TerraFIRMA: Future Impacts Risks and Mitigation Actions

TerraFIRMA aims to increase our understanding of the risks and impacts associated with global climate change. It also will assess a number of leading mitigation options aimed at limiting the magnitude of future climate change. It will do this by developing and then applying advanced models of the coupled Earth system, meaning computer-mathematical models for the atmosphere, ocean, land, sea ice and land ice, encompassing relevant physical, chemical and biological processes and process interactions. These models are run for the past, to evaluate their accuracy in simulating key Earth system phenomena, including any trends in variables, such as in surface air temperature. The models are then run into the future using a range of assumed future emissions of greenhouse gases, such as carbon dioxide, methane, and nitrous oxide, as well as aerosols and estimates of future land use. In TerraFIRMA we will design future emissions that see global warming exceed some of the key international policy targets, such as 2 degreeC warmer than pre-industrial values, rising to 3C, before then cooling back down to the 2C level at some later date. This cooling assumes widespread deployment of technologies that remove carbon dioxide from the atmosphere. Using these, so-called overshoot scenarios, we will investigate the risk for rapid changes in three features of the Earth system; Antarctic ice sheets that may impact global sea-level rise, marine ecosystems, and fisheries and tropical forests, such as the Amazon. We aim to determine the risk for rapid change in these phenomena as the climate warms and whether such rapid changes if triggered after a certain amount of warming, are reversible if the climate is cooled back below a given target. Using the same experiments we will also assess the impact of global warming exceeding key targets on the following phenomena that all impact human activities and well-being; (i) water resources and water availability, (ii) air pollution, (iii) wildfires, (iv) marine ecosystems and fisheries and (v) global sea-level rise. For the first four of these impacts, we concentrate on three primary geographical areas: (a) sub-Saharan Africa, (b) the South Asian monsoon region, covering both land and adjacent oceans, and (c) the North-East Atlantic and the UK. In addition to analyzing the overshoot scenarios, we will also design a set of model experiments to investigate the efficacy of two widely discussed options for limiting (mitigating) future climate change. The first action is to rapidly reduce the emission of non-CO2 gases known as Near Term Climate Forcers (NTCFs). Unlike carbon dioxide, which has a lifetime of hundreds of years in the atmosphere, NTCFs (such as methane, ozone, nitrous oxide, and aerosols) have atmospheric lifetimes ranging from days to a decade. Hence, large emission reductions in these gases can impact the amount of climate warming quite rapidly (i.e. in the near term). We will design experiments to assess the efficacy of emission reductions in gases such as methane to see whether they can help reduce near-term climate change and be applied in addition to carbon dioxide emission reductions that have a longer-term impact on warming. The second action is the widespread planting of trees (afforestation), potentially combined with direct Carbon capture, so-called Bio-Energy with Carbon Capture Storage (BECCS). We will design a set of model experiments to assess the impact widespread afforestation has on atmospheric carbon dioxide (trees remove carbon dioxide from the atmosphere when they grow), while also considering the direct impact of afforestation on the local climate where the trees are located. We aim to get a good idea of how much cooling we can expect, and on what timescale from such widespread afforestation. The mitigation experiments we design, as well as the results, will be discussed with UK government departments involved in setting UK climate policy