UKESM Earth System Components
UKESM1 will be built on around the physical global atmosphere-ocean climate modelling system used at the Met Office, HadGEM3. This uses the NEMO ocean model and the CICE sea-ice, as well as the JULES land surface model, with TRIFFID dynamic vegetation. In addition, UKESM will simulate atmospheric chemistry and aerosols using UKCA, and marine biogeochemistry with MEDUSA. Dynamic ice-sheets are provided by the BISICLES model. The interface between the various submodels will use the OASIS coupler.
Coupling the models and evaluating and tuning the results is the responsibility of the UKESM core team.
Atmospheric physics
Almost all energy on Earth can be derived from the Sun, with the majority found in the form of incoming solar radiation. The atmosphere, the thin layer of gases that surrounds and protects Earth, is responsible for the transfer of this energy around the globe and into other parts of the Earth System such as the oceans. It absorbs UV, visible, and infrared radiation from space, and emits infrared radiation back again once it has been reflected off Earth’s surface. Ultimately, global warming is driven by processes that interfere with earth’s radiation budget (the incoming solar radiation vs the outgoing terrestrial radiation). In order to understand the long term changes to our climate, the behaviour of energy in our atmosphere, including the scattering of waves and ions, cloud formation, the circulation of heat and fluids, and the interactions of radiation with the atmosphere itself, all need to be considered.
The atmosphere is the relatively thin layer of gases around our planet that protects Earth’s life from harmful radiation and matter from space. The behaviour of the atmosphere, and its ability to carry out its function, is intrinsically linked to its composition. The careful mix of gases, aerosols and solid particles supports life and has a huge influence over Earth’s climate. Atmospheric ozone prevents too much UV radiation from reaching Earth’s surface, whilst greenhouse gases (GHGs) help to control Earth’s temperature. We use models to simulate Earth’s atmosphere and use this to predict how it will affect climate change in future as a consequence of human interference in atmospheric chemistry.
Read more about atmospheric chemistry and aerosols in UKESM1…
Floating sea-ice regulates the transfer of heat and momentum between the atmosphere and the ocean in polar regions, particularly the penetration of the sun’s (solar) radiation into the ocean. It also provides a barrier to the exchange of water, gases and aerosols. Sea-ice is acutely sensitive to changes in climate and, as the planet warms, decreasing sea-ice will lead to less reflection of solar radiation back to space, which instead will be absorbed by the ocean, warming the planet further and locally melting even more sea ice. This is an example of a positive climate feedback, which amplifies the initial warming due to increasing greenhouse gases. Climate change has already had a major impact on sea-ice; for example the seasonal minimum ice cover in the Arctic has decreased by ~40% over the last 30 years.
Rising sea levels on our warming planet are set to impact the lives of millions of people – 11 of the world’s 15 largest cities are near the coast. Being able to predict how the huge ice sheets that sit on Greenland and Antarctica are going to change in the future is a major part of making estimates of how much sea levels will rise, and which countries will be most affected. There are many open scientific questions and technical difficulties in building ice sheets into a global climate model that we are exploring as we build UKESM1, but when complete, UKESM will be a world-leader in its ice modelling capabilities.
Living organisms in the ocean, principally microscopic plankton, play an important role in the climate system through the oceanic carbon cycle. Regulated by light and nutrients, their growth absorbs carbon dioxide at the surface and stores some of this deep within the ocean. Climate change and ocean acidification are expected to change this, so our model needs to include marine ecosystems.
The ocean is the “heat engine” of the planet, storing and transporting the majority of the energy in the Earth system. Ocean currents carry heat from the tropics towards the poles, and in the process make some regions, such as the UK and Western Europe, warmer than they would otherwise be. Ocean circulation also transports heat from the surface to the deep ocean, greatly reducing the degree of global warming we experience at the Earth’s surface: more than 90% of the excess heat trapped by greenhouse gases has been absorbed by the oceans. We use Earth system models to understand how these currents will change as climate change affects the winds and surface heating which drive them.
The Terrestrial biosphere plays a key role in regulating atmospheric chemistry and climate. Vegetation acts as a carbon sink, restraining the growth rate of atmospheric CO2 from fossil fuel burning and land use, acting as a break on human-induced climate change. At the same time, changes in temperature, climate and human interaction can alter the rate of carbon loss through ecosystem respiration and disturbances such as fire and deforestation, which may upset carbon uptake in the future. Plants also have direct effect on climate by altering evaporation, releasing organic compounds that affect cloud formation, and by changing the reflectance and therefore energy absorbed at the Earth’s surface.
Terrestrial physics
In prep.
