Climate modelling is based on the fundamental laws of physics and has improved immensely over the last few decades, the Met Office’s chief scientific adviser, Prof. Dame Julia Slingo, told a lecture audience at the IOP.
Speaking on 2 September at the Institute’s London centre, she described the large strides that have been made in modelling the Earth’s climate systems. “I think this is a major achievement for physics that is never celebrated. It’s a really exciting time for getting to grips with these tricky problems,” she said.
Giving a detailed description of some of the phenomena contributing to the Earth’s climate system, such as solar radiation, fluid flows in the oceans and the atmosphere, the water cycle and the rotation of the planet, as well as smaller-scale effects, Prof. Slingo said: “All of that complexity has to be included in the climate models if they are to do the job required of them.”
It was important to remember that climate modelling was based on some fundamental equations of physics including Newton’s Second Law, the Ideal Gas Equation and Planck’s Law, she said. To derive climate models from these and other equations involved solving them numerically using computers. A huge amount of work had gone into doing so, and the Met Office now had a supercomputer that could operate at 1 petaflop.
To simulate how the climate behaves, the surface of the Earth, for example, is divided into a grid on which a model operates. The resolution of the grids had increased dramatically since she began her career, so that scientists were able to understand the climate at ever smaller scales. Prof. Slingo said she had pushed to achieve higher resolution and now, for example, a model of the ocean had a resolution of half a degree. “I think we are entering an amazing period in being able to simulate the climate system,” she said.
The title of her lecture was “Taking the planet into uncharted territory: what climate models can tell us about the future” and although she had not come to give a lecture on climate change, she said, she did touch on global warming. She explained, for example, that H2O is a major greenhouse gas that absorbs and emits solar radiation, but not across the whole spectrum. There is a hole in the H2O spectrum, she said, but CO2 unfortunately sits in that hole, as does ozone. “If it didn’t, we wouldn’t be nearly as worried,” she said.
Prof. Slingo said: “Make no mistake – we are taking the planet into uncharted territory, at least in comparison with the last 800,000 years.” Even at the peak of the interglacial period, CO2 levels did not exceed 300 parts per million (ppm), and now we were crossing the 400 ppm threshold and might even get beyond that, she said. “That enormously rapid rise in CO2 is due to what we are doing and to how we live now.” This had to be seen in the context of other global factors such as rapid population growth, urbanisation and limited natural resources, which were much less of an issue in such times as the Medieval Warming Period.
It was not up to scientists to take the decisions on responding to climate change, but to offer the best advice that they could, she said. It was important to explain to the public that, though the climate involved chaotic systems, this did not mean that these were random or were not understood, but that they were sensitive to initial conditions. “People think that uncertainty means that you don’t know, or that a chaotic system is a random system.” It might be better, she said, to talk about confidence, reliability and probabilities.
In a question and answer session, Prof. Slingo was asked about specific phenomena in the climate and whether the models failed to predict these or were not being taken into account. As scientists we did not close our minds, she said, and work on understanding them better was continuing.