WHETHER 4 November 2016 will go down in history as a moment worth celebrating depends on the guidance of climate science, the ingenuity of engineers, the courage of political leaders and the will of civil society.
This is the day the much-heralded Paris agreement on climate change was due to come into legal force. Prime ministers and presidents will throw down the gauntlet to the scientific community: show us how to hold 鈥渢he increase in the global average temperature to well below 2 掳C鈥� above pre-industrial levels and 鈥減ursue efforts to limit the temperature increase to 1.5 掳C鈥�.
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Long before the political elite chinked their Parisian champagne glasses with 鈥渓ow-carbon鈥� celebrities, a cadre of climate scientists and engineers had been burning the midnight oil in preparation for this call to arms.
The fast-diminishing carbon budgets associated with temperature rises across the century emphasise the challenge of delivering on the agreement. The mitigation pledges submitted in Paris last December will still lead to an ongoing rise in emissions as we keep burning fossil fuels, enough to squander the carbon budget for 1.5 掳C in five years and 2 掳C by 2030.
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Yet there鈥檚 no need to fear, apparently: the theory goes that we can use all of our carbon budget today, and even go into carbon debt, but then compensate for it.
We are developing a technical fix that will enable fossil fuel use for decades. Shiny bits of engineering kit will suck billions of tonnes of carbon dioxide from the air and store it underground for millennia.
Biomass energy with carbon capture and storage (BECCS) has emerged as the front runner from an array of technologies, even though it is highly uncertain how much 鈥渟ucking鈥� is required. And BECCS is already ubiquitous in models guiding governments on mitigation.
So what鈥檚 the problem? Not least the need to build BECCS power stations magically fast, and the sheer scale of carbon storage and biomass infrastructure required. There are also challenging technical hurdles, competition for biomass and multiple competing pressures for land.
Perhaps we can engineer carbon-sucking machines. The problem arises if we can鈥檛 scale them to the incredible level assumed in models. If we act today like we have enough of these machines tomorrow, we will bequeath future generations the climate Paris seeks to avoid.
Given the huge risk of the technologies not working at the scale promised, negative emissions should, at best, be a small dollop of cream on top of an enormous and fast-baked carbon-mitigation cake.
This article appeared in print under the headline 鈥淎ct now, not tomorrow鈥�
