target at all?

But there is a growing group of energy experts, environmentalists and conservation scientists who are worried by the environmental movement’s failure to process the full implications of the climate challenge.

Take the Greens’ promise to achieve 90% renewable electricity by 2030. There are several major economies – Switzerland, Norway, Sweden, France – that already have near-zero-emission electricity. But all of them use large amounts of hydroelectricity, nuclear power, or both.

Rather than follow the only proven path to clean electricity, the Greens propose that Australia should emulate Germany’s Energiewende policy.

While Energiewende has expanded renewable energy, it has failed to cut emissions. True, the emissions intensity of German electricity is about 40% lower than Australia’s. But both Germany’s total greenhouse emissions and the carbon intensity of its electricity have plateaued, despite record investments in renewable energy. German emissions intensity remains an order of magnitude higher than those of the nuclear/hydro countries such as Switzerland and France.

Germany’s problem is that it has had to back up its intermittent wind and solar generation with fossil fuels. The Greens promise that canny Australian engineers will succeed where Germans have failed, by using “pumped hydro” power storage power storage and concentrated solar thermal energy.

However, the jury is still out on these technologies – and even ClimateWorks, whose modelling the Greens uses, acknowledges that “large investments in Research and Design are needed to improve the performance of existing low-carbon technologies to required levels”.

Spain’s 20-megawatt Gemasolar power plant shows that solar thermal and storage can supply baseload power. But it would take around 100 Gemasolars to replace a typical major coal-fired power station, and bigger solar thermal plants, such as Ivanpah, the world’s largest, have not produced the expected output. While it would be foolhardy to write off solar thermal, it’s also mightily brave to bet the climate on it.

Making up the shortfall

Is an all-renewables future possible in Australia? Of course. But it won’t come fast, cheaply or without significant environmental impacts. The most authoritative “100% renewables study” so far was released in 2013 by the Australian Energy Market Operator (AEMO). Although the Greens requested this report, they didn’t like its conclusions: that an all-renewable grid would need baseload power from geothermal (not yet a scalable technology) and bioenergy (which has a range of knock-on environmental impacts).

Part of the problem with the Greens’ approach is that it made many of its energy choices long before climate change was a major issue. The party emerged as a political force through campaigns against nuclear technologies and the Franklin River dam. It has always backed wind and solar (which now provide around 2% of global energy), but has opposed the world’s two largest sources of low-carbon energy: hydroelectrcity (6.8%) and nuclear (now 4.4%).

Am I suggesting that the Greens embrace nuclear power? While that is unlikely given their deeply held political commitments, it is not unreasonable to ask for an end to the anti-nuclear fearmongering. The Greens’ national policy platform demands the closure of the OPAL reactor south of Sydney, which produces radioisotopes for cancer detection and treatment. Without such reactors, life-saving nuclear medicine would become impossible.

The Greens are right that nuclear cannot compete on cost with coal, and if we only wanted to halve our emissions then gas and renewables would be the logical choice. But if our goal is zero-carbon electricity, and given the uncertainty about the pace of innovation in other low-carbon technologies, it is worth heeding the advice of South Australia’s nuclear Royal Commission that “action is taken now to plan for [nuclear’s] potential implementation”.

Of course the Greens are right that wind and solar must make a much larger contribution to our future energy mix. But to hope that we can avoid dangerous warming without drawing on every available tool is to put ideology before arithmetic.

Truly radical climate action means we shouldn’t unconditionally rule out any promising technology – from carbon capture and storage to low-methane genetically modified crops.

Rather than accept the Intergovernmental Panel on Climate Change’s (IPCC) findings about carbon budget overshoot and the consequent need for “negative emissions” technologies such as carbon capture and storage, Green politicians promote alternative research outlining all-renewable paths to global decarbonisation. Such studies assume both unprecedented technological progress, and extreme global inequality in energy use (for example by assuming that Indians will be content to use 84% less energy than Australians).

Embracing science

Of course, this is not to say that the two major Australian parties, with their underwhelming climate ambitions, are any better. Yet so successfully have the Greens cast themselves as the party of climate science that it’s easy to forget how radically they dissent from a scientific worldview in their responses to climate change.

Former NASA climatologist James Hansen, often dubbed the father of climate awareness, has branded green opposition to nuclear power as a major obstacle to solving the climate problem. In response, he was pilloried and branded a “denier”.

The idea that greedy polluters are the only barrier to an all-renewable future presents climate action as a simple moral choice. Unfortunately, caring for the planet is not so easy. Effective mitigation requires tough choices among imperfect options.

To be effective, we environmentalists must examine our own biases as carefully as we do those of our opponents. And we must do more than accept climate science; we must also use science in our search for solutions.