Atmospheric physicist Joanna Haigh takes on climate change at the IOP

9 June 2016

A diverse audience packed a lecture theatre at the IOP’s London centre on 8 June to hear Professor Joanna Haigh explore the Earth’s changing climate.

Atmospheric physicist Joanna Haigh takes on climate change at the IOP

The event, called appropriately enough “Brewing up a storm”, was held indoors instead of on the Canal Steps at King's Cross, as thunderstorms earlier in the afternoon led to a change of venue.

But this did not seem to dampen the enthusiasm of those who came, and a programme of activities went ahead almost as planned before the talk. It was not possible to use solar telescopes to observe the Sun, as had been hoped, but creative agency super/collider enabled audience members to make cyanotypes – photographic prints using uv light on specially treated paper to produce silhouettes.

A team from the Grantham Institute for Climate Change and the Environment also used dry ice to make unusual bubbles and repeated the demonstration to illustrate part of Haigh’s talk.

Haigh, who is Professor of Atmospheric Physics at Imperial College London and co-director of the Grantham, said she had worked on the physics of the atmosphere and the climate for some time and still found it fun and relevant.

She described how the pressure of the atmosphere decreased exponentially with height, and the temperature also dropped with height as far up as the stratosphere at 12km above the surface, where it began to increase again due to solar radiation. This meant a comparatively hot layer was sitting on a colder layer.

Describing how clouds form, how bright white clouds reflect sunshine back to space, and how the atmosphere and ocean currents are in motion due to radiative heating and temperature differences, she explained how these combined to affect the weather and produce such phenomena as Hadley cells, the north east trade winds, storm tracks and the jet stream.

The Met Office used such knowledge and basic laws of physics such as Newton’s second law, the conservation of mass, conservation of energy and the ideal gas law to produce weather forecasting models. Solving the equations involved was not easy and required considerable computational power, she said, which was why weather forecasters were constantly asking for more powerful computing ability. To enable them to construct more accurate models of the weather, they devised a horizontal and vertical mathematical grid to divide the atmosphere up into squares and input data for each square. The smaller the grid sections, the more accurate their models could be.

The data on initial conditions that fed into the models also had a profound effect on the predicted outcomes, she said, as attested by chaos theory. It was one reason why most forecasters did not predict the UK’s “Great Storm” in 1987: some crucial data on an area over the Atlantic had been missing, she said.

She explained how the Earth’s climate was driven by the Sun and how greenhouse gases were keeping the surface at about 14°C when the planet as a whole was at about -18°C. The most important greenhouse gas producing this effect was water vapour, she said. It had a gap in its absorption spectrum just at the point where carbon dioxide (CO2) had very strong absorption of radiation from the Sun, which meant that CO2 had “a much bigger bang per buck” and was responsible for a third of the warming effect, she said.

Over timescales of thousands of years, factors such as the Earth’s elliptical orbit round the Sun, its tilt, and the precession of its spin axis combined to affect the climate. One result was the occurrence of ice ages on a timescale of about 100,000 years, she said. About 20,000 years ago the Earth’s temperature was about 5°C colder and there had been gradual warming since then. But in the last 100 years alone it had warmed by 1°C she said.

The concentration of CO2 in the atmosphere was also increasing, now standing at 400ppm when it had been 300ppm before the industrial revolution. It had not been at the current level in human history, she said. While doubling CO2 levels should theoretically increase the temperature by 1.5°C, it was increasing faster than that because of feedback effects such as more water vapour in the atmosphere and melting polar ice.

“Increased CO2 is going to heat the planet more – that’s absolutely without doubt. The question is by how much, and what other effects will it have,” she said. It was possible to make some assumptions, e.g. that if humanity carried on without reducing carbon emissions, the climate would be 5°C hotter than it was in pre-industrial days by the end of the next century. To achieve no temperature rise at all would mean stopping CO2 emissions completely, she argued.

Haigh said she was optimistic about the future, following the COP21 climate change conference in Paris in December, where 195 countries agreed to act on climate change to keep the temperature rise to below 2°C.

In a Q&A session, Haigh said some measures to mitigate climate change were already necessary, and innovative technology such as carbon sequestration and storage might help. But she rejected large-scale geoengineering solutions that had been proposed, such as putting a giant mirror in space. If this suddenly failed or had to be stopped for some reason, it could result in rapid climate change. “I don’t think it’s a very good idea at all,” she said.

Asked what individuals could do to address this challenge, she said: “You might think that what you are doing can’t have any effect at all, but group action can and if everyone was to use less energy that would have a huge impact.”

At the talk, the IOP’s head of outreach and engagement, Johanna Kieniewicz, told the audience that the Summer Sessions were part of the Institute’s endeavour to show that physics is an important part of our culture. “It’s something we can enjoy, that enriches our lives and helps us to engage with the fundamental issues of our age,” she said.

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