A NASA instrument designed to track carbon in Earth’s atmosphere is headed to the International Space Station next week, and the president isn’t happy about it.

Trump slashed funding for the Orbiting Carbon Observatory 3 and four other Earth science missions in his proposed spending plan for the 2018 fiscal year, citing “budget constraints” and “higher priorities within Science.” His budget for fiscal year 2019 tried to defund them again.

In both cases, Congress decided to keep the OCO-3 mission going anyway. Now it is set to launch as soon as Tuesday.


OCO-3 was built at the Jet Propulsion Laboratory in La Cañada Flintridge for less than $100 million, using parts left over from its predecessor, OCO-2. Once the carbon observatory gets to the ISS, a robotic arm will mount it on the underside of the space station so it can keep a close eye on the carbon dioxide in Earth’s atmosphere.

That will help scientists answer questions about how and why levels of the greenhouse gas fluctuate over days, months and years.

“Our goal is to get really good data so we can make informed decisions about how to manage carbon and carbon emissions in the future,” said Annmarie Eldering, the mission’s project scientist at JPL.


Carbon dioxide makes up a tiny fraction of the molecules in our atmosphere — roughly 400 parts per million. But seemingly small changes in the amount of carbon dioxide in the atmosphere have an outsized effect on the planet’s temperature.

“Carbon is really effective at trapping heat,” Eldering said. “Even changing the ratio from 300 parts per million to 400 parts per million makes a big difference.”

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OCO-3 is so sensitive that it can detect changes as small as 1 part per million. So if CO2 levels go from 406 ppm one day to 407 ppm the next, the observatory will record the increase.


Eldering, who also worked on OCO-2, spoke to The Times about the difference between the two instruments, the new information she hopes to learn from OCO-3, and how she and her team managed to keep their cool when their project seemed headed for the chopping block.

What are the main science questions you hope OCO-3 will answer?

The big science question is about the movement of carbon dioxide between plants and the atmosphere.

If you look at the ground-based data, it almost looks like the planet is breathing. Plants in the northern hemisphere take up carbon dioxide as they grow in the spring and summer, reducing the amount of CO2 in the atmosphere by a few parts per million. In the fall, the leaves drop and carbon is released back into the air.

But every year is different. There are changes in the forests in Canada. El Niño years affect the carbon cycle.


What we want to do is find drivers of the plant uptake of carbon and use that to better predict what will happen in the future. If we have a warmer, drier climate, will plants keep taking up as much carbon?

Why is it helpful to look at Earth’s carbon cycle from space?

We have Earth-based data, but having a satellite observatory lets you see things in a bigger context. That includes data over the oceans that the ground-based measurements generally don’t see.

Can you give me an example of something you learned from data collected by OCO-2?

In 2015 and 2016, there was a global weather pattern called an El Niño that had a big impact on the carbon cycle in South America, South Africa and Indonesia, but in different ways.

South America had drought, so the plants there were not as active and did not remove as much carbon dioxide as they usually do. In the tropical part of Africa it was super hot, so the plant material was decomposing fast and releasing carbon dioxide. And Indonesia was on fire — that put a lot of carbon back in the air.


Before we would have said, “El Niño is affecting the tropics” and just leave it at that. Now we can tease that apart in more detail, and that is really exciting as a scientist.

How is OCO-3 different than OCO-2?

The main purpose of OCO-3 is to make sure we have a continuous record of carbon dioxide levels in the atmosphere, but we are adding some new capabilities. One of those is to take a snapshot of carbon levels over an area of 50 miles by 50 miles. This will feed a bunch of science investigations of emission hot spots, like cities or volcanoes.

We can also look at how plant activity changes over the course of a day, which is something OCO-2 could not do.

How does OCO-3 work?

OCO-3 is a spectrometer that looks at Earth’s surface in three wavelengths: two for carbon dioxide, and one for the type of light your eyes see. Every molecule has a unique way that it absorbs light, almost like a fingerprint, and that’s what we exploit in our instrument.


If the CO2 levels are 405 ppm, we will see a certain amount of light change in the CO2 band. If it is 406, we’ll see just a bit more.

President Trump tried to cancel this mission twice. How stressful was that for you and your team?

I’ve been over at JPL for 20 years now, and this is not the first mission I’ve worked on that has had funding ups and downs. We are fortunate that we have three branches of government, and that Congress is very active and has kept the importance of this work in mind as they created the budget.

My strategy for getting my work done is just to put on blinders and get the work done.

This interview has been edited for length and clarity.