Taking Earth's temperature

01 October 2019

Interview with 

Helen Brindley, Imperial College London

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this is a picture of a satellite orbiting Earth

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The European Space Agency (ESA) have this week announced a new project to take the Earth’s temperature. Scheduled to launch in 2026, it’s a satellite dubbed FORUM, which stands for “Far-infrared Outgoing Radiation Understanding and Monitoring”. Its job will be to measure, for the first time, the energy emitted from Earth in the far-infra red part of the electromagnetic spectrum. The purpose is to help build better models of how the climate will change in future. Katie Haylor spoke to mission scientist Helen Brindley from Imperial College London...

Helen - We have a lot of satellites in space, and a lot of them measure the Earth's outgoing energy at wavelengths in the so-called mid-infrared. However, a lot of the energy emitted by the Earth is actually at longer wavelengths. And what we're going to do with FORUM is measure them for the first time. And these energies actually comprise about 50% of the Earth's greenhouse effect if our models are correct, and we really haven't measured in the far infrared at all. And we think that when we go and measure over there we'll actually get some surprises about what we see. The energy in the region is very strongly controlled by water vapor absorption and also by ice clouds, which we've recently realized they’re much more widespread than we originally thought, and we're not entirely sure whether they heat or cool the planet.

Katie - Is it too crude to say the aim is to quantify how much energy there is in this far infrared bit of the spectrum and where it is?

Helen - Pretty much, yeah. To test how much is there, what it looks like spectrally, and tying those signals to actually what is happening in the atmosphere and at the surface at the same time.

Katie - Tell us a bit about the satellite then, what kit has it got on it to allow it to get the data that you're interested in?

Helen -  Two instruments. One is the interferometer - essentially moving mirrors which introduce path differences into the light beam going through the instrument and essentially allow you to measure the energy distribution that's coming into the instrument. And that gives us the actual spectrum. And then there's a second, simpler instrument on board which is an imager. So this measures across a narrow band of frequencies or wavelengths and is there really to tell us at higher spatial resolution how homogeneous the scene is underneath. So it gives you an idea of what we're looking at; are we looking at clear ocean, are we looking high ice cloud, or are we looking at a mixture of different scenes.

Katie - So once you have measurements of this far infrared energy how will that translate into us better being able to predict climate change in the future, because that's the overall aim, right?

Helen - That's right. With our climate models at the moment, when we compare them with standard metrics of what the climate is doing, like, for example, the global mean surface temperature, historically all the models do rather well. But as you go into the future, no matter what scenario you consider, whether it's one where we keep going as we are at the moment, which is what we call ‘business as usual’: pumping out quite a lot of greenhouse gases and not doing too much about it, or whether we go to a scenario where we start transitioning to a more green economy, the models diverge as they go into the future, so that there is a large spread in their predictions, and we're really not sure which one is right.

What we hope to do with these measurements is use them to help establish which models now are doing well for the right reasons. So at the moment they are essentially tuning the models to broad band measures of the energy balance, so the total amount that's being emitted. When you start looking at the energy distribution, you get a better idea of how that energy is being emitted and the processes that are going on within the climate system, which are therefore important for what's going to happen into the future.

So we think these measurements will help us understand those processes better and therefore understand which models are doing well for the right reasons, and we can have more confidence in those models moving towards the future.

Climate feedbacks, things like water vapour and whether the distribution of clouds are going to change and things like that. These are the things that we think are causing the large uncertainty in the future. And if we could pinpoint those feedbacks and understand them more, then we'll be able to reduce the uncertainty moving into the future and that's what we think what we have to do with FORUM and for some of those feedbacks.

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