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Is the ocean the last bastion against climate change?

“We are reaching the ocean’s limits as a climate safeguard”

Jean-Pierre Gattuso, CNRS Research Director in Oceanography at Sorbonne Université and IDDRI-Sciences Po     and Alexandre Magnan, Senior Researcher in "Adaptation to Climate Change" at Institut du Développement Durable et des Relations Internationales (IDDRI-Sciences Po)
On January 25th, 2022 |
3 min reading time
Alexandre Magnan
Alexandre Magnan
Senior Researcher in "Adaptation to Climate Change" at Institut du Développement Durable et des Relations Internationales (IDDRI-Sciences Po)
Jean-Pierre Gattuso
Jean-Pierre Gattuso
CNRS Research Director in Oceanography at Sorbonne Université and IDDRI-Sciences Po    
Key takeaways
  • The ocean is a “climate regulator” for the planet. Over the last 50 years, it has absorbed 93% of the excess heat on earth, thus limiting the warming of the atmosphere.
  • However, this has been at the cost of significant consequences on its chemical and physical processes, including warming, acidification, deoxygenation, and rising sea levels.
  • The ocean offers different solutions to limit global warming, which researchers have categorised as Decisive, Low Regret, Unproven and Risky.
  • While the Decisive and Low Regret measures are clearly priorities for action, they will not be sufficient. Scientific research must continue to explore the field of Unproven solutions and to understand the application conditions of Risky solutions.

The goal is clear: to keep glob­al warm­ing “well below +2°C” by 2100 (rel­a­tive to the pre-indus­tri­al era). How­ev­er, glob­al efforts to mit­i­gate green­house gas emis­sions are insuf­fi­cient. To achieve the UN’s sus­tain­able devel­op­ment goals, it is now crit­i­cal for deci­sion-mak­ers world­wide to be more ambi­tious in terms of both mit­i­ga­tion as well as ecosys­tem and soci­etal adap­ta­tion. This rais­es the ques­tion as to what oppor­tu­ni­ties are pro­vid­ed by the ocean to sup­port inter­na­tion­al cli­mate action.

“More than just a victim, the ocean is also a source of solutions”

The ocean – includ­ing land­locked and mar­gin­al seas – is a ‘cli­mate reg­u­la­tor’ for the plan­et (Fig. 1). Since the 1970s, it has absorbed 93% of excess heat, lim­it­ing the warm­ing of the atmos­phere. It has also sequestered 25–30% of man-made CO2 emis­sions since 1750 and has received almost all the water released by melt­ing glac­i­ers and polar ice caps. With­out the ocean, cli­mate change would be much more intense than it is today.

How­ev­er, this has come at the cost of sig­nif­i­cant con­se­quences on the chem­i­cal and phys­i­cal process­es in the ocean, such as warm­ing, acid­i­fi­ca­tion, deoxy­gena­tion, and ris­ing sea lev­els. These upheavals have already had detectable impli­ca­tions for ecosys­tems and their ser­vices, and for soci­eties around the world12. The ocean is how­ev­er more than just a vic­tim of cli­mate change, it is also a source of poten­tial solu­tions. We have assessed the main ocean-based mea­sures that have been described in the sci­en­tif­ic lit­er­a­ture3. They cov­er both mit­i­ga­tion and adap­ta­tion45 and refer to address­ing the caus­es of cli­mate change, pro­mot­ing bio­log­i­cal, eco­log­i­cal and soci­etal adap­ta­tion, and man­ag­ing solar radiation.

