How to monitor climate change from space

Fol­low­ing the COP26 in Glas­gow, there has been much talk about how to mon­it­or cli­mate change around the world and its effects. In the Dynam­ic Met­eor­o­logy Labor­at­ory (LMD), we focus on Earth obser­va­tions using satel­lites to improve our under­stand­ing of our plan­et’s cli­mate and changes that are hap­pen­ing. This is pos­sible mainly thanks to pro­gress in satel­lite tech­no­logy, and our abil­ity to ana­lyse the data gathered.

Watch­ing Earth from the skies

We have two object­ives when we observe the Earth from out­er orbit. First, we aim to under­stand the plan­et as a whole, ask­ing fun­da­ment­al ques­tions like: how did Earth become to be the way it is now? How is it evolving? But we are also look­ing at key cri­ter­ia that hold answers to some of today’s biggest soci­et­al issues, such as the UN Sus­tain­able Devel­op­ment Goals (many of which are cli­mate related)¹ or under­stand­ing risks of hur­ricanes, earth­quakes and oth­er nat­ur­al disasters.

Efforts are glob­al, with dif­fer­ent States around the world turn­ing their focus to vari­ous tech­nic­al areas. In France, at the Nation­al Centre for Space Stud­ies (CNES), NASA was our top part­ner for a long time along with the European Space Agency (ESA).  But in recent years we have seen some big changes in the Earth Obser­va­tion sec­tor. Col­lab­or­a­tions with India, China and oth­er smal­ler European agen­cies in Ger­many and the UK have swelled. And, with the advent of nanosatel­lites [tiny, light­weight satel­lites designed for highly spe­cif­ic mis­sions] dozens of new, smal­ler space agen­cies have been cre­ated around the world work­ing on diverse pro­jects – so many that we struggle to keep up with all of them!

Moreover, the field has received both pub­lic and polit­ic­al recog­ni­tion – espe­cially thanks to the COP21 in 2015 that saw the selec­tion of 2 French space pro­grams ded­ic­ated to the mon­it­or­ing of CO₂ and CH₄: Micro­Carb² and Mer­lin³, respect­ively. Add to that the oth­er game-changer for us: the European Space pro­gramme, Coper­ni­cus⁴. Oper­a­tion­al since 2014, it com­prises now 8 satel­lites (known as Sen­tinels) in orbit around the globe, each observing dif­fer­ent com­part­ments of the Earth sys­tem. Anoth­er 10 are in pre­par­a­tion for con­tinu­ous launches up to 2030 and we are already plan­ning the next pro­gramme with at least 6 more! 

The pro­gramme is ded­ic­ated to provid­ing autonom­ous and inde­pend­ent access to inform­a­tion in the domains of envir­on­ment and secur­ity on a glob­al level in order to help ser­vice pro­viders, pub­lic author­it­ies and oth­er inter­na­tion­al organ­isa­tions. All Coper­ni­cus data is also open source. This means it is free to access for agen­cies, labor­at­or­ies or oth­er entit­ies around the world who may wish to use it (includ­ing com­mer­cial enter­prises). And one of its big­ger users is the sci­entif­ic community.

Tech­no­lo­gic­al innov­a­tion for new capabilities

In France, we have three fields of excel­lence, which allow us to study pre­cise changes in so-called essen­tial cli­mate vari­ables, a set of 54 geo­phys­ic­al vari­ables that crit­ic­ally con­trib­ute to the char­ac­ter­isa­tion of Earth’s cli­mate, of which about 60% can be addressed only by satel­lite data: alti­metry, optic­al imagery and atmo­spher­ic sounding. 

Using alti­metry, from the pion­eer­ing mis­sions TOPEX/Poseidon, Jason and now Sentinel‑6, we can mon­it­or sea water levels over time, a hugely import­ant factor in glob­al cli­mate change. Our sys­tem can keep track of ocean depth changes and is able to see the 3.3 mm annu­al increase, which has driv­en the 10 cm rise in sea levels over the last 30 years!

