May we discuss 'net zero' 2050?

Since 1900, the global population has jumped fivefold. World greenhouse gas (GHG) emissions are 15-20 times higher. Real Gross World Product has soared even more.

Earth and seas used to reabsorb "natural" or background emissions. They can't handle the "anthropogenic" load.

So atmospheric CO2 and land-ocean temperatures keep rising . Much of that rise comes in recent decades.

In Australia, setting aside fluctuating estimates of "land use" (LULUCF) emissions, emissions have risen from 400s of megatonnes (Mt) in 1990 to the 500s today.

Before any "offsets", our latest projection for 2030 is 511 Mt. Slashed from 563.

From 1990, our population has grown 40 per cent. So growth looks "decoupled" from emissions. Similarly, with global growth. Problem, the constant-sized earth reads aggregate and not per capita emissions. Hence, still-rising CO2.

Claims the European Climate Foundation, this inexorable 20th century trend can be overturned. World emissions neutralised.

To limit global warming, the Paris Agreement urges global Net Zero "as soon as possible" after 2050. "Developed economies" should get there no later than 2050.

Such might happen, via two avenues.

First, "emissions reductions". Humans could get a much better handle on decarbonising electricity, plus electrifying (or otherwise transforming) industry and transport. These fossil-fuel intensive sectors account for most emissions today.

Second, "negative emissions". Earth, rather than just producing its own (LULUCF) emissions, could be groomed intensively to "capture" excess human emissions.

"Net Zero" happens, when these two balance out. Residual emissions are offset by CO2 (or GHG) removals.

Australian Government isn't buying, not yet. The Opposition is, provided we retain coal exports. Our states are on board. The big champion for Australian Net Zero is economist Ross Garnaut, in the book Superpower.

Says Garnaut, two-thirds of the emissions savings to Net Zero would come from relinquishing fossil fuels. Land use "transformation" would deliver the rest.

His "intermittent renewables" would meet electricity needs as early as the 2030s, with emissions savings also flowing to increasingly electrified industry and transport sectors.

But there's scientific to and fro, as to whether you can approach 100 per cent renewables, via "pure" wind, water and solar. Even if you sort your energy mix, there are barriers, in terms of networks, transmission, storage and grid fluctuations .

Garnaut glosses the physical and logistical problems of nullifying power/industry/transport emissions. He does indicate the increasing affordability and desirability of Australian transition towards renewables. Also, that the technical "intermittency" of renewable power could be managed better.

It's the remaining LULUCF sector where things get interesting. In effect, Garnaut offers the attractions of indefinite economic expansion, plus a Rolls Royce environment that handily reabsorbs the emissions of such expansion.

Here's mainstream economics, which likes to "externalise" the environment, co-opting it as a get-out-of-jail card. Who said this was a dismal science?

Let's step back. No question, lands and seas "sink" CO2 and other GHG. As above, they more or less neutralise "background" emissions.

Some landscape types absorb, better than others. But landscapes also emit GHG, naturally. Or, dramatically. Our 2019-20 forest fires unlocked maybe two-thirds of "official" annual emissions.

Earth, exuding CO2 during fires or droughts, inhales in wetter spells. Over two decades, CSIRO estimated Australia reabsorbed just one-third of the CO2 emitted via its own fossil-fuel use.

World findings are not dissimilar. Lands and oceans, each might mop up roughly a quarter, of the human-related emissions.

Couldn't we just "plant more trees", or otherwise engineer the environment, to increase the rate of CO2 absorption? It's problematic.

Environmental corrections swim against continuing environmental degradations. We see this tension, in Australia's five-yearly State of the Environment (SoE) reports.

By 2050, the official program calls for an Australian population north of 35 million. There's no end in sight, to our permissive legal framework, for land clearing and habitat removal. Mega fires have scarcely paused Victorian and NSW logging.

Second problem, while measurement of anthropogenic emissions is imperfect, it beats measurement of the earth's feedback loops. Crucial landscapes might reabsorb much less GHG than we expect. Other landscapes might do better than expected. If we weren't trashing them.

Land-related carbon capture is apples. Fossil-fuel based emissions are oranges. The apples are continually recalculated, highly approximate and less permanent.

It's a stretch to put them into the same mitigation equation as the oranges. That tempts us to defer present day "emissions reductions" in favour of "negative emissions" promised land.

Nevertheless, Garnaut's 2008 climate review estimated our rangelands and forests could be cultivated to reabsorb over 500 Mt emissions a year. His claims run much higher now. We'd have a "surplus" of carbon "credits" to sell worldwide.

Overall, his Net Zero seems a bridge too far. More likely, energy transition could be part of an industrial transition, away from our houses and holes economy.

Instead of unfurling the Net Zero banner, I'd rather we underpromise and overdeliver.

After all, this nation has Olympic medals for emissions fudges. It sat in the naughty corner at the Madrid climate talkfest.

Back at Kyoto 1997, Australia negotiated an emissions "reduction" task, that was actually an increase of 8 per cent. We finessed an "Australia Clause". Which allowed us (in particular) substantial emissions "credits" via a reduction in land clearing.

Now we're a global deforestation hotspot. Still our 2030 emissions reduction of "26-28 per cent" leans on discredited Kyoto "credits".

Rather than spurring action, the 2050 pledge might kick the can further down the road. And not even a clean emissions sheet, I argue, meaningfully "saves our environment". Especially if you're among its hundreds of fire-threatened species.

Fire and virus challenge Australia's vaunted "economic miracle". Is 2.75-3 per cent growth still going to return, as the Treasury and RBA have forecast monotonously? Or, will wealthy nations finally have to lower their growth horizons?

Australians, it seems, want coal exit, energy transition and Net Zero. The first two are plenty difficult enough. The third is something else.

It assumes bold science and engineering fixes, to ensure full-on renewable energy. It repurposes the struggling environment, as a high-performance carbon-sink. To that sink, it confidently assigns the permanence, to mop up pesky human emissions.

Aspirational Net Zero looks like yet another proxy, for expansive growth on a non-expansive planet. As if we can grow to ten billion total, lift billions (of low-emitters) out of poverty, then sprint to the line for 2050.