Making categories for more efficient action

Accord­ing to dif­fer­ent cri­te­ria – effec­tive­ness, fea­si­bil­i­ty, dura­tion of effects, co-ben­e­fits, dis­ad­van­tages, cost-effec­tive­ness, and gov­ern­abil­i­ty – the ocean-based mea­sures we assessed can be grouped into 4 cat­e­gories: Deci­sive, Low Regret, Unproven, and Risky. Such cat­e­gori­sa­tion is intend­ed to guide the devel­op­ment and imple­men­ta­tion of cli­mate poli­cies, com­bin­ing mit­i­ga­tion and adap­ta­tion, at var­i­ous stages of action: from the inter­na­tion­al lev­el, under the frame­work of the revi­sion of Nation­al­ly Deter­mined Con­tri­bu­tions, to the local lev­el, through con­crete and planned action strate­gies, and pass­ing through the nation­al lev­el when defin­ing Cli­mate Plans.

This cat­e­gori­sa­tion sug­gests that, more ambi­tious con­tri­bu­tions should stim­u­late action based on ocean-based solu­tions by pri­ori­tis­ing Deci­sive (e.g. marine renew­able ener­gy) and Low Regret mea­sures (e.g. con­ser­va­tion and restora­tion of coastal veg­e­ta­tion, involve­ment of local com­mu­ni­ties in adap­ta­tion actions, or revi­sion of risk reduc­tion poli­cies to bet­ter take into account antic­i­pat­ed cli­mate change).

Unproven mea­sures have very high poten­tial effec­tive­ness but have so far been through lit­tle or no test­ing and as some of them, such as improv­ing pro­duc­tiv­i­ty in the open sea and alka­lin­i­sa­tion, may have high poten­tial draw­backs. There is a need to improve knowl­edge of these Unproven mea­sures as well as those that are con­sid­ered Risky due to their poten­tial neg­a­tive col­lat­er­al effects (e.g. solar radi­a­tion management).

No action without planning

It is also cru­cial to note that the rel­e­vance of some mea­sures will depend on the con­text in which they are deployed. While infra­struc­ture-based adap­ta­tion (e.g. coastal dykes) may, in some sit­u­a­tions, offer a sus­tain­able solu­tion for cli­mate risk reduc­tion (Deci­sive), in oth­er con­texts it will prove coun­ter­pro­duc­tive in the long term (Risky). Sim­i­lar­ly, the relo­ca­tion of peo­ple and eco­nom­ic activ­i­ties can be deci­sive in the long term for low-lying coastal areas (Deci­sive), pro­vid­ed that it is sup­port­ed by a long plan­ning and sup­port process before­hand, and with­out which there is a high risk of increas­ing the vul­ner­a­bil­i­ty of relo­cat­ed pop­u­la­tions and activ­i­ties (Risky).

Anoth­er lev­el of com­plex­i­ty lies in the fact that none of the mea­sures will be suf­fi­cient on their own, and there­fore that the design of any robust “cli­mate solu­tion” nec­es­sar­i­ly relies on the iden­ti­fi­ca­tion of con­text-spe­cif­ic com­bi­na­tions of respons­es. While Deci­sive and Low Regret mea­sures are clear­ly pri­or­i­ties for action, it is impor­tant to under­stand that full imple­men­ta­tion of Deci­sive mea­sures will not com­plete­ly elim­i­nate coastal risks. Also, the long-term effec­tive­ness of Low Regret mea­sures, par­tic­u­lar­ly nature-based solu­tions, will be deter­mined by the future lev­el of glob­al warm­ing. There­fore, sci­en­tif­ic research must con­tin­ue to explore the field of Unproven solu­tions and to under­stand the con­di­tions of appli­ca­tion of Risky solu­tions.

This ele­ment of diag­no­sis refers to a key prin­ci­ple of cli­mate action: rather than think­ing in terms of indi­vid­ual, ide­alised solu­tions, a more promis­ing avenue con­sists of think­ing in terms of mit­i­ga­tion and adap­ta­tion “tra­jec­to­ries”. The “tra­jec­to­ry” lens refers to the sequenc­ing of a diver­si­ty of respons­es over time, accord­ing to new knowl­edge on cli­mate change and its impacts at both glob­al and local levels.


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