Optic­al imagery allows us to fol­low what’s hap­pen­ing on Earth with extreme spa­tial res­ol­u­tion (up to 10 metres). Using this tech­nique, mis­sions like TRISHNA allow us to ana­lyse ground humid­ity and fol­low crop har­vests from the skies as a way of keep­ing track of human-driv­en changes to the planet’s sur­face⁵. 

Finally, atmo­spher­ic sounders let us meas­ure radi­ation com­ing from vari­ous lay­ers of the atmo­sphere across the whole light spec­trum – even that which we can­not see – to offer indic­a­tions for the pres­ence of green­house gases and oth­er major pol­lut­ants. These meas­ures are key to under­stand­ing the com­pos­i­tion of the Earth’s atmo­sphere and, more import­antly, how it is chan­ging over time due to human activ­ity. The IASI instru­ment developed by CNES in cooper­a­tion with the European Organ­isa­tion for the Exploit­a­tion of Met­eor­o­lo­gic­al Satel­lites (EUMETSAT)⁶⁷ has recently provided a unique view on the trans­port all around the world of car­bon monox­ide emit­ted by dra­mat­ic Cali­for­ni­an fires and allowed track­ing sev­er­al desert storms respons­ible for “yel­low sky” in Europe.

Data treat­ment back on land 

Satel­lites take vari­ous meas­ures or images from the upper atmo­sphere, yet most of the data is ana­lysed on the ground. How­ever, it is very rare that we can dir­ectly meas­ure exactly what we need. Hence, to make sense of satel­lite meas­ure­ments we need to inter­pret them in terms of geo­phys­ic­al inform­a­tion by design­ing innov­at­ive algorithms, such as machine learn­ing, cap­able of trans­form­ing data into use­ful inform­a­tion. Moreover, to be use­ful and add inform­a­tion to the one already provided by ground-based obser­va­tion net­works, we need to reach a high level of accur­acy. For instance, to isol­ate the very small sig­na­tures of cli­mate change, we need to be able to detect a small trend of 0.1 K annu­al increase… from meas­ure­ments made at 800 km from the surface! 

Anoth­er chal­lenge is to cre­ate an integ­rated obser­va­tion sys­tem that can com­bine space data with meas­ures from the sur­face or in the air [such as weath­er bal­loons or research aicrafts] in an integ­rated obser­va­tion sys­tem. Our goal: to link these obser­va­tions togeth­er in order to gen­er­ate mean­ing – and for that we need accur­ate meas­ure­ments and numer­ic­al mod­els of the Earth sys­tem to assim­il­ate them.

Plan­ning the next step 

What we need for the com­ing years is innov­a­tion… and more con­tinu­ity in space mis­sions. Innov­a­tion to observe new geo­phys­ic­al vari­ables, such as cloud con­vec­tion, and to improve the obser­va­tions: to allow study­ing low-scale pro­cesses, it is needed to increase the spa­tial res­ol­u­tion from 10 to 2 m in car­to­graphy or from 75 to 15 km in alti­metry. Con­tinu­ity to mon­it­or glob­al change: if we con­sider cli­mate stud­ies, it takes at least 20 years to see trends in the data. Back in the 1950s mis­sions las­ted only 5 years. Where­as, these days, we are now closer to 12 years. Even so, we still need more per­man­ency, coupled with the capa­city to link data from one plat­form to anoth­er: this is key if we wish to make long-stand­ing com­par­is­ons in cli­mate data year on year. As such, we need long-term pro­grams with long-term budgets. 

And this is chal­len­ging also from a man­age­ment point of view! For instance, the IASI mis­sion was designed from the start to last 20 years, by build­ing three satel­lites before 2006, of which one was launched straight away and the oth­er two were kept in stor­age for 4–8 years. In that time tech­no­logy can change and engin­eers move on or retire, tak­ing the skills and com­pet­en­cies away with them. We are already plan­ning anoth­er three mis­sions for launch in 2023, 2030 and 2037. So, we need to be able to hold onto our engin­eers and assure that the satel­lites age well whilst they wait in the hangar for over a dec­ade before they are launched!