CRI­SIS man­age­ment the nat­u­ral way

EX­PERTS HAVE COME UP WITH SEVEN WAYS TO EN­GI­NEER THE CLI­MATE BUT ARE ANY OF THEM FEA­SI­BLE?

The Nation - - SCIENCE & ENVIRONMENT -

DIS­MISSED A decade ago as far­fetched and dan­ger­ous, schemes to tame global warm­ing by en­gi­neer­ing the cli­mate have mi­grated from the mar­gins of pol­icy de­bates towards cen­tre stage.

“Plan A” re­mains tack­ling the prob­lem at its source. But a ma­jor UN cli­mate sci­ence re­port re­leased in South Korea on Mon­day makes it clear that slash­ing car­bon pol­lu­tion – even dras­ti­cally – won’t be enough to keep Earth from se­ri­ously over­heat­ing.

Here, then, is a menu of “Plan B” geo-en­gi­neer­ing so­lu­tions:

Di­rect CO2 cap­ture

Ex­per­i­ments have shown it is pos­si­ble to suck car­bon diox­ide di­rectly from the air, con­vert­ing it into fuel pel­lets or stor­ing it un­der­ground.

A Cana­dian com­pany backed by Mi­crosoft co- founder Bill Gates launched a pi­lot fa­cil­ity in Canada in 2015, and an­other com­pany un­veiled one in Ice­land ear­lier this year.

Draw­back: As of now, the tech­nol­ogy is pro­hib­i­tively ex­pen­sive and can­not op­er­ate at scale.

Mas­sive af­foresta­tion

Ex­ten­sive plant­ing of trees could sig­nif­i­cantly slow the con­cen­tra­tion of CO2 in the at­mos­phere, which cur­rently stands at more than 400 parts per mil­lion.

Draw­back: Even if de­for­esta­tion could be re­versed – mil­lions of hectares of trop­i­cal forests still dis­ap­pear each year – the num­ber of trees needed to put a dent in CO2 emis­sions would clash with food and bio­fuel crops.

BECCS

Bioen­ergy with car­bon cap­ture and stor­age (BECCS) mar­ries a nat­u­ral process with a high-tech one.

Step 1: Plant rape­seed, sug­ar­cane, corn or “sec­ond-gen­er­a­tion” bio­fuel crops such as switch­grass, which pull CO2 from the air while grow­ing.

Step 2: While burn­ing the har­vested plants for en­ergy, se­quester the CO2 pro­duced.

The re­sult is “neg­a­tive emis­sions”, with less CO2 in the at­mos­phere than when the process started.

Vir­tu­ally all cli­mate change mod­els pro­ject­ing a fu­ture con­sis­tent with the Paris Agree­ment’s target of cap­ping global warm­ing at “well be­low” two de­grees Cel­sius, or 1.5C if pos­si­ble, as­sume a key role for BECCS.

Draw­back: Stud­ies cal­cu­late that up­ward of 40 per cent of arable land – twice the area of In­dia – would need to be given over to bio­fuel crops, putting the scheme in con­flict with food crops.

Ocean fer­til­i­sa­tion

Mi­cro­scopic ocean plants called phy­to­plank­ton gob­ble up CO2 and drag it to the bot­tom of the ocean when they die.

Their colony size is lim­ited by a lack of nat­u­ral iron, but ex­per­i­ments have shown that sow­ing the ocean with iron sul­phate pow­der cre­ates large blooms.

Draw­back: Sci­en­tists worry about un­in­tended im­pacts. Die-offs of plank­ton, for ex­am­ple, use up oxy­gen, which could cre­ate mas­sive “dead zones” in the oceans, some­thing al­ready on the rise.

En­hanced weath­er­ing

Nat­u­ral weath­er­ing of rocks – a chem­i­cal process – re­moves about one bil­lion tonnes of CO2 from the at­mos­phere ev­ery year, about two per cent of to­tal man-made C02 emis­sions. What if tech­nol­ogy could ac­cel­er­ate that process?

Spread­ing a pow­dered form of a green­ish iron sil­i­cate called olivine across cer­tain land­scapes – es­pe­cially over the oceans and in the trop­ics – does just that, ex­per­i­ments have shown.

Draw­back: En­hanced weath­er­ing could prob­a­bly be rapidly scaled up, but it would be ex­pen­sive to mine and mill enough olivine to make a dif­fer­ence.

Biochar

Biochar is char­coal made by heat­ing plant waste – rice straw, peanut shells, wood scraps – over long pe­ri­ods in low-oxy­gen con­di­tions, for ex­am­ple buried in the ground. It can store CO2 for long pe­ri­ods, and also en­riches soil.

Draw­back: The sci­en­tific jury is still out on how quickly this method could be scaled up, and on the sta­bil­ity of biochar used as a fer­tiliser.

So­lar ra­di­a­tion man­age­ment

Unlike other strategies, so­lar ra­di­a­tion man­age­ment does not target CO2. The goal is sim­ple: pre­vent some of the sun’s rays from hit­ting the planet’s sur­face, forc­ing them back up into space.

One idea is to inject or spray tiny re­flec­tive par­ti­cles into the strato­sphere – pos­si­ble with bal­loons, air­craft or through gi­ant tubes.

Na­ture some­times does the same: De­bris from the 1991 erup­tion of Mount Pi­natubo in the Philip­pines low­ered the planet’s av­er­age sur­face tem­per­a­ture for a year or two af­ter­wards.

Sci­en­tists have also cal­cu­lated ways to al­ter clouds that could help beat the heat. One is to brighten the white, bil­lowy ocean clouds that re­flect sun­light. An­other would thin cir­rus clouds, which unlike other types ab­sorb more heat than they re­flect.

Draw­back: Even if it works as in­tended, so­lar ra­di­a­tion man­age­ment would do noth­ing to re­duce at­mo­spheric CO2, which is mak­ing oceans too acidic. There is also the dan­ger of knock-on con­se­quences, in­clud­ing changes in rain­fall pat­terns, and what sci­en­tists call “ter­mi­na­tion shock” – a sud­den warm­ing if the sys­tem were to fail.

Biochar stores CO2 for long pe­ri­ods and also en­riches soil.

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