Met Office scientist Nick Dunstone reflects on the latest ‘Earthrise’ image captured recently by Artemis 1 and how our climate has changed in the 54 years since Apollo 8 took the original iconic photo.
“Oh my God! Look at that picture over there! There’s the Earth coming up. Wow, that’s pretty,” said NASA astronaut Bill Anders’ when seeing the Earth appearing to rise above the lunar horizon as their Apollo 8 spacecraft came around the moon on Christmas Eve 1968.
It was a unique vantage point: the first-time any human had seen our planet at such a distance, and from another celestial body.
As fellow astronaut Jim Lovell said a few hours later: “The Earth from here is a grand oasis in the big vastness of space.”
That original Earthrise image is widely credited with helping to set the mainstream environmental movement in motion. Although I wasn’t born when the original Apollo 8 photo was taken, a framed print of it hangs above my desk as a reminder of the beauty and fragility of our planet.
Artemis is the new NASA programme to return humans to the Moon and then beyond to Mars. Artemis 1 is the unmanned test flight before the crewed Artemis 2 mission in 2024, and so there was no one scrambling to find the colour film for this new image. Much has changed since 1968, and I wanted to reflect briefly on the changes to our planet between these two beautiful images, taken 54 years apart.
Firstly, there are a lot more of us on the planet now. This year we passed the 8 billion global population milestone, meaning the number of people on the planet has more than doubled from the ~3.5 billion in 1968. Half a century of continued industrial development – driven primarily by burning fossil fuels – has led to a rapid increase in the concentration of carbon dioxide (and other greenhouse gases) in our atmosphere.
This is clearly illustrated by the iconic ‘Keeling curve’, which plots the continuous record of atmospheric carbon dioxide from Mauna Loa Observatory in Hawaii (started by Charles Keeling in 1958).
This curve, shown below, shows a steep and steady upwards trajectory, increasing from ~320 ppm in 1968 to almost 420 ppm in 2022 – that’s a 100 ppm (31%) increase – with no sign yet of slowing down.
This additional ‘blanket’ of greenhouse gases has increased the surface temperature of our planet. The World Meteorological Organisation (WMO) global temperature record is plotted above and made from five different analyses of global temperature data, including the Met Office’s own HadCRUT5. It shows the Earth’s surface has warmed by approximately +1°C since the Apollo 8 Earthrise photo was taken.
Given that current global temperature is +1.2°C above the pre-industrial 19th Century climate, we can see that by far the most of this warming has occurred in the last half century. Whilst an average global temperature increase of +1°C may not sound large, it means that extreme hot climate events are much more likely. For example, the UK experienced another very warm summer this year placing it amongst the hottest five summers on record, with four of those five having occurred since 2000.
During this summer, the UK experienced a new daily maximum temperature record, when 40.3°C was recorded at Coningsby, Lincolnshire on 19 July. This is the first time that 40°C has been recorded in the UK, and Met Office research has estimated that this event is as much as 10 times more likely in the current climate than under a natural climate unaffected by human influence.
There is an enduring legacy of the technologies developed during the mid-20th century space race that have transformed our ability to understand, monitor and predict changes to our climate. Thanks to the many Earth observation satellites launched in the past half century we now have continuous monitoring of many key components of the climate system, including sea-surface temperature, sea level, polar sea-ice extent, glaciers and land-surface changes.
Unfortunately, many of these reveal worrying trends, such as increased frequency of terrestrial and marine heatwaves, Arctic sea-ice loss, glacial retreat, ice sheet mass loss, deforestation of tropical rainforests and relentless sea-level rise. The other technological ‘quantum leap’ since 1968 is the enormous increase in computing power that allows us to simulate the global climate system.
By combining improved Earth observations and climate models run on powerful supercomputers, we can seamlessly predict global weather and climate from hours to centuries. Thanks to these efforts our understanding of the global mean climate response due to rising greenhouse gases is now mature and provides clear evidence for the mitigation pathways needed to avoid dangerous levels of climate change.
However, one of the key remaining challenges in climate science is understanding the detailed dynamical changes that will drive regional climate change. For example, the regional changes in monsoon systems and the mid-latitude jet streams are still uncertain with a large spread in their projected changes between different climate models.
Recent work – led by Met Office scientists – has used seasonal to decadal climate predictions, which are on timescales short enough to be verified, to identify that current climate models have spuriously weak signals in extratropical circulation. Whilst we do not yet fully understand the cause of this issue, we are becoming increasingly aware that such large-scale dynamics is connected via feedback loops to small-scale processes, such as transient eddies in the atmosphere, air-sea interactions and intense local convection.
Many of these physical features are not explicitly simulated at the relatively coarse resolutions (~50-150 km grid spacing) of the current generation of climate models that are used to make decadal to centennial climate predictions. Therefore, we are now striving as a community to push towards higher-resolution global climate models where these processes can be modelled more fully; allowing us to better quantify the regional responses to climate variability and change. To enable us to start running such models we are taking advantage of more powerful supercomputer facilities and optimising our climate models to make best use of them.
Looking ahead, I hope that by the time astronauts take the first Earthrise photo from Mars (perhaps in the mid to late 2030s), we as a global society are making good on our carbon emission reduction pledges. Then, as we head towards net-zero carbon emissions, the Keeling curve will be starting to level-off and global temperature will have begun to stabilise. Achieving net-zero is this century’s ‘Moonshot’ and the prize is minimising the severity of the worst of the projected climate impacts of global heating (including heatwaves, droughts, floods, sea-level rise) and hence leaving our children, and future generations, with a sustainable ‘grand oasis’ in space.
Nick Dunstone’s work at the Met Office includes the global temperature forecast. The forecast for 2023 has been published here.